Modeling, CG, Programming,

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Modeling, CG, Programming,

• Jyun-Ming Chen
• Fall 1999

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Contents

• Modeling
• geometric modeling
• model segmentation
• Image-based vs. geometry-based systems
• Programming

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Geometric Modeling

• 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
  polygonal

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Animation

• 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
• model size retrieving, rendering
• hardware
• displaying/shading mode

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Computer Graphics Primer
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Model Segmentation

• especially important for walkthrough applications
  in a large geometric database
• 1-500 million polygons 10 frames/sec

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Cell Segmentation

• manage model complexity
• auto-segmentation
• separating plane priority
• priority 0.5occlusion 0.3balance 0.2split

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Level of Detail (LOD)

• multi-resolution model
• automatic model simplification
• change based on distance or image size
• hysteresis problems
• model morphing
• mipmap

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Image-based VR

• compared to geometry-based VR
• able to keep constant framerate regardless of the
  scene complexity
• authoring tools
• camera setup procedure
• hybrid-VR

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Image Acquisition
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Image Warping
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Stitched Panorama
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Kinematics Primer
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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

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Exercises

• sketch the 3D model of the given VRML file.

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VR Programming

• toolkit
• event-loop structure
• WTK code examples
• authoring tools
• example VRCreator, CosmoWorld