CAD CAM

INDIAN INSTITUTE OF TECHNOLOGY ROORKEEDEPARTMENT OF CIVIL ENGINEERING

CE‐201: Computer Aided GraphicsWeek 2

Rajat Rastogi

[email protected]@iitr.ernet.in

Last weekLast week

• Intro to CGIntro to CG– Graphics, sketching, photography

• Rendering Modelling and Animation• Rendering, Modelling and Animation

• Applications of CG– Movies, Games, Entertainment, CAD, Art, Interactive graphics, Education, Training, Vi li ti D i iVisualization, Designing

• Advancement in GPUs

August 19, 2010 2Rajat Rastogi

OutlineOutline

• Graphic PipelineGraphic Pipeline

• CG Processes

G hi i l S d h l i• Graphic Display Systems and technologies

• Display Devices

• Input‐Output Devices

August 19, 2010 Rajat Rastogi 3

GRAPHIC PIPELINEComputer Aided Graphics

GRAPHIC PIPELINE

August 19, 2010 Rajat Rastogi, DOCE 4

Graphic Pipeline….1Graphic Pipeline….1

1. Geometric 2. Transformations1. Geometric Representation• Formation of an object

2. Transformations• Adjusting the object to get a desired formT f ti• Working from object space

to image space• Transformation processes

3. Viewing• Scan ‐Converting the gdesired object for display systems

• Viewing Transformations


Graphic Pipeline….2Graphic Pipeline….2Architecture of Graphical system

yy y

x

x x

Geometric Representation(joining vertices

Transformation(Placement of triangle (s)

Scan Conversion (lines drawn using a set ofusing two‐

dimensional Cartesian coordinates)

triangle (s) –location, orientation; size of triangle)

using a set of pixels)


coordinates)

Graphic Pipeline…3Graphic Pipeline…3

Object spacey

x

Image space



• Geometrical Representation:Geometrical Representation:– Drawing primitives like point, line, circle, polygon

Coordinate system to represent such primitives– Coordinate system to represent such primitives

– Working with concepts and algorithms

P j ti t lik ti– Projection systems like perspective or orthographic systems



• Transformations:Transformations:– Using transformations to define location, orientation and size of an objectorientation and size of an object

– Involves basic transformations like scale, translation and rotation, as well as, specifictranslation and rotation, as well as, specific translations like shear and reflection

– Knowledge of matrix operations is neededg p

– Homogenous coordinate system is adopted



• Transformations:Transformations:– Also involves various processes like

• ModellingModelling

• Hidden surface or a line

• Depth cueingp g

• Depth clipping

• Wireframes

• Shading and textures

• Curved surfaces

fl d d l• Reflections and displacements, etc.



• Viewing:Viewing:– Scan‐conversion of objects for display systems

Working with coordinate systems like viewing– Working with coordinate systems like viewing coordinate system, display coordinate system, world coordinate system, etc.world coordinate system, etc.

– Possible to display complete or a part of the object as in case of media wallsj



• Viewing:Viewing:– Aliasing effect of conversion

• Distortion induced by the conversion from continuousDistortion induced by the conversion from continuous space to discrete space

• Effect changes with the change in size of pixel

• Pixels define memory space required– If one pixel is cut in half, horizontally and vertically, then it requires four time memory spacerequires four time memory space

• Anti‐aliasing: area of CG where negative impact of aliasing effect is alleviated.



• 3‐Dimensional Graphics3 Dimensional Graphics– Profound difference between object and its representation onto a 2‐dimensional displayrepresentation onto a 2 dimensional display surface

– Projection methods are needed to represent 3‐Projection methods are needed to represent 3dimensional objects

HiddenHidden surfaces



• 3‐Dimensional Graphics3 Dimensional Graphics– Adding projection and hidden surface removal to simple graphic pipeline right after transformationsimple graphic pipeline, right after transformation but before scan conversion, results in a three‐dimensional graphics.

