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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Thu, 2 Oct 2003 03:14:23 GMT
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Viewed:
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8334 times
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In lugnet.cad.dat.parts.primitives, Don Heyse wrote:
> In lugnet.cad.dat.parts.primitives, Travis Cobbs wrote:
> > 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.
>
> I don't think the S curve problem goes away. The tangent control point
> works perfectly for two (same radius) curves that both curl in the same
> direction. It also works perfectly for a curve joining a flat edge
> along the tangent.
>
> However it only reduces the problem (by half) for two curves joined
> in an S shape. However with your fix, the problem also approches
> 0 as the number of segments in the curve approaches infinity. I think
> it's good enough for low res curves when used for tiny geometry like
> studs, and good enough with the higher resolution curves for larger
> bits.
>
> So if the primitives haven't been updated with the tangent control
> points at the ends, they should be.
>
> Any volunteers?
>
> > . My vote
>
> And mine.
>
> > 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.
Ok... I'm a bit lost is all this mess.
I need to know where we stand on this issue. I have a Primitive Generator
program written with Visual Basic available for people to download and use. If I
have handled this incorrecly, I need to know so I can try to fix the program.
I brought this up again, since I was reviewing my previous votes on the Parts
Tracker;
http://www.ldraw.org/cgi-bin/ptdetail.cgi?f=p/1-16cyli.dat
Paul
If you would like to try out the Primitive Generator, it can be downloaded from
this page;
http://www.geocities.com/pneaster/prim-gen.htm
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