Hybrid Scene Structuring with Application to Ray Tracing

1. Hybrid Scene Structuringwith Application to Ray Tracing Gordon Müller, Dieter Fellner Institute of ComputerGraphics, TU Braunschweig {gordon.mueller,d.fellner}@tu-bs.de Gordon Müller, Dieter Fellner

2. Overview • Ray Acceleration • Our Algorithm • Bounding Volume Optimization • Node Classification • Space Subdivision • Results • Conclusions Gordon Müller, Dieter Fellner

3. 5 6 1 3 7 4 2 8 5 6 1 3 7 4 2 8 Ray Accelerationprevious work • Hierarchical bounding volumes(Kay/Kajiya 1986, Goldsmith/Salmon 1987) • Uniform space subdivision(Fujimoto et al. 1986) • Octrees, BSP-trees, …(Glassner 1984,…) • Adaptive grids, HUG(Cazals et al. 1995) Gordon Müller, Dieter Fellner

4. Algorithm Overview • Hierarchical bounding volume construction based on a cost function • Identification of uniform regions by classification of sub-scenes • Locally space subdivision of uniform regions Gordon Müller, Dieter Fellner

5. Step 1:Bounding Volume Optimization • Recursively subdivide the set of objects into two disjoint sub-scenes • Objects are sorted along coordinate axes • No fixed subdivision position... Gordon Müller, Dieter Fellner

6. Step 1:Bounding Volume Optimization • …instead, we minimize a cost function describing the approximated ray/scene intersection costs • Object-specific intersection costs • O(n logn) on average Gordon Müller, Dieter Fellner

7. Example (subdivision) Gordon Müller, Dieter Fellner

8. Step 2: Node Classification • Goal: detect scene nodes that are suitable base nodes for a uniform space subdivision • Recursively classify scene nodes based on • surface area of neighbor hierarchy nodes • volume of neighbor hierarchy nodes • average size of elementary objects below a hierarchy node • Threshold constants determined empirically Gordon Müller, Dieter Fellner

9. Step 2: Node Classification • Scene nodes hold a counter representing the number of uniform classified sub-nodes(used in step 3) • Classification does not destroy hierarchy! • O(n) Gordon Müller, Dieter Fellner

10. Example (classification) Gordon Müller, Dieter Fellner

11. Step 3: Uniform Space Subdivision • Build uniform space subdivisions for sub-scenes marked in the previous step • Recursively subdivide the bounding box of a scene node along the dominant axis • Sub-node counter used to determine number of voxels / subdivisions • Use available bounding volume hierarchy to speed-up voxel membership tests ! • O(n) on average Gordon Müller, Dieter Fellner

12. Timings Gordon Müller, Dieter Fellner

13. Conclusions • Hybrid ray acceleration • run-time efficient • space efficient • easy to implement • easy to use Gordon Müller, Dieter Fellner

14. Future Work • Bounding volume hierarchies • View frustum/occlusion culling • Dynamic environments • Collision detection • Parallelization • Clustering • Hierarchical Radiosity Gordon Müller, Dieter Fellner

15. Thank you! Gordon Müller, Dieter Fellner