Visualization Enhancements of Dense Particle Data Sets

1. Visualization Enhancements of Dense Particle Data Sets James L. Bigler School of Computing University of Utah November 8, 2004

2. Outline • Motivation and Introduction • Ambient Occlusion Shading • Silhouette Edges

3. Phong Shaded Data courtesy: Gerald T. Seidler University of Washington

4. With Silhouettes

5. With Ambient Occlusion

6. With Ambient Occlusion and Silhouettes

7. Why Particle Visualization? Macro Micro Crop by value

8. How are Particles Visualized?

9. Local Lighting Models Good for local (micro) structure, bad for global (macro) structure.

10. Shadows

11. Global Illumination • Variation in ambient regions • Soft shadows • Interreflection of light between surfaces

12. Wyman Global Illumination for Interactive Isosurfaces Wyman et al. cached global illumination values on a grid. Goal was to maintain interactivity during rendering.

13. Ambient Occlusion or Obscurances Zhukov et al. Iones et al. Precomputed Stored as textures Geometric property

14. Vicinity Shading • James Stewart • Similar to Wyman, precomputes and stores in a texture volume for later use in interactive applications.

15. Silhouette Edges from Depth Buffer • Usually black, emphasizes view dependent hull of objects • Saito and Takahashi (“Comprehensible Rendering of 3-D Shapes”) • Cache various aspects of the rendered image • Use depth and convolution to find silhouette edges

16. Particle Ray Tracing • Parker et al. show in “Interactive ray tracing” that large numbers of particles can interactively be rendered using a parallel ray tracer.

17. Ambient Occlusion

18. Texture Resolution • 16x16 provides a nice compromise • Fidelity • Memory • Computation time

19. Precomputation Time and Memory Bullet Fireball Foam • Using 20 R14K processors on an SGI Origin 3800 (muse.sci.utah.edu). Textures were 16x16 with 49 samples per texel. 543,088 33 min. 132 MB 955,000 66 min. 233 MB 952,755 261 min. 232 MB 7,157,720 12 hours 1,747 MB

20. Impact on Performance • 10% slower than direct lighting alone. • However, using only the ambient occlusion values can yield as good as or better performance than direct lighting alone.

21. Direct Lighting only Images Direct lighting with ambient occlusion textures Ambient occlusion textures only Cylinder 22 Bullet 6 Fireball 11

22. Impact on Performance • 10% slower than direct lighting alone. • However, using only the ambient occlusion values can yield as good as or better performance than direct lighting alone.

23. Silhouette Edges • Two options • Precomputation (object based) • Run time • Object based • Image based

24. Ingredients for Edges • Image buffer • Depth buffer • Edge detection kernel • Threshold for zero crossings Laplacian kernel

25. Threshold Edge Response

26. Depth Buffer • Anatomy of a ray • If a and |b| are the same for each pixel we can use the collection of t as a depth buffer. p(t) = a + tb t

27. Performance A B C D E

28. Movie

29. Movie

30. Questions?