1. 1 Interactive Volume Rendering Aurora on the GPU Orion Sky Lawlor, Jon Genetti University of Alaska Fairbanks 2011-02-01 http://www.cs.uaf.edu/ 8

2. Structure of talk: (1) What are the Aurora? (2) How do we represent Aurora on the GPU? (3) How do we render Aurora efficiently? (4) How do we render Aurora on a powerwall? (5) Conclusions & future work

3. (1) What are the Aurora?

4. Charged particles from the Sun Image credit: NASA

5. Particles intersect Magnetosphere Image credit: Wikipedia

6. What are the Aurora? Sheets of electrons coming down Earth's magnetic field lines, and hitting the upper atmosphere

7. What are the Aurora? electrons: 1-20kV, millions of amps magnetic field: inclined to surface atmosphere: 50-500km up

8. Aurora: Best Viewed From Orbit Image credit: NASA (ISS)

9. (2) Representing Aurora on the GPU

10. Prior Aurora Representations Nonphysical hacks [e.g., screensavers] 100% phemonological No planet, no units, no atmosphere, etc. But it looks good Individual Charged Particles [Baranoski, Rokne, et al] Easy to physically transport through magnetosphere Nearly zero data storage requirements Difficult to render from arbitrary viewpoint (sampling!) Volume-Rendered Voxel Grid [Genetti] Easy to render from arbitrary viewpoint (raycasting) 10000 km * 10000 km * 500 km thick = serious RAM! Only feasible with hierarchical storage (slow render)

11. Our Aurora Representation Factor 3D aurora display into 2D * height 2D is electron intensity map: “curtain footprints” Stored as 16384 2 2D texture (polar coordinates) Currently generated with phenomological fluid hack Working on output from a real HPC simulation Height-dependent electron deposition function Given electron intensity and height, return emission Also stored as a 2D texture, 1024 2 Computed from particle scattering laws [Lazarev] Uses MSIS upper atmosphere model Auroral electrons are moving at relativistic speeds (60000 km/s for 10KeV), so this approximation is quite accurate

12. 2D Curtain Footprints: Fluids Hack

13. Deposition Function: MSIS Atmosphere

14. Deposition Function vs Altitude

15. “Height” includes Magnetic Inclination

16. (3) Speeding up Rendering

17. Explicit list of compositing orders Don't use Recursive Raytracing!

18. Begin with 2D Curtain Footprints

19. Build Distance Field to find Curtains Algorithm: Jump Flooding [Rong & Tan]

20. Algorithm: Proximity Clouds [Cohen & Sheffer] Use Distance Field to Render Curtains

21. Measured “Performance Image” White = 200ns/pixel Black = 10ns/pixel

22. Compounding Speedups Factor 3D into 2D + height: 2x Use GPU instead of CPU: 100x Non-recursive raytracer: 3x Distance field acceleration: 3.5x Old version: 10 minutes/frame New version: 20-60 frames/sec

23. (4) MPIglut & 1x10 9 rays/second Powerwall Aurora Rendering

24. Sequential OpenGL Application

25. Parallel Powerwall Application

27. Compounding Speedups Factor 3D into 2D + height: 2x Use GPU instead of CPU: 100x Non-recursive raytracer: 3x Distance field acceleration: 3.5x Use ten GPUs with MPIglut: 8x Old version: 10 minutes/frame @ 1080p New version: 30 frames/sec @ 8400x4200

28. Powerwall Aurora Rendering Demo Movie

29. (5) Future Work: Moving curtains! Red slow-glow Terrain Geometry Clouds & Sunrise Planetarium Show

30. Questions?