Subject:
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Re: Collinear vertices warning on very small triangels
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Newsgroups:
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lugnet.cad.dat.parts
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Date:
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Tue, 1 Mar 2005 01:18:44 GMT
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Viewed:
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3276 times
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In lugnet.cad.dat.parts, Willy Tschager wrote:
> In lugnet.cad.dat.parts, Ross Crawford wrote:
> > In lugnet.cad.dat.parts, Willy Tschager wrote:
> > > hi lars,
> > >
> > > I get L3P collinear vertices warning on these very small triangels:
> >
> > Hi Willy, there was a thread about that recently, coincidentally someone else
> > named Will :) http://news.lugnet.com/cad/dev/?n=10023
>
> hi rosco,
>
> thx for pointing. interesting thread. even after so many years I still find out
> something new (that's why I love LDraw :-) L3Lab and L3p share code ... hmmm ...
Yes, reading and parsing files is common code. You can read more here:
http://www.hassings.dk/l3/l3lab.html
The next version of L3P/L3Lab do accept your small triangles, see
http://news.lugnet.com/cad/dev/?n=10033
If you set the warning level to 2 (-w2) you will see L3P's warnings
(which should have been errors, since they are skipped...)
> L3Lab does not draw concave quads like this:
>
> 4 4 0.603 19.885 1.569 0.902 19.803 1.569 0.294 19.935 1.569 1.348 23.306 1.569
> 4 4 1.962 19.146 1.569 2.19 18.899 1.569 1.718 19.357 1.569 4.658 22.467 1.569
> 4 4 3.365 15.157 1.569 3.413 14.491 1.569 3.302 15.76 1.569 8.689 15.058 1.569
> 4 4 3.46 10.85 1.569 8.857 11.827 1.569 8.844 11.056 1.569 8.806 10.292 1.569
I just copied the four quads into a file and opened it in L3Lab
and they showed up nicely. You may set the zoom to 4000.
> but you won't get any warning when checking with L3P. you will have to use
> LDView to find out what's wrong:
>
> Concave quad split into two triangles.
> File: C:\...\Concave.dat
> Line #7
> Line: 4 4 0.603 19.885 1.569 0.902 19.803 1.569 0.294 19.935 1.569 1.348 23.306 1.569
> Original Quad: <0.603 19.9 1.57> <0.902 19.8 1.57> <0.294 19.9 1.57> <1.35 23.3
> 1.57>
> Triangle 1: <0.603 19.9 1.57> <0.902 19.8 1.57> <1.35 23.3 1.57>
> Triangle 2: <0.902 19.8 1.57> <0.294 19.9 1.57> <1.35 23.3 1.57>
>
> lars, will "concave-checking" be part of the new L3P version?
But there's nothing wrong!
Most (if not all) programs only deal with triangles and thus split a quad into two triangles.
You can split a convex quad in two ways, but there's only one way to split a concave quad.
L3Lab (and L3P) correctly detects the concave quad and splits the quad the right way.
/Lars
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