Aabsolute coordinates (n) Coordinatesassociated with an origin that never changeslocation and thus gives a stable method oflocating geometry in space. The absolutecoordinate system is also called the world orglobal coordinate system.

absolute scale (n) A data scale that has both adefined zero point and units. The Kelvintemperature scale is an example of an absolutescale.

actual size (n) A tolerancing measure usedto describe the size of a finished part aftermachining.

additive (adj. or v) A process or state wherebyelements combine together, such as twoprimitive shapes combining to form a larger,more complex one. Additive is the oppositeof subtractive.

additive primaries (n) The three primarycolors: red, green, and blue. Color systems usethese primaries in differing amounts, workingon the principle of adding spectral wavelengthsto the light energy to create new colors. Thissystem is used in lighting and computerdisplay graphics. The complementary colorsare the subtractive primaries: cyan, magenta,and yellow.

adjacent areas (n) Surfaces that are separatedon a multiview drawing by lines that representa change of planes. No two adjacent areas canlie in the same plane.

adjacent view (n) Orthographic views that arealigned to each other, allowing dimensionalinformation to be shared. Examples are thefront and top views or the front and right sideviews.

aerial perspective (n) A perceptual cue whereobjects farther away appear bluer and hazier.The cue is based on the effect of particles inthe atmosphere blocking the passage of light.

aerospace engineering (n) A field ofengineering concerned with the design andoperation of aircraft, missiles, and spacevehicles.

G-1

aesthetics (n) The artistic qualities or aspectsthat elicit an emotional response to an object.

agricultural engineering (n) A field ofengineering concerned with productionagriculture and its natural resource base andthe processing and chemistry of biologicalmaterials for food and industrial products.

aligned dimensions (n) A style ofdimensioning in which text is placed parallel tothe dimension line, with vertical dimensionsread from the right of the drawing sheet. Thealigned method of dimensioning is notapproved by the current ANSI standards butmay be seen on older drawings.

aligned section (n) A section view created bybending the cutting plane line to pass throughan angled feature. The resulting section doesnot show the section in true projection, yet itgives the clearest possible representation of thefeatures.

allowance (n) A tolerancing measure used todescribe the minimum clearance or maximuminterference between parts. Allowance is thetightest fit between two mating parts.

alphabet of lines (n) The standard linestylesestablished by ANSI to be used for technicaldrawing. The standards specify both thethickness and the design (i.e., dashed, solid,etc.) of the lines.

alternate four-center ellipse method (n) Amethod of creating an approximate ellipse. Themethod is used for cavalier oblique drawings.

ambient light source (n) A light sourcedefined by its lack of orientation or location.Fluorescent lighting in an office is an exampleof ambient lighting. In renderings, an ambientlight source is sometimes used as a defaultlight source to give a baseline level of lightingto the model.

analogous (adj.) A concept meaning similar orcomparable in some respects. The concept isused to describe the extent to which a graphicrepresentation compares with a real object.

analytic geometry (n) The analysis of geometricstructures and properties, principally using

Glossary

algebraic operations and position coordinates.The term also refers to a particular geometricmethod for describing 3-D solid models.

angle (n) The relative orientation of two linearelements with respect to each other. The angleis usually measured relative to the point ofintersection or termination of the two lines.

angularity (n) An orientation control forgeometric dimensioning and tolerancing.Angularity is a condition of a surface, centerplane, or axis at an angle other than a rightangle to a datum plane or datum axis.

apparent motion (n) The sense of motioninduced by rapidly displaying a series of imagesof an object to make the object appear to changelocation or shape. Animation techniques takeadvantage of this perceptual effect.

archiving (v) A term used to describe thestoring and retrieval process for engineeringdocumentation. Although originally involvingpaper documents, the term increasingly refersto the storage of computer-generatedinformation on magnetic or optical media.

area rendering (n) A data visualizationtechnique in which the pixels in a 2-D area areeach assigned a value. A color lookup tablemaps a specific color to each data value tocreate a rendered region.

arrow plot (n) A visualization technique inwhich the dependent variable is a vector ratherthan a scalar and is represented by line orarrow marks. Because there are typically alarge number of arrow marks in a small region,pattern (texture) perception can be used toevaluate trends in the data.

artistic drawing (n) A type of drawing used toexpress aesthetic, philosophical, and abstractideas. These types of drawings are not intendedto communicate clear, concise informationpertaining to a design.

artwork drawing (n) See fabrication drawing.

assembly drawing (n) A drawing showinghow each part of a design is put together. Anassembly drawing normally consists of all theparts drawn in their operating positions and aparts list or bill of materials.

assembly section (n) A section view ofmultiple parts in an assembly. Differingsection line designs differentiate betweendifferent materials, or between similarmaterials belonging to different parts.

authoring (v) The process of using computerprogramming tools to assemble different mediainto an interactive presentation.

automation (n) The use of machinery in placeof human labor.

autorouting (v) A specialized softwareprocess that suggests routing connectionsbetween components on a circuit board.Autorouting is usually part of a suite of CADelectronics software functions that also includeautomated component placement,programming of CNC board drilling, andcomponent insertion equipment.

auxiliary section (n) A section view derivedfrom an auxiliary view. The term distinguishesfrom section views derived from standardorthographic views.

auxiliary view (n) A view derived from anyimage plane other than the frontal, horizontal,or profile planes. Auxiliary views are usuallytermed primary or secondary, depending onwhether or not they are perpendicular to one ofthe above-mentioned primary projectionplanes. Primary auxiliary views are termeddepth, height, or width auxiliaries, dependingon the dimension transferred from themeasuring view.

axis (n) The line or vector representing acenter of rotation, such as the longitudinalcenter line that passes through a screw threadcylinder. Also, a vector indicating a dimensionin model space or in a visualization such as agraph.

axonometric axes (n) The axes used to definethe orientation of the primary dimensions in anaxonometric pictorial projection. The relativeangle of the axes to each other determines thetype of axonometric projection.

axonometric projection (n) A parallelprojection technique used to create pictorialdrawings of objects by rotating the object onan axis relative to a projection plane.

BB-spline curve (n) A parametrically definedfreeform curve that approximates a curve to aset of control points and provides for localcontrol. Multiple 2-D curves are oftencombined to create 3-D surface patches.

backface culling (n) In rendering, apreprocessing step that removes all faces of themodel that will be completely hidden fromview.

bar graph (n) A graph (usually 2-D) in whichone dimension represents the independent

G-2 GLOSSARY

variable and the other represents the dependentvariable. The magnitude of the dependentvariable is represented by a line or area ofuniform width (a bar).

basic dimension (n) A tolerancing measureused to describe the theoretically exact size ofa feature.

basic size (n) A tolerancing measure used todescribe the theoretical size used as a startingpoint for the application of tolerances.

bearing (n) A mechanical device designed totransfer radial or axial loads from a shaft whileminimizing energy loss due to friction from therotating shaft. Bearings are usually dividedinto two general categories: plain and rollingcontact.

Bezier curve (n) A special case of the B-spline curve. Unlike a standard B-splinecurve, the Bezier does not provide for localcontrol, meaning that changing one controlpoint affects the entire curve.

bicubic surface patch (n) A 3-D freeformsurface bounded by a set of curves describedby third degree (cubic) functions. Thebounding curves, often B-spline or Beziercurves, and their associated control points areused to manipulate the shape of the surface.

bill of materials (n) A listing of parts ormaterials used in an assembled object. Thelisting is usually included as part of theworking drawing of the full assembly.

binary tree (n) A hierarchical, logicalstructure used to organize related elements.Each node on the tree is linked to exactly twoleaves on the next level down. Binary trees areused to describe the relationship of geometricelements in a CSG solid modeler.

bird’s eye view (n) In a perspective pictorial, aviewpoint looking down from above the object.From this viewpoint, the ground line is belowthe horizon line of the object.

blind hole (n) A hole that does not gocompletely through the material. Blind holescan be created by any cutting device (such as atwist drill bit) that is capable of plunging intothe material.

block diagram (n) A relatively simple diagramthat quickly identifies the relationships betweensystems, groups, people, or other physical orabstract entities. (See also flow diagrams.)

boldface (adj.) A style of text in which the linesthat make up the letters are thicker than normal.This technique is used to make words or lettersstand out visually from the rest of the text.

bolt (n) A mechanical fastening device with ahead on one end of an externally threadedshaft. A nut is placed on the threaded shaft androtated to clamp the material between the headand nut.

bonding (v) A process in which a material(usually, a hardening liquid) is added to anassembly to hold parts together. Bonding is apermanent fastening method, using processessuch as welding, soldering, brazing, and gluing.

Boolean operations (v) Local operations usedto define the relationship between twogeometric objects. Boolean operations betweennew and existing geometry are usedextensively to modify solid models in 3-Dmodeling software.

bottom view (n) A principal view of an object,created by rotating the object 90 degrees aboutthe horizontal axis below the front view. Thisview is not typically included in a standardmultiview drawing.

boundary representation (B-rep) (n) Apopular method of representing solid models.This database structure describes thegeometric and topological elements of thesurface of the model. Unlike wireframemodeling, a B-rep explicitly defines thesurface of the model. Unlike CSG modeling, aB-rep does not explicitly define the interiorvolume of the object.

bounding box (n) An imaginary boxrepresenting the maximum dimensions of theobject being drawn. Sketches of objects oftenbegin with this box, and it is used to define theboundaries and guide the placement ofindividual features.

brainstorming (v) A process used to identifyas many solutions to a design problem aspossible by freely suggesting ideas withoutcriticism or discussion of feasibility. Abrainstorming session will normally have amoderator and a recorder.

break lines (n) Freehand lines used to showwhere an object is broken to reveal interiorfeatures of a part. Such lines can also be usedto show where a portion of a line or object hasbeen left out for clarity or because of spacelimitations.

broken-out section (n) A section view used toreveal interior features of a part by breakingaway a portion of the object. A broken-outsection is often used instead of a half or fullsection view when the feature of interest is notsymmetrical with the overall object. The resultis a more efficient drawing. Unlike most othersection views, a cutting plane line is notdefined in an adjacent view.

bump mapping (n) A rendering techniqueused to add surface detail to a model. Bumpmapping perturbs the normals used in shadingthe surface polygons in such a way as to givethe impression of a regularly undulatingsurface (i.e., texture). A golf ball could berepresented as a shaded sphere, with thedimples created through bump mapping.

GLOSSARY G-3

Ccabinet oblique (n) A type of oblique pictorialdrawing in which the two dimensions of thefrontal surface are drawn parallel to the frontalplane, and the third (receding) axis is drawnobliquely at half the scale of the frontal plane.The receding axis is typically drawn at anangle of between 45 and 60 degrees.

cabling diagram (n) See wiring diagram.

CAD (v or n) Acronym for computer-aideddrafting, computer-aided design, or computer-aided design/drafting. The usage depends onthe context in the design process and onwhether the acronym refers to the physicalcomputer system or the activity of using such asystem to support technical and engineeringgraphics.

callouts (n) See line balloon.

cam (n) A mechanical device used totransform rotary motion into reciprocatingmotion, using a rolling or sliding contact withanother part called a cam follower. Radialcams move the follower perpendicular to theshaft; cylindrical cams move the followerparallel to the shaft. The shape of the contactsurface determines the motion of the follower.

CAM (n) Acronym for computer-aidedmanufacturing, which is the use of computersto control the production process. Examplesare robots for assembly and numericallycontrolled machine tools. CAM is oftencombined with CAD to describe the integrationof design and manufacturing through the use ofa common computer database.

cam follower (n) A mechanical device in whichone end follows a linear, reciprocating path asthe other end traces the surface of a rotating cam.Followers are often spring loaded to guarantee agood contact with the surface of the cam.

cap screw (n) A mechanical threaded fastenerwith a head on one end, used to screw into amating part. Differing from a bolt, a cap screwhas a longer thread length and does not use a nut.

CAPP (n) Acronym for computer-aidedprocess planning, a technique that usescomputers to assist in the planning process.CAPP is an expert computer system that can beused to determine the optimal sequence ofoperations for a part and can then generate theoptimal process and routing sheets necessary tomake the part.

Cartesian coordinate system (n) Commoncoordinate system used in mathematics andgraphics to locate the position of geometry inspace. First introduced in 1637 by ReneDescartes (1596–1650), the system is typicallyused to locate points in 2-D (X,Y) or 3-D(X,Y,Z) space by assigning values to the pointsbased on the mutually perpendicular(orthogonal) axes.

cavalier oblique (n) A type of pictorialdrawing in which the two dimensions of thefrontal surface are drawn parallel to the frontalplane, and the third (receding) axis is drawnobliquely to the frontal plane and at the samescale. The receding axis is typically drawn atan angle of between 45 and 60 degrees.

CD-ROM (n) Acronym for compact disk-readonly memory, a mass storage device that usesoptical technology to store large amounts ofinformation on a small reflective platter.Information is written to the disk only once, atwhich point the disk is unchangeable. CD-ROMs are used for archiving audio, graphic,and textual information, and for publishing anddistributing software, graphic images,multimedia materials, etc.

center lines (n) A type of linestyle used torepresent symmetry and paths of motion and tomark the centers of circles and the axes ofsymmetrical parts, such as cylinders and bolts.Unlike visible and hidden lines, center lines donot represent geometry directly.

central view (n) The view from which relatedviews are aligned in an orthographic drawing.Distances and features are projected ormeasured from the central view to create theadjacent views.

ceramics (n) Materials, usually with crystalstructures, created from compounds of metallicand nonmetallic elements. Ceramics canwithstand high temperatures and resist wear.Some ceramics, such as glass, are notcrystalline in structure.

chamfer (n or v) A beveled corner used on theopening of a hole and the end of a cylindricalpart to eliminate sharp corners. Chamfersfacilitate the assembly of parts and arespecified by giving a linear and angulardimension. When used as a verb, the termrefers to the process of creating a chamfer onan object.

check print (n) A type of hard-copy outputused to check the accuracy and format of atechnical drawing. The check print is a low-quality, high-speed method oftroubleshooting the final print or plot.

chemical engineering (n) A field ofengineering that includes all phases oftechnical activities in which a knowledge ofchemistry, along with other basic sciences, isused to solve problems related to energy,health, the environment, food, clothing, shelter,and materials.

CIM (n) Acronym for computer-integratedmanufacturing, a system for linkingmanufacturing operations into a singleintegrated computer system. CIM differs fromCAD/CAM primarily in its integration ofbusiness functions, such as accounting,

marketing, and personnel, into a commoncomputer database shared by all components ofthe business.

circle (n) A closed, planar curve that, at allpoints, is an equal distance (the radius) from apoint designated as the center. A circular arcis an open, planar curve equidistant from acenter. The arc will subtend an angle of lessthan 360 degrees. A circle is sometimesdescribed as a 360-degree arc.

circuit side (n) The side of a printed circuitboard on which a majority of the circuitconnections for components are made. Theopposite side of the board is called thecomponent side.

circularity (roundness) (n) A form control forgeometric dimensioning and tolerancing. For acylinder or cone, circularity means that allpoints on a surface intersected by a planepassing perpendicular to a common axis areequidistant to that axis. For a sphere, all pointson a surface intersected by a plane passingthrough the center are equidistant to thatcenter.

civil engineering (n) A field of engineeringinvolved with planning, design, construction,operation, and maintenance of transportation,environmental, and construction systems.Along with military engineering, this field isoften considered the first true engineeringfield.

clash (v) A condition in which two parts of amechanism partially overlap in space, causinginterference. Kinematic analysis using theBoolean intersection operation is often used toevaluate clashes in computer models of themechanism.

clearance fit (n) A tolerancing measure usedto describe a fit in which two mating partsalways leave a space when assembled. Theresulting space is called an allowance or aclearance and is usually specified in theassembly drawings.

clip (v) The rendering process of removingportions of lines or surfaces that reside outsidethe view volume. Clipping refers to removingthe portion of the model that resides outsidethe horizontal and vertical bounds of theviewing area and outside the specified near andfar depth (Z) bounds.

clock speed (n) The rate at which the centralprocessing unit (CPU) of the computerperforms functions. The clock speed ismeasured in megahertz (MHz). The higher theclock speed, the more powerful the CPU.

closed loop (n) The condition required for agroup of edges to form a face (surface) on anobject. The edges must be connected end toend, forming a continuous path around theperimeter of the face.

