CellProjection of Convex Polyhedra

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Cell-Projectionof Convex Polyhedra

• Stefan Roettger
• Thomas Ertl
• University of Erlangen

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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

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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)

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Projection of Convex Polyhedra

• The graphics hardware can take over the
  projection of arbitrary convex polyhedra
• Based on bounded layered fog (Mech JGT 01)

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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 rgbemission/2

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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

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Example Images
Campfire 50 fps
Bluntfin 8 fps
Neghip 22 fps
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Ground Fog

• Triangulated terrain
• Place prism on every base triangle
• Assume constant emission in each prism

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Emission vs. MIP
50 fps
25 fps
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Fin

• Thanks for your attention!