Chapter 5: Accurate Modeling

Thecursorcanalwaysmovefreelyinspace,butchancesare,youwillwanttorelateyourmodelingelementstotheconstructionplanegrid,existingobjects,orcoordinatesinspace.Youcanrestrictthecursorsmovementtothegrid,enterspecificdistancesandanglesfromapoint,snaptospecificlocationsonexistingobjects,andenterCartesiancoordinatestolocatepointsin2-Dor3-Dspace.

The Rhino cursorTherearetwopartsofthecursor:thecursor (1)andthemarker (2).Thecursoralwaysfollowthemousemovement.Themarkersometimesleavesthecenterofthecursorbecauseofsomeconstraintonitsuchasgridsnaporortho.Themarkerisadynamicpreviewofthepointthatwillbepickedwhentheleftmousebuttonisclicked.Whenthemarkerisconstrained,inelevatormode,forexample,atracking line (3)alsodisplays.Constraintsmoveyourmarkertoaspecificpointinspaceormakeitsmovementtrackaccordingtotheconstraintsoyoucanmodelaccurately.

Snap to the construction plane gridGridsnapconstrainsthemarkertoanimaginarygridthatextendsinfinitely.Youcansetthesnapspacingtoanyvalue.ClicktheGrid Snapbuttononthestatusbartoturngridsnaponandoff.

Tip:Toreadmoreaboutacommand,clickthered,underlinedcommandnamelink.

Constrain the angle of movementOrthomodeconstrainsthemarkermovementorobjectdraggingtoaspecificsetofangles.Bydefault,thisisparalleltothegridlines,butyoucanchangethis.Orthoissimilartotheaxislockfunctionfoundindrawingoranimationprograms.ClicktheOrthopaneonthestatusbartoturnorthoonandoff.PressandholdtheShiftkeytotemporarilytoggletheorthomode.Anothercommonusefororthoistoconstrainobjectdraggingtoaspecificaxis.

33

Chapter 5: Accurate Modeling

Orthoisactiveafterthefirstpointforacommand.Forexample,afterpickingthefirstpointforaline,thesecondpointisconstrainedtotheorthoangle.

Ortho off (left); Ortho on (right).Ifyouonlyneedadifferentangleforasingleoperation,angleconstraintisfastertouse.Enteraspecificangleforoneoperationinsteadofchangingtheorthoangleandthenchangingitback.

Snap to existing objectsObject snapsconstrainthemarkertospecificpointsonanobject.WhenRhinoasksyoutospecifyapoint,youcanconstrainthemarkertospecificpartsofexistinggeometry.Whenanobjectsnapisactive,movingthecursornearaspecifiedpointonanobjectcausesthemarkertojumptothatpoint.Objectsnapscanpersistfrompicktopick,orcanbeactivatedforonepickonly.Multiplepersistentobjectsnapscanbesetfromthestatusbar.Allobjectsnapsbehavesimilarly,butsnaptodifferentpartsofexistinggeometry.Inaddition,therearespecialobjectsnapsthatworkforonepickonly.

Persistent object snapsUsepersistentobjectssnapstomaintainanobjectsnapthroughchoosingseveralpoints.Sincepersistentobjectsnapsareeasytoturnonandoff,youcansetthemandleavethemonuntiltheygetinyourway.Youcanthensetadifferentoneorjustdisablethem.Sometimesobjectsnapsinterferewitheachotherandwithgridsnaporortho.Objectsnapsnormallytakeprecedenceovergridsnaporotherconstraints.Thereareothersituationswhereobjectsnapsworkinconjunctionwithotherconstraints.Youwillseeexamplesofthisinthischapter.Formoreinformationincludingvideodemonstrations,seetheRhinohelptopicObject snaps.

Open the Osnap control4 ClicktheOsnappaneinthestatusbar.

TheOsnapcontrolopens.Thiscontrolisusuallydockedatthebottomofthescreen.

4 Clickacheckboxtoturnonanobjectsnap.4 Rightclickacheckboxtoturnanobjectsnaponandturnoffallotherobjectsnaps.4 Whenanobjectsnapisactive,movingthecursornearaneligiblepointonanobjectcausesthe

markertojumptothatpointandatooltiptoappear.ThebuttonsontheOsnaptoolbarallowsingle-useoverridesforthepersistentobjectsnaps.

To suspend all persistent object snaps4 IntheOsnaptoolbar,clicktheDisablebutton.

Allpersistentobjectsnapswillbesuspended,butremainchecked.

34

Chapter 5: Accurate Modeling

To clear all persistent object snaps4 IntheOsnaptoolbar,clicktheDisablebuttonwiththerightmousebutton.

Allpersistentobjectsnapswillbecleared.

To turn on one object snap and turn all others off with one click4 IntheOsnaptoolbar,right-clicktheobjectsnapyouwanttoturnon.

Special case object snapsComplexobjectsnapsthatallowselectingmultiplereferencepointsoraddotheradvancedcontrols.SeetheRhinohelptopicObject snapsformoreinformation.ThesearealsoavailablefromtheOsnapcontrol.

To turn on complex object snaps4 HoldtheCtrlkeyandhoverovertheOsnapcontrol.

Analternatesetofcontrolsappears.

Cursor constraintsWhenenteringpoints,youcanconstrainthemarkertoadistanceoranglefromthepreviouspoint.Onceyouhavesetthedistance,dragthelinearoundtoanyangle.Youcanalsousefurthersnapstopointthelineinaspecificdirection.

