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Interactive Volume Rendering Aurora on the GPU

Orion Sky Lawlor, Jon Genetti University of Alaska Fairbanks 2011-02-01 http://www.cs.uaf.edu/. Interactive Volume Rendering Aurora on the GPU. 8. Structure of talk: (1) What are the Aurora? (2) How do we represent Aurora on the GPU? (3) How do we render Aurora efficiently?

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Interactive Volume Rendering Aurora on the GPU

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  1. Orion Sky Lawlor, Jon Genetti University of Alaska Fairbanks 2011-02-01 http://www.cs.uaf.edu/ Interactive Volume Rendering Aurora on the GPU 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 163842 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, 10242 • 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. Use Distance Field to Render Curtains Algorithm: Proximity Clouds [Cohen & Sheffer]

  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 & 1x109 rays/second Powerwall Aurora Rendering

  24. Sequential OpenGL Application

  25. Parallel Powerwall Application

  26. 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

  27. Powerwall Aurora Rendering Demo Movie

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

  29. Questions?

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