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From: jwp@utah-cs.UUCP (John W Peterson)
Newsgroups: net.graphics
Subject: Re: Intersect line with polygon
Message-ID: <3122@utah-cs.UUCP>
Date: Tue, 27-Nov-84 16:09:33 EST
Article-I.D.: utah-cs.3122
Posted: Tue Nov 27 16:09:33 1984
Date-Received: Thu, 29-Nov-84 03:37:04 EST
References: <4663@utz, <148@gcc-opus.ARPA>
Organization: Univ of Utah CS Dept
Lines: 18

You can substitute the line equation into the plane equation of the polygon
(derived from its normal), to find where the line (or ray) intersects
the plane.  (If you find yourself dividing by zero someplace, the line
and plane are parallel).

Once you've found the intersection point, there is a nifty algorithm
(for convex polygons) to determine if the point is inside the polygon.

This algorithm, along with an excellent discussion of the geometry involved,
is given in:

	Sutherland, I, Sproull, R., and Schumacker, R., "A Characterization
	of Ten Hidden-Surface Algorithms", Computer Surveys, 6(1):1,
	March, 1974.

This paper is a must-read for anybody doing 3D shaded graphics, whether it's
ray-tracing or scanlines.  It has an amazing store of good information and
handy tricks.