Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site utah-cs.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!ihnp4!zehntel!tektronix!hplabs!utah-cs!jwp 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.