Projection system

Hidden surfaces



CPU

GPU


Transformation, Projection, Cuing, Clipping, Surfaces,

CG PROCESSES

a s o at o , oject o , Cu g, C pp g, Su aces,Shading, Mapping

CG PROCESSES


ModellingModelling

• generating modelsg g– lines, curves, polygons, smooth surfaces– digital geometry

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Modelling Transformation: Object PlacementModelling Transformation: Object Placement

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Viewing Transformation: Camera PlacementViewing Transformation: Camera Placement

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Perspective ProjectionPerspective Projection

20

Depth CueingDepth Cueing

21

Depth ClippingDepth Clipping

22

Colored WireframesColored Wireframes

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Hidden Line RemovalHidden Line Removal

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Hidden Surface RemovalHidden Surface Removal

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Curved SurfacesCurved Surfaces

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Per‐Polygon ShadingPer Polygon Shading

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Gouraud ShadingGouraud Shading

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Phong ShadingPhong Shading

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Complex Lighting and ShadingComplex Lighting and Shading

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Texture MappingTexture Mapping

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Displacement MappingDisplacement Mapping

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Reflection MappingReflection Mapping

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Specular ReflectionSpecular Reflection

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RENDERINGChanges occurred during last 5‐10 years


RenderingRendering

• Creating images from modelsCreating images from models– geometric objects

• lines, polygons, curves, curved surfaces, p yg , ,

– camera• pinhole camera, lens systems, orthogonal

– shading• light interacting with material

• illustration of rendering capabilities


Computer GraphicsComputer Graphics

• Difference between • One is offline and otherDifference between watching a fiction movie or playing a

One is offline and other is interactive

computer game?


Interactive GraphicsInteractive Graphics

Frame rate and flicker rate

System latency


Offline Rendering some years backOffline Rendering some years back


Modern RenderingModern Rendering


Interactive Rendering some years back


Interactive Rendering nowInteractive Rendering now


AnimationAnimation

• generating motiongenerating motion– interpolating between frames, states

http://www.cs.ubc.ca/~van/papers/doodle.html

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AnimationAnimation

Sequence of still frames per secondSequence of still frames per second– Update rate: minimum of 24 hz

Video playback: minimum of 30 hz– Video playback: minimum of 30 hz

– Flicker rate: minimum of 50 hz

“Rule 1”:All discontinuous frame to frame changes– All discontinuous frame‐to‐frame changes correspond to discontinuous scene or visibility changes

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changes

GRAPHIC SYSTEMSVideo Display Technologies

GRAPHIC SYSTEMS


Cathode Ray Tubes (CRTs)Cathode Ray Tubes (CRTs)

• Most common display device todayMost common display device today

• Extremely high voltage

• ComponentsComponents– Electron gun– Focusing and deflection systems– Phosphor‐coated screen– Glass tube envelope maintaining

vacuumvacuum


CRTs…1CRTs…1


CRTs…2CRTs…2

• Electron GunElectron Gun– Contains a heating filament that emits a stream of electrons

– Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tubepicture tube

– The front surface of the picture tube is coated with small phospher dots

– When the beam hits a phospher dot it glows with a brightness proportional to the strength of the beam and how long it is hithow long it is hit


CRTs…3CRTs…3

• Intensity of the electron beam is controlled by setting voltage y y g glevel on the control grid. Negative voltage will decrease the number of electrons passing through.

A th di t t ll d b b i t d th• As the distance travelled by a beam increases towards the periphery of the screen, due to its curvature, displayed image become blurred.

• Deflection of the electron beam can be controlled either with electric field or with magnetic field.

El f h h hi h i d• Electrons transfer energy to phosphor, which excites and on heating gives light energy producing glowing spot, which fades as phosphor returns back to ground energy level.


CRTs…4CRTs…4

The frequency or color of the light emitted byof the light emitted by the phosphor is proportional to the

diffenergy difference between the excited quantum state and the


ground state.

CRTs…5CRTs…5

• Phosphors are defined either by colour or their persistence (how long they continue to emit light).

• Persistence is defined as time it takes the emitted light from the screen to decay to one‐tenth of its original intensity.

