Subject:
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Re: Stud5 and type 5 lines at edge of cylinders.
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Newsgroups:
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lugnet.cad.dat.parts.primitives
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Date:
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Sun, 17 Aug 2003 18:03:31 GMT
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Viewed:
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3472 times
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In lugnet.cad.dat.parts.primitives, Don Heyse wrote:
> In lugnet.cad.dat.parts.primitives, Mark Kennedy wrote:
> > I recently reworked the stud 5 primitive to make use of more quarter
> > cylinders. I then noticed that when viewed there were edge lines
> > apearing where they shouldn't. If you look at the primitive from
> > various points you can see this occur.
>
> Ahh, the dreaded S-curve cylinder join rears it's ugly head again.
> I voted to ignore this a while back and gave my reasons.
>
> http://news.lugnet.com/cad/dev/?n=7192
>
> Nobody disagreed at the time.
Is there a reason that the cylinder primitives haven't been updated to work like
the sphere primitive? As long as there are type 5 lines on both ends of each
partial cylinder, and the control point out in space is tangent to the cylinder
instead of being at the next point on the cylinder approximation, the problem
goes away.
It's kind of difficult to explain, but the two joining type 5 lines cooperate to
product correct rendering when two cylinders are connected, and it gets rid of
this problem on S-curves and when cylinders are joined to non-cylinders (say if
you want to have a rounded corner). LDView actually does this when it uses
primitive substitution on cylinder primitives, and the phantom line doesn't
appear.
This was discussed here:
http://news.lugnet.com/cad/dev/?n=7176
Note that it's tough to understand at first; you may have to read a large part
of the thread, but the article I linked to has the short description. My vote
would be to update the partial cylinder primitives. Note that the partial
sphere primitive is already coded in this way; I'm not sure why the partial
cylinder primitives aren't.
--Travis Cobbs
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