volume visualization with ray casting
DESCRIPTION
Volume Visualization with Ray Casting. http://web.cs.wpi.edu/~matt/courses/cs563/talks/powwie/p1/ray-cast.htm www.cs.technion.ac.il/~zdevir/ volume / Volume .ppt. Volume Rendering. render an image a volume CT, X-ray, PET, MRI scans Clouds Compressible fluids - PowerPoint PPT PresentationTRANSCRIPT
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Volume Visualization with
Ray Castinghttp://web.cs.wpi.edu/~matt/courses/cs563/talks/powwie/p1/ray-cast.htm
www.cs.technion.ac.il/~zdevir/volume/Volume.ppt
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Volume Rendering
•render an image a volume
✦ CT, X-ray, PET, MRI scans
✦ Clouds
✦ Compressible fluids
•volume represented by 3D cell grid
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Volume Rendering
Typical sizes128x128x128256x256x256
Display approachesExtract surfaces
Ray trace
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Ray Casting
•Generate image directly from density data
•Cast ray through density volume
•Accumulate colors as ray passes through semi-transparent cells
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Accumulate illuminated densities
Density: D(t) = D(x(t), y(t), z(t))
illumination: I(x,y,z)
L
R
I(t)D(t)P(Cos)
Phase function: P
t1
t2
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I(t)
Radiation from light sourceAttenuated, shadowed by volume
Only needed where internal shadows are importante.g., clouds, fire, smoke
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Attenuation along a ray
2
1
)(t
tdssD
e
dtPtDtIeB
t
tdssDt
t
))(cos)()()( 12
1
)(
converts density to attenuation
R
t1
t2
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Outgoing light• light reflected in view direction from light
source
• incoming light filtered by the voxel
• light emitted by the voxel
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Ray casting algorithm
For every pixel in output image
• shoot ray into volume
• at evenly spaced ray locations, obtain color and opacity by interpolation
• merge color and opacities
- front to back
- back to front
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Visualization pipeline
•Shade volume data
•compute local gradient -> voxel normal
•produce RGB intensity for every voxel
•determine opacity of each voxel
- application dependent
- e.g. X-ray absorption coefficient
•Ray cast volume
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Voxel values•C(X) - shade
•a(X) - opacity
•Cout = Cin(1-a(Xi))+c(Xi)a(Xi)
Often parallel projection is used to simplify calcs
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Packages
•AVS: Application Visualization System
•IBM Data Explorer (DX)
•Data Visualizer
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Display issues
How to represent:
•Temporal information
•Non-spatial information
•Multi-dimensional information
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Examples
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Examples
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Examples
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Examples
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Speed-ups
•Hierarchical spatial enumeration
•adaptive termination
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Hierarchical Spatial Enumeration
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Traversing Volume
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Examples
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Examples