CNC (n) Acronym for computer numericcontrol, which describes a form ofprogrammable automation of a machine toolusing a computer in the controller unit. In acomputer controlled manufacturing center, theindividual machines would use CNC programs,either sent from a main computer orprogrammed locally.

color (n) The perceptual quality of a surfacethat results from the combined response tolightness, hue, and value. Hue is oftenconfused with color since the names of hues(e.g., red, purple, yellow, etc.) are used as theprimary classification terms for color.

color lookup table (n) A modular databasethat allows colors to be mapped to specific datavalues in a visualization. The color lookuptable can be associated with a single renderedimage or be used as a standard table in alibrary. Color lookup tables are often referredto as palettes.

command history (n) A listing of commandsentered into the CAD system by the user, alongwith the values of the specified parameters.Command histories can be used as a “script” toreplay sequences of commands or track downinput errors.

composites (n) The combination of two ormore materials, one a reinforcing element andthe other a resin binder or matrix. A commoncomposite is fiberglass, which is made of glassfibers and a resin. The more advancedreinforcing elements include carbon/graphite,boron, and Kevlar (aramid), which are stiff,strong, and lightweight.

computer animation and simulation (n)Simulation is the precise modeling of complexsituations that involve a time element;animation is the imprecise modeling ofcomplex situations over time. An animationwill replicate a real situation by approximatemeans; a simulation will replicate a realsituation by accurate means.

computer numeric control (CNC) (n) SeeCNC.

computer-aided drafting/design (CAD) (n)See CAD.

computer-aided manufacturing (CAM) (n)See CAM.

computer-integrated manufacturing (CIM)(n) See CIM.

conciseness (adj.) A term used to describe oneattribute of a CAD database. The more concisethe database, the less space each record takesin the hard drive of the computer.

concurrent (adj.) The technique of organizingnumerous steps so that they happen in parallelrather than one after another (serially).Concurrent engineering, for example, involvesall members of the design process working

G-4 GLOSSARY

simultaneously in close coordination with eachother rather than each member waiting forother members to finish with their componentsof the design.

cone (n) A geometric solid described by astraight line (the generatrix), one end of whichis attached to a fixed point (the vertex) and theother end of which traces a closed, curvedpath. The most common cone is a right circularcone, for which the curved path is a circle andthe vertex lies on an axis that is perpendicularto the circle and through its center.

cone of vision (n) A term used to describe theamount of space visible by the human eyelooking in a fixed direction. The visiblevolume is approximately described by a right-angled cone for which the vertex is at the eyeand the axis is aligned with the view direction.

conics (n) Special case single-curved lines thatcan be described in many different ways:sections of a cone, an algebraic equation, andthe locus of points. For our purposes, conicsare sections of a right circular cone and includethe ellipse, parabola, and hyperbola. The circleis a special-case conic.

connection list (n) The list of all connectionsthat need to be made between components onan electronic circuit board. This list is usuallymanaged by the electronic CAD program.

connectors (n) Devices used to join electroniccomponents together to allow the transmissionof signals. Connectors include plugs (externalcomponents) and jacks or receptacles (internalcomponents) and can provide either temporaryor permanent connections. Devices used formechanical connection are typically calledfasteners.

construction lines (n) Light, thin lines drawnto lay out the framework or structure of adrawing or sketch. Portions of these lines areoften overdrawn with the final linework.

constructive solid geometry (CSG) (n) Amethod of 3-D solid modeling in whichgeometric primitives are related to each otherin a binary tree structure via Booleanoperations. Each primitive is defined as a solidby a group of analytic surfaces (half-spaces),and the final object is defined by thecalculation of the Boolean operations betweenprimitives.

continuity (adj.) A term used to describe thetransition between two elements. Elements arecontinuous if there is no gap or break betweenthem and there is a single mathematicalfunction used to describe the two combinedelements. Continuity is often used to describethe connection of two curved lines or surfaces.

contour line (n) A line that represents theindependent variable (X,Y) combinations thatresult in a constant dependent variable value

(also called an isoline). A contour line can alsorepresent the juncture between two surfaces ofdiffering orientations or depths. In thisdefinition, a contour line is an alternate termfor edge.

contour plot (n) A visualization in which thehorizontal and vertical scales both representindependent variable values, and the contourlines show the mapping of constant, dependentvariable values. Multiple contour lines aretypically drawn on a plot, representing auniform sampling of dependent variable values.

control points (n) Points used in conjunctionwith spline curves. These points are not part ofthe curve proper, but the relationship betweenthe control points and the points on the curve isused to define the shape of the curve.

controlling (v) The procedures used to controlmaterials, machines, and processes in themanufacturing and production cycle throughautomation, measuring, inspection, and testing.

conventions (n) Commonly acceptedpractices, rules, or methods. In technicaldrawing, a convention is the use of dashedlines to designate a feature hidden from thecurrent viewpoint.

convolute (n) A single-curved surfacegenerated by a straight line moving such that itis always tangent to a double-curved line.

Coons’ surface (n) A 3-D surface defined byinput curves. This surface was named afterSteven A. Coons, who developed themathematical method for defining complexshapes used in the design of aircraft,automobiles, and ships’ hulls.

coordinate dimensioning (n) A technique inwhich all dimensions are calculated asCartesian X and Y distances from an originpoint, usually located at the lower left-handcorner of the part. Also known as datumdimensioning or baseline dimensioning,coordinate dimensioning should be usedcautiously because of the tolerance stackupthat takes place.

coordinates (n) A set of real numbers definingthe location of a point in space. One value isgiven for each dimension of the space (i.e.,2-D, 3-D), and each value is determined by thepoint’s distance from the defined origin.

corner (n) The nontangential intersection oftwo or more surfaces of an object. Theintersection of two surfaces is usually referredto as an edge. Corners are represented on adrawing by either a single line or multiple co-terminating lines.

CPU (n) Acronym for central processing unit.The CPU is the heart of the computer,coordinating all primary activities of thecomputer and processing a majority ofoperations or “calls” from the software.

GLOSSARY G-5

Computers are often classified by their CPUs.Examples are Intel’s PentiumTM andMotorola’s PowerPCTM 601.

crest (n) A threading term describing the peakor top surface of a screw thread.

cross-hatch lines (n) An alternate term forsection lines. Cross-hatch often refers tosection line symbols in which the lines crosseach other rather than simply running parallelto each other.

curved line (n) A line which does not follow astraight path. Curved lines are often classifiedby their underlying mathematical functions.Examples are circular and elliptical curves.

cutting plane (n) An imaginary plane in spaceused to define the division between two partsof an object. A cutting plane is often used todefine a portion of an object to be removed inorder to reveal the interior detail.

cutting plane lines (n) A line showing thelocation of a cutting plane in section drawings.The cutting plane line is drawn in the view forwhich the line of sight is parallel to the cuttingplane. Arrows on the ends of the section linepoint toward the material to be retained in thecorresponding section view.

cycle time (n) The total time required for aprocess to take place.

cycloid (n) A curve generated by the motion ofa point on the circumference of a circle that isrolled in a plane along a straight line.

cylinder (n) A planar geometric soliddescribed by a straight line (the generatrix) thattraces a closed, curved path and always staysparallel to itself. The most common cylinder isa right circular cylinder for which the curvedpath is a circle and the generatrix isperpendicular to the path.

cylindrical coordinates (n) A system forlocating points in space with one angle and twolengths. Cylindrical coordinates describe apoint as a distance from the origin, its angle inthe X–Y plane, and its Z value. Cylindricalcoordinates are useful when designing circularshapes and geographic applications.

cylindricity (n) A form control for geometricdimensioning and tolerancing. Cylindricityindicates that all points on the surface shouldbe equidistant from a common axis. Unlikecircularity, cylindricity refers to both thecircular and the linear (longitudinal) elementson the surface.

Ddata region (n) The region in a visualizationwhere the actual data is represented. In a graphor plot, the region would be bounded by thescales (axes) where the point or line markersrepresenting the data are drawn.

data visualization (n or v) The method or endresult of transforming numeric and textualinformation into a graphic format.Visualizations are used to explore largequantities of data holistically in order tounderstand trends or principles.

datum (n) A theoretically exact point, axis, orplane used as a reference for tabulardimensioning. A datum marks the origin fromwhich the location and orientation of geometricfeatures are established.

datum feature (n) A term used in geometricdimensioning and tolerancing to describe a realor theoretical feature selected to ensure theproper orientation or location of other featureson a part. Controls define features on the partrelative to the datum features.

datum reference frame (n) A term used ingeometric dimensioning and tolerancing todescribe the theoretical reference frame used toevaluate the location and orientation offeatures of a part. The frame consists of threemutually perpendicular (orthogonal) planes,which typically correspond to the principalplanes of projection in a multiview drawing orthe global coordinate system in a 3-Dmodeling system. In inspections, a physicalsurface may be established to simulate one ofthe reference planes.

declarative information (n) A term used todescribe the current state of an object. Thistype of information can be thought of asdescriptive nouns. The location of a point in acoordinate system (8,3,5) is an example ofdeclarative information.

density slicing (n) A visualization technique,used with area and volume renderings, inwhich a particular data value or small range ofvalues is highlighted in contrasting color. Thistechnique can be used either for a single staticimage or for sequential images highlightingdifferent data values in the image.

dependent variable (n) A variable dependenton the response of the model and not controlledby the experimenter. Every dependent variablevalue is paired with one or more independentvariables and represents the model’s responseto the independent variable values.

depth (n) One of the three principaldimensions of an object. The depth dimensionis described in the right side and top views of amultiview drawing. The depth dimension isoften associated with the Z axis in a 3-Dmodeling system. Depth can also refer to thedistance cut into an object using a machiningprocess (e.g., the distance measured betweenthe crest and root of a thread normal to the axisor the depth of a drilled hole).

descriptive geometry (n) The fundamentalbasis of the science of projection drawing,

attributed to the work of Gaspard Monge(1746–1818). It is the basis of all types of 3-D representations on 2-D media used today.

design analysis (n) The evaluation of aproposed design during the refinement process,using the criteria established in the ideationphase. The refinement stage is normally thesecond of three major phases in the designprocess.

design for manufacturability (DFM) (n) Atechnique in which ways are found to simplifya design and reduce manufacturing costs.Using CAD/CAM technology, DFMdetermines the manufacturability of a designbefore it is produced.

design process (n) The method used to createa solution to an engineering or technicalproblem. The result is often a product, eitherone of a kind or mass produced. The designprocess, though unique to each problem,typically includes standard stages and usesgraphics to communicate information betweenand within these stages.

design visualization (n) A process using thefundamental capabilities of a human visualsystem; the ability to perceive 3-D form, color,and pattern. Visualization is an analysismethod used in the second stage of the designprocess, the refinement phase.

detail drawing (n) A dimensioned multiviewdrawing of a single part, using ANSI standardconventions to describe the part’s shape, size,material, and finish. Detail drawings aresufficiently descriptive that the part can bemanufactured using the drawing as the onlycommunications device. Detail drawings areproduced from design sketches or extractedfrom a 3-D computer model.

development (n) An alternative description ofthe surfaces of a 3-D object as a 2-D pattern.The creation of a development is often thoughtof as an unfolding of the surfaces of an object.A developable surface, then, can be unfoldedor unrolled onto a plane without distortion.Single-curved surfaces, such as cylinders andcones, are also developable.

deviation (n) A tolerancing measure used todescribe the difference between the size of aproduced part and the basic size.

DFM (n) See design for manufacturability.

diameter symbol (n) A symbol used in ANSIdimensioning that precedes a numerical value,indicating that the value shows the diameter ofa circle. The symbol used is the Greek letterphi (ø).

difference (−) (n) The Boolean operation thatsubtracts, or removes, the intersecting geometryfrom the specified solid. For example, in theBoolean operation A − B, the intersection ofsolids A and B is removed from A.

diffuse (adj.) A term describing a reflection oflight that strikes a surface and reflectsuniformly in all directions, creating nohighlights or hot spots.

digital terrain model (DTM) (n) A 3-Dcomputer model of a land form generated fromsurvey data. Such models are often used bycivil engineers and land planners to explorepossible placements of structures or changes tothe terrain before actual construction begins.

dimension (n or v) The physical size of anobject, or the process of documenting physicalsizes. The number of dimensions used todescribe the object depends on whether length(1-D), area (2-D), or volume (3-D) is beingmeasured. Dimensioning can also refer to themeasurement of size, location, and orientationof particular features on an object.

dihedral angle (n) The angle between twoplanes. Finding the true measurement of adihedral angle requires an edge view of the twoplanes and is a common application for the useof auxiliary views.

dimension line (n) A thin, solid line thatshows the extent and direction of a dimension.Dimension lines are paired with the numberrepresenting the physical size of the feature,and extension lines are used to associate thedimension to the corresponding feature on thedrawing.

dimetric projection (n) An axonometricprojection in which two of the three axes havethe same scale and the same angle relative tothe third axis. A dimetric drawing is lesspleasing to the eye than a trimetric projectionbut is easier to draw.

direct data exchange (n) A method of dataexchange between CAD systems. Data isdirectly translated from the format native to onesystem to the format native to another system.

direct view (n) A descriptive geometrytechnique (sometimes referred to as the naturalmethod) that places the observer at an infinitedistance from the object, with the observer’sline of sight perpendicular to the geometry inquestion. In third-angle projection, a projectionplane is placed between the observer and theobject, and the geometry is projected onto theprojection plane.

directrix (n) A line (typically curved) thatdescribes the path of a straight line (thegeneratrix). The path of the generatrix alongthe directrix describes ruled surfaces or solids.

discretization (v) The method of dividingmore complex geometry into simplergeometry. A discretized model can bemanipulated using techniques such as finiteelement analysis, in which all the simplegeometric components of a model areevaluated simultaneously.

G-6 GLOSSARY

displacement (n) The linear or angulardistance moved by a part or mechanism. Incam design, a displacement diagram is used tochart the linear location of the follower relativeto the angular position of the cam.

display devices (n) The hardware used todisplay output text and graphics of computersoftware, such as CAD. The most commondisplay device is the cathode ray tube, or CRT,used in computer monitors.

dither pattern (n) A method of simulatingvarying value (gray) levels within an imagewhen only one color of ink (usually black) isavailable. The patterns are achieved bygrouping square matrices of pixels in an image(e.g., 3 × 3) and coloring a pattern of pixels inthe matrix, based on the average value level inthe matrix region. Because of the small size ofthe pixels relative to the size of the image, thepixel patterns give the impression of valuechanges when viewed at a distance.

document sketches (n) A more formal type offreehand sketch used during the refinementstage of the design process. These sketchesoften contain many of the conventions found inmore formal drawings.

domain (n) A term that describes the types ofobjects that can or cannot be represented by acomputer modeler. The larger the domain, thegreater the number of objects the CAD systemcan describe.

donut (n) See feed-through.

double-curved surface/line (n) A surface orline that curves in two orthogonal dimensionsat the same time. A sphere is an example of adouble-curved surface.

double-line drawing (n) See piping drawing.

drill drawing (n) See fabrication drawing.

drawing exchange format (n) See DXF.

drilling (v) A process that uses a rotatingcutting tool to produce holes. It can also refermore specifically to a process that producesholes using twist drill bits.

DTM (n) See digital terrain model.

