Subject:
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Re: Question about generating curves
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Newsgroups:
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lugnet.cad.dat.parts
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Date:
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Wed, 10 Jan 2001 15:00:36 GMT
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Viewed:
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614 times
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In lugnet.cad.dat.parts, Tony Hafner wrote:
> What is an optional line? These seem to be used for modeling curves, but I
> don't have a clue how to use them.
See <http://www.ldraw.org/faq/>, question 20, linetype 5.
Basically, if you're modeling a curved surface, and as part of the model,
you've got two adjacent triangles, ABC and ABD:
A
/|\
C | D
\|/
B
The common edge, AB, needs to be modeled as a conditional line. You'd
write this like:
5 24 <A> <B> <C> <D>
Where each <A> represents the coordinates for a vertex. The important
thing is to put the vertices for the commen edge *first*.
If you have quads instead of triangles, you *should* be able use any of the
non-common vertices in place of <C> and <D> (one vertex from each quad, of
course). But I'd use ones which are both adjacent to the the same common
vertex.
> While I'm asking, what is a BFC statement?
It's a metastatement which supports a proposed standard for formatting DAT
parts to speed up rendering (and support other graphic utility programs as
well). The main point of BFC is that points on quads and triangles have to
be written in either clockwise or counterclockwise order. There are a
number of other twists, because of the DAT format and LDraw conventions.
You can see the most recent proposed BFC standard at
<http://www.geocities.com/partsref/bfcspecv4.txt>. This proposal is
implemented by both L3Lab and MLCad, almost exactly.
> Um... and why does MLCAD use a German-localized cancel button for the BFC
> statement dialog?
Maybe Michael develops in German? I believe he's Austrian, so that would
make sense...
Steve
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Message is in Reply To:
 | | Question about generating curves
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| What is an optional line? These seem to be used for modeling curves, but I don't have a clue how to use them. While I'm asking, what is a BFC statement? Um... and why does MLCAD use a German-localized cancel button for the BFC statement dialog? -- (...) (24 years ago, 10-Jan-01, to lugnet.cad.dat.parts)
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