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CAD Software and Hardware

ICG (Interactive Computer Graphics)

ICG denotes a user oriented system.

User

CRT

ICG magnifies the power of designer.

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CAD Software/Graphics software(GS)

Set of programs

Rules for development of GS:1. Simplicity2. Consistency3. Completeness4. Robustness5. Performance6. Economy

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Design workstation

Configuration

Application Database

Application Program

Graphics Package

Graphics Terminal

I/P Devices

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Functions of GS

Generation of Graphics element

Transformations

Display control and windowing function

Segmenting function

User input functions

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Generation of Graphics element

Graphic elements

Primitives

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Transformations

Scaling

Translation

Rotation

Reflection

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Display control and windowing function

Visualization

Windowing

Hidden line removal

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Segmenting function

Segment

Storage type CRT

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User input functions

To enter commands

User-friendly

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Design workstation

Hardware

Secondary storage

O/P Devices

CPUInput

DevicesGraphics Terminal

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Design workstation

System InterfaceFunctions Interface with CPUSteady Graphic ImageProvide digital description of the graphic

imageTranslate computer commandsCommunication

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Graphics Terminal (GT)

GT is an important component of CAD providing a window through which the communication with the computer can be realized.

Graphics terminals are classified as1. CRT2. Flat Screen

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Graphics Terminal (GT)

Two basic image generation Techniques.1) Stroke Writing

Random positioningLine drawingVector writing

Uses an electron beam which operates like pencil.

The image is constructed out of a sequence of straight line segment.

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Stroke Writing

Smooth curves can be created.

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Raster Scan

The viewing screen is divided into a large no of discrete phosphor elements.

Matrix of pixels constitute a raster.256X256, 1024X1024.

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Raster Scan

Each pixel on screen can be made to glow with a different brightness.

Color screen provide for the pixels to have different color as well as brightness.

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Raster Scan

The electron beam creates image by sweeping along horizontal line.

Sweeping is from left to right. Pixels are energized during sweep. When sweep on one line is completed, the electron

beam moves to next line below.

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Raster Scan

After sweeping entire screen the process is

repeated.

Rate of entire scan of screen is 30 to 60 scan

per sec.

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Graphics Terminal

1. Direct Beam Refresh2. Direct View storage tube (DVST)3. Raster scan (Digital TV)

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Direct Beam Refresh

Uses stroke writing approach

Refresh

Easy to provide animation

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Direct View storage tube (DVST)

Stroke writing approachStorage tubeFlicker freeNo TrimLow cost

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Raster scan (Digital TV)

Uses Raster Scan ApproachFrame/Refresh BufferHigh Cost

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Input Devices

1. Cursor control devices2. Digitizers

3. Alphanumeric and other key board terminals

Graphical interaction with System

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Cursor control devices

Cursor normally takes the bright spot on CRT1. Thumbwheel2. Direction Key/Key board Terminal3. Joysticks4. Tracker Ball5. Light Pen6. Electronic tablet

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Plotters and O/P Devices

Pen PlottersHard copy UnitElectrostatic PlottersComputer output to micro film units

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