RE: DEMs, TINs, orthos, draping

[David Freda <David.J.Freda@jpl.nasa.gov>]

At 11:45 AM 13-03-98 -0600, Crispen, Bob wrote:
>
>Let me ask a couple of very simpleminded
>questions if y'all don't mind (again!).
>
>   
> <SNIP>
>
>What about going the other way -- from elevation
>data on a regular grid to thinned elevation data
>with irregularly spaced points (in VRML, from
>ElevationGrid to IndexedFaceSet)?  Is there a
>conventional way to do this?  I think graphics
>folks would use a mesh decimation algorithm
>here.

We use decimation schemes whenever it's indicated, because they preserve
the overall geometry while reducing the polygon count.  Of course, this
means not using the ElevationGrid node.  We undersample the regular grid
frequently because it meets the need in many cases, and then wrap it all in
an LOD of some sort.

For those that don't want to code up some published decimation scheme from
scratch, take a look at the Visualization Toolkit (VTK), by Lorensen et al,
ISBN 0-13-199837-4.  It's got a decimation routine that ought to be pretty
handy - it's what I'm going to use.  Furthermore, there are Java bindings
that ought to permit someone to extend Justin's tool to use the decimation
scheme, should they have the time.

And then there's A. Gueziec's tool, that in my opinion would be ideal for
dealing with loading multires data of any sort, as he demonstrated so well.

-david

+----------------------------------------------------------------------------+
+   David Freda, MTS, JPL 4800 Oak Grove Dr., MS168-514, Pasadena, CA 91109  +
+   Work: david.freda@jpl.nasa.gov          Personal: dfreda@cogent.net      +
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