Subject:
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Re: stl2dat conversion tool beta2
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 11 Feb 2000 18:30:06 GMT
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Viewed:
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1181 times
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On Fri, 11 Feb 2000 17:29:13 GMT, Rui Martins <Rui.Martins@link.pt>
wrote:
> Does STL allow only for triangles ? no Quads ? no N sided Polygons ?
No ONLY Triangles. Look for STL format description
http://www.eng.clemson.edu/~wfeng/stl_fmt.htm
http://www.sdsc.edu/tmf/Stl-specs/stl.html
http://www.ennex.com/fabbers/StL.sht
> > > Buy the way, do you correctly generate these lines (expecially the
> > > optional ones) ?
<SNIP>
> The optional lines are required only to complement the silhuete of the
> part, so if the angle is different from zero (0) then it's a candidate
> for an optional line.
> Since we use optional lines to define this silhuete for aproximated round
> parts, this value should be defined by the less precision we accept
> (8 sub divisions in a circle) which ields 45 has the angle of choice
> (AKA default value), but his value should be configurable.
The program check the angle between two adjacent facets
if abs(angle ) < 1e-5
No Edge
if abs(angle) < 45°
Optional Edge
else
Normal Edge
The angle is the only way to detect if an edge is between two facets
of a cylindric face or an edge between two faces.
This information is lost in the STL format.
A value between 45° and 22.5° should be ok.
> > Are you interested to be able to change this value ?
>
> Of course !
I will do that.
> > However, the program only check strictly
> > adjacent facets. I have to improve it so it check also
> > partial adjacent facets.
>
> I don't know exactly what you mean by partial adjacent faces, but if
> what you mean is something like this:
>
> 1------------2
> | |
> 3------------4-----5
> | |
> | |
> 6------------------7 • <SNIP>
> Just don't bother, because this is Plain BAD Modeling, and no conscious
> modeller will do this, instead he should break the bottom poly into three
> triangles using vertex 4, or define another point below vertex 4 and break
> into two quads.
>
> Tesselation algorithms will NEVER do this.
Yes, I meant that. Looking the STL format and your comment this
appears to be a bug in my program. I will have a look.
Marc Klein
A Mindstorms fan.
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Message has 1 Reply:
 | | Re: stl2dat conversion tool beta2
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| (...) Both those constant should be configurable, eventually within predefined ranges. Maybe You should allow the use of the abs() function to be optional, because if the face normal are correctly calculated (the faces are well defined, CCW or CW) (...) (25 years ago, 11-Feb-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: stl2dat conversion tool beta2
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| (...) Ok, my cad program can do that, but I have to mess with it because the options to tesselate a surface are somewhat complex, at least if you want to be able to have some control on the number of polys generated. Does STL allow only for (...) (25 years ago, 11-Feb-00, to lugnet.cad.dev)
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