Re: VRML, STL and other animals

From: Anthony D. Martin (
Date: Tue Jan 09 1996 - 22:18:59 EET

On Tue, 9 Jan 1996, Yuval Roth wrote:
> 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).

Definitely, triangles only. With any more vertices, you have to start
playing with what is planar vs. non-planar.

> 2. Indexed vertex representation.

This is acceptable.

> 3. Color and Normals representation but such that it is valid and simple
> to omit (on write) or to ignore (on read).

OK, but a single normal for each vertice is not necessary, however...

> 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).

Per-vertex definition of normals is _very_ useful. The main reason that
people trash polygonal representations is that curved surfaces can only
be approximated with facets, and generally the part that is produced will
be faceted (although with a sufficient number of facets, this is
unnoticeable). However, if there is a normal defined for each vertex,
curved surfaces can be represented very accurately with a reasonably
small number of facets (like Phong or Gourad shading). This is a very
good feature that definitely doesn't exist with the STL standard.


I'm for that.

> 6. ????
> In fact, I have started playing around with syntax definitions for a
> format I coined TFF (Triangular Facet File). I will be more than
> happy to share this discussion directly with all interested, or if
> enough interest is generated, to open the discussion on the mailing list.

I think this list is a good place to discuss this.

BTW, if anyone wants to play with this stuff, or just want to verify, and
if necessary correct STL files, you can get my _free_ STL processing
program from:

and you can read about its features at:

This program comes with source, (in fact it only comes with source, but
it is very easy to compile), and it should run on any Unix machine or
probably even Windows NT. This program can output a shared vertices
file. Currently it just outputs OFF format which is used by Geomview, a
free viewing program, but it should only take a few lines of code to
support other formats.


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