Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!bloom-beacon!athena.mit.edu!tuna From: tuna@athena.mit.edu (Kirk 'UhOh' Johnson) Newsgroups: comp.graphics Subject: Re: Intersection between a line and a polygon (UNDECIDABLE??) Summary: no, no, No, No, NO, NO Message-ID: <14759@bloom-beacon.MIT.EDU> Date: 29 Sep 89 03:59:56 GMT References: <2972@ndsuvax.UUCP> <32610@cornell.UUCP> Sender: news@bloom-beacon.MIT.EDU Reply-To: tuna@athena.mit.edu (Kirk 'UhOh' Johnson) Organization: Massachusetts Institute of Technology Lines: 27 In article <32610@cornell.UUCP> deb@charisma.graphics.cornell.edu writes: % In article <2972@ndsuvax.UUCP> ncsmith@ndsuvax.UUCP writes: % > % > I need to find a formula/algorithm to determine if a line intersects % > a polygon. I would perfer a method that would do this in as litte % > time as possible. I need this for use in a forward raytracing % > program. % % I think that this is a very difficult problem. To start with, % lines and polygons are semi-algebraic sets which both contain % uncountable number of points. Here are a few off-the-cuff % ideas. % % [ .... egregious volumes of hairy sounding stuff deleted .... ] look in any respectable introductory graphics book (foley and van dam, newman and sproull, etc.) and you'll see that this is a solved (many times over) problem. it is definitely _FAR_ from undecidable; it's actually fairly simple to solve. if after you've found such a book and read what it has to say you find yourself still completely confused, then try asking the net for guidance. kirk