Revision as of 21:49, 5 October 2015 by MarkMiller (talk | contribs) (Add minor note to motivate why volume rendering can be important)

The Volume plot uses a visualization technique known as volume-rendering, which assigns color and opacity values to a range of data values. The colors and opacities are collectively known as a volume transfer function. The volume transfer function determines the colors of the plot and which parts are visible.

Volume rendering is one of the few visualization techniques for 3D data that, with proper configuration, can wind up incorporating 'all the input data in the final rendered image. With traditional opaque surface based techniques, the final rendered images contain only what is visible from a given eye point.


Volume Plot Attributes.
Head, ray-cast.
  1. Open CThead_mid.silo.
  2. Create a Volume plot of head.
  3. Add a Box operator by selecting Box from the Operators->Selection sub menu.
  4. Open the Box operator attributes window by selecting OpAtts->Selection->Box from the Main menu.
  5. Type 13. for X-minimum.
  6. Type 95. for X-maximum.
  7. Type 0. for Y-minimum.
  8. Type 120. for Y-maximum.
  9. Type 0. for Z-minimum.
  10. Type 113. for Z-maximum.
  11. Click the Apply button.
  12. Open the Volume plot attributes window.
  13. Change the number of sample points to 1000000. Click Apply.
  14. Change the Rendering Method to 3D Texturing. Click Apply.
  15. Change the Number of slices to 800. Click Apply.
  16. Click on the 1D transfer function tab.
  17. Change color table from 'Default' to 'xray'. Click Apply.
  18. Go back to 'Renderer option's tab.
  19. Change the Rendering method to Ray-casting: compositing. Click Apply.
  20. Change the Rendering method to Ray-casting: integration. Click Apply.
  21. Click 'Reset' in the Volume plot attributes window.
  22. Delete the plot.
  23. Close the active source.

Transfer functions

Gaussian opacity controls.
Freeform opacity.
  1. Open noise.silo
  2. Create a Volume plot of 'hardyglobal'.
  3. Open the Volume plot attributes window.
  4. Change the Rendering method to 3D texturing. Click Apply.
  5. Click on the 1D transfer function tab.
  6. In the Opacity section, click on the black box to clear out the opacity curves
  7. Using the mouse and clicking on different sections, create opacity curves.
  8. Click Apply.
  9. Click the Gaussian radio button to change to a Gaussian opacity curve.
  10. Create some curves by clicking in the opacity control. Move the control points for the curves to change their shapes.
  11. Change the opacity attenuation to 40%
  12. Click Apply

Saving/Loading Volume attributes

noise.silo, ray-cast.
noise.silo, opacity.
  1. Click Save. Browse to desired location and enter a name.
  2. Click Reset.
  3. Click Load. Browse to location where you saved previously, highlight the appropriate file name and click Open.
  4. Click Apply.

Ray-casting sampling methods & lighting

  1. Open the Renderer options tab.
  2. Change rendering method to Ray-casting: compositing. Click Apply.
  3. Change sampling method to Trilinear Click apply.
  4. Change Reduction factor to High. Click Apply.

Slivr sampling method and lighting.

  1. Change Rendering method to SLIVR. Click Apply.
  2. Click 'Auto apply' in the main gui window to see future changes immediately.
  3. Using up/down arrow keys for the lighting options, play with each setting and watch how the changes affect the plot.

Slivr & 2D transfer function.

  1. Change Transfer function to 2D
  2. Switch to the 2D transfer function tab
  3. Click a widget button in the Widget list.
  4. Play with its control points and change its color.
  5. Select another widget and play with its controls & color.