DXF (n) Acronym for drawing exchangeformat, a nonproprietary CAD data formatdeveloped by Autodesk to facilitate theexchange of CAD-based graphic information.It has become a de facto neutral data exchangeformat for the microcomputer CAD industry.

dynamic analysis (n) The evaluation of adesign as it changes over time. Unlikekinematic analysis, dynamic analysis assumesthat forces (e.g., gravity, angular momentum)are both acting on and created by themechanism being analyzed.

EECO (n) See engineering change order.

edge (n) The intersection or boundary of twonontangential surfaces (faces). An edge isrepresented on a technical drawing as a line ora change in shading gradients in a renderedimage.

edge view (n) The view of a surface such thatit is seen as a line. For a planar surface, theedge view is an orthographic view parallel tothe plane in which the surface resides.

efficiency (adj.) With respect to CAD, thespeed with which software can execute acommand. This is reflected in the amount ofcomputer processing time required to execute acommand.

elastomers (n) A special class of polymers thatcan withstand elastic deformation, then returnto their original shape and size. Natural rubber,polyacrylate, ethylene propylene, neoprene,polysulfide, silicone, and urethane are types ofelastomers.

electrical engineering (n) A field ofengineering that includes the research,development, design, and operation of electricaland electronic systems and their components.

elevation drawing (n) A type of drawingcommonly used in civil, architectural, orengineering projects involving large structurallayouts. An elevation drawing (sometimescalled an elevation view) is an orthographicview perpendicular to the line of gravity (i.e.,parallel to the terrain). These drawings areuseful in planning the vertical arrangement ofcomponents within a structure, or of thestructure relative to the terrain, and are alsoused to make aesthetic judgments since thisview closely matches how the structure wouldbe seen.

ellipse (n) A single-curved line primitive. Anellipse is a conic section produced when aplane is passed through a right circular coneoblique to the axis and at a greater angle withthe axis than the elements. An ellipse alsodescribes a circle or circular arc viewed at anyangle other than normal (perpendicular).

engineer (n) A professional concerned withapplying scientific knowledge to practicalproblems. The discipline is divided into anumber of specialties, such as civil,mechanical, chemical, electronic, aerospace,electrical, and industrial engineering.

engineering change order (ECO) (n) Adocument that begins the process for makingchanges in a design. Normally, the ECO willbe documented in an engineering change note(ECN). A copy of the engineering drawing isattached to the order, with sketches and awritten description of the change. A referencenumber is given to the change order so that itcan be traced within the organization.

GLOSSARY G-7

engineering graphics (n) A communicationsmethod used by engineers and other technicalprofessionals during the process of findingsolutions to technical problems. Engineeringgraphics are produced according to certainstandards and conventions so that they can beread and accurately interpreted by anyone whohas learned those standards and conventions.

envelope principle (n) A term used ingeometric dimensioning and tolerancing todescribe how much a feature can deviate fromideal form, orientation, or position as it departsfrom maximum material condition.

ergonomics (n) A technical field concernedwith optimizing the interface between humansand technology. The field has numerousspecialties, including industrial safety andhygiene, human–computer interface design,and the design of control panels inmanufacturing plants, cars, airplanes, etc.

error bar (n) A mark added to data points ingraphs and plots to indicate the range ofprobable values. Since perfect accuracy is notpossible in any kind of experimental method,the error bar represents the degree of certaintyin the data value. The length of the bar usuallyrepresents the statistic of standard deviation.

error checking (v) The process of evaluatingactions requested by the operator to determineif such actions resulted in invalid geometry.Depending on the system, error checking maybe done automatically (such as when a file issaved to disk) or manually at the request ofthe user.

etching (n) The method of creating patterns,typically in metal, using chemical processes. Inthe electronics industry, etching is used toremove conductive material, usually copper,from printed circuit boards to create wiringpatterns. The wiring pattern is printed on theboard in a chemically resistant ink, and the restof the conductive material is then dissolvedaway in a chemical bath.

Euler operations (v) Low-level operationsused to construct models from geometricprimitives, such as vertices, edges, and faces.The validity of the model is guaranteed by asimple mathematical formula, credited to bothLeonhard Euler (1707–1783) and Jules HenriPoincaré (1854–1912).

evaluated (adj.) A description of a model forwhich the final form is explicitly represented inthe database. An evaluated model is notconcise (it may take up large amounts ofmemory), but it is efficient (calculations on themodel are processed quickly).

exploded assembly (n) An assembly drawing,usually a pictorial, in which the parts of theassembly are spread apart (exploded) fromtheir functional location in order to provide alarger, clearer view of the features of the

individual parts. Flow lines are used to relatethe parts to each other and to demonstrateassembly. This type of assembly drawing isused extensively for technical illustrations insuch applications as parts catalogs andassembly instructions.

exposure (n) The orientation of a principalsurface of an object relative to the image plane.The greater the exposure, the closer thesurface(s) is to being parallel to the imageplane and, therefore, the lower the distortioncaused by foreshortening.

extension line (n) A thin, solid lineperpendicular to a dimension line, indicatingwhich feature is associated with the dimension.

Ffabrication drawing (n) An electronicsdrawing that presents the complete engineeringfor the manufacture of a printed circuit board.The fabrication drawing contains an accurateto-scale layout of the board shape, drill holelocations, material and manufacturingspecifications, and conductor pattern. Theconductor pattern is broken out to make anartwork drawing, a screen print drawing, andthe mask used in board etching. The drill holeinformation is sometimes broken out into aseparate drill drawing for use in programmingthe drill patterns.

face (n) A distinct planar or curved surface orregion on an object. One or more faces joinedtogether at edges define the boundary betweenobject and nonobject. A face is a topologicalelement in a 3-D model.

face-edge-vertex graph (n) The data structureused by boundary representation (B-rep) 3-Dsolid modelers. The graph contains bothgeometric information on the location and sizeof geometric elements and topologicalinformation on how they are linked together.

facets (n) Repeating groups of polygons ofsimilar topology, forming an approximaterepresentation of a curved surface. Curvedsurfaces such as cylinders and spheres aresubdivided into a series of faceted planarsurfaces, which approximate the originalsurface. This transformation is often used sothat curved surfaces can be rendered usingalgorithms that only support planar surfaces.

faithful (adj.) A measure of whether acomputer model contains or imparts sufficientinformation to fulfill its task. In order to definethe faithfulness of a model, the exact use of themodel must be known.

familiar size (n) A perceptual cue in which theknown (familiar) size of an object is used tojudge its distance from the observer. Often, thecomparison of the perceived size of twoobjects is used to judge their relative locationsin depth.

family of parts (n) Similar parts that can begrouped together. A family of parts might be aseries of air cylinders that have many commontopologies but have variations in the geometryof certain features, such as the diameter orlength of the head. Parametric techniques canbe used to represent a family of parts on thecomputer or in drawings.

fastener (n) A mechanical device thatconstrains two or more parts. Fasteners canrigidly join parts or can allow certain degreesof freedom. Some fasteners are meant to bedisassembled for maintenance (e.g., screws andbolts), while others are considered permanent(e.g., rivets).

feature (n) A general term applied to physicalportions of a part. Features typically serve afunction, either in the final application of thepart or in the specification or manufacture of it.Examples are a hole, slot, stud, or surface.

feature control frame (n) A rectangularoutline containing geometric dimensioning andtolerancing information used in theengineering, production, and inspection of apart. The left-hand compartment inside theframe contains the symbol of the geometriccontrol being applied. The middlecompartment contains the size of the tolerancezone. The right-hand compartment contains thedatum identification symbol(s).

feature of size (n) A feature that ismeasurable; specifically, a spherical orcylindrical surface, or a pair of parallel planesurfaces, associated with a feature.

feed-through (n) A through-hole in a printedcircuit board which has a conductive surroundon at least one side of the board and sometimesin the hole. The conductive pads or donuts oneither side of the hole are used to makeelectrical connections through the board andwith component wires that are soldered intothe holes.

FEM/FEA (n) See finite element modelingand analysis.

fillet (n) A rounded interior corner normallyfound on cast, forged, or molded parts. Like around, a fillet can indicate that a surface is notmachine finished. A fillet is indicated onengineering drawings as a small arc.

finite element modeling and analysis(FEM/FEA) (n) An analysis technique usedextensively to model and analyze forces withina computer model or a proposed design. In themodeling phase, the continuous surface orvolume is discretized into a finite number oflinked primitive geometries. In the analysisphase, the model is subjected to theoreticalforces applied at certain locations, and theresulting forces are calculated across the rest ofthe model.

fittings (n) A term used to describe componentsthat connect pipes, valves, and other fluid andgas-handling equipment. Fittings are oftenclassified by the method used to join thecomponents together. Some of the most commontypes are welded, threaded, and flanged (bolted).

fixture (n) A rigidly held production tool thatsecurely holds, supports, and locates theworkpiece. Unlike a jig, a fixture is not used toguide a cutting tool.

flat shading (v) A rendering method thatuniformly adjusts the value of a surface colorbased on its orientation to the light. Thismethod is considered the simplest shadingmethod since it only requires the calculation ofa single surface normal.

flatness (n) A form control for geometricdimensioning and tolerancing. Flatnessindicates that all points on the surface must liein a plane. Flatness for a planar surface iscomparable to straightness for a line.

flexible manufacturing system (FMS) (n) Agroup of machines that can be programmed toproduce a variety of similar products. Forexample, an automobile parts supplier mightspecialize in the production of gears fortransmissions. An FMS cell might be used toproduce the gears for more than one automobilemanufacturer because the parts are similar.

flow charts (n) A visualization technique fordisplaying relationships in time, particularlyfor data that doesn’t conform well to scalarmapping. PERT charts and other types of flowcharts are project management tools used tomap the relationship of specified project tasks,personnel, and other resources on a singletimeline.

flow diagram (chart) (n) A diagram used inelectronic and piping systems to describe thesystem’s process and the flow of material (orelectronic signals) through the proposeddesign. Since these diagrams only depict thefunctional nature of the system, they do notshow the true spatial layout or geometry of thecomponents.

flow lines (n) Lines used primarily in technicalillustrations to indicate the assembly of parts inan exploded assembly. Flow lines are thinphantom lines drawn parallel to the line ofassembly between two parts. Right-angle jogsare placed in the flow line when the drawing ofthe part has been moved away from the directline of assembly for reasons of clarity.

FMS (n) See flexible manufacturing system.

focus point (n) A location where reflectingrays from a (parabolic or hyperbolic) surfaceconverge. Focus point describes both thephysical phenomenon of light rays reflectingfrom a mirrored surface and the abstractgeometric calculations of line paths.

G-8 GLOSSARY

fold line (n) A basic concept in descriptivegeometry used to define a line that isperpendicular to projection lines and is sharedbetween views of a drawing. A fold line canalso describe the “hinge” line between theimage planes of the glass box used to defineorthographic multiviews.

font (n) The size and style of text characters.

foreshortened (adj.) The reduction in size ofone or more dimensions of a planar face due tothe face not being perpendicular (normal) tothe line of sight. The dimension foreshortenedis defined by the axis of rotation of the face outof a plane normal to the line of sight. When theface is rotated in its edge view, theforeshortening is applied to a line.

forming (v) A process in which componentsare held together by virtue of their shape. Thisis the least expensive fastening method, and itmay or may not be permanent. Heating and airconditioning ductwork is held together byforming the sheet metal.

four-color printing (n) A color printingprocess in which a full-color image is dividedinto four separate images, each representing theamount of one of the three subtractive primarycolors (cyan, magenta, and yellow) or blackcontained in the image. Printing plates aremade from the new images, and each is printedin a single ink color as an overlay. This processis also called the CMYK system, an acronymfor the four ink colors, where K is for black.

fractal (adj.) The term, short for fractionaldimensional, used to describe graphics withrandomly generated curves and surfaces thatexhibit a degree of self-similarity. Fractaldesign tools provide new opportunities fordesigners to produce complex patterns withmore visual realism than can be output fromconventional geometry programs.

free-form surface (n) Three-dimensionalsurfaces that do not have a constantgeometrical shape. Free-form surfaces followno set pattern, are classified by their use asconstrained or unconstrained, and are typicallyproduced using sophisticated CAD programs.

front view (n) A principal view of an object,typically the first one defined, orienting theobject such that the majority of its features willbe located in the front, right side, and topviews.

frontal line (n) A line that is seen in its truesize in the frontal plane.

frontal plane (n) A principal orthographicplane of projection. This plane is used todefine both the front and back orthographicviews.

full section (n) A sectional view generated bypassing a single cutting plane completelythrough the object.

functional analysis and design (n) A designdriven by the intended use of the product.Functional analysis determines if the design isan answer to the problem statement writtenduring the ideation phase. Aestheticconsiderations are often considered the foil tofunctional considerations.

fundamental deviation (n) A tolerancingmeasure used to describe the deviation closestto the basic size.

Ggamut (n) The range of colors possible at asingle pixel on the computer monitor. Thegamut is not the full range of colors perceivableby the eye but is typically quite large. Thehardware and software of the computer systemdetermine what that gamut will be.

gear (n) A toothed wheel device that acts as amechanical linkage to transmit power andmotion between machine parts. Most gearstransfer rotary motion from one shaft to another.They change the location and can change boththe orientation and speed of the rotary motion.Certain gear types transform rotary motion intolinear (reciprocating) motion.

gear train (n) A mechanism consisting of twoor more gears and used to transmit power.Normally, gear trains are used to do one ormore of the following: increase speed, decreasespeed, or change the direction of motion.

general notes (n) Text placed in the drawingarea, including general information that cannotbe effectively or quickly communicatedthrough graphical means.

general oblique (n) A type of oblique pictorialdrawing in which the two dimensions of thefrontal surface are drawn parallel to the frontalplane and the third (receding) axis is drawnobliquely at any scale between 50 and 100percent of the frontal plane dimensions. Thereceding axis is typically drawn at an angle ofbetween 45 and 60 degrees.

general-purpose section line (n) A defaultsection line symbol used to indicate the cutsurface of a sectional view. This symbol isused to represent cast iron, or an anonymousmaterial if none is defined.

generatrix (n) A straight line for which thepath through space describes ruled surfaces orsolids. The path the generatrix follows is calledthe directrix.

geometric dimension (n) A dimension thatspecifies the size and location of a feature, aswell as other geometric qualities such as formand orientation. Geometric dimensioning andtolerancing, combined with statistical processcontrol, provide a robust approach toinspection and quality control formanufactured parts.

GLOSSARY G-9

geometric transformations (v) Basicoperations used to modify existing geometrycontained in the CAD database. Examples oftransformations include translation androtation. Most transformations used in CADsystems are executed as matrix operationsbased on linear algebra theory.

geometry (n) The mathematical method bywhich elements in space are described andmanipulated. Geometry forms the buildingblocks of engineering and technical graphics.The term is also used to mean shape or form.

glyph (n) A compound mark used in avisualization that cannot be classified by othercommonly used marks. Glyphs are usuallycustom designed to encode multiple elementsof data into a single mark. The objective fordesigning glyphs or any other marks is to tapinto the innate perceptual abilities of theviewer.

Gouraud shading (v) A rendering method thatuniformly adjusts the value of a surface colorbased on the relationship of the light source tonormals calculated for each vertex of themodel. Gouraud shading is sometimes calledsmooth shading because the vertex normalsallow interpolation of shading values acrossmultiple polygons representing the facets of acurved surface.

graphical analysis (n) Analytic techniquesemploying primarily graphics to evaluate apotential design, such as the fit of mating partsor the movement of parts in a mechanism.

graphics (n) A mode of communication usingspatial/geometric representations.

grid (n) A regular pattern of points or linesused to help locate and orient specific marks orfeatures or to help guide the development ofsketches and roughly proportion features.

ground line (n) In a perspective drawing orsketch, the point of the object closest to theobserver.

ground’s eye view (n) In a perspectivepictorial, a viewpoint looking up at the object.From this viewpoint, the horizon line is levelwith the ground line of the object.

group technology (n) The process ofidentifying items with similar design ormanufacturing characteristics. Items with similarcharacteristics are grouped into part families.

guideline (n) A type of construction line usedto guide the lettering on the drawing. The termcan also refer to lines used for the placement ofother elements in a drawing or sketch.

