Cad Module 1

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CAD

Computer Aided DesignMEE 403

Kuwar MausamME Deptt.,GLAITM, Mathura

[email protected]@gla.ac.in

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Module No.1 12

Introduction:Introduction to CAD/CAED/CAE, Elements of CAD, Essential Requirements of CAD,

Concepts of Integrated CAD/CAM, Necessity & Its Importance, Engineering Applications

Computer Graphics-I

CAD/CAM Systems, Graphics Input Devices-Cursor Control Devices, Digitizers,

Keyboard Terminals, Image Scanner, Speech Control Devices and Touch, Panels,

Graphics Display Devices-Cathode Ray Tube, Random & Raster Scan Display, Color

CRT Monitors, Direct View Storage Tubes, Flat Panel Display, Hard Copy Printers and

Plotters.

Computer Graphics-II

Graphics Standards, Graphics Software, Software Configuration, Graphics Functions,

Output Primitives- Bresenhams Line Drawing Algorithm and Bresenhams Circle

Generating Algorithm.

Geometric Transformations:

World/Device Coordinate Representation, Windowing and Clipping, 2 D Geometric

Transformations- Translation, Scaling, Shearing, Rotation & Reflection Matrix

Representation, Composite Transformation, 3DTransformations, Multiple

Transformation.

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3

Module No.II 12Curves:

Curves Representation, Properties of Curve Design and

Representation, Interpolation Vs Approximation, ParametricRepresentation of Analytic Curves, Parametric Continuity Conditions,

Parametric Representation of Synthetic Curves-Hermite Cubic Splines-

Blending Function Formulation and Its Properties, Bezier Curves-

Blending Function Formulation and Its Properties, Composite Bezier

Curves, B-Spline Curves and Its Properties, Periodic and Non-Periodic

B-Spline Curves.

3D Graphics:

Polygon Surfaces-Polygon Mesh Representations, Quadric and

Superquadric Surfaces and Blobby Objects; Solid Modeling-Solid

Entities, Fundamentals of Solid Modeling-Set Theory, Regularized SetOperations; Half Spaces, Boundary Representation, Constructive Solid

Geometry, Sweep Representation, Color Models. Application

Commands for AutoCAD & Pro-E Software


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4

Numerical Methods With Programming in C/C++:

Introduction, Errors in Numbers, Binary Representation ofNumbers, Root Finding- Bisection Method, Newton Raphson

Method, Curve Fitting-Least Square Method, Numerical

Differentiation-Newtons Interpolation, Numerical

Integration-Trapezoidal and Simpson Method

Finite Element Method:Introduction, Principles of Finite Elements Modeling, Stiffness

Matrix/Displacement Matrix, Stiffness Matrix for Spring

System, Bar & Beam Elements, Bar Elements in 2D Space

(Truss Element).Continuum Problems: Classification of Differential

Equations, Variational Formulation Approach, Ritz Method,

Generalized Definition of An Element, Element Equations

From Variations.

Module No.III 14


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Books for CAD

COMPUTER AIDED DESIGN BYR.K.SRIVASTAVA

COMPUTER AIDED DESIGN BY VIKRAMSHARMA

CAD\CAM BY GROOVER AND ZIMMERS CAD BY S.SINGH

MATHEMATICAL ELEMENTS FOR COMPUTERGRAPHICS-ROGERS &ADAMS

COMPUTER ORIENTED NUMERICALMETHODS BY RAJARAMAN

CAD\CAM BY IBRAHIM ZED

FEM BY S.S.RAO

LET US C 5


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Module No.1

6

Introduction:

Introduction to CAD/CAED/CAE, Elements of CAD, Essential Requirements of CAD,

Concepts of Integrated CAD/CAM, Necessity & Its Importance, EngineeringApplications

Computer Graphics-I

CAD/CAM Systems, Graphics Input Devices-Cursor Control Devices, Digitizers,

Keyboard Terminals, Image Scanner, Speech Control Devices and Touch, Panels,

Graphics Display Devices-Cathode Ray Tube, Random & Raster Scan Display,

Color CRT Monitors, Direct View Storage Tubes, Flat Panel Display, Hard Copy

Printers and Plotters.


Graphics Standards, Graphics Software, Software Configuration, Graphics

Functions, Output Primitives- Bresenhams Line Drawing Algorithm and

BresenhamsCircle Generating Algorithm.

Geometric Transformations:

World/Device Coordinate Representation, Windowing and Clipping, 2 D Geometric

Transformations- Translation, Scaling, Shearing, Rotation & Reflection Matrix

Representation, Composite Transformation, 3DTransformations, Multiple

Transformation.


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What is CAD

CAD= C + A + D

C:- Computer

A:- Aided (HELP)

D:- DesignNow we leave first two terms .

And make a discussion on the Design.

What is design?Or

What is design Process?7


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BUT>>>>>>>>>

Before starting on the details discussion ONE Question:-

WHY WE STUDY CAD?

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SIMPEL:-

TO CREAT A BACKGROUND FOR DESIGN

PROCESS.

TO ASSIST OUR SISTER ENGINEERING BRANCH.

TO UNDERSTAND THE FUNDAMENTALS WHICHWORKS BEHIND THE ANY DESIGN AND DRAFTING

SOFTWARE.

