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From: jtevik@gisplot1.nrri.umn.edu (John Tevik)
Newsgroups: comp.graphics
Subject: Need to find polygon direction (cw/ccw)
Keywords: polygon direction
Message-ID: <548@ub.d.umn.edu>
Date: 9 Dec 90 19:40:14 GMT
Sender: news@ub.d.umn.edu
Followup-To: comp.graphics
Organization: Univ. of Minnesota, Duluth, N.R.R.I.
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Here's one for the FAQ.  I need to find the direction (whether clockwise or
counter-clockwise) of a 2D polygon.  I'm writing a program to translate
census tract data into SPSS Graphics and need to find the direction of
each polygon to properly assign left and right area ID's.  Polygons are
normally closed and are represented as a linked list of coordinate pairs
This exact problem is left as an exercise in Foley & van Dam (problem 
A.3.a pg. 1112).

Thanks in advance.

John Tevik                        jtevik@gisplot1.nrri.umn.edu (128.101.45.101)
Programmer                        jtevik@madonna.d.umn.edu (131.212.32.9)
University of Minnesota           (218)720-4247 (voice)
Natural Resources Research Institute