The topic of STL file format and its possible extension and/or replacement
by other 3D geometry formats has been discussed several times before in this
group.
The addition of extensions to the STL specification is ill-advised for a
number of reasons. (1) It's already a bad format at the outset - any given
vertex is defined at least three times, wasting storage space. (2) If it
were to be properly extended it should include specs not only for material
properties (colors, transparency, opacity, etc.), but for specifying
adjacency, for grouping objects, for specifying object hierarchies, and so
forth. (3) The STL format is of use only in the RP community. Extending its
specs would still not make it any more attractive to other graphics
communities. In fact, just the opposite. A lot of energy would be expended
for little positive (if not negative) return. (4) So far as I know, there is
no standards committee for STL format specifications. If people start
writing their own flavors of STL files, we'll soon wind up in the morass we
now find ourselves in with image formats. (Thankfully, DICOM 3 is beginning
to clear up some of the mess in medical imaging).
I would suggest instead that we promote the use of alternate formats that
already have the desired specifications and that are de facto standards in
the graphics community. Perhaps Alias/Wavefront OBJ format (See:
http://wotsit.org/cgi-bin/download.cgi?w_obj ) or perhaps VRML (which
actually embodies most of OBJ) (See:
http://www.biba.uni-bremen.de/users/bau/s2v.html ). As I see it, one way to
encourage this is to NOT fiddle with the STL format, but rather to offer the
customer either standard STL, OBJ/VRML or both.
Regards
Charles Knox
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Image3, LLC, Midwest Office
1000 Ingerson Road
Shoreview MN 55126-8146, USA
Tel/FAX: (651)482-7938
http://www.image3.com
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -----Original Message-----
> From: owner-rp-ml@bart.lpt.fi [mailto:owner-rp-ml@bart.lpt.fi]On Behalf
> Of Aad van der Geest
> Sent: Thursday, December 09, 1999 8:55 AM
> To: rp-ml@bart.lpt.fi
> Subject: eXtended STL-Format
>
>
>
> Dear List,
>
> For my full colour 3D-printer (which was shown on the Euromold) I use a
> specially adapted binary stl-files.
> For every triangle the colour information is in the attribute
> count (16 bits).
> bit 15 always 1 (to distinguish from normal stl files)
> bit 10 to 14 intensity level for red (0 to 31)
> bit 5 to 9 intensity level for green (0 to 31)
> bit 0 to 4 intensity level for blue (0 to 31)
> In this way there are 32768 different colours.
>
> Several CAD-suppliers are considering implementing this adapted STL-file.
>
> Best Regards,
> Aad van der Geest
>
>
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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