AND THE LAST NO ONE CREAT A PERFECT

DESIGN WITH OUT THE KNOWLEDGE OF

MATHEMATICS OF DESIGN.

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DESIGN PROCESS

The Design processdeals with the conversionof ideas in to reality.

OR

IT is the form of human

activity which aims atfulfilling human needs

OR

The design process is theprocess of produce the

prototype, which is usedas the sample forreproducing the

particular, goods orservice as many time to

satisfy consumers needs

RECOGNITIONOF NEED

DEFINITION OF

PROBLEM

SYNTHASIS

ANALYSIS AND

OPTIMIZATION

EVALUATION

PRESENTATION

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St i th d i


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Steps in the design process:-

(Given by Shigley)

1. Recognition of need

2. Definition of the problem3. Synthesis

4. Analysis and Optimization

5. Evolution6. Presentation

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Some traditional design procedures:-

1. Design by craft evolution.

2. Design by drawing.

1. Design by craft evolution:-

The designing of Bullock cart , rowing boat, razor etcare some product produce by craft evolution process.

Features of craft evolution:-

The craft man doesnt prepare the dimensioneddrawing of their products.

They can not offer proper justification for the design. The product design was very time consuming.

The change in product design is very slow or nearlynegligible.

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Design by drawing:-

To over come the limitation of design by craft, a new method

of design is developed this method is called Design by

Drawing.

Features of Design by drawing :-

1. The dimensioning of product is specified.

2. The complete manufacturing or design ofthe product can be subdivided into

separate pieces, which can be made by

different people.

3. When the product is to be developed by

trial and error, the process is carried out

on a drawing board instead of shop floor.13


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FLOW CHART FOR DESIGN PROCESS WITHOUT

INLEMENTATION OF CAD

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RECOGNITION

OF NEED

DEFINITION OFPROBLEM

SYNTHASIS

ANALYSIS AND

OPTIMIZATION

EVALUATION

PRESENTATIONAUTOMAT

EDRAFTING

DESIGN

REVIEW AND

EVALUATION

ENGG.

ANALYSIS

GEO.

MODELLING

CAD ELEMENT\TOOLS

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FLOW CHART FOR DESIGN PROCESS WITH

INLEMENTATION OF CAD

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Product

Concept

Process

Planning

Costumer

And Market

Production

Design

Engineering

Drafting

Product

Schedules

Quality

control

New

Equipment

and Tooling

PRODUCT CYCLEAll product cycle starts from the customers and markets and involves three steps. ---

Product specification

Design and optimization engineering

Drafting

Product cycle without implementation of CAD 19


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Product

Concept

New

Equipment

and

Tooling

Design

Engineerin

g

Process

Planning

Costumer

And

Market

Production Product

Schedules

Drafting

Quality

control

Computerized

Scheduling,

Mrp, Shop floor

Control

Computer

control, robets,

machine OR

CAM

CAQc

CADDCAD

CAPP

Product cycle

with

implementation

of CAD

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Typical product cycle

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OVERVIEW OF CAD

What is CAD?

CAD if often defined in a variety of ways and includes a large

range of activities. Very broadly it can be said to be the

integration of computer science (or software) techniques in

engineering design.

OR

CAD is a creation and development of prototype on a

computer to assist the engineer in design process.OR

CAD can be defined as the use of computer system to assist

in the creation, modification analysis or optimization of design.

OR

CAD also describe as the automation of the design process.CAD plays the role in the area such as design, analysis,

production, planning, documentation, tool fabrication, quality

control and testing.

Cad system is also useful in improving the performance and

productivity. 22

A typical


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A typical

CAD process

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At one end when we talk of modeling, it encompasses the following:

Use of computers (hardware & software) for designing products

Numerical method, optimizations etc.

2D/3D drafting 3D modeling for visualization

Modeling curves, surfaces, solids, mechanism, assemblies, etc.The models thus developed are first visualized on display monitors using a

variety of techniques including wire frame display, shaded image

display, hidden surface removed display and so on. Once the designer

is satisfied, these models are then used for various types of analysis /applications. Thus, at the other end it includes a number of analysis

activities. These could be:

Stress (or deflection) analysis, i.e. numerical methods meant for estimating

the behavior of an artifact with respect to these parameters. It includes

tools like the Finite Element Method (FEM).

Simulation of actual use

Optimization Other applications like

CAD/CAM integration

Process planning

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Aspects to CAD:-

1. Modeling

2. Display/ Visualization

3. Applications

MODELING

1. Modelling typically includes a set of activities like2. Defining objects

3. Defining relation between objects

4. Defining properties of objects

5. Defining the orientations of the objects in suitable co-

ordinate systems

6. Modification of existing definition (editing)

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The figure below explains what a typical CAD model would need

to define, what kind of entities need to be defined and what

relationships exist between them.

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DISPLAY / VISUALIZATION


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DISPLAY / VISUALIZATION

Displaying the model requires the following:

Mapping objects onto screen coordinates: Models are typically made in a model

coordinate system. this could be the world coordinate system, or a coordinate

system local to the object. these coordinate systems are typically three dimensional

in nature. To display the object on a 2D screen, the object coordinates need to bemapped on to the 2D coordinate system of the screen. This requires two steps:

Viewing transformations: The coordinates of the object are transformed in a

manner as if one is looking at the object through the screen. This coordinate

system is referred to as the viewing coordinate system.

