24/02/1999

Gordon Müller, Dieter Fellner

1Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Hybrid Scene Structuringwith Application to Ray Tracing

Gordon Müller, Dieter Fellner

Institute of ComputerGraphics, TU Braunschweig

{gordon.mueller,d.fellner}@tu-bs.de

24/02/1999

Gordon Müller, Dieter Fellner

2Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Overview Ray Acceleration Our Algorithm

Bounding Volume Optimization Node Classification Space Subdivision

Results Conclusions

24/02/1999

Gordon Müller, Dieter Fellner

3Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Ray Accelerationprevious work

Hierarchical bounding volumes(Kay/Kajiya 1986, Goldsmith/Salmon 1987)

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Uniform space subdivision (Fujimoto et al. 1986)

Octrees, BSP-trees, … (Glassner 1984,…)

Adaptive grids, HUG (Cazals et al. 1995)

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24/02/1999

Gordon Müller, Dieter Fellner

4Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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

24/02/1999

Gordon Müller, Dieter Fellner

5Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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...

24/02/1999

Gordon Müller, Dieter Fellner

6Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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

24/02/1999

Gordon Müller, Dieter Fellner

7Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Example (subdivision)

24/02/1999

Gordon Müller, Dieter Fellner

8Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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

24/02/1999

Gordon Müller, Dieter Fellner

9Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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)

24/02/1999

Gordon Müller, Dieter Fellner

10Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Example (classification)

24/02/1999

Gordon Müller, Dieter Fellner

11Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

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

24/02/1999

Gordon Müller, Dieter Fellner

12Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Timings

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BVolC

RegSub

KDTree

HUG

Hybrid

24/02/1999

Gordon Müller, Dieter Fellner

13Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Conclusions Hybrid ray acceleration

run-time efficient space efficient easy to implement easy to use

24/02/1999

Gordon Müller, Dieter Fellner

14Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Future Work Bounding volume hierarchies

View frustum/occlusion culling Dynamic environments Collision detection Parallelization

Clustering Hierarchical Radiosity

24/02/1999

Gordon Müller, Dieter Fellner

15Institute of ComputerGraphics, TU Braunschweig

Hybrid Scene Structuring with Application to Ray Tracing

Thank you!