Re: STL spec

Date: Fri May 07 1999 - 19:33:14 EEST


Glancing at the binary STL file spec on your site.... I believe there is room
in the spec to add color or layer information for each triangle. (Or anything
else, such as storing supports and part in the same file.) Where? The 3
4-byte floats storing normal information seem redundant. The normals can be
computed on-the-fly by looking at the clockwise-orientation of each triangles
3 vertices. Therefore these normal bytes can be used for storing other info.

This method would actually be backwards compatible with older software. I
regularly feed stl files to programs like Solidview, Deskartes viewer,
Allegro, etc. that have ZEROES where the normal info is stored. None of
these programs seem to have a problem with that. (we use some custom
programs made by a programmmer too lazy to add normal-computation to the stl
output routines.) In other words, for example, I don't think Solidview even
looks at the normal data.

In addition, the 80 byte header could be used to store translation
information concerning the new information stored where the normals were.

It seems to me that we could get a lot more mileage out of the STL spec for
use in future technologies and software. I leave it up to the keepers of the
format, 3D Systems, to do something to bring this file format into the 21st
century. It could start with a simple re-write of the STL spec, or a
users-group initiative.

Gentle Giant Studios.

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