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From: jack@shograf.UUCP (Jack Ritter)
Newsgroups: comp.graphics
Subject: Re: Need to find polygon direction (cw/ccw)
Message-ID: <295@shograf.UUCP>
Date: 13 Dec 90 23:01:55 GMT
References: <548@ub.d.umn.edu> <LAMBERT.90Dec11000343@nankeen.spectrum.cs.unsw.oz.au>
Organization: SHOgraphics
Lines: 9

In article <LAMBERT.90Dec11000343@nankeen.spectrum.cs.unsw.oz.au>, lambert@spectrum.cs.unsw.oz.au (Tim Lambert) writes:
> >>>>> On 9 Dec 90 19:40:14 GMT, jtevik@gisplot1.nrri.umn.edu (John Tevik) said:
> Calculate the *signed* area:
>   A = 0.5*\sum_{i=1,2..n} x_i * (y_{i+1} - y_{i-1})

The question of polygon handedness seems to come
up frequently. Look in the upcomming "More Graphics Gems"
for what I feel is the fastest method for (convex) polys:
  "Fast Sign of Cross Product Calculation".