Volume rendering structured grid data...

[Charles Law]

<x-flowed>If your structured grid forms a shell around the earth, you should be able 
to use
vtkStructuredGridGeometryFilter to extract the spheres to render as Bill 
suggested.
It would be faster than cutting.

For faster rendering (Lisa's LODs) you could use fewer spheres, but 
ideally, you would
want to sub sample the grid.  I do not know how to do thing in VTK.  You would
have to write a filter (it would be pretty easy to write).

Charles.


At 10:17 PM 10/7/99 -0400, Bill Lorensen wrote:
>You might be able to "slice" with concentric spheres. Use the combVol 
>script with a sphere for the cut function. I think resulting slices would 
>be spherical.
>
>Bill
>
>At 11:28 AM 10/7/99 -0700, Terry J. Ligocki wrote:
> >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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