Projections: The object in the viewing coordinate system is then projected onto

the two dimensional plane of the screen.

Surface display or shading / rendering: In displaying the objects on the screen one

often likes to get a shaded display of the object and get a good feel of the three

dimensional shape of the object. This requires special techniques to render thesurface based on its shape, lighting conditions and its texture.

Hidden line removal when multiple surfaces are displayed: In order to get a proper

feel of the three dimensional shape of an object, one often desires that the lines /

surfaces which are not visible should not be displayed. this is referred to as hidden

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Once a model is visualized on the screen and approved by the conceptual

designer, it has to go through a number of analysis. Some of the kinds of

usage this model might have to go through are the following:

Estimating stresses / strains / deflections in the objects under various staticloading conditions

Estimating the same under dynamic loading conditions

Visualizing how a set of objects connected together would move when

subject to external loading. This leads to a whole set of activities undersimulation. These activities would vary depend upon the application the

object is to be subject to.

Optimizing the objects for

Developing 2D engineering drawings of the object

Developing a process plan of the object

Manufacturing the object using NC / CNC machines and generating the

programs for these machines so as to manufacture these objects.

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Applications:-Its include the following:

An overview of the hardware systems used in CAD

2D and 3D transformations used to shift between coordinate systems

Projection transformation used to get the object in screen coordinate

systems

Modeling of curves and surfaces

Modeling of solids

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CAE


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CAD

(DRAFTING)

CAPM

(COMPUTER

ADIED

PRODUCTION

MANAGEMENT)

CAD

CAM

CAE 1.Materialinventory control

2.Plant layout

3.Pay Roll4.Production

Planning and

Control

5.Group tech.

6.Computer aided

scheduling

CAE

(COMPUTER AIDED ENGINEERING)

CAE DEFINED AS A PRODUCT DESIGN DEVELOPMENT PHILOSOPY THAT BRINGS TOGETHER ALL THE

ENGINEERING ACTIVITIES.

ORCAE IS A COMBINATION OF TECHIQUES IN WHICH MAN AND MACHINE ARE BLENDED IN TO A PROBLEM

SOLVING TEAM WITH THE BEST CHARACTERISTICS OF EACH.

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DATA

MANAGEMENT

CAD

QUALITY

ACCURANCE

BUILD AND TEST

PROTOTYPE

COM. AIDED

DRAFTING

CAM

COMPUTER

SIMULATION

CAPM

CAE

CAE ACTIVITIES

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CIMS


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Mechanicaldesign

Post production

management

Product designand planning

Manufacturing

Mechanical

drafting

Business

Management

Process design

and control

Productspecification

CIMS

COMPUTER INTREGATED MANUFACTURING SYSTEM

CIMS IS AN INTREGATION OF CAD\CAM SYSTEM THAT CONTROL ALL ACTIVITIES

FROM PLANNING, DESIGN OF PRODUCT TO ITS MANUFACTURING AND SHIPPING.

Main component of CIMSThe aim of CIMS is to optimize the entire operation from design to manufacture to

sale. 33


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Elements of CAD

Computer aided design consists of 3 levels i.e. Drafting, Modeling, Analysis and

blended in to two main factors.

1.Human factor

2.Machine factor

These factors working together to active the optimum design.

Level I Level II Level III

Drafting & Documentation Geometric Modeling Analysis & Testing

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CAD SYSTEM

HUMAN

FACTOR

SYSTEMFACTOR

GEOMETRIC

MODELING

ENGINEERING

ANALYSIS

DESIGN

REVIEW &

EVALUATION

AUTOMATED

DRAFTING

DATABASE

HARDWARE

SOFTWARE

Element of CAD

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Human Factor

Human factor is the key of the success of CAD system. This concerns the training of designer or the

engineer, with out when the CAD system become redundant.

The trained designer may be activity involved in CAD process due to following factors.

Geometric modeling

Engineering/ Computer Aided analysis

Design review and evaluation

Automated drafting

1:-Geometric Modeling

In computer aided design geometric modeling is concerned with computer compatible

mathematical description of the geometry of an object. The mathematical description

allows the images of the object to be displayed and manipulated on a graphic terminal

through signals from the CPU of the CAD system.

In geometric modeling the designer constructs the image of the object. On the CRTscreen of the interactive computer graphics system by in putting three type of

command

The first type of command generates basic geometric elements. Such as points lines

and circle.

The second type of command is meant to accomplish translation scaling, rotation or

other transformations of the elements.

The third type of command joins the various elements to give the desired object.

During the above process the computer converts the commands into a mathematical

model stores it in the computer data files and displays it as an image on the CRT

screen.

.

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Th l diff t th d f ti th bj t i t i


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There are several different methods of representing the object in geometric

modeling. The basic form uses wireframesto represents the object. In this form

the object represent by the interconnecting lines.

Types of wire frame modeling.

1. 2D 2. 2.5D 3. 3D

1. 2D:- Twodimensional representation is used for a flat object.2. 2.5 D:- This goes some what beyond the 2D capability by permitting a 3D object to be

represented as long as it has no side wall details.

