Re: [rp-ml] STL files

From: Todd Pederzani <>
Date: Wed Dec 06 2006 - 18:15:07 EET

Adrian Bowyer wrote:
> This was a problem with a known simple solution when the STL format
> was defined. As that solution had been around since the time of
> Poincaré (1854 - 1912), if not Euler (1707 - 1783), that is a bit
> annoying. It's the sort of thing that happens when you let mechanical
> engineers (like me) define a data structure...
Are you sure that the problem with STL aren't due to incomplete
specifications? The 3D Lightyear help file (interestingly enough
labeled 1.2.1 even in the 1.5.1 release) has a section in "STL Format"
with the following rules:

1. All triangles much conform to the right hand rule
2. All exterior surfaces must be devoid of gaps
3. Each triangle must share two of its vertices with each adjacent triangle

I presume these rules are in the spec by 3D Systems. You can't easily
derive all of these rules from the reverse engineering of the file.

Steve touched on something in his first post that made me think that it
would be nice to be able to test if STL files conformed to what 3D
Systems intended. (Think "syntax checker.") I repair some of the
customer files that come through our operations, and Magics, 3D
Lightyear, and SolidView all disagree about what a "good" file is...
Which is disconcerting, to say the least.

Todd Pederzani
ProtoCAM                System Administrator
3848 Cherryville Road   Phone: (610) 261-9010
Northampton, PA 18067   Fax:   (610) 261-9350
Received on Wed Dec 06 17:14:36 2006

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