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Cell-Projection of Convex Polyhedra

Cell-Projection of Convex Polyhedra. Stefan Roettger Thomas Ertl University of Erlangen. Introduction. Unstructured volume rendering Cell-projection = PT algorithm of Shirley and Tuchman (’90) Main bottlenecks: sorting and tetrahedral decomposition (Wittenbrink ‘99)

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Cell-Projection of Convex Polyhedra

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  1. Cell-Projectionof Convex Polyhedra • Stefan Roettger • Thomas Ertl • University of Erlangen

  2. Introduction • Unstructured volume rendering • Cell-projection = PT algorithm of Shirley and Tuchman (’90) • Main bottlenecks: sorting and tetrahedral decomposition (Wittenbrink ‘99) • Current performance 600,000 tet/s (Guthe ‘02) • Above 1,000,000 tet/s performance is completely memory bandwidth limited

  3. Emissive Optical Model • Use emissive optical model (Max ‘95) • Does not require sorting • Ray integral = length of ray segment times average emission (assuming linear interpolation)

  4. Projection of Convex Polyhedra • The graphics hardware can take over the projection of arbitrary convex polyhedra • Based on bounded layered fog (Mech JGT ‘01)

  5. PCP Algorithm • 1st pass • enable A writing and front face culling • draw primitive with alpha=(d-min d)/d • 2nd pass • enable subtractive blending and back face culling • draw primitive again • 3rd pass • disable A writing and culling • enable additive blending with alpha multiplied • draw primitive with rgb=emission/2

  6. Performance • Emissive model: 212,000 hex/s on NVIDIA GeForce3 (Guthe ‘02: 120,000 hex/s) • For maximum intensity projection one only needs to render each face once • Performance is about 600,000 hex/s • Performance drop is mainly due to additional passes

  7. Example Images Campfire 50 fps Bluntfin 8 fps Neghip 22 fps

  8. Ground Fog • Triangulated terrain • Place prism on every base triangle • Assume constant emission in each prism

  9. Emission vs. MIP 50 fps 25 fps

  10. Fin Thanks for your attention!

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