Hhalf section (n) A section view generated bypassing a cutting plane halfway through anobject. The result depicts half the viewsectioned.

half-space (n) A mathematically definedboundary between two regions. The term isused in constructive solid geometry (CSG)modelers to define the boundary between thesolid and the void (nonsolid). Geometricprimitives in CSG modelers are defined asgroups of half-spaces.

halftone approximation (n) A method ofsimulating varying value (gray) levels withinan image when only one color of ink (usually)black is available. Dots of varying size areprinted based on the average value level in theregion. Because of the small size of the dotscompared with the size of the image, thechanges of dot size (and therefore ink density)give the impression of value changes whenviewed at a distance. Halftones from full-coloror gray-scale images can be created bothelectronically or photographically.

hardware (n) A term used to define physicalcomputer equipment. Examples of hardwareinclude the monitor (CRT), keyboard, harddisk, and CPU.

height (n) One of the three principaldimensions of an object. The height dimensionis described in the right side and front views ofa multiview drawing. The height dimension isoften associated with the Y axis in a 3-Dmodeling system.

helix (n) A 3-D curve characterized by aconstant rate of curvature about twodimensions and a constant linear translationin the third. Threads on screws and bolts arehelical and are classified as being either right- or left-handed.

hidden line (n) A line used to represent afeature that cannot be seen in the current view.Like a visible line, a hidden line representseither the boundary between two surfaces(faces) that are not tangent, or the limitingelement of a curved surface. A specificlinestyle is defined by ANSI for hidden lines.

hidden surface removal (v) The renderingprocess of removing the elements of a modelnot visible from a particular viewpoint. Theremoval is accomplished by calculating therelationship of edges and surfaces along thedepth axis.

hierarchy (n) An ordered set of elements inwhich each element belongs to a specific level.An element at each level can be a parent toelements below it on the hierarchy, or a childto elements above it, or both. Hierarchies areused to describe the organization of files in acomputer system, or geometric primitives in aCAD model.

highway diagram (n) See wiring diagram.

histogram (n) A visualization technique usedto summarize data by reporting the number ofdata points that fall within a certain range of

values. Histograms are often represented as bargraphs. Because histograms provide only asummary, they depict the original informationonly indirectly.

hole basis (n) A tolerancing measure used todescribe a system of fits in which the minimumhole size is the basic size.

hole loop (n) A close group of edges on theinterior of an object, defining a penetration thatgoes part or all the way through. The numberof hole loops is one of the variables in theEuler–Poincaré formula used to validate thetopology of a model.

horizon line (n) In a perspective sketch, ahorizontal line marking the location where allprojection lines from the observer converge.

horizontal line (n) A line seen in its true sizein the horizontal plane.

horizontal plane (n) A principal orthographicplane of projection, used to define both the topand bottom orthographic views.

HSV color model (n) A model based on theperceptual components of color, that is, (H)ue,(S)aturation, and (V)alue (lightness), modeledas a hexacone. Hue is laid out in a radialpattern around the hexacone, saturation rangeslinearly from full saturation at the perimeter towhite at the center, and value runs from thebase of the hexacone (white) to the point(black).

hue (n) The dominant spectral wavelength of aperceived color. Hue and color are oftenconfused because the name given to the hue isoften synonymous with the name of the color.

human factors analysis (v) A process forevaluating a design to determine if the productserves the physical, emotional (aesthetic),quality, mental, and safety needs of theconsumer. Specialists in human factors orergonomics are often employed to conduct thisevaluation.

human’s eye view (n) In a perspectivepictorial, a viewpoint looking slightly down atthe object. From this viewpoint, the groundline is equivalent to six feet below the horizonline of the object.

hybrid modeler (n) A 3-D modeling systemthat combines the operations and databasestructure of more than one of the commonlydefined modeling systems. Used with morepowerful computing systems, these modelerscombine the advantages of more than onesystem. An example is the combination ofCSG and surface modeling technology.

hyperbola (n) A single-curved surfaceprimitive, created when a plane intersects aright circular cone at an angle with the axisthat is smaller than that made by the elements.

hypermedia (n) An interactive, computer-based information system, created withauthoring tools, which allows flexible,nonlinear access. Information is linked boththrough elements selected within the body ofthe information and through sophisticatedsearch engines.

Iideation (n) A structured approach to thinkingfor the purpose of solving a problem, oftenemploying graphics. Ideation is the conceptualphase of the design process. Feasibility studiesare often performed to define the problem,identify important factors that limit the scopeof the design, evaluate anticipated difficulties,and consider the consequences of the design.

ideation drawings/sketches (n) A type offreehand sketch or drawing used early in thedesign process to explore design ideas quickly.These sketches are usually rough andincomplete, typically not following many ofthe conventions used for more finisheddrawings.

IGES (n) Acronym for initial graphicsexchange specification, an indirect dataexchange standard used largely in the UnitedStates to exchange CAD information betweendisparate systems. Originally developed by theU.S. government and major defense contractors,it is used mainly on workstation, minicomputer,and mainframe-based CAD systems.

image plane (n) An imaginary plane on whichan object is projected. The graphicrepresentation of an object on a computerscreen or paper is an example of a projectionas it would appear on an image plane.

inclined edge/line (n) An edge of a face that isparallel to a plane of projection but inclined tothe adjacent orthogonal planes. The edgeappears as an inclined, true-length line in oneof the principal views and is foreshortened inthe two adjacent views.

inclined face (n) A planar face (surface) of anobject that has been rotated about one axisfrom one of the principal image planes. Aninclined face will appear foreshortened in twoof the principal views and as an edge in thethird.

independent variable (n) A variable for whichthe values are controlled by the experimenterto create a response in the model as measuredby the dependent variable. Every independentvariable value is paired with one or moredependent variables and represents theexperimental manipulation of the model.

indirect data exchange A method oftranslating data from one CAD system toanother through an intermediate, neutral dataformat. Examples of intermediate data formatsinclude IGES and DXF.

G-10 GLOSSARY

industrial engineering (n) A field ofengineering concerned with the analysis anddesign of systems for organizing the basicproduction resources such as personnel,information, materials, and equipment.Industrial engineers use mathematics, thephysical and engineering sciences, and themanagement and behavioral sciences.

infinite light source (n) A light source locatedat a theoretically infinite point in space. Thesun is analogous to an infinite light source. Inrendering, the user specifies an orientation forthe light rays, all of which are parallel to eachother.

initial graphics exchange specification (n)See IGES.

input device (n) Computer hardware used bythe operator to input information into asoftware program. Examples are keyboard,mouse, scanner, etc.

instances (n) Cloned copies of geometryalready existing in a database. Typically, aninstance is linked directly to the geometric andtopological information of its parent butcontains unique information pertaining to itslocation, orientation, and scale in themodel/drawing. Some systems refer toinstances as symbols.

integrated circuit (n) An electroniccomponent made up of a large number ofdiodes, transistors, and resisters and integratedonto a single semiconductor substrate such assilicon. An example of an integrated circuit is acentral processing unit (CPU) in a computer.

intensity depth cueing (n) A renderingtechnique which calculates the Z-depths of theedges in a model and sets their brightness(intensity) relative to their depths. Thistechnique taps the aerial perceptual depth cueand has the effect of making the model fade asit goes back in depth.

interconnection diagram (n) See wiringdiagram.

interference fit (n) A fit in which twotoleranced mating parts will always interferewhen assembled because the “male” part islarger than the “female” part. The resultingdifference in sizes, also called the allowance,means that force is required to assemble thepart. An interference fit fixes or anchors thetwo parts as if they were one.

International System of Units (n) See SI.

international tolerance grade (n) A group oftolerances that vary depending on basic sizebut have the same level of accuracy with agiven grade. The smaller the grade number, thesmaller the tolerance zone.

intersecting lines (n) Lines that share one ormore common points in space. Lines that share

all their points in common, or lines for whichone could be considered a subset of the other,are called coincident.

intersection (n) The Boolean operation inwhich only the intersecting geometry of twosolids remains.

interval scale (n) A data scale that preservesthe units used but does not have a natural zeropoint. Interval scales often result from thedifference between two values using the samescale.

involute (n) A curve defined as the spiral traceof a point on a flexible line unwinding fromaround a line, circle, or polygon. Thecontacting surfaces between gear teeth aredesigned as involutes.

isometric drawing (n) A pictorialrepresentation of an object rotated 45 degrees,tilted 36 degrees 16 minutes, then drawn fullscale. An isometric drawing differs from anisometric projection in that all threedimensions are drawn at full scale rather thanforeshortening to the true projection.

isometric ellipses (n) A special type of ellipseused to represent holes and ends of cylinders inisometric drawings. In an isometric drawing,circular features are often not viewednormally, foreshortening them and makingthem appear as ellipses.

isometric grid (n) A network of evenly spacedlines drawn at 30, 90, and 120 degrees. Paperpreprinted with this grid is used to sketchisometric drawings.

isometric line/plane (n) A line or plane that isparallel to one of the principal isometric axesor to two adjacent isometric axes, respectively.Isometric lines and planes are typically thesimplest elements to represent in an isometricdrawing.

isometric projection (n) An axonometricprojection in which three of the axes aremeasured on the same scale and are at thesame angle relative to each other. An isometricdrawing is less pleasing to the eye than othertypes of axonometric projections, but it is themost common since it is the easiest to draw.

isosurfaces (n) A surface in 3-D space thatdefines constant values of a dependentvariable. Isosurfaces are the logical extensionof contour lines (isolines), which map constantvalues in 2-D space. Every point on anisosurface identifies the location where threeindependent variable values result in thedependent variable value of interest. Likeisolines, multiple isosurfaces can be used tomap different dependent variable values.

italic (adj.) A style of text in which verticalelements of letters are slanted forward. Thistechnique is used to make words or lettersvisually stand out from the rest of the text.

(U)

GLOSSARY G-11

Jjig (n) A special device that holds and supportsthe workpiece and guides the cutting tool asthe workpiece is machined. Jigs may not berigidly held to the machine.

JIT (n) An acronym for just-in-time, aplanning strategy used to reduce cycle timeand waste in production processes. JITrecognizes waste as anything that does not addvalue, including storing parts in warehouses.On the other hand, a production process suchas drilling is a value added procedure becauseit increases the value of the product.

joining (v) The bringing together of two ormore parts of an assembly in such a way as toovercome the natural forces that wouldseparate them. Joining can be done withmechanical fasteners, adhesives, etc., and canbe either temporary or permanent.

joints (n) An element in a kinematic modeldefining the constraints between two rigidparts of the assembly (called the links). Jointsdefine how the links can move relative to eachother, in rotation and translation.

just-in-time (n) See JIT.

KKBE (n) See knowledge-based engineering.

key (n) A fastening device used to attach shaftsto transmit power to gears, pulleys, and othermechanical devices. Common keys are plain,gib head, Woodruff, and Pratt & Whitney. Thekey is placed into a groove cut into the shaft(the keyseat) and one cut into the hub (thekeyway), aligning and locking the partstogether. Standard keys are specified using thesize of the shaft as the determining factor.

keyboard (n) A computer input device derivedfrom the typewriter, where keys pressedcommunicate discrete commands to thecomputer. Although most often used to input theletters of the alphabet, most keyboards containspecial character keys programmed by the useror the software to perform specialized tasks.

kinematic analysis (n) The evaluation of adesign as it changes over time. Of particularinterest is multicomponent mechanisms inwhich parts move at varying rates throughdifferent volumes of space. The positions ofthe parts relative to each other at various pointsin time are studied through kinematic analysis.

kinetic depth effect (n) A perceptual effect inwhich the changing movement of 2-D patternscreates the sense of a third dimension (depth).Related to apparent motion, this effect assistsin the interpretation of 3-D objects in animatedsequences.

knowledge-based engineering (KBE) (n)Software systems that complement CAD byadding the engineering knowledge necessary for

product design. A KBE system stores productinformation in a comprehensive model that iscomposed of design engineering rules, standardpractices, and general rules that describe how aproduct is designed and produced.

Llayering (v) A scheme by which the variousgraphic elements of a drawing can be groupedtogether in the CAD database. This facility isused most often to control what is seen oreditable on the screen and what is printed orplotted. Layering in most systems isnonhierarchical.

lead (n) A thread term describing the lineardistance a screw will travel when turned 360degrees, or 1 revolution. Lead is closely relatedto the pitch of a thread.

leader line (n) A thin, solid line used toindicate the feature with which a dimension,note, or symbol is associated. Leader lines areterminated at one end with an arrow touchingthe part or detail and a short horizontalshoulder on the other end. Text is extendedfrom the shoulder of the leader.

least material condition (LMC) (n) Atolerancing term indicating the condition ofa part when it contains the least amount ofmaterial possible. The LMC of an externalfeature is the lower limit of the part. TheLMC of an internal feature is the upper limitof the part.

left side view (n) A principal view of anobject, created by rotating the viewpoint 90 degrees about the vertical axis to the left ofthe front view. This view is not typicallyincluded in a standard multiview drawing.

legend (n) The region of a visualization wherean explanation is given regarding how thevariables are coded. This is usually done byequating a text description to a symbol of thecode. The legend is also called the key.

lightness (n) A perceptual quality of colorindicating the absolute quantity of light energy.On a gray scale, the lightest color, pure white,has the highest quantity of light. In rendering,lightness (also called value) is used to indicatethe orientation of the surface to the lightsource.

limiting element (n) The boundary of theprojection of an object. The term is usuallyused to describe the edge defining the apex ofa curved surface.

limits (n) The maximum and minimum sizesshown by the toleranced dimension. The largervalue in a toleranced dimension is called theupper limit and the smaller value is the lowerlimit.

line (n) A geometric element that connects twopoints in space. Although a line itself is 2-D in

nature, it may connect points in 3-D space.Lines are typically classified as either straight(linear) or curved. Lines are the mostprominent element in technical drawings,defining edges of objects, indicatingsymmetry, relating text elements to geometricelements, creating borders, etc.

line balloon (callout) (n) A note added to adrawing to relate an alphanumeric code with apart. A line balloon usually consists of a circleor a regular polygon enclosing the code and aleader pointing to the part. They are usedextensively in assembly drawings either todirectly specify a part or give an index valuethat references a parts list or separate catalog.

line graph (n) A visualization technique,usually 2-D, in which line marks are used toindicate trends in data. In a 2-D line graph, theindependent variable is represented on thehorizontal scale, and the dependent variable isshown on the vertical scale. The line markrepresents the mapping of the two variables.

line of sight (LOS) (n) Imaginary rays of lightradiating from an observer’s eye to the object.In perspective projection, all lines of sight startat a single point; in parallel projection, all linesof sight are parallel. LOS is sometimes referredto as the viewpoint.

line rendering (n) A technique used in technicalillustration for adding realism and readability to apictorial drawing by altering qualities of thelinework on the drawing. The thickness of theline and the positions of line breaks or gaps arealtered to differentiate between geometricfeatures of a part or assembly. Line rendering ispopular because it is fast, can be done withstandard drawing instruments or CAD tools, andcan be reproduced by most popular reproductiontechniques.

link charts (n) A visualization technique usedextensively in ergonomics to depict the spatialarrangement of controls, displays, andpersonnel associated with a work environment.Line marks show the connections between aworker and a control or display or incommunication with other personnel. Some ofthe variables typically coded include frequencyof usage and type of information exchange(i.e., auditory, visual, physical, etc.).

linkages (n) Rigid bodies (parts) that transmitlinear or rotational force. Linkages are multiplelinks that are combined through joints.Constraints applied to the joints define themovement of the individual links. Commontypes of linkages include rocker arm, crank,lever, and four-bar.

links (n) In a kinematic model, the geometricform representing a unique part of amechanism. Links are related to each otherthrough joints, which define how they canorient relative to each other.

