C3 – THE IMPACT OF CAD/CAM ON MANUFACTURING Option C: CAD/CAM.
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Transcript of 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
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GRAPHIC PIPELINEComputer Aided Graphics
GRAPHIC PIPELINE
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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
August 19, 2010 Rajat Rastogi, DOCE 5
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)
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coordinates)
Graphic Pipeline…3Graphic Pipeline…3
Object spacey
x
Image space
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Graphic Pipeline…4Graphic Pipeline…4
• 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
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Graphic Pipeline…5Graphic Pipeline…5
• 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
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Graphic Pipeline…6Graphic Pipeline…6
• 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.
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Graphic Pipeline…7Graphic Pipeline…7
• 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
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Graphic Pipeline…8Graphic Pipeline…8
• 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.
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Graphic Pipeline…9Graphic Pipeline…9
• 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
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Graphic Pipeline…10Graphic Pipeline…10
• 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
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Graphic Pipeline…11Graphic Pipeline…11
CPU
GPU
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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
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ModellingModelling
• generating modelsg g– lines, curves, polygons, smooth surfaces– digital geometry
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Modelling Transformation: Object PlacementModelling Transformation: Object Placement
18
Viewing Transformation: Camera PlacementViewing Transformation: Camera Placement
19
Perspective ProjectionPerspective Projection
20
Depth CueingDepth Cueing
21
Depth ClippingDepth Clipping
22
Colored WireframesColored Wireframes
23
Hidden Line RemovalHidden Line Removal
24
Hidden Surface RemovalHidden Surface Removal
25
Curved SurfacesCurved Surfaces
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Per‐Polygon ShadingPer Polygon Shading
27
Gouraud ShadingGouraud Shading
28
Phong ShadingPhong Shading
29
Complex Lighting and ShadingComplex Lighting and Shading
30
Texture MappingTexture Mapping
31
Displacement MappingDisplacement Mapping
32
Reflection MappingReflection Mapping
33
Specular ReflectionSpecular Reflection
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RENDERINGChanges occurred during last 5‐10 years
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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
August 19, 2010 Rajat Rastogi, DOCE 36
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?
August 19, 2010 Rajat Rastogi, DOCE 37
Interactive GraphicsInteractive Graphics
Frame rate and flicker rate
System latency
August 19, 2010 Rajat Rastogi, DOCE 38
Offline Rendering some years backOffline Rendering some years back
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Modern RenderingModern Rendering
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Modern RenderingModern Rendering
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Interactive Rendering some years back
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Interactive Rendering nowInteractive Rendering now
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Interactive Rendering nowInteractive Rendering now
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AnimationAnimation
• generating motiongenerating motion– interpolating between frames, states
http://www.cs.ubc.ca/~van/papers/doodle.html
45
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
46
changes
GRAPHIC SYSTEMSVideo Display Technologies
GRAPHIC SYSTEMS
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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
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CRTs…1CRTs…1
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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
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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.
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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
August 19, 2010 52Rajat Rastogi
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.
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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
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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
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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.
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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
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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
August 19, 2010 Rajat Rastogi 58
glowing plasma of electrons and ions
Plasma Panels…1Plasma Panels…1
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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.
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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
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LCD…1LCD…1
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LCD…2LCD…2
• Passive matrix LCDPassive matrix LCD
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LCD…3LCD…3
• Active‐Activematrix LCDLCD
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Virtual Reality SystemsVirtual Reality Systems
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Media Walls – Multiscreen DisplayMedia Walls Multiscreen Display
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Media Walls – Multiscreen DisplayMedia Walls Multiscreen Display
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Graphic Monitors / WorkstationsGraphic Monitors / Workstations
August 19, 2010 Rajat Rastogi 68
Input DevicesInput Devices
Spaceball
Trackball
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Output DevicesOutput Devices
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