3. 3D:- This allows more complex or 3D geometry.

The new advance method of geometric modeling is solid modeling in three dimensions. In

this the colors are added to image the resulting pictures become realistic.

There are two basic approaches of solid modeling:-

Constructive solid geometry (CSG or C-rep) also called building block approach.

Boundary representation [B-rep]

C-rep or CSGIt allows the user to build the model out of solid graphic primitives, such

as rectangular block, cubes, sphears, cylinders and pyramids.

B-repIt is used to draw outline or boundary of object or CRT screen. e.gTo draw

unusual shapes.

Another feature is colour graphic capability. Colour images helps to clarity components in

assembly.

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2 d wire frame model

3-d wire

frame

model2.5-d wire

frame

model

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2:-Engineering AnalysisIn the formulation of any design project, some sort of analysis is


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required the analysis may be stress-strain calculations heat transfer computation or the use of

differential equation to describe the dynamic behaviour of the system being designed.

The computer can be used to aid in this analysis work.

Trunkey CAD/CAM system can be integrated to engineering analysis software which can be called

to operate on the current design model. The two most powerful analysis features of CAD system is

a.Finite Element Method

b.Analysis of Mass Properties.

3:-Design review and evaluation

Checking the accuracy of the design can be accomplished conveniently on the graphics terminal.\

Semi-automatic dimensioning and tolerance routines which assign size, specification to surfaces

indicated by the user help to reduce the possibility of dimensioning errors.

The designer can zoom in on part design detail and magnify the image on the graphics screen for

close scrutiny. A procedure called layering is often helpful in design review.

The another related procedure for design review in interference checking one of the most

interesting evaluation features available on some computer aided design system is kinematics.

The available kinematics package provides the capability to animate the motion of simple designed

mechanisms such as hinged components and linkages. The capability enhances the designers

visualization of operation of mechanism and helps to ensure against interference with other

components.

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4:-Automated Drafting

Automated drafting involves the creation of hard copy engineering drawings directly from

CAD database. Some times automation of drafting process represented the principal

justification for investing the CAD station.

Computer aided drafting is known as the design work station. The CAD work station is

the system interface with the outside world. The work of CAD work stationInterface with the central processing unit of the computer.

Generate the steady graphic image for the user.

Provide digital description of the graphic image.

Translate computer command into operating function.

Be user friendly.

Some times automated drafting also used with features of automatic dimensioning

generation of cross hatched area, scaling of drawing and capability to developed

sectional view and enlarged views of particular par details.

2:System Factor :

The other component or element is system factor. It contains two main sub components

- a:-Hardware b:-Software.

A:-HardwareThe hardware stands for physical component hardware list.

The CAD workstationDisplay devices

Interaction devices

Output device

B:-SoftwareIt is second subsystem which is a set of instructions, procedures and

rules that direct the operation of the computer. Now present time many softwares are

available.

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Reasons for Implementation of CAD System


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p y

1.To increase the productivity of the designer

2. To improve the quality of design

3. To improve communication

4. To create the database for manufacturing

5. For better and improved design

6. For reducing the engineering personnel requirement

7. For easier modification and alternations

8. For minimized design and transaction errors

9. For greater accuracy

10. For shorter lead time 43

Main Advantages or Benefits of CAD


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Main Advantages or Benefits of CAD

Improved engineering productivity

Shorter lead time

Improve the quality of design

Helps in design analysis

Lower design error

Grater accuracy in design calculation

Reduced engineering personal requirement

Customer modifications are easier to make

Improve accuracy of designProvides better functional analysis to reduces prototype testing

Assistance in preparation of documentation

Design have more standardization

Improved productivity in tool design

Reduce training time for routine drafting tasksLower response to requests for quotation

To improve communication

Easier modification and alteration

Design/drawing are more understandable44

C t G hi I


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Computer GraphicsI

Computer systems Graphics input devices- cursor control

devices, Digitizers Scanners, speechoriented devices and touch panels

Graphics display devicesCRT, colorCRT monitors, DVST, Flat- panel display

Graphics output Devices.

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COMPUTER SYSTEM FOR CAD


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COMPUTER SYSTEM FOR CAD

OR

BASIC REQUIREMENT CAD SYSTEM

There are two type of requirement for any cad software:-

Hardware requirement

Software requirement1:- Hardware Requirement

There are three basic hardware component of a general purpose computer:-

Central Processing unit

Memory

Input\output device section

HARDWARE STRUCTURE.

CPU

Control

unit

ALU

INPUT/OUTPUT

DEVICE

MEMORY

Outside world

Peripheral device

Mass Memory

(printer)

(Tape, disk

etc)

Computer46


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Graphics Display devices

CRT

Color CRT monitors

DVST

Flat- panel display

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Introduction


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Introduction Normally the display o/p devices divided in to two category:-

1. Display devices for display the images on computer monitor.

2. Plotting, printing devices for the hard copy generation.In today world most of the display devices follow the RASTER Scan technique and

most of the raster devices works on the DIGITAL FRAME BUFFER

DIGITAL FRAME BUFFER:- This frame buffer store a matrix of Pixel intensity

value, so this is called Memory Bank.

