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From: heroux@cemmva.cem.msu.edu (Brett Heroux)
Newsgroups: comp.lang.c,comp.graphics
Subject: Re: Polygon operations?
Message-ID: <00942848.C5ABBCE0@cemmva.cem.msu.edu>
Date: 11 Jan 91 02:15:57 GMT
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Reply-To: heroux@cemmva.cem.msu.edu (Brett Heroux)
Organization: MSU_Chemistry
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In article <4bWuKJW00VpMIo80Z=@andrew.cmu.edu>, sa1z+@andrew.cmu.edu (Sudheer Apte) writes:
>
>I need (pointers to) a geometric modeller or other program that can do
>general 2-d polygon intersections, differences, additions, etc. based
>on any representation

Polygon intersection is usefully reduced to segment(line) intersections. I may
be able to find the code, if I can I'll e-mail, but the method goes:
Given: segment a from (x1,y1) to (x2,y2)
  and  segment b from (x3,y3) to (x4,y4)
Define: parametric equations a x = x1 + t(x2-x1) and y = y1 + t(y2-y1)
  and   "                  " b x = x3 + s(x4-x3) and y = y3 + s(y4-y3)
Find: s and t
If 0<s<1 and 0<t<1, the segments intersect, the polygons intersect.