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MathGroup Archive 2000

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RE: Point inside a plygon? and PointInsidePolyhedronQ

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25374] RE: [mg25239] Point inside a plygon? and [mg24992]PointInsidePolyhedronQ
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sun, 24 Sep 2000 16:29:08 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear MathGroup,

It looks to me that Will Self's windingNumber procedure is the best so far.

He has pointed out a second counter example where the line intersection
method does fail. This is when the test line is outside the polygon but
tangent to it at a vertex. My routine counts one (false) crossing. Another
counter example would be when the test line crosses the polygon by lying
exactly on top of an edge. My routine would not count it as a crossing.

The line crossing method is very nice mathematics. It is not quite so
convenient computationally.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/



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