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 16:35:46 GMT
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Viewed:
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719 times
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Steve Bliss wrote in message <37f4ab7d.64002272@lugnet.com>...
> On Thu, 30 Sep 1999 16:28:48 GMT, "Gary Williams" <graywolf@pcpros.net>
> wrote:
>
> > A hypothetical batch dat fixer program could examine the primitives first
> > and flag the ones that were not closed volumes, since those would be the
> > only ones that would need to have their reference orientation matrices
> > mirrored and rotated.
>
> It wouldn't matter if they were closed-volume or not--they could still be
> turned inside out accidently. And an inside-out closed-volume primitive
> wouldn't do anybody any good.
Doh'! You're right.
> > I think there could be problems if some of those non-closed primitives are
> > asymmetrical.
>
> Why?
I'm having a difficult time picturing in my mind how an asymmetrical part
can have its orientation matrix in the parent dat file mirrored and rotated
(to flip the CW-ness of each polygon) and still have the same shape.
Maybe I'm thinking of something totally different from what you're thinking.
:/
-Gary
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Message has 2 Replies:
 | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| Gary Williams wrote in message ... (...) *a lightbulb appears above my head* Nevermind, I understand now. For some reason I was imagining inverting all three axes, but now I realize only two would need to be inverted, before the part is rotated 180 (...) (25 years ago, 1-Oct-99, to lugnet.cad.dev)
| | | Re: CW/CCW, vertex sequence, co-planar, convex, (115kB)
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| (...) OIC now. I think. If an asymmetrical part is mirrored, it keeps the same shape, but is turned inside out. To get it right-side-out again, it must be re-mirrored. In other words, there's no way to produce left- and right-handed pairs of (...) (25 years ago, 3-Oct-99, to lugnet.cad.dev)
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