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Modeling, CG, and others

Modeling, CG, and others. Jyun-Ming Chen Fall 2001. Modeling geometric modeling model segmentation LOD Image-based vs. geometry-based systems. Primers on Computer Graphics Kinematics. Contents. how 3D objects are described in the geometric database shape

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Modeling, CG, and others

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  1. Modeling, CG, and others Jyun-Ming Chen Fall 2001

  2. Modeling geometric modeling model segmentation LOD Image-based vs. geometry-based systems Primers on Computer Graphics Kinematics Contents

  3. how 3D objects are described in the geometric database shape primitives: box, cylinder, sphere, cone, indexed face set watch for the face orientation (used for backface culling) procedurally defined shape: extrusion, sweep, in rendering, all objects are converted to triangles Geometric Modeling

  4. Computer Graphics Primer

  5. displaying a sequence of rendered scenes frame 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 Animation

  6. especially important for walkthrough applications in a large geometric database 1-500 million polygons; 10 frames/sec Model Segmentation

  7. 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 Cell Segmentation

  8. Change based on: distance or image size multi-resolution model automatic model simplification Borrel & Rossignac (92) Edge Collapsing … Level of Detail (LOD)

  9. Model flickering problem: Hysteresis Model morphing Mipmap: LOD concepts applied to texture mapping LOD (cont) Implement this in VRML Proto

  10. Rational Reducer (Systems in Motion) Price: 4,950 USD !!

  11. Generating Mipmaps

  12. compared to “geometry-based” VR able to keep constant frame rate regardless of the scene complexity authoring tools camera setup procedure “hybrid”-VR Image-based VR

  13. Image Acquisition

  14. Image Warping

  15. Stitched Panorama

  16. Kinematics Primer

  17. Kinematics in VRML • Syntax of Transform Node (partial) • usually interpretation using local axes is easier • the two-link arm in VRML • take advantage of “short hand notation” • center • t + r • explore other fields (scale, scaleOrientation) on your own

  18. Transform in VRML97

  19. Exercises • sketch the 3D model of the given VRML file • Biped model: • Construct each rigid part at default position • Use transform to take them to due places • Animate joint angles using OrientationInterpolators • Coordinate your animation using ScalarInterpolators

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