Re: [rp-ml] STL files

From: Ruggero Gabbrielli <>
Date: Wed Dec 06 2006 - 14:10:12 EET

Hello guys,

no one, I think, wanted to decry the idea underlying the STL format
structure. Storing 3D shapes listing triangular facets and the coordinates
of their vertices is really useful.
The problem with the actual STL format is HOW this has been done. The ASCII
standard contains overabundant information. The same coordinates of a
vertex are repeated each time for every single facet that owns that vertex,
whether identifying it with a number would save plenty of memory space.

Ruggero Gabbrielli

--On 06 December 2006 08:56 +0100 Delft Spline Systems <>

> 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:

Ruggero Gabbrielli
Department of Mechanical Engineering
University of Bath
Bath BA2 7AY
Received on Wed Dec 06 12:51:01 2006

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