Subject:
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Re: Very small triangle and a quad that thinks its a tri
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Newsgroups:
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lugnet.cad.dev
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Date:
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Sat, 8 Jan 2005 02:17:32 GMT
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Viewed:
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1568 times
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In lugnet.cad.dev, Ross Crawford wrote:
> In lugnet.cad.dev, William Howard wrote:
> > Whilst working out the non-right-angled cylinder intersection sub-parts for the
> > Boat Rigging pieces I have run into two related problems
> >
> > 1) I have a triangle A-B-C that is so tiny that L3P reports it as co-linear and
> > L3Lab doesn't render it (it looks OK in MLCad though)
> > 2) I have a large quad C-B-D-E that L3P reports B-C-E as co-linear and L3Lab
> > doesn't render (but again looks OK in MLCad)
> >
> > Now the triangle and the quad share the very short edge B-C but are not
> > co-planar so I can't replace them by any larger combinations. Also, omitting
> > A-B-C and making the quad into a tri leaves obvious gaps as the sub-part is
> > scaled when it is used.
> >
> > Should I
> > a) ignore these "errors" as they arn't really errors and assume that other
> > renders will render them OK (like MLCad does)
> > b) pre-scale the sub-part (which seems counter-intuitative as it then doesn't
> > follow the pattern of the right-angled cylinder intersection sub-parts)
>
> I'm guessing this is a limitation of the accuracy of the l3p -check, so probably
> ignorable.
I think so too.
William, could you please e-mail me the actual coordinates of A, B, etc.,
and perhaps the whole file.
> Does the -dist option affect this test too, or just the coplanar quad test?
Good question!
> Maybe there could be another option in l3p to adjust the accuracy of the
> colinearity test? Or is there one already and I missed it?
The colinearity test currently has a hardcoded threshold of 0.01.
The colinearity test is carried out like this:
Length = | (P1-P3) x (P2-P3) |
I.e. the length of the cross product of the two vectors spawning the triangle.
If the cross product is zero then the two vectors are parallel, i.e. the three points are colinear.
I could add an option for setting another threshold for the minimum length.
/Lars
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Message has 1 Reply:
Message is in Reply To:
 | | Re: Very small triangle and a quad that thinks its a tri
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| (...) I'm guessing this is a limitation of the accuracy of the l3p -check, so probably ignorable. Does the -dist option affect this test too, or just the coplanar quad test? Maybe there could be another option in l3p to adjust the accuracy of the (...) (20 years ago, 8-Jan-05, to lugnet.cad.dev)
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