From: Yair Kurzion (yair++at++polygon.engr.sgi.com)
Date: 10/09/2000 10:47:27
Hello Mark !
> I'm trying to create a large-scale terrain vis, so pfASD is the obvious way
> to go. I have some (what seem to be) pretty basic questions about pfASD:
>
> How can I construct a pfASD node -- is it the same as assembling an LOD
> structure?
ASDGen is a tool for generating large pfASD objects. Please run a search in
the 1999 info-performer archive under:
http://reality.sgi.com/performer/
Search for ``ASDGen''.
> Will I be able to use polygon meshes generated from a CAD/3d modeling
> package such as Lightwave, or 3d Studio? (I will probably go .3ds -->
> .iv --> .pfb)? If so, can someone please point me to a code sample that
> demostrates how this is done?
ASDGen expects a user function that returns the elevation at a given point.
It does not read in any specific file format.
> I saw some discussion from a few years back about pfASD requiring regular
> grids/height fields. Is this still the case, or will I be able to work with
> irregular polygon meshes? the Perf. Prog. Guide seems to indicate that
> irregular polygon meshes can be used, but it doesn't say how.
First, a limitation: pfASD replaces each low-resolution triangle with at most
four higher-resolution triangles. Moreover, every vertex in the pfASD mesh
can morph its position only between the LOD that introduces it to it's lower
resolution neighbor. The vertex position is fixed in all other LOD's.
ASDGen expects a regular grid of heights. It assumes that this is all the
information you have. If you already have a polygon mesh, you are on your own:
ASDGen won't use it. I suggest that you take a look at Chapter 15 of The
Performer Programmer's Guide. It contains a long discussion of the internal
structure of pfASD. You can use it to represent your irregular mesh as a
pfASD.
-yair
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