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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Wed, 29 Sep 1999 20:50:31 GMT
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Viewed:
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528 times
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Leonardo Zide <leonardo@centroin.com.br> wrote in message
news:37F24ACE.49636FC@centroin.com.br...
> "Lars C. Hassing" wrote:
> >
> > Here are 50 messages regarding the above subjects.
> > The first from January 1998 where Leonardo Zide suggested CW/CCW.
>
> I miss that kind of discussion, those were very interesting subjects.
> Also, where's Jeff Findley ?
>
> > I support the CW/CCW idea (isn't it annoying knowing almost 50% of all
> > faces are drawn to waste), though it will cost a considerable effort
> > fixing old parts. The process can however be automated: Leonardo already
> > has a program showing faces as red or green and Gary suggested a
> > ray-algorithm for automatically determining CW/CCW-ness.
>
> I've already thought about a ray intersection algorithm but I've never
> tried to implement it, I might try do it now. Some problems that I
> remember is that LDraw parts are not closed volumes (that's not the best
> description), for example: trace a ray from the top of a 1x1 brick and
> it will intersect 3 surfaces, and the program can't decide what's the
> correct orientation of the face in the middle.
What if when a ray intersected 3 surfaces, it made the first CCW, the last CW,
and left the middle surface unmarked. If you traced enough rays from
different angles and starting positions, I think you would eventually be able
to mark all surfaces. In your 1x1 brick example, when you traced a ray that
didn't go through the top stud, you would have an even number of surfaces and
so could correctly mark them.
About the only time I see this not working is if a single quad is used both as
an outer and an inner surface, which wouldn't exactly be great part design
form.
-John Van
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Message has 1 Reply:
 | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| John VanZwieten wrote in message ... (...) Me too! (...) "enough rays" - exactly what stroke me too when I read Leonardo's posting! With the fast computers nowadays we could shoot millions of rays at the part from all possible viewing angles (this (...) (25 years ago, 30-Sep-99, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| (...) I miss that kind of discussion, those were very interesting subjects. Also, where's Jeff Findley ? (...) I've already thought about a ray intersection algorithm but I've never tried to implement it, I might try do it now. Some problems that I (...) (25 years ago, 29-Sep-99, to lugnet.cad.dev)
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