1. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 1 Hybrid Scene Structuring with Application to Ray Tracing Gordon Müller, Dieter Fellner Institute of ComputerGraphics, TU Braunschweig {gordon.mueller,d.fellner}@tu-bs.de

2. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 2 Overview u Ray Acceleration u Our Algorithm l Bounding Volume Optimization l Node Classification l Space Subdivision u Results u Conclusions

3. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 3 Ray Acceleration previous work u Hierarchical bounding volumes (Kay/Kajiya 1986, Goldsmith/Salmon 1987) u Uniform space subdivision (Fujimoto et al. 1986) u Octrees, BSP-trees, … (Glassner 1984,…) u Adaptive grids, HUG (Cazals et al. 1995)

4. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 4 Algorithm Overview u Hierarchical bounding volume construction based on a cost function u Identification of uniform regions by classification of sub-scenes u Locally space subdivision of uniform regions

5. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 5 Step 1:Bounding Volume Optimization u Recursively subdivide the set of objects into two disjoint sub-scenes u Objects are sorted along coordinate axes u No fixed subdivision position...

6. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 6 Step 1:Bounding Volume Optimization u …instead, we minimize a cost function describing the approximated ray/scene intersection costs u Object-specific intersection costs u O(n logn) on average

7. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 7 Example (subdivision)

8. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 8 Step 2: Node Classification u Goal: detect scene nodes that are suitable base nodes for a uniform space subdivision u Recursively classify scene nodes based on l surface area of neighbor hierarchy nodes l volume of neighbor hierarchy nodes l average size of elementary objects below a hierarchy node u Threshold constants determined empirically

9. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 9 Step 2: Node Classification u Scene nodes hold a counter representing the number of uniform classified sub-nodes (used in step 3) u Classification does not destroy hierarchy! u O(n)

10. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 10 Example (classification)

11. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 11 Step 3: Uniform Space Subdivision u Build uniform space subdivisions for sub-scenes marked in the previous step u Recursively subdivide the bounding box of a scene node along the dominant axis u Sub-node counter used to determine number of voxels / subdivisions u Use available bounding volume hierarchy to speed- up voxel membership tests ! u O(n) on average

12. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 12 Timings

13. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 13 Conclusions u Hybrid ray acceleration l run-time efficient l space efficient l easy to implement l easy to use

14. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 14 Future Work u Bounding volume hierarchies l View frustum/occlusion culling l Dynamic environments l Collision detection l Parallelization u Clustering l Hierarchical Radiosity

15. Institute of C omputer G raphics, TU Braunschweig Hybrid Scene Structuring with Application to Ray Tracing 24/02/1999 Gordon Müller, Dieter Fellner 15 Thank you!