Xref: utzoo comp.graphics:1876 comp.sys.ibm.pc:12713
Path: utzoo!dciem!trigraph!michael
From: michael@trigraph.UUCP (Michael Winser)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: COMPLICATED PROBLEM; ONLY INTELLIGENT PEOPLE SHOULD READ
Message-ID: <384@trigraph.UUCP>
Date: 3 Mar 88 15:27:36 GMT
Article-I.D.: trigraph.384
Posted: Thu Mar  3 10:27:36 1988
References: <971@ut-emx.UUCP>
Reply-To: michael@trigraph.UUCP (Michael Winser)
Organization: Trigraph Inc., Toronto, Canada
Lines: 29

In article <971@ut-emx.UUCP> jezebel@ut-emx.UUCP (Jim @ MAC@/) writes:
>Have a nice one here:
>Have a boundary defined on the screen. Boundary is composed of points
>joined by lines... Now some random points are generated and I want to check
>if a given point is within or outside the existing boundary.. Any algorithm for
>this ? Is it at all possible ????
>Running with GKS....under Fortran...
>Mind-boggling for you ? If not, you are the guy/gal who has the
>solution to my problem.....
>Please respond.....
>Jim

All you have to do is "draw" a line from the given point to a point known to be
outside the boundary, then see how many times that line intersects with the set
of lines that make up the boundary.  If the number of intersections is odd then
your point is inside the boundary.  You must also check for the special case of
the intersection occuring at one of the boundary points, such a point must only
be counted once.

GKS may have some nice routine defined that does this for you, but I'd be quite
surprised.

Michael

-- 
...mnetor!utzoo!trigraph!michael      Michael Winser
michael@trigraph.UUCP                 Trigraph Inc.
                                      5 Lower Sherbourne St. #201
(416) 363-8841                        Toronto,Ontario M5R 3H8