Interactive Pointbased Isosurface Exploration and Highquality Rendering

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Interactive Point-based Isosurface Exploration
and High-quality Rendering
V I S
2 0 0 6

• Haitao Zhang Arie Kaufman
• Stony Brook University

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Isosurface Exploration

• Isosurface extraction
• Isosurface rendering
• Interactive rate
• Changing view
• Change isovalue
• High quality rendering

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Existing Methods

• Marching Cubes Lorensen Cline 87
• Huge number of triangles within 1-pixel size
• Point-based methods
• Projection-based method Co et al. 03,04
• Accurate point position with expensive
  projection operator
• Active cell center Rymon-Lipinski et al. 04
• Fast but inaccurate point position
• Dividing Cubes Cline et al. 88
• High-quality but very expensive O(n3)

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Our Point-based Methods

• Active edge instead of active cell
• Easier to position points on the isosurface
• Incorporate together isosurface extraction
  rendering
• No overhead when changing isovalue
• Edge splatting
• Efficient with accurate point position
• Edge kernel method
• View-dependent subdivision O(n2)

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Edge Splatting

• Send active edge info to GPU
• Use span-triangle for active edge query
• Rymon-Lipinski et al. 04
• Generate point along active edge
• Intersection between active edge and isosurface
• Surface splatting for rendering
• Efficient rendering

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Edge Data Structure

• Span-triangle data structure for active edge
  query
• Sort by min and max value (minltmax)
• Linear storage of edge info

Base Array Span Array
Edge Info Array
...
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Point Generation

• Edge information
• Position endpoint with min value
• Orientation 6 possible directions
• Normal gradient at edge center
• Values min max value

Edge-Isosurface Intersection Computation
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Use center of active cell 26,044 active cell
Edge splatting 26,042 active edge
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Use center of active cell 368,296 active cell
Edge splatting 370,122 active edge
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Artifacts in Close View

• Fixed number of point (active edge) for a
  given isovale.

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Edge Kernel Method

• Subdividing active cell
• sub-cell projection lt 1 pixel

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Edge Kernel Method

• Subdividing active cell
• sub-cell projection lt 1 pixel

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Edge Kernel Method

• Subdividing active cell
• sub-cell projection lt 1 pixel

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Edge Kernel Method

• Subdividing into k3 sub-cells
• At most one intersection for k sub-edges on same
  line along X, Y or Z direction

k sub-edges
1 edge
k3 edges ? 3k2 edges
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Edge Kernel

• Edge kernel E(k) 3k2 edges ltc, s, tgt
• c orientation (X-, Y-, or Z-oriented)
• (s,t) local coordinate of edge endpoint

Edgelt 0, 2/3, 1/3 gt Intersection
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Edge Kernel Encoding Rendering

• E(k) 3k2 edges ltc, s, tgt ? ltc, sk, tkgt
• lt 0, 2/3, 1/3 gt ? lt0, 2, 1gt
• E1 E2 E3 E4 E5
• Store one kernel with largest possible size in
  VBO E(1000) with 6MB data
• Rendering
• CPU select kernel size k for each active cell
• GPU render first 3k2 points of the stored edge
  kernel with 1-pixel size

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Inside an Active Cell
Edge splatting Marching Cubes Edge kernel
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Two Neighboring Active Cells

• Marching Cubes Edge kernel

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Smooth Shading

• Per-pixel shading Hadwiger et al. 05
• Render point position to texture
• Shading from volume gradient map

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Results

• 3.59GHz PC with NVIDIA Quadro FX 4500 card

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Rendering of Edge Splatting
Isovalue1405 (15.2 fps) 426,749 active
edges 422,244 active cells
Isovalue840 (19.1 fps) 388,754 active
edges 385,470 active cells
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Rendering of Foot (isovalue36)
Edge Kernel 5.2 fps
Edge Splatting 19.1 fps
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Rendering of Foot (isovalue70)
Edge Splatting 96 fps
Edge Kernel 3.1 fps
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Head MRT Angiography
Edge Kernel 0.8 fps
Edge Splatting 47.5 fps
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Head MRT Angiography
Edge Splatting 123 fps
Edge Kernel 3.1 fps
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Head MRT Angiography
Edge Splatting 86.5 fps
Edge Kernel 4.2 fps
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Conclusion

• Interactive isosurface exploration system with
  high quality rendering
• Edge splatting
• Accurate point position
• Integrating point generation in rendering
• Edge kernel method
• High quality rendering under close view
• 3D subdivision with complexity O(n2)

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Future Work

• Very large volume data
• Design hierarchical data structure
• Improve edge kernel method speed
• GPU implementation using Geometry Shader
• Deal with volume with anisotropic grid

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• Thank you!