Subject:
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Re: Quad intersections
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Newsgroups:
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lugnet.cad.dev
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Date:
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Fri, 16 Apr 1999 17:35:09 GMT
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Viewed:
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842 times
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Based on Dave's formulae, I have been able to calculate the intersection of a
plane (given three points) and a line (given two points). How do I then
determine whether the point of intersection falls within a quad (as in Dave's
"exercise left for the reader")?
-John Van
Dave Hylands wrote in message
<snip>
> Of course, now that you've found y, you probably need to verify that (x, y,
> z) actually falls within the given quad (as they say in the textbooks, this
> is an exercise left for the reader).
>
> If anyone is interested in a more detailed derivation, I'd be happy to share
> the gory details.
>
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Message has 2 Replies:
 | | Re: Quad intersections
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| (...) Using quad points Q0 - Q3, point of intersection I. For all lines QmQn, where I.X is between Qm.X and Qn.X, interpolate the point Jmn on QmQn where Jmn.X = I.X. If I.Z is between min(Jmn.Z) and max(Jmn.Z) then I lies within quad Q. If I.Z is (...) (25 years ago, 16-Apr-99, to lugnet.cad.dev)
| | | Re: Quad intersections
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| (...) Here's what I use, it works for triangles but you can easily change it for a quad. The idea is to check the angles between the vectors formed by each vertex and the point you're testing. x,y,z: point p1,p2,p3: vertex (float[3]) double pa1[3], (...) (25 years ago, 16-Apr-99, to lugnet.cad.dev)
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Message is in Reply To:
| | RE: Quad intersections
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| Hi Steve, I've been lurking for a while and thought your post was interesting enough to figure it out. I brushed off my Calculus text book, and after a page and a half of algebra, and remembering what determinants and cross products are all about I (...) (25 years ago, 5-Apr-99, to lugnet.cad.dev)
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