MR.E.S.AGRAWAL SGGSIE&T, NANDED CAD Software and Hardware
Dec 18, 2015
ICG (Interactive Computer Graphics)
ICG denotes a user oriented system.
User
CRT
ICG magnifies the power of designer.
SGGS Institute of engineering and Technology Nanded
CAD Software/Graphics software(GS)
Set of programs
Rules for development of GS:1. Simplicity2. Consistency3. Completeness4. Robustness5. Performance6. Economy
SGGS Institute of engineering and Technology Nanded
Design workstation
Configuration
Application Database
Application Program
Graphics Package
Graphics Terminal
I/P Devices
SGGS Institute of engineering and Technology Nanded
Functions of GS
Generation of Graphics element
Transformations
Display control and windowing function
Segmenting function
User input functions
SGGS Institute of engineering and Technology Nanded
Generation of Graphics element
Graphic elements
Primitives
SGGS Institute of engineering and Technology Nanded
Transformations
Scaling
Translation
Rotation
Reflection
SGGS Institute of engineering and Technology Nanded
Display control and windowing function
Visualization
Windowing
Hidden line removal
SGGS Institute of engineering and Technology Nanded
User input functions
To enter commands
User-friendly
SGGS Institute of engineering and Technology Nanded
Design workstation
Hardware
Secondary storage
O/P Devices
CPUInput
DevicesGraphics Terminal
SGGS Institute of engineering and Technology Nanded
Design workstation
System InterfaceFunctions Interface with CPUSteady Graphic ImageProvide digital description of the graphic
imageTranslate computer commandsCommunication
SGGS Institute of engineering and Technology Nanded
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
SGGS Institute of engineering and Technology Nanded
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.
SGGS Institute of engineering and Technology Nanded
Raster Scan
The viewing screen is divided into a large no of discrete phosphor elements.
Matrix of pixels constitute a raster.256X256, 1024X1024.
SGGS Institute of engineering and Technology Nanded
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.
SGGS Institute of engineering and Technology Nanded
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.
SGGS Institute of engineering and Technology Nanded
Raster Scan
After sweeping entire screen the process is
repeated.
Rate of entire scan of screen is 30 to 60 scan
per sec.
SGGS Institute of engineering and Technology Nanded
Graphics Terminal
1. Direct Beam Refresh2. Direct View storage tube (DVST)3. Raster scan (Digital TV)
SGGS Institute of engineering and Technology Nanded
Direct Beam Refresh
Uses stroke writing approach
Refresh
Easy to provide animation
SGGS Institute of engineering and Technology Nanded
Direct View storage tube (DVST)
Stroke writing approachStorage tubeFlicker freeNo TrimLow cost
SGGS Institute of engineering and Technology Nanded
Raster scan (Digital TV)
Uses Raster Scan ApproachFrame/Refresh BufferHigh Cost
SGGS Institute of engineering and Technology Nanded
Input Devices
1. Cursor control devices2. Digitizers
3. Alphanumeric and other key board terminals
Graphical interaction with System
SGGS Institute of engineering and Technology Nanded
Cursor control devices
Cursor normally takes the bright spot on CRT1. Thumbwheel2. Direction Key/Key board Terminal3. Joysticks4. Tracker Ball5. Light Pen6. Electronic tablet
SGGS Institute of engineering and Technology Nanded