Modeling, CG, and others

Jyun-Ming ChenFall 2001

Contents

Modeling geometric

modeling model

segmentation LOD

Image-based vs. geometry-based systems

Primers on Computer

Graphics Kinematics

Geometric Modelinghow 3D objects are described in the geometric databaseshape

primitives: box, cylinder, sphere, cone,

indexed face set watch for the face orien

tation (used for backface culling)

procedurally defined shape: extrusion, sweep,

in rendering, all objects are converted to triangles

Computer Graphics Primer

Animation

displaying a sequence of rendered scenesframe rate: number of scenes displayed per second

movie: 24-30 NTSC: 29.97 VR: at least 16 to be

flicker-free; the higher the better

factors affecting frame rate size of rendering

area model complexity:

retrieving, rendering

hardware displaying/shading

mode

Model Segmentation

especially important for walkthrough applications in a large geometric database 1-500 million

polygons; 10 frames/sec

Cell Segmentation

manage model complexity by grouping objects visible from different rooms

Leaf nodes store corresponding links to visible objects

Visibility problem

auto-segmentation separating plane priority priority = 0.5*occlusion

+ 0.3*balance + 0.2*split

Level of Detail (LOD)

Change based on: distance or image

size

multi-resolution model automatic model si

mplification Borrel & Rossignac

(92) Edge Collapsing …

LOD (cont)

Model flickering problem: Hysteresis Model morphing

Mipmap: LOD concepts appli

ed to texture mapping

Implement this in VRML Proto

Rational Reducer (Systems in Motion)

Price: 4,950 USD !!

Generating Mipmaps

Image-based VR

compared to “geometry-based” VR

able to keep constant frame rate regardless of the scene complexity

authoring tools camera setup procedure“hybrid”-VR

Image Acquisition

Image Warping

Stitched Panorama

Kinematics Primer

Kinematics in VRML

Syntax of Transform Node (partial)usually interpretation using local axes is easierthe two-link arm in VRMLtake advantage of “short hand notation” center t + r

explore other fields (scale, scaleOrientation) on your own

Transform in VRML97

Exercises

sketch the 3D model of the given VRML fileBiped model: Construct each rigid part at default position Use transform to take them to due places Animate joint angles using OrientationInterpola

tors Coordinate your animation using ScalarInterpol

ators