Subject:
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Re: Precision in .DAT files
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Newsgroups:
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lugnet.cad
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Date:
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Fri, 12 Jul 2002 11:18:42 GMT
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Viewed:
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752 times
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In lugnet.cad, Lars C. Hassing writes:
> Marek Idec wrote...
> >
> > Another question related to this subject. If one uses only lines, triangles
> > and quads in created part, then is very easy to judge whether there are gaps
> > between them or no. What about other primitives used, especialy transformed
> > (scalled, rotated etc.)? How to stick other vertices to them? What is the
> > maximum distance between two points to be considered as one point?
>
> That's a good question!
> When you interface to primitives I think it is important to stick to the scaled coordinates
> from the primitive file.
> E.g. if you scale a 4-4cyli.dat by 10 this quad from 4-4cyli.dat
> 4 16 0.9239 0 0.3827 0.7071 0 0.7071 0.7071 1 0.7071 0.9239 1 0.3827
> in effect becomes
> 4 16 9.239 0 3.827 7.071 0 7.071 7.071 1 7.071 9.239 1 3.827
> and you should stick to these values, and not to:
> 4 16 9.2388 0 3.8268 7.071 0 7.071 7.071 1 7.071 9.2388 1 3.8268
> (higher precision 4 decimals)
You are absolutely right. Usually scalling to bigger sizes decreases
precision. Considering however fractional factors (not only decreasing sizes
of primitives, but also more precise like 5.3 instead of 5) or rotations of
primitives answer is not so simple. It depends on calculation algorithm used
in programs.
> Several programs (including LDView and L3Lab) analyze vertices.
It's nice to hear that several programs analyze vertices. IMHO it should be
a standard feature of rendering programs. Otherwise unexpected small gaps
could be visible on renderings.
> Although they have to allow for small differences, ...
Of course, the question is how small. It's hard to believe that one needs
distance of 0.0001 ldu between two vertices (about 40 nano meters if my
calculations are correct).
Marek
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Message is in Reply To:
 | | Re: Precision in .DAT files [DAT]
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| Marek Idec wrote... (...) That's a good question! When you interface to primitives I think it is important to stick to the scaled coordinates from the primitive file. E.g. if you scale a 4-4cyli.dat by 10 this quad from 4-4cyli.dat 4 16 0.9239 0 (...) (22 years ago, 11-Jul-02, to lugnet.cad)
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