This memory bank change according to the requirement.(up to a certain limit.) In a simple monochrome display the buffer contains the one memory bit for

each pixel in the each display device, thus if there are 1280x1024 pixels on the

display device, the buffer contains the same number of memory bits in a single

bit plane.

The memory bits have binary value of either 0 or 1 .

Zero value for unlighted pixel.

One value for lighted pixel.

If color and shade are required then additional bit are allocated on each pixel.

Total number of color available is 2n.

Total number of color are limited by Speed and bandwidth of display system.

Normally 4096 color are available in common cad system.

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Frame Buffers

A frame buffer may be thought of as computer memoryorganized as a two-dimensional array with each (x,y)addressable location corresponding to one pixel.

Bit Planes or Bit Depthis the number of bits corresponding toeach pixel.

A typical frame buffer resolution might be

640 x 480 x 8

1280 x 1024 x 8

1280 x 1024 x 24 50


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Monochrome Display(Bit-map Display)

Electron

Gun

1 bit

2 levels

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Fig. 1-19 A Single-bit-plane black-and-white buffer raster CRT graphics device

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Fig. 1-20 An N-bit-plane gray level frame buffer

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3-Bit Color Display

3

red

green

blue

COLOR: black red green blue yellow cyan magenta white

R

G

B

0

0

0

1

0

0

0

1

0

0

0

1

1

1

0

0

1

1

1

0

1

1

1

1

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Fig. 1-21 A 24-bit-plane color frame buffer

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True ColorDisplay24 bit planes, 8 bits per color gun.

224= 16,777,216

Green

Red

Blue

N

N

N

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Fig. 1-22 A 24-bit-

plane color frame

buffer with 10-bit-widelook up table

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Color Map Look-Up Tables


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Color Map Look-Up Tables Extends the number of colors that can be displayed by a

given number of bit-planes.

0100

001

1

67

100110100001

0

67

255

1001 1010 0001

R G B

RED

GREEN

BLUE

Pixel displayed

at x', y'

Pixel in

bit map

at x', y'

0 x

0

y

xmax

maxy

Bit map Look-up table Display

Video look-up table organization: each table entry is a 12 bit per entry.

A pixel with value 67 is displayed on the screen with the red electron gun

at 9/15 (binary 1001) of maximum, green at 10/15, and the blue is 1/15.

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Performance measurements


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Performance measurements

The performance of a monitor is measured by the following

parameters:

Luminanceis measured in candelas per square meter (cd/m2

also called a Nit). active (black) to inactive (white) and back to active (black)

again, measured in milliseconds. Lower numbers mean faster

transitions and therefore fewer visible image artifacts.

Contrast ratiois the ratio of the luminosity of the brightest color

(white) to that of the darkest color (black) that the monitor iscapable of producing.

Power consumptionis measured in watts.

Viewing angleis the maximum angle at which images on the

monitor can be viewed, without excessive degradation to the

image. It is measured in degrees horizontally and vertically.

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O/P Devices, Graphics Displays Contd
http://en.wikipedia.org/wiki/Luminancehttp://en.wikipedia.org/wiki/Contrast_ratiohttp://en.wikipedia.org/wiki/Power_consumptionhttp://en.wikipedia.org/wiki/Viewing_anglehttp://en.wikipedia.org/wiki/Viewing_anglehttp://en.wikipedia.org/wiki/Power_consumptionhttp://en.wikipedia.org/wiki/Contrast_ratiohttp://en.wikipedia.org/wiki/Luminance


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O/P Devices, Graphics Displays Contd

Dot pitchis the distance between subpixels of the same

color in millimeters. In general, the smaller the dot pitch, the

sharper the picture will appear.

Refresh rateis the number of times in a second that adisplay is illuminated. Maximum refresh rate is limited by

response time.

Response timeis the time a pixel in a monitor takes to go

from active (black) to inactive (white) and back to active

(black) again, measured in milliseconds. Lower numbersmean faster transitions and therefore fewer visible image

artifacts.

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http://en.wikipedia.org/wiki/Dot_pitchhttp://en.wikipedia.org/wiki/Refresh_ratehttp://en.wikipedia.org/wiki/Response_timehttp://en.wikipedia.org/wiki/Response_timehttp://en.wikipedia.org/wiki/Refresh_ratehttp://en.wikipedia.org/wiki/Dot_pitch


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CATHODE RAY TUBE

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Main Component of CRT


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Main Component of CRT

1. Vacuum tube

2. Elector gun

3. Control grid

4. Cathode

5. Beam Focusing unit

6. Deflection system:- a. Vertical system

b. Horizontal system

7.CRT screen

Fig. illustrates the basic operation of a CRT. A beam of electrons(cathode rays), emitted by an electron gun, passes throughfocusing and deflection systems that direct the beam towards

specified position on the phosphor-coated screen.

The phosphor then emits a small spot of light at each positioncontacted by the electron beam. Because the light emitted by thephosphor fades very rapidly, some method is needed formaintaining the screen picture.

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A refresh CRT is used.

The primary components of an electron gun in a CRT are the heatedmetal cathode and a control grid.

Heat is supplied to the cathode by directing a current through a coil ofwire, called the filament, inside the cylindrical cathode structure.

This causes electrons to be? boiled off? the hot cathode surface. Inthe vacuum inside the CRT envelope, negatively charged electrons arethen accelerated toward the phosphor coating by a high positive

voltage.