• Phosphor with lower persistence is useful for animation; and with higher persistence is useful for highly complex, static pictures.

• Usual persistence range for graphic monitors is 10 to 60 microseconds.

• Resolution of CRT is defined as maximum number of points per centimeter that can be plotted horizontally or vertically.


CRTs…6CRTs…6

• Resolution:– Two illuminated phosphor spots are distinguishable when their separation is greater than the diameter at hich a spot intensit has fallen to 60 percent ofwhich a spot intensity has fallen to 60 percent of

maximum– Dependent uponp p

• Type of phosphor• Intensity to be displayed• Focusing and deflection systems• Focusing and deflection systems

– High definition system: basically high resolution system, 1280 x 1024 or higher


CRTs…7CRTs…7

• Aspect Ratio:p– Ratio of vertical points to horizontal points necessary to produce equal length lines in both directions on the screen.screen.

– Ex. ¾ means length of 3 points on vertical line = length of 4 points on horizontal line

• Measuring capabilities of CRT• Measuring capabilities of CRT– Size of tube (= length of screen diagonal)– Brightness of phosphers vs. darkness of tube– Speed of electron gun– Width of electron beam – Pixels


Direct‐View Storage Tubes (DVST)Direct View Storage Tubes (DVST)

• DVST stores the picture information as a charge S s o es e p c u e o a o as a c a gedistribution just behind the phosphor coated screen.

• It uses two electron guns, primary gun stores picture pattern and flood gun maintains picture display.

• There is no need to refresh screen, hence very complex i t b di l d t hi h l tipictures can be displayed at very high resolutions

without flicker.

• Because of storage process a section of picture cannotBecause of storage process, a section of picture cannot be erased and the whole picture is to be erased and redrawn. Now replaced by raster systems.


Flat Panel DisplaysFlat Panel Displays

• Flat CRTsFlat CRTs

• Plasma Panels

i id l di l• Liquid crystal displays– Two categories

• Emissive displays: devices that convert electrical energy into light. Ex. Plasma panel, thin‐film electroluminescent displays, light‐emitting diodeselectroluminescent displays, light emitting diodes

• Non‐emissive or reflective displays: use optical effects to convert light from a source into graphic patterns. Ex. LCD


Plasma PanelsPlasma Panels

• Also called gas‐discharge displays, constructed by filling a so ca ed gas d sc a ge d sp ays, co s uc ed by g amixture of gas (usually has neon) between two glass plates.

• The gas is excited by electric field emitting UV light.

• UV light excites phorphor.

• Phosphor relaxes and emits some other colour

Gas at intersection of hori. and vert. conductors break down on application of high voltage into glowing plasma of electrons and


glowing plasma of electrons and ions

Plasma Panels…1Plasma Panels…1


Organic Light Emitting DiodeOrganic Light Emitting Diode

• The display of the future? Many think so.The display of the future? Many think so.

• OLEDs function like regular semiconductor LEDs

• But they emit lightBut they emit light– Thin‐film deposition of organic, light‐emitting molecules through vapor sublimation in a vacuum.

– Dope emissive layers with fluorescent molecules to create colormolecules to create color.


Liquid Crystal Display (LCD)Liquid Crystal Display (LCD)

• LCDs: organic molecules, naturally in crystalline state,LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field

• Crystalline state twists polarized light 90º y p g

• Flat panel displays commonly use nematic (threadlike) liquid crystal compoundsq y p

• It consists of – Liquid crystals

– Glass plates ‐ 2

– Light polarizer – 2 at 90o

– Transparent conductors – built into glass plates at 90o


LCD…1LCD…1


LCD…2LCD…2

• Passive matrix LCDPassive matrix LCD


LCD…3LCD…3

• Active‐Activematrix LCDLCD


Virtual Reality SystemsVirtual Reality Systems


Media Walls – Multiscreen DisplayMedia Walls Multiscreen Display


Graphic Monitors / WorkstationsGraphic Monitors / Workstations


Input DevicesInput Devices

Spaceball

Trackball


Output DevicesOutput Devices


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