LMC (n) See least material condition.

local coordinate system (n) A transientcoordinate system that can be positionedanywhere in space. The local coordinatesystem is used to assist in the construction ofgeometry, and the origin is usually definedrelative to the feature of current interest.

locus (n) A graphic element representing allpossible allowable locations of a point. Thelocus of points may be drawn as a line, circle,or arc. For example, a circle is a locus of allpoints at a distance from the center, equal tothe radius of the circle. Loci are usedextensively in geometric constructions as atool for finding the centers of tangent arcs, theendpoints of lines, etc.

logic drawing (n) See schematic drawing.

logic gates (n) Electronic components that takeinput signals and create output signals basedon the input states and the logic of the circuit.Types of logic gates include AND, OR,NAND, NOR, and inverters.

long-axis isometric (n) A variation of theregular isometric pictorial view. In a regularisometric, it appears as if the viewer is lookingdown on the object from the top; in a long-axisisometric, it appears as if the viewer is lookingfrom the right or the left of the object, with oneof the axes drawn at 60 degrees from thehorizontal.

LOS (n) See line of sight.

lower deviation (n) A tolerancing termdescribing the difference between the minimumsize limit and the basic size.

Mmachine (n) A combination of interrelatedparts used for applying, storing, ortransforming energy to do work. Machinesconsist of one or more assemblies, which areanalyzed using techniques such as kinematicsand dynamics.

machine control (n) A process that directs themachine tools necessary to transform rawmaterials into a finished product. Machinecontrol has evolved from human control tomachine automation using numerical control(NC) and then computer numerical control(CNC).

machine screw (n) A mechanical fasteningdevice with a slotted head on one end andthreads on the other. The threaded end canscrew into either a mating part or a nut. Amachine screw is similar to a slotted head capscrew but is normally smaller.

machine tool (n) A production device used tochange the shape, finish, or size of a piece ofmaterial, typically using some type of cuttingedge.

G-12 GLOSSARY

major axis (n) The long axis of an ellipse. In apictorial projection, this axis represents thetrue diameter of the circle being projected.

major diameter (n) A threading term referringto the largest diameter on an internal orexternal thread.

manifold models (n) Models thatunambiguously define a boundary between theinside and outside of an object. Solid modelersare usually restricted to manifold objects,whereas surface modelers often defineunclosed, nonmanifold objects with no cleardivision between inside and outside.

manufacturing automation protocol (n) SeeMAP.

manufacturing processing (v) An activityconcerned with the scheduling, forming,treating, shaping, joining, and cutting of rawmaterial in the production of goods.

MAP (n) An acronym for manufacturingautomation protocol, a communicationsstandard being developed for compatibilitybetween different automated manufacturingsystems. The goal of MAP is the totalintegration of islands of automation inmanufacturing, regardless of the type ofhardware and software used in each system.

marketing (n) The division of a businessinvolved with convincing customers topurchase the product or service provided bythe company. In order to sell the product moreeffectively, marketing will gather informationon potential customers, both directly andindirectly, and will use these data to influencethe design of the product so that it moreclosely matches the customer’s needs.

marks (n) The fundamental graphic elementsused to encode data in a visualization. Markscan be thought of as graphic primitives and aretypically classified as either simple or complex.Simple marks include points, lines, areas, andvolumes. Complex marks are also calledglyphs. All marks interrelate closely with thedimension of the data type.

mass properties analysis (n) Analytictechniques directly related to the geometricproperties of an object. Typical calculationsare the mass, centroids (center of gravity), andintertial properties of the object. In order tosuccessfully use these techniques, the modelmust be able to unambiguously define thevolume the object occupies and the density ofthe material within the volume.

material control (n) A term describing themanagement of the flow of materials throughthe production process. Just-in time (JIT)techniques are used to recognize which rawmaterials are needed and when.

materials engineering (n) A field ofengineering that comprises a wide spectrum of

activities directed toward the design,development, and production of metals, alloys,ceramics, semiconductors, and other materialsfor engineering applications.

material requirement planning (n) See MRP.

mathematics (n) An abstract symbol-basedcommunications system based on formal logic.Geometry is one of the oldest fields ofmathematics and underlies most of theprinciples used in technical graphics and CAD.

matrix charts (n) A visualization techniquethat uses grids to show relationships betweenat least two, often qualitative, variables. Eachvariable is represented along a scale, and theinterior grid cells represent possiblecombinations of variable values. Marks areplaced in the grid cells, representing therelationship between variable values.

maximum material condition (MMC) Atolerancing term defining the condition of apart when it contains the most amount ofmaterial. The MMC of an external feature,such as a shaft, is the upper limit. The MMC ofan internal feature, such as a hole, is the lowerlimit.

mechanical engineering (n) A field ofengineering comprising a wide range ofactivities, including research, design,development, manufacturing, management, andcontrol for engineering systems and theircomponents. Mechanical engineers work insuch fields as transportation, power generation,energy conversion, environmental control,aeronautics, marine science, and manufacturing.

mechanical fastening (v) A process that usesa manufactured device added to an assembly tohold parts together. Mechanical fastenersinclude threaded and nonthreaded fasteners,such as rivets, keys, pins, snap rings, and clips.

mechanics (n) An area of applied physicswhich, at a macro level, deals with theresponse of bodies (parts) to the action offorces, and, at the micro level, with theresponse of materials.

mechanism (n) A mechanical system made ofrigid structures, such as shafts, housings, andpillow blocks, and connected by variouslinkages, such as gears, cams, and cranks. Amechanism is activated by applying a load orforce at one or more points in the mechanism.

mechanism analysis (n) An analytic techniquethat determines the motions and loadsassociated with mechanical systems made ofrigid bodies (links) connected by joints. Thetwo most common types of mechanismanalysis are kinematic and dynamic.

media (n) A means of conveyinginformation, both graphic and textual.Traditionally, this refers to the types of paperused in drafting; more recently, it has also

GLOSSARY G-13

come to refer to the types of informationstorage and playback technology, such asvideo, audio, CD-ROM, etc.

memory device (n) Computer hardware usedto store information, such as CAD data.Transient storage is random access memory(RAM); more permanent storage includesfloppy disks, CD-ROMs, magnetic tape, etc.

minor axis (n) The short axis of an ellipse. Ina pictorial projection, the length of this axisvaries with the relationship of the viewdirection to the surface of the circle the ellipserepresents.

minor diameter (n) A threading term referringto the smallest diameter on an internal orexternal thread.

miter line (n) A special construction line usedto share the depth dimension between the topand right side views of a multiview drawing.The line is drawn at a 45-degree angle and isused as a point of intersection for lines comingto and from the right side and top views.

MMC (n) See maximum material condition.

model solid (n) In a modeling system, thesolid object being manipulated by tool solidsduring the course of creating the final model.Whereas the tool solids are transient in nature,the model solid defines the state of the objectas it evolves into the final model.

modeling (v and n) Often referred to asgeometric modeling, which is both a processand a product. Modeling is used to analyzepreliminary and final design solutions, as wellas provide input to the production process inthe form of a computer database. Modeling is aproduct since it is a result of the designprocess, which uses graphics as a tool tovisualize possible solutions and to documentthe design for communications purposes.

modem (n) A computer hardware device thatuses standard telecommunications lines (phonelines) to send computer data from onecomputer to another. Modems are used toconnect computers at remote sites notconnected by local area networks. The speed inwhich modems can transfer information ismeasured in bits per second, or baud.

motion (n) The movement of a part, eitherlinearly or angularly, over time and space.

mouse (n) A small, hand-held computer inputdevice that rests on a work surface and ismoved in two dimensions to correspond tolocations on the computer monitor. A cursor onthe screen indicates the current location of themouse and buttons on the top of the mouse areused to indicate the action to be performed atthat location.

MRP (n) An acronym for materialrequirement planning, a process used tocalculate the amount of raw materials

necessary to manufacture a specified numberof products. MRP uses the bill of materialsfrom the engineering drawings or CADtechniques such as attribute assignments. MRPhas evolved into material resource planning,which includes both materials and financing.

multimedia (n or adj.) A term used to refer tothe systems or methods that conveyinformation in more than one media form andoften through more than one sense. Theintegration of text and graphics could bethought of as a simple multimedia system.

multiple-line graph (n) A visualizationtechnique similar to a regular line graph,except that an additional independent variableis mapped. The second independent variabletypically has only a few discrete values, eachof which is mapped as a separate line on thegraph. Color or symbol coding is used todistinguish between the lines on the graph.

multiview drawing/sketch (n) A type oforthographic drawing based on multiviewprojection techniques in which two or moreviews of an object are arranged in a singledrawing. Each view shows only twodimensions of the object and is chosen todepict specific features of the object clearlyand distinctly.

multiview projection (n) A special type oforthographic projection that places the object ina unique position behind a projection planesuch that a view is produced that shows onlytwo dimensions of the object. The outline of thefeatures of the part shows where the parallellines of sight pierce the projection plane.

mutually perpendicular (adj.) Two or morelines or planes that are at 90 degrees (rightangles) to each other, that is, orthogonal.

NNC (n) Acronym for numeric control, a formof programmable automation of a machinetool, using numbers, letters, and symbols.Unlike on an engineering drawing, the partgeometry must be defined using coordinatesinstead of graphics. All NC systems today usecomputers and are called computer numericalcontrol (CNC) machine tools.

networked hierarchy (n) A hierarchical partsstructure used by modeling systems. In anetworked hierarchy, parts can be sharedacross assemblies by means of software linksset up external to any one file. These partsstructures are often managed by specialdatabase software networked acrossworkstations within an organization.

nominal scale (n) A qualitative data scale thathas no inherent order to it (e.g., New York,Boston, and Houston).

nominal size (n) A dimension used to describethe general size of an object, usually expressedin common fractions. For example, a boltmight have a nominal size of 1/2′′.nonhierarchical (n) A structure in whichelements may be sorted into separate groups,but there is no defined linkage or ordering ofthe groups. Layering in CAD systems is oftendefined as being nonhierarchical.

nonisometric line/plane (n) A line or planethat is not parallel to one of the principalisometric axes or to two adjacent isometricaxes, respectively. In an isometric drawing,nonisometric lines and planes are typicallymore difficult to draw than isometric elements.

nonuniform rational B-spline (n) See NURBS.

normal (adj. or n) A term describing adirection perpendicular to a planar surface, or avector representing a perpendicular direction.Normals are used to calculate the orientation ofa surface with respect to a light source or viewpoint.

normal edge/line (n) An edge of a faceparallel to a plane of projection andperpendicular to the adjacent orthogonalplanes. The edge appears as an orthogonal,true-length line in two of the principal viewsand as a point in the third view.

normal face (n) A planar surface of an objectthat is parallel to one of the principal imageplanes. A normal face is seen in its true sizeand shape in the image plane to which it isparallel and is seen as an edge in the other twoprincipal image planes. The normal face isnamed for the image plane to which it isparallel.

nuclear engineering (n) A field of engineeringthat includes all areas of research,development, and application of nuclearenergy. Areas of specialty include reactorengineering, reactor control, nuclear materials,reactor physics, controlled thermonuclearfusion, reactor safety, fuel management, andshielding.

numeric control (n) See NC.

NURBS (n) Acronym for nonuniform rationalB-spline, a type of free-form curve that usesrational B-splines and allows for a weightingvalue at each point on the surface. BecauseNURBS can also precisely describe conicsurfaces, they are gaining popularity in taskspreviously done with other types of 3-Dmodelers.

nut (n) An internally threaded device used onthe ends of threaded fasteners to join materials.Nuts are an alternative to threading the partitself and are often paired with a washer toassist in distributing the pressure and/orsecuring the nut.

Ooblique (adj.) A direction that is neitherparallel nor perpendicular to a plane.

oblique edge/line (n) An edge of a face that isnot parallel to any of the three primaryorthogonal planes. The edge appearsforeshortened in all three principal views of amultiview drawing.

oblique face (n) A planar surface of an objectthat has been rotated about two axes from oneof the principal image planes. An oblique facewill appear foreshortened in all three of theprincipal views. Unlike inclined and normalfaces, an oblique face is not seen as an edge inany of the principal image planes.

oblique projection (n) A form of parallelprojection used to create oblique pictorials.Oblique projection results when the projectorsare parallel to each other but at some angleother than perpendicular to the projectionplane. Typically the most descriptive face of anobject is placed parallel to the frontal plane.

offset coordinate method (n) A constructionmethod used to construct non-normal views ofcylinders, circles, arcs, and other curved orirregular features. The feature is first drawn inan orthographic view, and then regularlyspaced coordinate points are transferred to theforeshortened view space, where they areconnected using an irregular curve.

offset section (n) A full section view generatedby multiple, connected cutting planes that areparallel but not coplanar. This technique isused to allow the cutting planes to pass througha series of features that do not all lie in thesame plane.

ogee curve (n) A curve that connects twoparallel lines with two arcs, forming a smoothcurve. Such curves are often seen inarchitectural details.

operating system (n) The software controlsthe basic functions of a computer system, suchas reading and writing files to the disk,communicating with the printer, etc. Commonoperating systems include UNIX, MS-DOS,and Macintosh OS.

ordinal scale A qualitative data scale that hasan inherent order. Even though ordinal data hasan order, the order is not quantitative becausethe individual data elements are symbolic andhave no inherent magnitude.

orthographic projection (n) A parallelprojection technique that creates a 2-D imageof 3-D objects or structures on an image planeperpendicular to the lines of sight. Theorthographic projection technique can producepictorial drawings, such as isometric oroblique, that show the three dimensions of anobject or multiviews that only show twodimensions of an object in a single view.

G-14 GLOSSARY

outline assembly (n) A general graphicdescription of the exterior shape of anassembly. Outline assemblies are used for partscatalogs and installation manuals or forproduction when the assembly is simpleenough to be visualized without the use ofother drawing techniques, such as sectioning.Hidden lines are omitted except for clarity.

output device (n) A peripheral hardwaredevice linked to a computer that allowsinformation in the computer to be accessible tothe human senses. Common types of outputdevices include computer monitors andprinters.

Ppainter’s algorithm (n) A rendering techniqueused to perform hidden surface removal. All ofthe polygons are sorted and then drawn on thescreen from back to front. Both the computerand a painter use this technique to ensure thatelements in the background are covered bythose in the front.

parabola (n) A single-curved surfaceprimitive, defined as the curve of intersectioncreated when a plane intersects a right circularcone parallel to one of the cone’s elements.

parallel lines (n) Two lines in a plane that stayequidistant from each other along their entirelogical length. The lines can be straight orcurved. Circular curved parallel lines share thesame center point and are referred to asconcentric.

parallel planes (n) Two planes that areequidistant from each other over their entiresurfaces. Two planes are considered parallelwhen intersecting lines in one plane areparallel to intersecting lines in the secondplane. Also, seen in edge view, the two planesappear as parallel lines.

parallel projection (n) A projection techniquein which all the projectors are parallel to eachother, eliminating convergence. All majorprojection techniques, except perspective, useparallel projection.

parallelism (n) An orientation control forgeometric dimensioning and tolerancing.Parallelism is a condition in which a surface oran axis is equidistant at all points from a datumplane or datum axis, respectively. The distancebetween the feature and the datum is thetolerance value given in the control frame.

parallelogram (n) A quadrilateral (four-sidedpolygon) in which opposite sides are parallel.The square, rectangle, rhombus, and rhomboidare all parallelograms.

parametric (adj.) A term used to classifycurves for which the path is described by amathematical function rather than a set ofcoordinates. A parameter within the function

(often specified as u or v) is varied from 0 to 1to define all the coordinate points along thecurve.

partial view (n) A view that shows only whatis necessary to completely describe the object.Partial views are used for symmetrical objects,for some types of auxiliary views, and forsome types of multiview drawings. A breakline or center line may be used to limit thepartial view.

patch (n) A closed series of parametric curvesthat describe a surface region. Series of patchesare usually combined together in surfacemodeling systems to describe an object.

patent (n) The “right to exclude others frommaking, using, or selling . . .” a product,granted by the federal government for a periodof 17 years. The patenting process wasdeveloped to encourage the free and promptdisclosure of technical advances. Patents oftenrequire specialized graphics as supportingdocumentation.

