Path: utzoo!attcan!uunet!wuarchive!mailrus!ames!ncar!gatech!mcnc!thorin!proline!brown From: brown@proline.cs.unc.edu (Randy Brown) Newsgroups: comp.graphics Subject: Re: Intersection between a line and a polygon (UNDECIDABLE??) Message-ID: <9751@thorin.cs.unc.edu> Date: 30 Sep 89 21:29:53 GMT References: <2972@ndsuvax.UUCP> <32610@cornell.UUCP> <14759@bloom-beacon.MIT.EDU> Sender: news@thorin.cs.unc.edu Reply-To: brown@proline.cs.unc.edu (Randy Brown) Organization: Clueless in the Second City of Two Cities Lines: 30 In article <14759@bloom.MIT.EDU> tuna@athena.mit.edu (Kirk Johnson) writes: * 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 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 .... ] ---> (but funny) <--- -->But an IMPORTANT inclusion, which was the "Tale of Two Cities" reference.<-- *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 I'm sorry, but I couldn't find the information about polygons in the referenced book, "A Tale of Two Cities", by Dickens. Do the vertices have to be ordered in clockwise or counterclockwise order, or does it matter? Dickens was quiet on the subject, and Newton has been dead even longer. But the ISBN for Principia Mathematica is #1066-ITS-A-JOKE. ---- brown@cs.unc.edu or uunet!mcnc!unc!brown "No-one gets a lifetime rehearsal, as specks of dust, we're universal."