Re: [rp-ml] STL files

From: Delft Spline Systems <>
Date: Wed Dec 06 2006 - 09:56:47 EET

Hi to all,

As a countermovement to all STL bashing on this list:
the STL format is the best CAD data exchange format I have ever worked with (and I am active in the field for over 20 years).

Positive points:
- all 3D CAD programs can export STL
- no incompatible variations do exist (I do not use color). Compare this to DXF, where the specification is changed with every new Autocad release, and to IGES, where every CAD system has its own flavour, often incompatible.
- there is no choice in entities (like a sphere being described OR as a center + radius OR as or NURBS surface OR as polygon data OR ...). All geometry is described using the same trangle entity. I think this is in fact the best point of STL.
- the specification is so very simple that there is not much room for error (it is also inefficient, however large files are not a large problem).
- it allways works, at least for me: our STL processing software does not care about cracks, gaps or orphan surfaces ( I would say that refusing to build is a problem of the RP software, not of the STL data format.

The only limitation is that STL can be used for downstream processes only, like RP and rendering. Modelling polygon data is not a good option. Since I am in model building this does not bother me.

Best Regards,

Lex Lennings.

At 20:11 05-12-2006, Adrian Bowyer wrote:
>Quoting Todd Pederzani <>:
>>steve wrote:
>>>I strongly urge all software vendors
>>>to support (at a minimum) PLY and COLLADA and to try to wean
>>>their customers off of STL as fast as they can run away!
>>You and I may agree, as programmers, that the STL format has
>>shortcomings, but from a user's perspective it "works."
>No it doesn't. I've lost count of the number of people coming to me with STL files that simply won't build because they do not obey the Euler formula for a solid.
>> What are the
>>"killer app" features of PLY or COLLADA that would motivate vendors to
>>implement support for those formats?
>That you can check it against the Euler-Poincaré formula - simple (and fundamental) as that.

Delft Spline Systems, The Netherlands.
We offer DeskProto: affordable Rapid Prototyping using CNC milling. --- website:
Received on Wed Dec 06 08:54:30 2006

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