PCB (n) Acronym for printed circuit board, arigid board typically made from fiberglass,approximately .060′′ thick, and used formounting electronics components as part of alarger assembly. This board, also called aprinted wiring board (PWB), has wiringpatterns formed by traces of a conductor, suchas copper, fused to the board. The wiringpattern is created either by depositing theconductor on the board or by starting with asolid film of the conductor and etching awaywhat is not needed.

PDES (n) An acronym for product dataexchange using STEP, a new data exchangestandard that attempts to incorporateinformation for the complete life cycle of theproduct. The type of information coveredincludes shape, design, manufacturing, qualityassurance, testing, support, etc. As indicated byits name, PDES incorporates the evolvingSTEP standard.

perception (n) The mental image orknowledge of the environment receivedthrough the senses. Real objects can beperceived through viewing or touching,whereas graphic representations are perceivedthrough viewing alone.

perfect form (n) A term used in geometricdimensioning and tolerancing to describe theideal shape of a feature. Form controls on afeature are defined relative to the perfect form.For example, the cylindricity tolerance zone isdefined as a perfect cylindrical shape.

perimeter loop (n) A closed set of edges andvertices that constitute the outer boundary of aface. The perimeter loop is a variable in theEuler–Poincaré formula used as part of theprocess of validating the topology of a model.

GLOSSARY G-15

perpendicular lines (n) Two or more linesthat intersect once at a right angle (90 degrees),sometimes referred to as normal.

perpendicular planes (n) Two planes orientedat right angles (90 degrees) to each other. Twoplanes each containing a line that isperpendicular to a line in the other plane, arealso perpendicular to each other. Multiviewsare generated by mutually perpendicular imageplanes.

perpendicularity (adj.) An orientation controlfor geometric dimensioning and tolerancing.Perpendicularity is the condition of a surface,center plane, or axis that is at a right angle to adatum plane or datum axis, respectively.

perspective projection (n) A projectiontechnique in which some or all of theprojectors converge at predefined points. Thispictorial projection technique is used toreplicate closely how humans perceive objectsin the real world.

phantom line (n) A line used to represent amoveable feature in its different positions aswell as a repeating pattern, such as screwthreads on a shaft.

Phong shading (v) A rendering method thatuniformly adjusts the value of a surface colorbased on the relationship of the light source tonormals calculated along each edge of themodel. Unlike Gouraud shading, Phongshading allows the representation of highlightsarising from specular reflection.

photorealistic (adj.) A term describing arendered object that attempts to match theperceptual effects of color, texture, lighting,etc., of a real object. This type of rendering isused by industrial designers, marketingexecutives, and others interested in gaging theaffects of its visual appearance.

physical prototypes (n) Physical models of aproposed design. These are used in theevaluation and testing of a product beforegoing into full production. Increasingly,simulated or virtual prototypes created withCAD/CAM tools are used for analysis.

pictorial assembly (n) A pictorial drawing(normally an axonometric view) of a partiallyor fully disassembled assembly. Center lines,called flow lines in this application, are used toshow how each part is assembled. The pictorialassembly is commonly used in installation andmaintenance manuals.

pictorial drawing/sketch (n) A drawing inwhich all three of the primary dimensions of anobject are seen in a single view. Thesedrawings are used to give a holistic view andare not used to depict specific features on theobject. Axonometric and perspective pictorialsare the two main types.

pin (n) A mechanical fastener, typicallycylindrical in shape, used to keep parts inposition or to prevent slippage after assembly.Some of the more common types of pins aredowel, straight, tapered, groove, spring, andcotter.

pinion (n) The smaller of two gears in ameshed pair of gears. The larger of the twogears is simply called the gear. A gear andpinion pair is used to change the speed of shaftrotation, with the pinion shaft rotating at ahigher rate than the gear shaft.

piping (n) A specialized engineering field forthe design of fluid and gas-carrying pipingsystems for process plants and other industrialand commercial structures.

piping drawing (n) A specialized drawingused in the design and maintenance of pipingsystems. The piping systems are shown in anorthographic plan view or in a pictorial viewsuch as isometric. The drawing can be done asa single-line drawing in which the componentsare represented as a single line or as a double-line drawing for a more realistic spatial layoutof the components. Specialized graphicsymbols are used to represent the pipes,fittings, and valves used in the system.

pitch (n) A thread term used to describe thedistance measured parallel to the axis betweencorresponding points on adjacent thread forms.The pitch is equal to 1 divided by the numberof threads per inch.

pixel (n) A single point on a display device,such as a computer monitor. Pixels arearranged in horizontal and vertical rows. On aCRT type monitor, a pixel is an electronicallycharged point on the screen. Pixel is often usedin describing the minimal unit of resolution ofany bitmapped graphic output.

plan drawing (n) A type of drawingcommonly used in civil, architectural, orengineering projects involving large structurallayouts. A plan drawing (sometimes called aplan view) is an orthographic view taken fromthe top and looking down parallel to the line ofgravity. These drawings are useful in planningthe flow of vehicles, people, or materialthrough constructed spaces or along the terrain.

plane (n) A region of space defined by aminimum of three noncoincident points inspace. For the simplest type of plane surface,all points can be described by two coordinateaxes; that is, the plane has no curvature.

plane geometry (n) The geometry of planarfigures, such as circles and triangles, and theirrelationships. This mathematical field is animportant part of traditional engineering andtechnical graphics.

plane of projection (n) An imaginary plane inspace upon which an object is projected. The

plane can be imagined as a pane of glass onwhich lines of sight from the object form anoutline of the object. This plane is also referredto as a picture plane.

plastics (n) A material made from natural orsynthetic resins that can be formed or shaped.Common industrial plastics includepolystyrene, acrylics, polycarbonate, ABS,PVC, acetals, nylon, polypropylene,polyethylene, epoxy, and phenolics.

plus and minus dimensioning (n) Atolerancing specification that gives theallowable positive and negative variance fromthe dimension specified. Sometimes, the plusand minus values will be equal; at other times,they will be different.

point (n) A singular location in space, usuallydefined by coordinate values (i.e., X,Y,Z).

point light source (n) A light source located ata specified point in space. In rendering, thepoint light source is usually close to the model.Because the light radiates omnidirectionallyfrom the point source, no two rays hit a planarsurface at the same angle. An uncoveredincandescent light bulb is analogous to a pointlight source.

point-to-point diagram (n) See wiring diagram.

polar coordinates (n) A 2-D coordinatesystem used to locate a point in a plane byspecifying a distance and an angle from thecoordinate origin. When another distancenormal to the coordinate origin is added,cylindrical coordinates can be specified.

polygon (n) A plane figure bounded bystraight lines. If the sides are of equal lengthand form equal angles with each other, thepolygon is considered a regular polygon (e.g.,a square or hexagon).

polygonal prism (n) A geometric solidconsisting of two equivalent polygonal basesparallel to each other. Each equivalent edge ofthe bases is connected to form a series ofparallelograms, bounding the sides of the solid.

polyhedron (n) A geometric solid bounded bypolygons. If the polygons are equal, regularpolygons, the solid is called a regularpolyhedron.

port (n) In 3-D modeling systems, a definedregion on the computer screen, used fordisplaying a single view of an object.Typically, a different set of view parameters isassigned to each port.

position (n) A control for geometricdimensioning and tolerancing. Positionspecifies the total zone specification for afeature, such as a diameter or the total height.

precedence of lines (n) A conventiondescribing the order of priority of differentlinestyles. For example, if a visible and hiddenline coincide, the visible line is the one drawn.

presentation graphics (n) Graphics intendedfor a wide audience and used to communicateinformation about a proposed product or designto other individuals within the company, toclients, or to the potential end user.

pressure angle (n) A term used in the designof gears and defined as the angle between thetangent to the pitch circles and the line drawnnormal to the surface of a gear tooth. Thepressure angle has been standardized by gearmanufacturers and by ANSI (14d degreesbeing the most common), and it determines theshape of the involute curve used to design thegear tooth.

primary auxiliary view (n) A single auxiliaryview projected from one of the six standardviews. Primary auxiliary views are used toshow inclined surfaces in their true size andshape. Secondary auxiliary views are used foroblique surfaces and are derived from primaryauxiliary views.

primary axes (n) Three mutuallyperpendicular axes representing the primarydimensions of an object. Each of these axes isnormal (perpendicular) to one of the primaryimage planes.

primitive (n or adj.) A term used primarily todescribe the fundamental geometric forms usedfor building 3-D CAD models. Primitives aretypically defined parametrically or with single-sweep operations. Primitives are used as toolsolids in Boolean operations.

principal plane (n) A plane that is seen in itstrue size and shape in two of the six principalviews and as an edge in the other four. Thethree principal planes are frontal, profile, andhorizontal. For example, the frontal plane isseen in its true size and shape in the front andrear views and as an edge in the other fourviews.

principal (standard) view (n) One of the sixmutually perpendicular views of an object,produced after an object’s position is selected.The six views can be created by positioning theobject inside a glass box and viewing the boxwith parallel lines of sight perpendicular to theglass planes. These views are the cornerstoneof multiview drawings.

printed circuit board (n) See PCB

printed wiring board (n) See PWB.

problem identification (n) A process used bythe design team during the ideation process toset the parameters of the design project beforeattempting to find a solution to the design. Thisprocess includes such stages as objectives,limitations, and scheduling.

procedural (adj.) A term used to describe theprocess by which a model is constructed.Procedural information can be thought of asactions, such as creating a face on the cube byfollowing the path made by edges 1 through 4.

G-16 GLOSSARY

process control (n) The measurement,analysis, and adjustment of manufacturingprocesses, such as drilling, milling, andturning. The quality of a product relies heavilyon process control techniques used to checkthe variability of machined parts and to detectdefects. The use of statistical techniques is animportant component of process control.

process planning (n) The stage in themanufacturing process in which the mostefficient way of producing the product isdetermined. In this stage, industrial engineersdetermine how parts will be fabricated and inwhat sequence.

product data exchange using STEP (n) SeePDES.

product (industrial) design (n) A complexactivity that includes function analysis, marketanalysis, production, sales, and service. Thegoal of product design is to produce a productthat will meet the wants and needs of theconsumer, can be economically produced, issafe for the consumer and the environment,and will be profitable.

production process (n) The planned actionused to convert raw materials into finishedproducts. The production process is sometimesreferred to as the manufacturing process.However, production is a more global term thatincludes both the manufacturing of productsand the construction of structures.

profile (n) A form control for geometricdimensioning and tolerancing. A profile is theoutline of a feature projected onto a plane.They usually consist of combinations ofcontiguous lines, arcs, and other curves. Theprofile tolerance zone may be made of acombination of straightness, roundness,parallelism, etc.

profile line (n) A line seen in its true length inthe profile plane, either the right or left sideview.

profile plane (n) A principal orthographicplane of projection. This plane is used to defineboth the right and left side orthographic views.

profile view (n) A principal orthographic viewcreated by a projection onto the profile plane.This term includes both the right and left sideviews.

projection line (n) A construction line drawnbetween views in a multiview drawing to align3-D space dimensions. This term is sometimesused in a more general sense to refer to linesrepresenting the transference of spatialinformation between objects, or between anobject and an image plane. The relationship ofthe projection lines to each other and to theimage plane defines whether the projectiontechnique is perspective, parallel, or oblique.

projection theory (n) The principles used torepresent objects and structures graphically on

2-D media. Some of the primary projectionmethods include orthographic, oblique, andperspective.

proportion (n) The comparative relation, orratio, between dimensions of a feature orobject.

prototyping (n or v) A term used to describethe process by which physical mockups aremade of proposed designs. Increasingly,prototyping is done using the databasesassociated with 3-D computer models. Becauseof the speed and efficiency, this technique isoften referred to as rapid prototyping.

PWB (printed wiring board) See PCB.

pyramid (n) A geometric solid consisting of apolygonal base and a series of triangular lateralfaces. The triangular faces each share one sidewith the polygonal base and the other two sideswith the neighboring triangular faces. Thetriangular faces all meet at a common pointcalled the vertex.

Qquadrilaterals (n) Four-sided polygons ofany shape. The sum of the angles inside aquadrilateral always equals 360 degrees.Quadrilaterals are classified by thecharacteristics of their sides. If opposite sidesof the quadrilateral are parallel, the shape isa parallelogram.

qualitative (adj.) A type of data used as amethod of labeling and identifying. Qualitativedata are classified as being either nominal orordinal.

quality (adj.) The capacity of a product orservice to consistently meet or exceed customerneeds and expectations. Quality includesperformance, special features, reliability,durability, and service after sale.

quantitative (adj.) A type of data that hasnumerical value. Quantitative data are furtherclassified by the number of components and bythe scales of values used (e.g., scalar, vector,or tensor).

Rradiosity (n) A rendering technique, based onthermal principles, in which there is aconservation of light energy in a closedenvironment. With radiosity methods, any sizeor shape surface is capable of both radiatingand absorbing light energy. The rate at whichenergy leaves a surface is its radiosity, and isthe result of all light energy received,absorbed, and then transmitted by the surface.

radius symbol (n) A symbol that precedes anumerical value, indicating that the associateddimension shows the radius of a circular arc.The radius symbol is the capital letter R.

range bars (n) Line or bar marks, such asthose used in bar charts, that indicate an

GLOSSARY G-17

interval of variable values. For example, rangebars could be used to indicate the period oftime that a product is in transit betweenmachining stations on a manufacturing line.

rapid prototyping (n) A broad term used todescribe several related processes that createphysical models directly from a CAD database.Prototyping systems use a variety oftechniques, including stereolithography andfused deposition modeling (FDM). Rapidprototyping is used to create prototypes forconcept modeling, injection molds, andinvestment casting.

ratio scale (n) A data scale that has a naturalzero point but is insensitive to the units used.Ratio values are often generated by dividingtwo values that have either similar ordissimilar units.

rats nest (n) The drawing representingstraight-line connections between all of theelectronic components on a printed circuitboard. Once the components are located on theboard, the rats nest is generated, using thecomponent connection list. The rats nestdrawing is part of the iterative design processto optimize placement of components.

ray (n) An entity of unspecified length, but nodepth or breadth, that extends into infinityfrom a specified point. In computer graphics,ray is a common term used, when rendering ascene, to describe the path a light ray follows.

ray tracing (n) A rendering technique thatcalculates the path of all rays of (a) theoreticallight source(s) within a model scene. Thetechnique includes tracing the path from thelight source, between all objects which mayreflect and pass the light, to the viewer’s eye.

reach envelope (n) A volume of spacerepresenting all possible locations in space thata human operator’s limbs could occupy. Reachenvelopes are used to analyze the locations ofcontrols, such as in the design of workstations,tools, cockpits, etc.

rear view (n) A principal view of an object,created by rotating the object 180 degreesabout the vertical axis from the front view.This view is not typically included in astandard multiview drawing.

reference dimension (n) A numerical value,enclosed in parentheses, provided forinformation only and not used in the fabricationof the part. A reference dimension is acalculated size used to show the intended designsize of a part. Drawings made to older standardsmay use REF placed next to a referencedimension, instead of using parentheses.