The accelerating voltage can be generated with a positively chargedmetal coating on the in side of the CRT envelope near the phosphorscreen, or an accelerating anode can be used, as in fig.

Sometimes the electron gun is built to contain the accelerating anodeand focusing system within the same unit.

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Spots of light are produced on the screen by the transfer of the CRT


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Spots of light are produced on the screen by the transfer of the CRTbeam energy to the phosphor.

When the electrons in the beam collide wit the phosphor coating, theyare stopped and there are stopped and their kinetic energy is

absorbed by the phosphor.

Part of the beam energy is converted by friction into heat energy, andthe remainder causes electron in the phosphor atoms to move up tohigher quantum-energy levels. After a short time, the? Excited?Phosphor

Electrons begin dropping back to their stable ground state, giving uptheir extra energy as small quantum of light energy.

What we see on the screen is the combined effect of all the electronslight emissions: a glowing spot that quickly fades after all the excitedphosphor electrons have returned to their ground energy level.

The frequency (or color) of the light emitted by the phosphor isproportional to the energy difference between the excited quantumstate and the ground state.

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Different kinds of phosphor are available for use in aCRT


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CRT.

Besides color, a major difference betweenphosphors is theirpersistence:

How long they continue to emit light (that is, haveexcited electrons returning to the ground state) afterthe CRT beam is removed.

Persistence is defined as the time it takes theemitted light from the screen to decay to one-tenth

of its original intensity. Lower-persistence phosphors require higher refresh

rates to maintain a picture on the screen withoutflicker.

A phosphor with low persistence is useful foranimation;

A high-persistence phosphor is useful for displayinghighly complex, static pictures.

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RASTER-SCAN DISPLAYS


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RASTER-SCAN DISPLAYS In a raster- scan system, the electron beam is swept across the

screen, one row at a time from top to bottom.

As the electron beam moves across each row, the beamintensity is turned on and off to create a pattern of illuminatedspots.

Picture definition is stored in memory area called the refresh

buffer or frame buffer.

This memory area holds the set of intensity values for all thescreen points. Stored intensity values are then retrieved fromthe refresh buffer and? Painted? On the screen one row (scanline) at a time.

Each screen point is referred to as a pixel (shortened forms ofpicture element).

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Refreshing on raster-scan displays is carried out at the rate of 60 to 80

frames per second.

At the end of each scan line, the electron beam returns to the left side of

the screen to begin displaying the next scan line.

The return to the left of the screen, after refreshing each scan line, is called

the horizontal retraceof the electron beam.

On some raster-scan systems (and in TV sets), each frame is displayed in

two passes using an interlaced refresh procedure.

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Random scan

Random scan monitors draw a picture one line at a time and forthis reason are also referred to as vectordisplays (or stroke-writingor calligraphicdisplays).

The component lines of a picture can be drawn and refreshedby a random-scan system in any specified order.

Sometimes the refresh display fileis called thedisplay list,

display program,or simply the refresh buffer. To display a specified picture, the system cycles through the

set of commands in the display file, drawing each componentline in turn.

After all line- drawing commands have been processed, thesystem cycles back to the first line command in the list.

Random-scan displays are designed to draw al the componentlines of a picture 30 to 60times each second.

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Video Controller Cycles through the frame buffer, one scan line at a time. Contents of the memoryare used the control the CRT's beam intensity or color.

X address

Y address

Pixel

value(s)

Raster scan

generator

Data

Horizontal

and vertical

deflection

signals

Intensity

or color

Linear

address

Set or increment

Set or decrement

M

e

m

o

r

y

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1. Persistence

2. Resolution

3. Addressability

4. Aspect ratio

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How long small spots continue to emitlight after the beam is moved. How long it

takes to the emitted light from the screen

to decay to one-tenth of its originalintensity.

Lower persistence requires high refresh rate

& it is good for animation High persistence is useful for displaying

highly complex static picture.

Graphics monitors are usually constructed

with 10 to 60 microseconds.75


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Resolution is the number of pointes per inch or centimeter

that can be plotted horizontally & vertically.

The smaller the spot size, the higher the resolution.

The higher the resolution, the better is the graphics system

High quality resolution is 1280x1024

The intensity distribution of spots on the screen haveGaussian shape.

Adjacent points will appear distinct as long as theirseparation is greater than the diameter at which each spothas intensity of about 60% of that at the center of the spot.

Intensity

distribution

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Addressability is a measure of the spacing

between the centers of vertical and horizontal

lines.

The picture on a screen consists of intensified

points.

The smallest addressable point on the screen iscalled pixel or picture element

In graphics mode there are 800x60077


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This number gives the ratio betweenvertical points and horizontal points

necessary to produce equal length lines

in both directions on the screen. Aspectratio = means: vertical line with 3

points is equal in length to horizontal line

of 4 points.

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DVST( )


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DVST(DIRECT VIEW STOREGE TUBE)

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The refresh display was obsolete by DVST because there

was refresh buffer memory could only display a few hundredvectors on the screen without flicker.

The speed of the electron beam in he DVST is slower than

refresh display due to elimination of refresh cycle.

The picture is stored as a charge in the phosphor meshlocated behind the screens surfaces. Therefore complex

picture could be drawn without flicking.

