Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 1 Oct 1999 14:24:00 GMT
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Viewed:
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907 times
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Lars:
> Leonardo Zide wrote
[...]
> > About that discussion, IMO it would be better to have *everything* CCW
> > instead of adding a keyword.
This would demand a lot of work before people could start
using programs that use this fact.
> I agree with John Van in that we need three keywords: CCW, CW, UNKNOWN.
Right.
> As the rendering program is going to keep track of the
> number of mirrorings of the transformations (or simply if
> the total transformation is a mirroring),
Just check the determinant of the rotation matrix (but you
know that I suppose).
> we will need a way to tell what is inside-out side of e.g.
> cylinder primitives.
> Then STUD2.DAT could use:
> 0 CCW
> 1 16 0 -4 0 4 0 0 0 4 0 0 0 4 4-4cyli.dat
> 0 CW
> 1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
I would rather use some "double-sided" directive - which
would work as UNKNOWN.
It looks like (C)CW settings should propagate to included
files.
> or maybe to make it easier to use for part authors:
> 1 16 0 -4 0 4 0 0 0 4 0 0 0 4 4-4cyli.dat
> 0 INSIDE-OUT 1
> 1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
> 0 INSIDE-OUT 0
What about:
0 FACE DOUBLE-SIDED
1 16 0 -4 0 6 0 0 0 4 0 0 0 6 4-4cyli.dat
?
> Whether it will be:
> "0 CCW", "0 CW", "0 UNKNOWN"
> "0 FACE CCW", "0 FACE CW", "0 FACE UNKNOWN"
I like this one best.
> "0 ORIENTATION CCW", "0 ORIENTATION CW", "0 ORIENTATION UNKNOWN"
> "0 INSIDEOUT 0", "0 INSIDEOUT 1"
> I don't have any meaning about (though I don't like the first one :-)
Neither do I, now that I think about it.
> A part with no keywords is interpreted like it had begun
> with "0 FACE UNKNOWN".
Shouldn't it rather inherit the setting from the file that
calls it? Or do we need a specific "0 FACE INHERITED" for
this purpose?
Open primitives should definitly work with inherited (C)CW
settings, unless they are intended to be closed up when
used (like primitives for patterned parts).
> The only use for the UNKNOWN keyword I can see, is for a
> section of a part you want to make compliant at a later
> time.
Yes.
Play well,
Jacob
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Message has 2 Replies:
 | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| Jacob Sparre Andersen <sparre@sys-323.risoe.dk> wrote in message news:FIxHC0.E2v@lugnet.com... (...) I'm not so sure about this anymore. I think the ideal would be a program that could change the part files so that they are completely CCW. Using (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
| | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| (...) That would be nice, but it's unrealistic. (...) No, they shouldn't. Just because the part XYZ is CW, a program can't assume that the primitive ABC is also CW. (...) I like this. I don't like it for use on primitives, but DOUBLE-SIDED could (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
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