reference lines (n) Lines used to correlatescale values with data markers in avisualization. Because reference lines are notthe central focus of a visualization, they tend tobe thin and sometimes dotted or dashed.

refinement (v) A repetitive process (iterativeor cyclical) used to test the preliminary design,make changes if necessary, and determine ifthe design meets the goals of the project.Models are used to analyze and visualize thedesign. Refinement drawings are used toanalyze the design in its current stage of thedesign process.

regression line (n) A line mark used inconjunction with point marks to represent datatrends in a visualization. Although this line,either linear or curved, can be drawn freehand,it is usually calculated using statisticaltechniques.

regular curve (n) A bent line composed ofconstant-radius arcs generated around a singlecenterpoint. With traditional tools, regularcurves are drawn using a compass or circletemplate; with CAD, they are constructed withthe CIRCLE and ARC commands.

regular isometric (n) An isometric pictorialdrawn as if the viewer is looking down on theobject from the top. In a regular isometric, the30-degree axes are drawn upward from thehorizontal. The regular method is the mostcommon type of isometric drawing.

related view (n) Views that are adjacent to thesame view in orthographic drawings. Theseviews are called related because distances ofcommon features are equal or related.

relative coordinates (n) Coordinate locationsspecified in reference to a previously definedlocation other than the origin. Relativecoordinates are sometimes referred to as deltacoordinates, meaning changed coordinates.

removed section (n) A section view that doesnot follow the standard alignment of viewspracticed in multiview drawing. This techniqueis used to show multiple section viewsgenerated from parallel cutting planes andviews placed on separate drawings or usingdifferent scales.

removed view (n) A complete or partialorthographic view that is not aligned with anyof the principal views. Removed views areoften shown on a different drawing sheet or ata different scale.

reprographics (n) The process of storing,retrieving, and copying engineering drawings.Often, specialized service bureaus are used toprovide these services to small firms.

reverse engineering (v) A method ofaccurately evaluating existing products, theninputting the information into a CAD database.Often a coordinate measuring machine(CMM), an electromechanical device with aprobe on one end that accurately measuresobjects, is used to input the 3-D data into theCAD system.

reversed axis isometric (n) A variation of theregular isometric pictorial. Whereas in a

regular isometric, it appears as though theviewer is looking down from the top of theobject, in the reversed axis isometric, itappears as if the viewer is looking up from thebottom of the object. The 30-degree axes aredrawn downward from the horizontal.

revision block (n) An area located next to thetitle block, listing the version, or revision, ofthe drawing depicted.

revolution (v) The rotation of a point, line,plane, or entire object about an axis parallel toa plane or projection. The revolution method isone of the standard techniques used indescriptive geometry.

revolved section (n) A section view made byrevolving the cross-section view of the part 90degrees and placing the section view on thepart. Visible lines adjacent to the revolvedview can be either drawn or broken out usingconventional breaks.

RGB color model (n) A color model based onthe three additive primaries: (R)ed, (G)reen, and(B)lue. This color model is used extensivelybecause of its close correlation to the hardwareimplementation of color on a computer monitor.

rib (web) (n) A thin, flat feature of an objectthat acts as a structural support. Ribs, webs,spokes, lugs and other thin features are notsection lined if a cutting plane passes parallelto the feature.

right side view (n) A principal view of anobject, created by rotating the line of sight 90degrees about the vertical axis to the right ofthe front view. This view is typically includedin a standard multiview drawing.

rigid-body transformations (n)Transformations applied to geometric forms.Such transformations affect the location ororientation in space but not the shape.Examples are translation and rotation.

rivet (n) A permanent mechanical fastener,consisting of a smooth metal shaft with a head.Rivets are placed in the part and held in placeby spreading the tip protruding through thematerial.

robot (n) A computer-controlled device usedin manufacturing for many purposes, such asassembly, painting, and material movement.Robotics is an important component ofCAD/CAM and in the automation ofproduction facilities.

root (n) A threading term used to describe thebottom of a screw thread cut into a cylinder.

roulette (n) The curve generated by the rollingcontact of one curve or line on another. Anypoint attached to the rolling curve will describea roulette curve. The moving point is called thegenerating point. The roulette is constructedby moving the rolling curve to a number ofnew positions and plotting the correspondingpositions of the generating point.

round (n) A round is an exterior cornernormally found on cast, forged, or molded parts.Like a fillet, a round can indicate that a surfaceis not machined finished. A round is indicatedon engineering drawings as a small arc.

roundness (n) See circularity.

rule 1 (n) A central principle to geometricdimensioning and tolerancing (ANSI Y14.5–1982). It stated that, where only a tolerance ofsize is specified, the limits of size of anindividual feature prescribe the extent to whichvariations in its geometric form, as well as itssize, are allowed.

ruled surface (n) A surface produced by themovement of a straight-line generatrixcontrolled by a directrix to form a plane, asingle-curved surface, or a warped surface.

runout (n) A filleted surface that runs tangentto a cylindrical one. A runout is drawn onmultiview drawings starting at the point oftangency, using a radius equal to that of thefilleted surface, with a curvature ofapproximately one-eighth of a circle.

Ssaturation (n) A perceptual color qualityindicating the ratio of the primary spectralwavelength (the hue) to all the wavelengths inthe color. A high saturation color has a vividhue, whereas a low saturation color approachesgray in appearance.

scalar value (n) A quantitative data type thatexpresses magnitude but not direction.

scale (n) A measuring tool used to calculatedistances on a technical drawing. Scale canrefer to both the physical tool, similar to aruler, and the mathematical ratio used tocalculate the size difference between the actualobject and the drawn representation of theobject. Scale lines in a visualization map thescale values to the graphic figure.

scale breaks (n) Interruptions, or breaks, in avisualization scale, used to reduce large blankareas in the visualization created by widelydispersed data. Scale breaks allow avisualization to preserve a larger magnificationby reducing the area required for the drawing.

scanner (n) A computer input device used tocapture information on paper and translate theinformation into a raster (bitmapped)computer image. Scanners can be used toconvert a drawing created with traditional toolsto a CAD drawing, to convert and enhancephotographs in desktop publishing, or to inputtext information into the computer.

scatter plot (n) A visualization technique thatmaps discrete values with point marks in either2-D or 3-D space. A regression line is oftenincluded in the visualization to help recognizedata trends.

G-18 GLOSSARY

schematic (logic) drawing (n) A type ofdrawing or diagram commonly used inelectronics to represent the logical andfunctional relationships of parts in anelectronic assembly, circuit, or device. Thedrawing details the signal flow and control butnot necessarily the spatial relationship of thefinal layout nor the actual point-to-point wiringthat will be used. Special design symbols areused to represent the different types ofelectronic components.

screen angle (n) The alignment angle of dotsin halftone images. The angle of the dots in animage, especially when multiple screens arebeing used, is critical for avoiding illusionaryand otherwise unwanted secondary patternsfrom appearing in the printed image.

screen coordinate system (n) A coordinatesystem used to map graphics created by thecomputer software to the monitor. Thecoordinate system often has its origin in theupper left-hand corner of the screen, with themeasurement unit in pixels.

screen print drawing (n) See fabricationdrawing.

secondary auxiliary view (n) An auxiliaryview projected from a primary auxiliary view.Secondary auxiliary views are used to depictoblique surfaces in their true size and shape.

section assembly (n) An assembly drawingthat provides a general graphic description ofthe interior shape of an assembly by passing acutting plane through the assembly. The sectionassembly is usually a multiview drawing of allthe assembled parts, with one view in fullsection. Other types of sections can also beused, such as broken-out and half sections.

section drawings (n) Drawings containingviews in which portions of the object havebeen removed. Section drawings typicallydepict the cutting plane used to define theremoved material in a view adjacent to theactual section view. The section view depictsthe cut surfaces with section line symbols.

section lines (n) A line used to representsurfaces of an object cut by a cutting plane insection views. Section lines are drawn in anumber of patterns (symbols) corresponding tothe type of material being sectioned.

serial slices (n) A visualization techniquebased on sectioning. A 3-D object is reduced toa series of 2-D images by representing two ofthe geometric dimensions in all slices, andeach slice represents a discrete value range forthe third geometric dimension.

servicing (v) An activity that supports theinstallation, training, maintenance, and repairof a product or structure for the consumer.Technical illustrations are found in manualsused to support servicing activities.

set screw (n) A mechanical threaded fastener,with or without a head, used to preventrotation or movement between parts, such as ashaft and a collar. Set screws have specialtypes of points for different applications.

shading (v) A rendering technique simulatingthe effect of light on the surface of an object.The angular relationship between the light andthe surface results in a variance in the value(darkness/lightness) of the surface. Abruptchanges in value typically indicate an edgebetween surfaces (faces).

shadow casting (v) A rendering techniqueused to simulate shadows cast by (a) lightsource(s). Based on methods similar to hiddensurface removal, the direction of the light raysis used to calculate which surfaces are nearestto the light source (and thus generate theshadow) and which are behind the nearsurfaces (and thus receive the shadow).

shaft basis (n) A tolerancing technique used todefine a system of fits and based on the basicsize as being the maximum size of the shaft.

shape (n) The internal spatial relationship ofvertices and edges that make up a face or thearrangement of faces on an object. Examplesof characteristics used to describe a face arethe number of edges (sides), the angle betweenedges, and the ordering of edges around theperimeter. Shape is independent of overallscale but not of viewpoint.

SI (n) Acronym for System Internationale (i.e.,International System of Units), the metricmeasurement system. For technical drawingsusing the SI units, the millimeter (mm), meter(m), and the kilometer (km) are the mostcommon units of measure. The internationalorganization that established the metricstandard is the International StandardsOrganization (ISO).

single-curved surface (n) A surface that curvesin only one dimension. A cylinder is an exampleof a single-curved surface. Single-curvedsurfaces can be developed without distorting oraltering the topology of any of the faces.

single-line drawing (n) See piping drawing.

size (n) The spatial dimension of an object.When used with a dimension (i.e., inches,centimeters), size refers to an absolutemeasurement. Size can also be used in arelative sense to compare features or objects.

sketch modelers (n) A term used to describecomputer modeling systems used in theideation phase of the design process. Sketchmodelers are defined by their ability toproduce approximately accurate modelsquickly and easily.

skew lines (n) Nonintersecting, nonparallellines in 3-D space. The relationship of skew

GLOSSARY G-19

lines, such as the shortest distance (clearance),can be calculated using descriptive geometrytechniques.

software (n) A set of coded instructions(programs) used to control the operation of acomputer. Software is often grouped intocategories, such as operating systems (e.g., MS-DOS), application programs (e.g., the CADprogram), and utilities (e.g., security programs).

solid geometry (n) The geometry of 3-Dobjects, such as cylinders, cubes, and spheres,and their relationships.

specular reflection (n) Light reflecting from asurface at the same angle at which it contactedthe surface. With a perfect mirror, 100 percentof the light is reflected in this manner.Specular refections are responsible forhighlighting, or hot spots, seen on real objectsand rendered models.

spherical coordinates (n) Coordinates used tolocate points on a spherical surface. Sphericalcoordinates are described by specifying adistance and an angle from the origin measuredin the X–Y plane and then an angle from theX–Y plane.

spiral (n) A curved line that begins at an originpoint, moves further away from the origin, anddecreases in curvature as it travels around theorigin. A spiral is sometimes referred to as aspiral of Archimedes.

spline (n or v) A free-form curve that connectsa series of control points with a smooth curve.Changing a control point results in a change inthe curve. The term also describes the processof connecting points to create a curve. B-splineand Bezier curves are examples of splinecurves.

spooling drawing (n) A piping drawing thatgives the information necessary for theconstruction of a subassembly of an overallpiping system. These drawings are used off siteto fabricate subassemblies that can then betaken to the project site for final assembly.

spot enlargements (n) Drawings used inconjunction with larger technical illustrationsof parts or assemblies to show a clearer viewof critical features. Spot enlargementstypically use a combination of increasedscale, reverse views, and sectioning to aid inviewing a feature. The enlargement is usuallyon the same sheet as the overall illustration,is isolated by ruled lines, and is keyed backto the overall drawing by a leader or aseparate callout.

spot light source (n) A light source located ata specified point and orientation in space. Inrendering, a spot light source is usually closeto the model. Besides a location and anorientation, the user also specifies an angle ofdispersion to create a cone of light. Aflashlight is analogous to a spot light source.

spring (n) A mechanical device, often in theform of a helix, that expands or contracts dueto pressure or force. Springs are classified ascompression, tension, extension, flat, andconstant force. A spring is further classified bythe material, gage, spring index, direction ofthe helix, and type of ends.

Standard for the Transfer and Exchange ofProduct Model Data (n) See STEP.

standards (n) Sets of rules that allow for theclear communication of technical ideas bygoverning how parts are made and representedin technical drawings. In the United States, theAmerican National Standards Institute (ANSI)is the governing body that sets the standardsused for engineering and technical drawings.

statics (n) An area of applied physics thatdeals with the analysis of forces in bodies(parts) at rest (in equilibrium).

station point (n) The eyepoint of the observerin a perspective drawing. The location of thestation point relative to the object, and thehorizon line determines the perspectiveviewpoint (i.e., bird’s eye, human’s eye, etc.).

statistical process control (n) The systemused for the selection of parts that are thenmeasured for accuracy. Mathematical statisticsis the tool used to analyze the measurements ofthe randomly selected parts. Consistent andaccurate measurements will indicate when amachine tool must be maintained or adjustedduring the manufacturing cycle.

steel (n) An alloy of iron, containing variousamounts of carbon, manganese, and one ormore other elements, such as sulfur, nickel,silicon, phosphorus, chromium, molybdenum,and vanadium. These elements, whencombined with iron, form different types ofsteels with varying properties.

STEP (n) An acronym for Standard for theTransfer and Exchange of Product ModelData, a neutral data exchange standarddeveloped by the ISO. The development of thisstandard is an attempt to integrate theEuropean standards and IGES and to embody alarger, more flexible subset of information.

stereolithography (n) A rapid prototypingtechnique in which the model is firstdecomposed into a series of thin layers andthen reconstructed. A pair of light beamsmoves a focal point about in a vat ofphotosensitive polymer, tracing one layer at atime. Once one layer of polymer has beenhardened by the light beams, the light beamstrace the next layer up.

straight line (n) A line generated by a pointmoving in a constant direction. Straight linescan be either infinite or finite in length. Afinite straight line is an entity of specificlength but no depth or breadth. An infinitestraight line is an entity of unspecified lengthbut no depth or breadth.

straightness (n) A form control for geometricdimensioning and tolerancing. Straightnessmeans that all points on a part have the samedirection throughout its length. Straightnessalso refers to the path describing the shortest(uniform) path between two points.

streamlines (n) Line marks, usually curved,used in visualizations to depict the path of flowof a fluid or gas. Streamlines are used inaerodynamic studies to evaluate the flow of airor water around a proposed design.

stretching (v) A modification technique thatchanges the location of individual points orgroups of connected points of an object.Stretching changes the geometry but not thetopology of the polygon or face of the solid. Ifthis technique is used on a 3-D solid, it issometimes referred to as tweaking.

stud (n) A mechanical fastening device thatconsists of a cylindrical rod threaded on one orboth ends and that screws into a mating part. Anut may be used on one end.

subassembly (n) A logical grouping of partsthat are only part of the total assembly. Often,a subassembly is a working mechanism in andof itself, but it works in concert with otherparts to form the complete assembly.

subtractive (adj. or v) A process or state inwhich elements are removed from each other.Subtractive is the opposite of additive.

subtractive primaries (n) The three primarycolors cyan, magenta, and yellow. Colorsystems using these primaries work on theprinciple of subtracting spectral wavelengthsfrom the light energy to create new colors.These systems are used in ink-based graphics,specifically four-color printing (the fourthcolor being black). The complementary colorsare the additive primaries: red, green, and blue.

successive auxiliary view (n) An auxiliaryview of an object created by projecting fromother auxiliary views. With the use ofsuccessive auxiliary views (e.g., secondaryauxiliary, tertiary auxiliary, etc.), it is possibleto create virtually any view of an object.

surface (n) A finite portion of a plane, or theouter face of an object, bounded by anidentifiable perimeter. A surface represents thepath of a moving straight or curved line, calleda generatrix. The path that the generatrixtravels is the directrix. In a 3-D model, thetopological equivalent of a surface is a face.

surface plot (n) A 3-D visualization techniqueused with two independent variables (X andY) and one dependent variable (Z). A surfaceconnecting the data points represents themapping of the independent and dependentvariables. Shading and other renderingtechniques are often used to help visualizethe surface.

sweeping (n) A 3-D modeling operation inwhich a closed polygon, called a profile, isdrawn on the workplane (the U–V plane) andis transformed along a defined path. Thesweeping technique is procedural in nature inthat instructions are given as to how far and inwhat direction the sweep of the profile is tooccur in order to create the solid.

symmetrical (adj.) A quality in which all thefeatures on either side of a point, line, or planeare identical. The matching features formbalanced, mirror images.

system (n) An orderly arrangement of partsthat are combined to serve the same generalfunction. Examples are the arrangement of theassembly process in a factory; the heating,ventilating, and air conditioning (HVAC)system in a structure; and the electrical systemin an automobile.