Once the picture displayed it remains on the screen until it is

explicitly erased. This is why the Storage tube name wassuggested.

The DVST cannot provide colors, animation, and use of a

lightpen as an input device.81

Flat panel display (LCD)


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s

cr

e

e

n

Color filter

Horizontal polarizing

filter

voltage

backlight

Hor. Glass groove panel

Ver .glass grooved panel

Ver .polarizing filter

Ver .molecule

Hor. molecule

Twisted LCM

p p y ( )

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LCDs: organic molecules, naturally in crystalline state, that

liquefy when excited by heat or E field

Crystalline state twists polarized light 90.

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Liquid- crystal displays (LCDs) are commonly used in systems,h l l t d t bl l t t


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such as calculators and portable, laptop computers.

These non-emissive devices produce a picture by passingpolarized light from the surrounding or from an internal lightsource through a liquid- crystal material that can be aligned to

either block or transmit the light.

A flat-panel display can then be constructed with a nematicliquid crystal, as demonstrated in fig.

Two glass plates, each containing a light polarizer at right

angles to the other palate, sandwich the liquid-crystal material. Rows of horizontal transparent conductors are built into one

glass plate, and columns of vertical conductors are put into theother plate.

The intersection of two conductors defines a pixel position.Normally, the molecules are aligned as shown in the fig.

Polarized light passing through the material is twisted so that itwill pass through the opposite polarizer. The light is reflectedback to the viewer.

To turn off the pixel, we apply voltage to the two intersectingconductors to align the molecules so that the light is nottwisted. 84


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Plasma display panels

Similar in principle tofluorescent light tubes

Small gas-filled capsules

are excited by electric field,emits UV light

UV excites phosphor

Phosphor relaxes, emits

some other color

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Plasma panels, also called gas discharge displays,are constructed by filling the region between two


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are constructed by filling the region between twoglass plates with a mixture of gases that usuallyinclude neon.

A series of vertical conducting ribbons is placed onone glass panel, and a set of horizontal ribbons isbuilt into the other glass panel.

Firing voltages applied to a pair of horizontal andvertical conductors cause the gas at the intersection

of the of two conductors to break down into aglowing plasma of electrons and ions.

Picture definition is stored in a refresh buffer, andthe firing voltages are applied to refresh the pixelpositions (at the intersections of the conductors) 60times per second.

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Color CRT Monitors

The beam penetration method for displaying color pictures has been used with random-

scan monitors.

Two layers of phosphor, usually red and green, are coated on to the inside of the CRTscreen, and the displayed color depends on how far the electron beam penetrates into

the phosphor layers.

Shadow-mask methods are commonly used in raster-scan systems (including color TV)

because they produce a much wider range of color than the beam penetration method.

A shadow-mask CRT has three phosphor color dots at each pixel position. One

phosphor dot emits a red light, another emits a green light, and the third emits a bluelight.

This type of CRT has three electron guns, one for each color dot, and a shadow- mask

grid just behind the phosphor ?coated screen. Fig. illustrates the delta-delta shadow-

mask method, commonly used in color CRT systems.

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Input device


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Input device

Key board

Mouse

Light pen

Joystick

Trackball

Digitizer

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Input Devices


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Input Devices

Locator Devices:

to indicate a position and/or orientation

to select a displayed entity

Tablet, Mouse, Trackball, Joystick, Touch Panel, Light Pen

Keyboard devices:

to input a character string

Alphanumeric keyboard (coded - get single ASCII character,unencoded - get state of all keys - more flexible)

Valuator Devices:

to input a single value in the space of real numbers

Rotary dials (Bounded or Unbounded), Linear sliders

Choice Devices: to select from a set of possible actions or choices

Function keys

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Key board

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Mouse

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Light pen

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Digitizing tablet is considered to be a locating as well as a

pointing device.

It is a small, low resolution digitizing board often used inconjunction with graphics display.

The tablet is a flat surface over which a stylus or a puck (a

hand-held cursor to differentiate it from a display screen

cursor) can be moved by the user. Operation is based on sensitizing its surface area to be able

to track the pointing element (stylus or puck) motion on the

surface.

The most common sensing technology electromagnetic isused in this, where the pointing elemnt generates an out of

phase magnetic field sensed by a wire grid in the tablet

surface (the pad).100


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Most tablets have designated areas to input digitizers

(usually called graphics areas.). The remaining area of the

tablet surface is used to input menu commands, thereforecalled the menu area.

Screens of the graphics display which the tablet is

connected to is mapped to the graphics area via the tablet

calibration process The mapping process (figure 1.15) lets the motion of the

screen cursor follow that of the pointing element. If the

pointing element leaves thee boundaries of the graphics

area on the tablet, the screen cursor always disappears fromthe screen.

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Fig. 1-15 Mapping between a tablet graphics area and a display screen

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OutPut devices


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OutPut devices

Monitor

Printer

Plotter

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Monitor


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Monitor

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Plotter


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Plotter

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Graphics Standards, Graphics Software, SoftwareConfiguration, Graphics Functions, Output

Primitives- Bresenhams Line Drawing Algorithm

and BresenhamsCircle Generating Algorithm.

