Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: Type 5 lines at the edge of primitives
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Newsgroups:
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lugnet.cad.dev
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Date:
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Tue, 7 May 2002 17:23:35 GMT
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Viewed:
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976 times
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In lugnet.cad.dev, Steve Bliss writes:
> In lugnet.cad.dev, Mark Kennedy wrote:
> > > Here is a model that demonstrates some of the problems with placing type 5
> > > lines at the edge of the cylinder primitive.
> > >
> > > 0
> > > 1 16 0 0 0 10 0 0 0 10 0 0 0 10 1-4cyli.dat
> > > 1 16 0 0 20 10 0 0 0 10 0 0 0 0 -10 1-4cyli.dat
> > > 1 16 -20 0 20 10 0 0 0 10 0 0 0 10 1-4cyli.dat
> > > 0
> > >
> > > Take a look at it from front, back, left, and right and you'll see type 5
> > > lines where they shouldn't be.
>
> I'm not following the problem with this one. Then again, I'm not sure
> where lines are supposed to be, and where they aren't--the construct is
> a bit abstract.
There are too many numbers in the 2nd cylinder line. Cut and paste
error? Give this one a spin. I think what he's trying to show is the
type 5 line where the 2 quarter cylinders meet.
0
1 16 0 0 0 10 0 0 0 10 0 0 0 10 1-4cyli.dat
1 16 0 0 20 0 0 -10 0 10 0 -10 0 0 1-4cyli.dat
0
It's first order continuous at the join, but the curves go in opposite
directions so the cooperating control point idea doesn't quite work
with the low-res primitives.
> > And then there is matching a sphere with a torus Which is demonstrated with
> > this file.
> > 0
> > 1 16 0 0 0 78 0 0 0 -78 0 0 0 78 1-8sphe.dat
> > 1 16 0 0 0 90 0 0 0 90 0 0 0 90 t04i1333.dat
> > 0
>
> Hmm. The only way to avoid this problem is to not include the edge
> lines in the primitives at all.
I disagree. This is the same situation as the S shaped curve created
by two quarter cylinders, but I don't think it's a problem. Admittedly
the type 5 line at the center of the S curve seems to appear out of
thin air at an odd time, but that's only because our cylinder
approximations are so rough. The "problem" reduces to zero as the
primitives approach true cylinders. Look at an S curve made of two
hi-res cylinders to see what I mean.
0
1 16 0 0 0 10 0 0 0 10 0 0 0 10 48/1-4cyli.dat
1 16 0 0 20 0 0 -10 0 10 0 -10 0 0 48/1-4cyli.dat
0
With primitive substitution this "problem" tends to go away, so I
say just ignore it.
> Have you found many parts with this kind of construct?
The new castle helmet?
Don
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Message is in Reply To:
 | | Re: Type 5 lines at the edge of primitives
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| (...) I'm not following the problem with this one. Then again, I'm not sure where lines are supposed to be, and where they aren't--the construct is a bit abstract. (...) Hmm. The only way to avoid this problem is to not include the edge lines in the (...) (22 years ago, 7-May-02, to lugnet.cad.dev)
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