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Freeform Geometric Models Yong-Joon Kim, Myung-Soo Kim (Seoul - PowerPoint PPT Presentation

Efficient Algorithms for Freeform Geometric Models Yong-Joon Kim, Myung-Soo Kim (Seoul National University) Gershon Elber (Technion, Israel) Collision Detection Collision Detection Minimum Distance Hausdorff Distance Convex Hull


  1. Efficient Algorithms for Freeform Geometric Models Yong-Joon Kim, Myung-Soo Kim (Seoul National University) Gershon Elber (Technion, Israel)

  2. Collision Detection

  3. Collision Detection

  4. Minimum Distance

  5. Hausdorff Distance

  6. Convex Hull Computation

  7. Previous Approach

  8. Problem Reduction to (u,v) • The bisector curve of C(u) and D(v) is reduced to solving F(u,v)=0. • Much lower degree than the bisector curve b(x,y)=0 itself in the xy-plane. • Many other geometric problems can be solved in a similar way. • But, this approach is too slow. => Preprocessing is needed!!!

  9. Preprocessing for Freeforms • Biarc approximation of planar curves • Segmentation of planar curves to monotone spiral curves • Support distance functions • Approximation with simple surfaces

  10. Background • IK Bi-National Grant (2007-2009) - Hausdorff distance computation for freeform curves and surfaces • Tang, Lee, and Kim (SIGGRAPH 2009) - Real-time HD computation for triangular meshes using BVH (prebuilt hierarchical data structure)

  11. Bounding Volume Hierarchy

  12. View Frustum Culling

  13. Conventional Bounding Volume

  14. Conventional BVH Complexity (Yoon and Manocha, EG2006)

  15. Coons Patch

  16. Approx. with Coons Patches

  17. Approx. with Coons Patches

  18. Bounding Coons Patches

  19. Two Steps of Approximation • Bezier surface by Coons patches ( ) • Coons patch by bilinear surfaces ( ) by approximating the boundary curves Bounding Volume • Bounding bilinear surface by tetrahedron and offset by maximum error

  20. Bounding Coons Patches

  21. Comparison

  22. BVH Complexity

  23. BVH Complexity

  24. BVH Complexity

  25. BVH Complexity

  26. Performance Comparison

  27. Performance Comparison

  28. Conclusions • Compact BVH for Freefrom Models • Efficient Geometric Algorithms - Collision detection - Minimum distance computation - Hausdorff distance computation - Convex hull computation

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