Dynamic View-Dependent Simplification for Polygonal Models

1. Dynamic View-Dependent Simplification for Polygonal Models By Julie C. Xia and Amitabh Varshney Presented by Jaya Sreevalsan Nair and Christopher Co Multiresolution (ECS 289L) - Winter 2003

2. Introduction Problem: Meshes too large AND Simplified mesh not necessarily visually accurate Desire: Visual accuracy of fine meshes with the efficiency of coarse representation Image from Xia96 Multiresolution (ECS 289L) - Winter 2003

3. Previous Work (1/2) • Level-of-Detail (LOD) Representations for Mesh Simplification • Statically generated • Vertex deletion (Schroeder et al) ,Vertex collapse (Rossignac and Borrel) , Edge collapse (Hoppe et al), Wavelet Decomposition (Gross et al), etc. • Curvature-guided simplification, proposed by Hamann and Turk • Change in tolerance volume (Gueziec) • Dynamically generated • Progressive Meshes (Hoppe) • ( M0, { split0, split1, split2, … splitk-1} ) • selective refinement • Continuous LOD Multiresolution (ECS 289L) - Winter 2003

4. Previous Work (2/2) • Issues not addressed by Progressive Mesh Representation • Non-optimal series of edge collapses (distance metric driven) • Linear time complexity for accessing node • No efficient updating of frame-to-frame selective refinements Multiresolution (ECS 289L) - Winter 2003

5. Guidelines for Image-Space Simplification • Local Illumination • Screen-Space Projections • Visibility Culling • Silhouette boundaries Multiresolution (ECS 289L) - Winter 2003

6. Overview of the Method • Hierarchy Construction • Preprocessing • Static • Hierarchy Traversal • Run time • Dynamic Multiresolution (ECS 289L) - Winter 2003

7. Construction • Merge tree (binary tree) • Edge collapse • Parent – child relationships • Euclidean distance stored (“upswitch” and “downswitch”) • Region of Influence • Termination • User specified minimum number of vertices • No more legal edge collapses • Dependencies Multiresolution (ECS 289L) - Winter 2003

8. Example for dependencies Image from Xia96 Multiresolution (ECS 289L) - Winter 2003

9. Traversal • Choosing display vertices • Check Upswitch / Downswitch distances • T > U : Vertex marked “inactive” for display • T < D : More refinement needed • Check dependencies • To select final list of display vertices • Frame-to-frame coherence • Display vertex list for the next frame • Choosing display triangles • Interleaved with display vertex selection • Immediate deletion and addition of triangles Multiresolution (ECS 289L) - Winter 2003

10. Results(1/2) Image from Xia96 Multiresolution (ECS 289L) - Winter 2003

11. Results(2/2) Image from Xia96 Multiresolution (ECS 289L) - Winter 2003

12. Conclusion (Pros vs. Cons) Contribution • Data structure (merge tree) for efficient mesh update for continuous LOD representation Advantages • Continuous LOD • Incremental update between frames • Avoids illegal edge collapses efficiently • Logarithmic vertex lookup Disadvantages • What should T be? • In core • Storage overhead (linear) Multiresolution (ECS 289L) - Winter 2003

13. Outside Reading • H. Hoppe. Progressive Meshes. Computer Graphics Proceedings, Annual Conference Series, ACM SIGGRAPH, 1996. • J. Xia, J. El-Sana, and A. Varshney. Adaptive Real-Time Level-of-detail-based Rendering for Polygonal Models. IEEE Transactions on Visualization and Computer Graphics. Vol. 3, No. 2, June 1997, pp 171 - 183 Multiresolution (ECS 289L) - Winter 2003