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From: "John D'Errico" <woodchips@rochester.rr.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to get the intersection point coordinate between polygon and segment
Date: Sat, 13 Dec 2008 14:21:02 +0000 (UTC)
Organization: John D'Errico (1-3LEW5R)
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"zedong 
" <zdongwu@gmail.com> wrote in message <gi0epq$lk3$1@fred.mathworks.com>...
> How to get the intersection point coordinate between polygon and segment;
> for example(a is a triangle a(i,:) is the ith coordinate of the triangle.b is an segment,b(i,:) is the side point coordinate):
> a=[0 0;1 0;0 1]; b=[0.4 0.4;1 1];
> I want to return c=[0.5 0.5;0.4 0.4]
> example2:
> a=[0 0;1 0;0 1]; b=[0.4 0;2 0];
> I want to return c=[0.4 0;1 0]
> example 3
> a=[0 0;1 0;0 1]; b=[0.4 0;0.5 0];
> I want to return c=[0.4 0;0.5 0];
> Thank you for your attention.Is there any mex implementation.and stable.I also write one but I think because of the eps I can't implement it well.
> thank you for another time.

Did you look on the file exchange? Try it.
Here are some good key words to use:

curve intersections

John