cad unit 1 ppt

8/11/2019 cad unit 1 ppt

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Rajasthan Institute of EngineeringAnd Technology

PRESENTED BY VIKRAM SINGH

SUBMITTED TO-PROF. KUNAL SHARMAHOD(ME)


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Introduction:Computer-aided design (CAD) is theuse of compute systems to

assist in the creation, modification,analysis, or optimizationof a design.


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(COMPUTER AIDED DESIGN)


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What is Computer Graphics?

Creation, Manipulation, and Storage ofgeometric objects (modeling) and theirimages (rendering)

Display those images on screens orhardcopy devices

Image processing

Others: GUI, Haptics, Displays (VR)...


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What drives computer graphics?

Movie Industry

Leaders in quality and artistry

Not slaves to conceptual purity

Big budgets and tight schedules

Reminder that there is more toCG than technology

Defines our expectations

Slide information from Leonard McMillian's slideshttp://www.cs.unc.edu/~mcmillan/comp136/Lecture1/compgraf.html


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What drives computer graphics? Game Industry

The newest driving force in CG Why? Volume and Profit

This is why we have commodity GPUs

Focus on interactivity

Cost effective solutions Avoiding computating and other tricks

Games drive the baseline

Slide information from Leonard McMillian's slideshttp://www.cs.unc.edu/~mcmillan/comp136/Lecture1/compgraf.html


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Modeling

Many model reps

Bezier, B-spline, box splines, simplex splines,polyhedral splines, quadrics, super-quadrics,implicit, parametric, subdivision, fractal, levelsets, etc (not to mention polygonal)


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Image Representation

Bitmap images (Dots used to draw theimage) Monochrome images

8 bit grey scale images 24 bit colour Colour lookup tables

Vector Graphics (Line art) Rasterisation

Two key concepts Image resolution Colour resolution


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1 Bit Images

Use a single bit to represent each pixel(dot on the screen)

00101


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Use more bits and display as a

grid


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Coordinate Systems

The use of coordinate systemsisfundamental to computer graphics

Coordinate systems are used todescribe the locations of points in space

Multiple coordinate systems make

graphics algorithms easier to understandand implement


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Coordinate Systems

Different coordinate systems representthe same point in different ways

Some operations are easier in onecoordinate system than in another

x

y

(2,3)

u

v

x

y

(1,2)

u

v


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Output graphics Display Devices

Most CG on video monitors

Still most popular: Cathode Ray Tube (CRT)

Other popular display types:

Liquid Crystal Display

Plasma display

Field Emission Displays Light Emitting Diodes

3D display devices (hologram or page scan

methods)


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1. cathode raysemitted by the

electron gun

CRT

2. focusing anddeflection

3. when electronbeams contact screenphosphor emits light

4. light fades, redrawrequired in a small

period (refresh)


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Flat CRT

Electron beams are accelerated parallel tothe screen, then deflected 90to thescreen.


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Raster Scan Displays

Raster: A rectangular array ofpoints or dots

Pixel:One dot or picture element of

the raster Scan Line:A row of pixels


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In a raster scan system, the electronbeam is swept across the screen, onerow at a time from top to bottom.


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As the electron beam moves acrosseach row, the beam intensity is turnedon and off to create a pattern of

illuminated spots. Picture definition is stored in a

memory area called the refresh

bufferor frame buffer


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Refresh bufferor frame buffer:This memory area holds the set ofintensity values for all the screen

points.

Stored intensity values thenretrieved from refresh buffer andpainted

on the screen one row

(scan line) at a time.


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Simple Raster Display System

Frame buffer: stored pixel map of screen

Video controller just refreshes the frame

buffer on the monitor periodically.

System Bus

CPU

SystemMemory

FrameBuffer

VideoController

PeripheralDevices

Monitor


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Digital Differential Analyzer (DDA):

Line Drawing Algorithm

(x0,y0)

(x1,y1)

dx

dy

Walk through the line, starting at (x0,y0)Constrain x, y increments to values in [0,1] rangeCase a: x is incrementing faster (m < 1)

Step in x=1 increments, compute and round yCase b: y is incrementing faster (m > 1)

Step in y=1 increments, compute and round x


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Bresenhams Line-Drawing Algorithm

Problem: Given endpoints (Ax, Ay) and (Bx,By) of a line, want to determine bestsequence of intervening pixels

First make two simplifying assumptions(remove later):

(Ax < Bx) and

(0 < m < 1)

Define Width W = BxAx

Height H = By - Ay


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