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From: bobr@zeus.UUCP
Newsgroups: comp.graphics
Subject: Re: Point inside of polygon revisited...
Message-ID: <1881@zeus.TEK.COM>
Date: Wed, 17-Jun-87 16:54:21 EDT
Article-I.D.: zeus.1881
Posted: Wed Jun 17 16:54:21 1987
Date-Received: Fri, 19-Jun-87 05:26:10 EDT
References: <948@elrond.CalComp.COM> <790@thumper.UUCP>
Reply-To: bobr@zeus.UUCP (Robert Reed)
Organization: CAE Systems Division, Tektronix Inc., Beaverton OR
Lines: 14

Steve Hawley writes:

    A somewhat better (but still fallable) way than arbitrarily picking a
    ray, is to use a vector that is defined by the given point and the
    midpoint of a particular edge.  The only reason for this is that it
    will be fast, and only less fallable in the sense that you know it will
    definitely cross ONE edge without intersecting a point.

There is no guarantee that a ray which intersects the midpoint of some edge
will not also hit a vertex, even if the polygon is convex.  Also, there is a
slight disadvantage in using an arbitrarily sloped ray, on the order of two
extra subtractions per intersection test.
-- 
Robert Reed, Tektronix CAE Systems Division, bobr@zeus.TEK