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Computer Graphics-IIGraphics standards


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Graphics standards

Graphic World With out Graphic standards:-

Old or existing software to run on new system are prohibitive. To run old one user pay some additional cost .

The procedure of running of old software on new one is timeconsuming.

Benefits Of Graphics Standards:- Program portability to any graphics installation. Programmer portability, a programmer can easily changes his

task without the need to learn new set of graphics commandsagain.

Graphics standards serves guideline for manufacturer of

graphics equipments in providing useful combination ofgraphics capability in a device, thus save time in creating owngraphics commands.

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Some Commonly used Graphics Standards


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1) GKS(Graphics Kernal System)

2) PHIGS(Programmers HierarchicalInteractive graphics system)

3) VDM(Virtual Device Metafile) or CGM

4) VDI(Virtual Device interface) or CGI

5) IGES(Initial graphics Exchange

Specification)

6) NAPLPS(North American Presentation-

level protocol syntax)

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PHIGS(Programmers Hierarchical Interactive graphics


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(Programmer s Hierarchical Interactive graphics

system)

It support High level work station and theirrelated CAD/CAM system.

It is Extension of GKS-3D.

It is used to display graphics and dynamicability to modify segment content and

relation-ship.

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IGES(I iti l hi E h


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(Initial graphics Exchange

Specification) It is capable to exchange the database

among the CAD/CAM system.

It is work at the level of object databaseand application data structure.

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Graphics Function


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Graphics Function

Graphics software provides user with several function forcreating and playing the images. These routine can bedeals with output ,input attributes, transformations,viewing and general control.

Such routines are called Graphics Functions.

Different Graphics Function:-

1. Output primitives and their attributes.

2. Geometric Transformation.

3. Viewing Transformation.

4. Input function.

5. Control Operation Function.

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Example of Graphics Function


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a p e o G ap cs u ct o

Output Primitives Their AttributesPolyline Line Type, Line Width, Scale Factor,

Color.

Polymarker Mark Type, Mark Width, Scale Factor,

Color.

Text Font. Precision, Height, Color.File Area Pattern Size, Style, Hatch Style.

GDP(Generalized Drawing primitives) Circle, Curve, Area, Spline.

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Output Primitives


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A drawing and solid models generates in a CAD packageby using certain basic graphical entities such as line,circle, polygon, ellipse, etc. These graphical entities are

called Output Primitives.These out put primitives can be drawn by given set ofcommand in CAD package.

E.G:-

For line the input required are co-ordinates of

end point position.

For Circle the input required center and radiusof the circle.

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Output Primitives


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Line 1Arc

1Line 2 Arc

2

Line 3

Line 4

Lin

e

5

Circle 1Polygon 1

Output Primitives

To generates these output primitive differentalgorithms are available.

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Algorithm


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Algorithm

Line

1. Algo Using Slope

method.

2. Digital Differential

Analyzer(DDA) Algo.

3. Bresenhams Line

Drawing Algo.

Circle

1. Mid point Circle Algo.

2. Bresenhams Circle

Drawing Algo.

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Line Algo Using Slope method


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Assume:- Equation of Line given by Y=mX+b

Steps:-1. Compute:-dx= X2-X1

2. Compute:- dY= Y2-Y1

3. Compute Slope:- dY/dX

4. Compute b=Y1-mX1

5. Set(X,Y) equal to lower left hand end point and Xend equal tolargest value of X.

IF dX0, X=X1, Y=Y1 and Xend=X2

6. Test to determine whether the entire line has been drawn.

If X=Xend, Stop.7. Plot the point at the Current (X,Y) Coordinates.

8. Increments X=X+1.

9. Compute the nearest value of Y,Y=mX+b.

10. Go to step 6.122

Digital Differential Analyzer(DDA)

ALGO


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ALGO

DDA is a scan conversion algo. based oncalculating either dy or dx for the line

segments, shown in fig:-

y

x

y2

y1

x2x1

m

1

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Digital Differential Analyzer(DDA) ALGO

Slope of line,


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p ,

m=y/x,y=mx orx=y/m.

Case 1:-1. If slope is less than one.

2. Positive

3. Start point of the line is:-

a) at the left:-

Then set the increment in x coordinate to unity.

Let a point (xk,Yk ) on the line the next point will be:-

xk+1 =xk + 1

Yk+1= Yk +m

b) at the right:-xk+1 =xk - 1

Yk+1= Yk -m

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Case 2:-

1. If slope is grater than one.


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p g

2. Positive

3. Start point of the line is:-a) at the left:-

Then set the increment in y coordinate tounity.

Let a point (xk,Yk ) on the line the next pointwill be:-

xk+1 =xk + 1/m

Yk+1= Yk +1

b) at the right:-

xk+1 =xk1/m

Yk+1= Yk -1125

Case 3:-

1. If slope is negative.


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a) If absolute value of m is less than one

Start point of the line is at the left:-

xk+1= xk- 1Yk+1= Ykm

b) If absolute value of m is grater than one.

Start point of the line is at the left:-

xk+1 = xk1/mYk+1= Yk+1

Disadvantage:-The value of the slope may be a real number hence the

value of the new coordinate also a real number, so

designer need to convert or round off these value tosome integer value because the pixels are arranged on

screen in the integer fashion These rounding off

Documents

Cad Module 1