Re: VRML, STL and other animals

From: Michael New (
Date: Tue Jan 09 1996 - 20:55:23 EET

Yuval Roth:
> However, I am extremely interested in participating in a serious discussion
> and effort to define a new format to enhance the STL format.
> The requirements of such a format (my private opinion) will be:
> 1. The file will represent only polygons (preferably only triangles - simpler).
> 2. Indexed vertex representation.
> 3. Color and Normals representation but such that it is valid and simple
> to omit (on write) or to ignore (on read).
> 4. For the color and normals: support for per vertex definition,
> or per part definition, specifically with the ability to define
> normals across creases (tangent discontinuities - at a single vertex
> more than a single normal).
> 6. ????

I second the motion. However, I have a few problems with #4 above. Color is a
property of a surface, so I think the polygon should contain that data.
Consider the differences:

 To represent two solid colors side by side along an edge, facet-tagged color
 would work, but would vertex-tagged color? I think this kind of representation
 would be the norm.

 To represent a color gradient accross on or more facets, the vertex-tagged
 color scheme would work, using the same way FEM results are often displayed.
 Facet-tagged color would not work.

I think the facet-tagged scheme would be simpler and would be more useful, but
if people need color gradients, BOTH facet- and vertex-tagged color could be used.

I also think that surface normal information is extranneous and should not be

Otherwise, I agree with all the opinions of Yuval's posting.

Mike New

----------------------------- _/ /\/\ /\/ ----------------------------
J. Michael New Michael.New@NRC.Ca
Integrated Manufacturing Technologies Institute (613)991-4371
National Research Council of Canada home: (613)230-7783

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