Distance constraintDuringanycommandthatrequirestwopoints,suchastheLinecommand,placethefirstpoint.Thenatthenextprompt,typeadistanceandpressEnter.Themarkerwillbeconstrainedtothespecifieddistancefromthepreviouspoint.Dragthecursoraroundthefirstpointandthenpickapoint.

Angle constraintAngleconstraintissimilartoortho,butyoucansetanyangleanditisaone-timesetting.The

Chapter 5: Accurate Modeling

Distance and angle togetherDistanceandangleconstraintscanbeusedatthesametime.

1. Atthecommandprompt,typethedistance,andpressEnter.2. Atthenextcommandprompt,typethe

Chapter 5: Accurate Modeling

Youcansnaptointersectionsofthetrackinglines,perpendiculars,anddirectlytosmartpointsaswellasintersectionsoftrackinglinesandrealcurves.Thetrackinglinesandsmartpointsaredisplayedforthedurationofacommand.

Coordinate systemsRhinousestwocoordinatesystems:constructionplanecoordinatesandworldcoordinates.Worldcoordinatesarefixedinspace.Constructionplanecoordinatesaredefinedforeachviewport.

Cartesian coordinatesWhenRhinopromptsyouforapoint,ifyoutypexandyCartesiancoordinates,thepointwilllieontheconstructionplaneofthecurrentviewport.Formoreinformationaboutcoordinatesystemsandnumericconstraints,seewww.mathopenref.com/coordinates.

Right-hand ruleRhinofollowswhatiscalledtheright-hand rule.Theright-handrulecanhelpyoudeterminethedirectionofthez-axis.Formarightanglewiththethumbandforefingerofyourrighthand.Whenyourthumbpointsinthepositivex-direction,yourforefingerpointsinthepositivey-direction,andthepalmofyourhandfacesinthepositivez-direction.

World coordinatesRhinocontainsoneworldcoordinatesystem.Theworldcoordinatesystemcannotbechanged.WhenRhinopromptsyouforapoint,youcantypecoordinatesintheworldcoordinatesystem.Thearrowiconinthelowerleftcornerofeachviewportdisplaysthedirectionoftheworldx-,y-,andz-axes.Thearrowsmovetoshowtheorientationoftheworldaxeswhenyourotateaview.

Construction plane coordinatesEachviewporthasaconstruction plane.Aconstructionplaneislikeatabletopthatthecursormovesonunlessyouusecoordinateinput,elevatormode,orobjectsnapsorafewotherinstanceswhereinputisconstrained.Theconstructionplanehasanorigin,x-andy-axes,andagrid.Theconstructionplanecanbesettoanyorientation.Bydefault,eachviewportsconstructionplaneisindependentofthoseinotherviewports.

37

Chapter 5: Accurate Modeling

Theconstructionplanerepresentsthelocalcoordinatesystemfortheviewportandcanbedifferentfromtheworldcoordinatesystem.

Rhinosstandardviewportscomewithconstructionplanesthatcorrespondtotheviewport.ThedefaultPerspectiveviewport,however,usestheworldTopconstructionplane,whichisthesameconstructionplanethatisusedintheTopviewport.Thegridliesontheconstructionplane.Thedarkredlinerepresentstheconstructionplanex-axis.Thedarkgreenlinerepresentstheconstructionplaney-axis.Theredandgreenlinesmeetattheconstructionplaneorigin.Tochangethedirectionandoriginofaconstructionplane,usetheCPlanecommand.Presetconstructionplanes(WorldTop,Right,andFront)giveyouquickaccesstocommonconstructionplanes.Inaddition,youcansaveandrestorenamedconstructionplanesandimportnamedconstructionplanesfromanotherRhinofile.

2-D construction plane coordinates4 Atacommandprompt,typethecoordinatesintheformatx,ywherexisthex-coordinateandyis

they-coordinateofthepoint.

A line from 1,1 to 4,2.

3-D construction plane coordinates4 Atacommandprompt,typethecoordinatesintheformatx,y,zwherexisthex-coordinate,yisthe

y-coordinate,andzisthez-coordinateofthepoint.Therearenospacesbetweenthecoordinatevalues.4 Toplaceapoint3unitsinthex-direction,4unitsinthey-direction,and10unitsinthez-direction

fromtheconstructionplaneorigin,type3,4,10attheprompt.

NoteIfyouenteronlyx-andy-coordinates,thepointwilllieontheconstructionplane.

38

Chapter 5: Accurate Modeling

Relative coordinatesRhinoremembersthelastpointused,soyoucanenterthenextpointrelativetoit.Relativecoordinatesareusefulforenteringalistofpointswheretherelativelocationsinsteadofabsolutelocationsofthepointsareknown.Userelativecoordinatestolocatepointsaccordingtotheirrelationshiptothepreviousactivepoint.

To use relative coordinates4 Atacommandprompt,typethecoordinatesintheformatrx,ywherersignifiesthatthecoordinate

isrelativetothepreviouspoint.

For example1. StarttheLinecommand.2. AttheStart of lineprompt,clicktoplacethefirstendoftheline.3. AttheEnd of lineprompt,typer2,3,andpressEnter.

Thelineisdrawntoapoint2unitsinthex-directionand3unitsinthey-directionfromthelastpoint.

39