39663

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From: [e-mail] (John Nagle)
Subject: Re: Point in Polygon routine needed
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Date: Mon, 17 May 1993 17:32:43 GMT
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Andrew Lewis Tepper <[e-mail]> writes:
>I don't know if this routine is "standard", I just came up with it recently:
>For a polygon of points p1...pn, and a point P, make a table as follows:
>T(1)= angle from p1 to P to p2
>T(2)= angle from p2 to P to p3
>...
>T(n)= angle from pn to P to p1
>express all angles as: -PI < angle < PI.
>Add all entries in the table. If the sum = 0, the point is outside. If
>the sum is +/- PI, the point is inside. If the point is +/- xPI, you
>have a strange polygon. If ANY angle was = +/-PI, the point is on the
>border.

     I think it's known, but it's neat.

     Can it be extended to 3D?

						John Nagle