Re: VRML instead of STL

From: Greg_Barnes_at_DTM__CORP@dtm-corp.com
Date: Tue Jan 02 1996 - 21:22:37 EET


______________________________ Reply Separator _________________________________
Subject: VRML instead of STL
Author: BAU@biba.uni-bremen.de (BAU) at DTM-CORP
Date: 1/2/96 12:18 PM

Use VRML as Standard for Rapid Prototyping !
     
*****
We have summarised aspects of the file-format discussion in this list,
and we make our own suggestion.
The following is an excerpt of a new wep page to be found at
http://www.biba.uni-bremen.de/docs/users/bau/bau.html
Have a look !
*****
     
Through many years, STL became the standard data format for 3D geometry
exchange in the Rapid
Prototyping scene. Now, we suggest to use the evolving VRML standard for
this purpose.
The pros and cons shall be discussed here on this page - we encourage
further contributions !
     
At first, a test:
Stereolithography User Part as uncompressed ASCII STL file: 370 kByte
The same, as uncompressed (ASCII) VRML .wrl file: 60 kByte
     
Why should I change ?
 As seen above, VRML files are smaller than STL.
This is just because it uses a list of numbered points followed by a
list of triangles (3 numbers,
 order indicates surface normal direction). STL has a large overhead:
For each triangle, not only all 3D
 points are given, the surface normal vector is included, too.
     
 Colour RP machines may me released - but colour could be included in
custom format,
 too. Chuck Kirschman made the suggestion how to include colour in the
old STL format.
VRML not only contains colour information, but even materials, textures
and colour gradients.
     
 Any software engineer could invent a new format which meets the current
RP needs. One example is the CLI
 format.
 VRML has a node structure ("tagged format"). RP-specific subnodes can
easily be defined when needed.
 By using VRML, all can be done with one standard. Limits interfacing and
conversion effort.
     
 Rapid Prototyping will only use a subset of VRML (Material and
IndexedFaceSet).
     
It is clear that for their genuine application, VRML models do not need
to be closed. Rendering software produces good pictures even with
inaccurate geometry. VRML will not solve general problems of solid 3d
representation, like open shapes, unconnected vertices, degenerated and
double polygons, etc.
Therefore, VRML is going to be the easy interface for all "3D hardprint"
tasks, as current and new 3D applications will have VRML output, even if
they did not even dream of such a solid hardprint.
     
VRML is the future. It is the 3D extension of the World Wide Web - A 3D
Telecommunication and Networking Standard.
VRML was carefully designed and discussed by well-regarded experts, and
it is a living standard.
     
 VRML reaches the mass market and therefore has enormous power - in
contrast to STL. As low-end
 '3D printers' appear, VRML can open the mass market to them.
     
What do you think ? Want to add something ?
     
Jrgen Bauer (bau@biba.uni-bremen.de) and Marcus Joppe
(jop@biba.uni-bremen.de).
Bremen Institute of Industrial Technology and Applied Work Science
(BIBA), P.O. Box 33 05 60, 28 335 Bremen, Germany,
Phone: +49/421/218-5595, Fax: +49/421/218-5510
     
     



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