CCL: calculating area of a ring

[Matthias Rarey <rarey() zbh.uni-hamburg.de>]

 Sent to CCL by: Matthias Rarey [rarey]^[zbh.uni-hamburg.de]
 Assuming your polygon has n points (x[i],y[i]), 0 <= i < n, then the
 following loop should do the job:
 area= 0;
 for(i=0; i<n; i++) area += ( x[i]*y[(i+1)mod n] - x[(i+1)mod n]*y[i] );
 return (area/2);
The function works even for a concave polygon, it should be simple,
 however (meaning it has no crossing edges).
 --
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 Prof. Dr. Matthias Rarey                       Tel. : +49 40 42838 7350
 Zentrum für Bioinformatik, Universität Hamburg Fax  : +49 40 42838
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Bundesstraße 43, 20146 Hamburg; Germany        eMail:
 rarey[at]zbh.uni-hamburg.de
 Mills, Nancy S. nmills ~ trinity.edu schrieb:
>  Sent to CCL by: "Mills, Nancy S." [nmills_._trinity.edu]
>  Is there a program that uses cartesian coordinates (effectively x,y coordinates)
>  to calculate the area of a flat ring? I am interested in rings that are not
>  necessarily perfect polygons.