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Volume Visualization with Ray Casting

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

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Volume Visualization with Ray Casting

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  1. 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

  2. Volume Rendering • render an image a volume • CT, X-ray, PET, MRI scans • Clouds • Compressible fluids • volume represented by 3D cell grid

  3. Volume Rendering Typical sizes 128x128x128 256x256x256 Display approaches Extract surfaces Ray trace

  4. Ray Casting • Generate image directly from density data • Cast ray through density volume • Accumulate colors as ray passes through semi-transparent cells

  5. Accumulate illuminated densities • Density: D(t) = D(x(t), y(t), z(t)) L illumination: I(x,y,z) R t2 t1 Phase function: P I(t)D(t)P(Cosq)

  6. I(t) Radiation from light source Attenuated, shadowed by volume Only needed where internal shadows are important e.g., clouds, fire, smoke

  7. R t2 t1 Attenuation along a ray t converts density to attenuation

  8. Outgoing light • light reflected in view direction from light source • incoming light filtered by the voxel • light emitted by the voxel

  9. 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

  10. 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

  11. 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

  12. Packages • AVS: Application Visualization System • IBM Data Explorer (DX) • Data Visualizer

  13. Display issues • How to represent: • Temporal information • Non-spatial information • Multi-dimensional information

  14. Examples

  15. Examples

  16. Examples

  17. Examples

  18. Speed-ups • Hierarchical spatial enumeration • adaptive termination

  19. Hierarchical Spatial Enumeration

  20. Traversing Volume

  21. Examples

  22. Examples

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