# Polygons & Nodal Points...

schoon at amgt.com schoon at amgt.com
Sun Jul 15 21:42:26 CDT 2001

~sdpm~
Yes, this is true, using a ray... But it fails when a point is right on
a boundary, and the polygon is odd shaped which would make an even
amount of crossings... Still a valid point, but fails the test...

.mark

>----------
>From: 	cabney[SMTP:cabney at cyberpass.net]
>Sent: 	Sunday, July 15, 2001 7:23 PM
>To: 	Mark Schoonover
>Cc: 	san-diego-pm-list at happyfunball.pm.org
>Subject: 	Re: Polygons & Nodal Points...
>
>On Sun, 15 Jul 2001 schoon at amgt.com wrote:
>
>> 	I have this polygon I need to split up into in smaller elements and
>> determine how many nodal points I have.... My first attempt was to brute
>> force the problem and just see if my nodal points fell within the
>> polygon, and start counting - but under certain conditions that fails.
>> It mostly fails when the point is on an edge of the polygon... My second
>> idea is to calculate how many nodal points I'm going to have by how many
>> subelements are present. I'm developing the application using Perl/Tk,
>> but I am new to using it. There might be a third way to determine nodal
>> points by using createRectangle. I'm not looking for a direct solution -
>> more along the lines of a brain storm. Any ideas greatly appreciated!!
>
>I think the standard way to do this is take a slice of the polygon at the
>point on the ordinal, and increment a count ever time you pass an edge.
>
>You are in the polygon (if it is one :) on the odd count.
>
>CA
>--
>There was a time
>A wind that blew so young
>For this could be the biggest sky
>And I could have the faintest idea
>
>
>

~sdpm~

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