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From: webber@brandx.rutgers.edu.UUCP
Newsgroups: comp.graphics
Subject: Re: Point inside of polygon revisited...
Message-ID: <260@brandx.rutgers.edu>
Date: Mon, 15-Jun-87 21:22:44 EDT
Article-I.D.: brandx.260
Posted: Mon Jun 15 21:22:44 1987
Date-Received: Thu, 18-Jun-87 00:42:14 EDT
References: <948@elrond.CalComp.COM>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 33
Keywords: ray tracing, graphics, polygon intersection
Summary: a reference detailing related problems in intersecting a line with a polygon to determine whether or not a point is within

In article <948@elrond.CalComp.COM>, amamaral@elrond.CalComp.COM (Alan Amaral) writes:
> 
> A while ago someone asked for a method for determining whether or not
> a point was inside or outside of a polygon.  I have the replies, and
> am in the process of implementing just such a function, but have come
> up against what I view as a significant problem. ...

A rather interesting article was written on the problem of this
method:
      A. R. Forrest, ``Computational geometry in practice,'' appeared in:
      R. A. Earnshaw (ed.), Fundamental Algorithms for Computer
      Graphics, NATO ASI Seires Vol. F17, Springer-Verlag, 1985, 707-724.
    

> HELP!

Said author's conclusions were:

      Simply by examining an apparently trivial operation which must
      have been implemented thousands of times in practice, we have 
      shown that such operations are by no means trivial.  It is
      doubtful indeed whether any completely sucessful implementations
      exist or indeed can ever exist.  We tend to take for granted in
      many algorithms the ability to implement these primitives successfully
      and we must realise that we do so at our peril.  Implementation
      requires careful attention to various geometric cass which must
      be correctly identified and to all arithmetic operations involved.
      The precision to which these operations must be carried out is 
      considerably higher than many realise.

Enjoy.

------ BOB (webber@aramis.rutgers.edu ; rutgers!aramis.rutgers.edu!webber)