Ttablet (n) A computer input device used tocontrol cursor movement and to select menuitems. The tablet can be covered with a thin,plastic overlay that contains the menu optionsfor a CAD software program. Attached to thetablet is the cursor control device, such as apuck or stylus. Specialized tablets, calleddigitizers, are used to convert a drawingcreated with traditional tools to a CADdrawing by tracing geometric elements withthe puck.

tangent (n) A condition in which a straightline is in contact with a curve at only onepoint. Tangents describe the smooth transitionfrom a linear/planar element to a curved one.Geometric construction techniques are used todefine tangent curves in an engineeringdrawing.

tap (n or v) The machine tool used to makethreads in holes. A drill bit (the tap drill),approximately equal to the diameter of thecrest, is used to make a hole in metal beforetapping an internal thread. The term is alsoused to describe the process of creating thethreads.

technical and office protocol (n) See TOP.

technical drawing/graphics (n) A specializedtype of graphics used to communicatetechnical information. Examples of technicalgraphics include 3-D computer models andillustrations of a technical device.

technical reports (n) In-depth accounts,containing text and graphics, documenting thedesign process. Progress reports are created inthe early stages of the design process todocument the decisions made by the designteam and are used to periodically review thestatus of a project. Final reports are written atthe end of the design cycle and are much moredetailed.

G-20 GLOSSARY

technical sketch (n) A type of sketch thatdepicts only certain features of an object orstructure. Sketches are used as part of thedesign process, in the same way as a technicaldrawing, but sketches are more informal andare typically used early in the design process.

technologists (n) Personnel who work with theengineers and are concerned with the practicalaspect of engineering in planning andproduction. The technologist must be able tocommunicate quickly and accurately usinggraphics, by sketching design problems andsolutions, analyzing design solutions, andspecifying production procedures.

template (n) A die-cut flexible sheet used toassist in the drawing of repetitive features,such as circles, ellipses, threaded fasteners, andarchitectural symbols. The circle template isused to draw regular-interval sized circles andarcs (e.g., 1-mm increments) quicker thanusing a compass.

tensor (n) A general term describing all typesof quantitative data. A tensor has two parts: thedimensionality of the coordinate system, d, andthe order of the tensor, n. The number ofcomponents (scalar values) needed to expressthe tensor is equal to dn. For example, a 2-Dvector is a tensor of order n = 1 with 21 = 2components.

tertiary auxiliary view (n) An auxiliary viewprojected from a secondary auxiliary view.

text alignment (n) The vertical alignment oflines of text. Also referred to as justification,lines of text can be aligned along such featuresas their right or left ends or the centers of thelines.

texture gradient (n) A perceptual cue thatuses changes in patterns to indicate changes ina surface (face). Gradual changes in thepatterns indicate changes in depth, curvature,orientation to light, or a combination thereof.Abrupt changes indicate a change of surfacesor objects.

texture mapping (n) A rendering techniquethat transfers a 2-D pattern (texture) to a 3-Dsurface. Although the name impliesmanipulating the geometry of the surface, thetechnique is limited to mapping color patterns,such as a logo or a fabric pattern, to a surfaceto enhance the realism of the model.

thread form (n) A threading term used todescribe the profile or shape of the thread cutinto the cylinder.

thread series (n) A threading term used todescribe the number of threads per inch for agiven diameter.

threaded fastener (n) A mechanical fastenerincorporating threads as a means of joiningparts, either directly by threading into one ormore of the parts or indirectly by using a nut.

tick marks (n) Short, perpendicular lineslocated along a primary line. Tick marks areused to mark important locations along theline, such as a point of tangency in a geometricconstruction or the regular divisions of unitsalong a scale line in a visualization.

time series analysis (n) A visualizationtechnique depicting a sequence of graphs in sucha way as to allow comparisons between them.The sequence of images can be shown serially inthe form of an animation or in parallel, with allthe images either superimposed on each other orshown side by side.

tolerance (n) The difference between themaximum and minimum size limits on a part.Tolerancing is a fundamental technique inprecision manufacturing applications.

tolerance zone (n) A tolerance term thatrepresents the tolerance and its position inrelation to the basic size.

tool solid (n) Transient solid objects used tomodify the solid model in a modeling system.Typically representing relative simplegeometric shapes, tool solids modify the solidmodel using Boolean operations.

tools (n) Devices used to create engineeringdrawings and models, including both hand andcomputer tools.

TOP (n) Acronym for technical and officeprotocol, a standard developed to assist in theintegration of technical information within anoffice environment. TOP allows file transfer,management, and access; message handling;standards for document revision and exchange;directory services; graphics; and databasemanagement.

top view (n) A principal view of an objectcreated by rotating the line of sight 90 degreesabout the horizontal axis above the front view.This view is typically included in a standardmultiview drawing.

topological (adj.) In 3-D modeling, a term thatrefers to the connectivity of the model, that is,how the elements of the object (i.e., the faces,edges, and vertices) are organized. Geometryspecifies where elements are located in spaceand how they are shaped; topology describeshow these elements are connected to eachother.

total quality management (TQM) (n) Theprocess of managing the entire organizationsuch that it excels in all areas of productionand service. The key is that quality extendsthroughout the organization, in everything thatit does, and quality is defined by the customer.

TQM (n) See total quality management.

traditional tools (n) Devices used to assist thehuman hand in making technical drawings,such as drawing lines straighter, circles morecircular, etc. Examples are mechanical pencils,

GLOSSARY G-21

straightedge scales, triangles, and compasses.Traditional tools are often compared withcomputer-based CAD tools.

transition fit (n) A fit that occurs when twotoleranced mating parts will sometimes be aninterference fit and sometimes be a clearancefit when assembled. Both the loosest andtightest fits for any two mating parts must becalculated, often using tables associated withstandard parts.

trimetric projection (n) An axonometricprojection in which none of the three axes ismeasured on the same scale or is at the sameangle relative to the others. A trimetricdrawing is the hardest to draw, but it is themost pleasing to the eye since it represents themost realistic positioning of the object.

true-length line (n) A line representing anedge that is parallel to a plane of projectionand perpendicular to the line of sight.

true-size plane (n) A plane parallel to theplane of projection and perpendicular to theline of sight. The plane is shown as an edge inthe adjacent, orthogonal projection planes.

tweaking (v) A general term encompassing avariety of techniques that involve changing thegeometry but not the topology of an object. Forexample, the radius of a sphere can be changedwithout adding or deleting any new faces. Thesize of a hole can also be changed, as long asthe enlargement does not cross the edges ofany other faces.

Uundevelopable surface (n) A surface of anobject that cannot be unfolded or unrolled ontoa plane without distortion.Double-curved surfaces, such as spheres, areundevelopable.

unevaluated (adj.) A description of a modelfor which the final form is not explicitlyrepresented in the database. An evaluatedmodel is concise (i.e., it takes up smalleramounts of memory), but it is not efficientsince portions of the model must be defined“on-the-fly” before the user-requestedoperations can be processed.

unidirectional dimensioning (n) A style ofdimensioning in which the dimension and notetext are oriented to be read from the bottom ofthe drawing, relative to the drawing format.This is an ANSI approved style ofdimensioning.

union (∪) (n) The Boolean operation thatcombines the two specified solids. If the twosolids intersect, the intersecting geometry isonly represented once in the resulting solid.

uniqueness (adj.) A term used to describe therepresentation of an object by a computermodeler. The term refers to how close the

correspondence is between the representationand the object and whether the representationcan in fact represent more than one possibleobject.

universal product code (n) See UPC.

UPC (n) Acronym for universal product code, acoded symbol placed on parts and products.UPC is part of a bar coding system forautomatic reading by a laser scanning device. Inmanufacturing, bar codes are attached to parts,assemblies, and finished products, for trackingthe product and for inventory purposes.

upper deviation (n) A tolerancing termdescribing the difference between themaximum size limit and the basic size.

Vvalidity (adj.) A term used to describe therepresentation of an object by a computermodeler. The term refers to whether therepresentation actually represents a form thatcould exist in the real world.

valves (n) Mechanical devices used to controlthe flow of liquids and gases through pipingsystems. The four major functions of valvesare to start and stop flow, regulate flow,prevent backflow, and relieve pressure. Valvescan either be manual or computer controlledand can be set to respond automatically toconditions in the pipe.

vanishing point (n) An imaginary point in aperspective drawing or sketch, often on thehorizon line, where all projection lines of onedimension of the object converge.

vector value (n) A quantitative data type thatexpresses both magnitude and direction.

vertex (n) The coincidental termination of twoor more edges, defined by a point in space.This point indicates a transition from one edgeto another and is often the juncture of two ormore faces (surfaces).

vertical plane (n) A plane parallel to theprofile plane of projection.

videodisk (n) An optical storage medium foranalog video information. The disk has theadvantages of efficient storage of analoginformation, high image quality, and almostimmediate random access; it is similar intechnology to the CD-ROM but larger indiameter.

view camera (n) In 3-D modeling, ametaphorical camera that records what is onthe image plane and then, much like a videomonitor, shows the image on the computerscreen. The image from the camera iscontained in a port on the computer screen.

view volume (n) A theoretical volume definingthe region to be rendered. The minimum andmaximum Z depths and the viewing bounds onthe screen define the three dimensions of the

volume. The volume appears as a rectilinearprism in parallel projection and as a truncatedpyramid in perspective projection.

virtual condition (n) The condition resultingfrom the worst-case combination of size andgeometric tolerance applied to a feature.Virtual condition is used in the design ofmating parts and for determining gage elementsizes. For an external feature, virtual conditionis the MMC size plus the geometric tolerance.For an internal feature, it is the MMC sizeminus the geometric tolerance.

virtual models (n) A computer-based modelanalogous to a real or proposed object. Virtualmodels are endowed with the qualities of a realobject, allowing the models to be used inevaluating a proposed design. Virtual modelsare useful for quickly performing multiple teststhat could be destructive to physical models.

virtual reality (VR) (n) A generic term usedto describe artificial environments in whichsome or all of the human senses are immersed.The term “presence” is often used to describethe degree to which one feels immersed in thevirtual environment. VR can be used inengineering design to allow more completeexamination of proposed designs withouthaving to build physical prototypes and placethem in their planned environments.

visible line (n) A line type used to representfeatures that can be seen in the current view. Avisible line represents the boundary betweentwo surfaces (faces) that are not tangent or thelimiting element of a curved surface.

visual inspection (v) The process ofevaluating a design visually. Visual analysis isoften used by industrial designers andmarketing professionals to assess theconsumer’s aesthetic reaction to a design. Thisanalysis can also be used by engineers toperform a quick confirmation of geometry.

visual science (n) The study of the visual andtechnical applications of graphics. Some of theapplications of visual science include printingtechnologies, communications media, visualdesign, engineering graphics, and artisticdrawing.

visualization (v) The process of mentallyunderstanding visual information.Visualization is used with both physical andvirtual models to better understand their formand function. The mental image may beanalogous to the object represented or ofsomething different. Graphics and the processof creating graphics are used to help stimulatethe visualization of proposed designs.

volume rendering (n) A visualizationtechnique used with three independentvariables mapped to the three geometricdimensions. Each dependent data value isrepresented by a 3-D volume unit called a

voxel, typically coded with color. Varioussectioning techniques are used to reveal datavalues on the interior of the data space.

voxel (n) The minimum 3-D unit in a volumerendering; equivalent to the pixel in a 2-Drendering.

VR (n) See virtual reality.

Wwarped surface (n) A single- or double-curved transitional surface (e.g.,cylindroids, conoids, helicoids, hyperbolicparaboloids). Warped surfaces are oftenapproximated by triangulated surface sections,and may join other surfaces or entitiestogether.

washer (n) A round piece of material with ahole in the center, used with mechanicalfasteners to improve the assembling surface,distribute load, and assist in locking nuts.Washers are specified by giving the insidediameter, outside diameter, thickness, type,and name.

web (rib) (n) A thin, flat feature of an objectthat acts as a structural support. Ribs, webs,spokes, lugs, and other thin features are notsection lined if a cutting plane passes throughtheir long dimension.

width (n) One of the three principaldimensions of an object. The width dimensionis described in the front and top views of amultiview drawing. The width dimension isoften associated with the X axis in a 3-Dmodeling system.

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winged-edge data structure (n) A common3-D database structure used by boundaryrepresentation (B-rep) modelers. This datastructure attempts to strike a balance betweenconciseness and efficiency by providing selectredundancy of edges and vertices.

wireframe (n) The simplest type of datarepresentation for 3-D models. Wireframemodeling is a natural outgrowth of 2-D CADin that such models only contain informationon edges and vertices. With a wireframemodeler, there is no implicit information on theboundary between inside and outside themodel volume. Wireframe can also refer to arendering technique in which only the edgesand vertices are represented in the image.

wiring (cabling) diagram (n) A diagram ordrawing showing how the components in anelectronic assembly will be connected. Sincewiring diagrams often depict the wiring of allthe components tied into a single wiringharness, they are also called cabling diagrams.When the drawing depicts how the componentsare connected to the cable, it is called aninterconnection (or point-to-point) diagram.When there are numerous cable connections, itis called a highway diagram.

working assembly drawing (n) A drawingthat combines the detail drawing with theassembly drawing. For relatively simpleassemblies using some standard parts, it ispossible to combine the detail drawing with theassembly drawing by using a section view.

working drawings (n) The complete set ofstandardized drawings that specify the

manufacture and assembly of a design.Depending on the complexity of the design,working drawings may be on more than onesheet and may contain written instructions,called specifications. Working drawings areoften synonymous with the “blueprints” of adesign.

workplane (n) Often called a constructionplane, a 2-D infinitely large plane that can beoriented anywhere in 3-D space. A workplaneusually has an associated local coordinate systemdesignated with unique letters (e.g., U, V, W).Workplanes are used to define 2-D geometryused in the development of 3-D models.

world coordinate system (n) A fixedcoordinate system, also referred to as a globalcoordinate system, used in CAD to define thegeometric properties of elements stored in thedatabase. The world coordinate systemtypically uses either a 2-D (X,Y) or 3-D(X,Y,Z) Cartesian coordinate system.

worm’s eye view (n) In a perspective pictorial,a viewpoint looking up at the object. From thisviewpoint, the ground line is substantiallyabove the horizon line of the object.

ZZ-buffer (n) A combination of computerhardware and software which stores depth (Z)information about a rendered model. A Z-buffer contains specialized memory formanaging depth information, thus speeding therendering process, especially in animatedsequences.