Volume rendering structured grid data...

[Terry J. Ligocki]

I need to volume render scalar data lying on a structured grid.  I've
searched the archived e-mail list and looked at the Vtk documentation
(book, pamphlet, and man page).  From this I've determined that two
techniques have been suggested in the past:

   * Resample/splat the data into a structured points form, e.g.
     "financialField.tcl" and go from there
   * Slice through the grid, creating planes of polygons, and render
     these back to front with appropriate colors and opacities, e.g.
     "combVol.tcl"

In my case, both these techniques are problematic.  I'm looking at
atmospheric data on the entire globe and, even with an exaggerated scale
for the atmospheric depth, the structured grid forms a thin shell around
the Earth.

Thus, in the first technique above the structured points would grossly
undersampled where the data is or grossly oversampled where the data
isn't.  The second technique works better in this regard but doesn't
have a mechanism to recompute the slices as the view moves (at least in
the example).  Such a mechanism could probably be added but the result
would be fairly slow (but interesting!).

What I'm looking for is volume rendering for structured grids which is
interactive (it would be fine if it achieved this via some LOD or model
switching technique) and produces accurate results (which the user may
have to wait for once things have stopped moving), i.e. functionality
like the existing raycasting for structured points.

Is there a way to do this in Vtk?  If not, has anyone written something
fits in with Vtk and addresses this?  Beyond this, any hints and/or
comments would be welcome.

Thanks for your time, interest, and help...

                                Terry J. (Ligocki, tjligocki at lbl.gov)



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