[mapserver-users] Finding the area of a polygon

[Riccardo Cohen]

>> If not, does anyone know of an algorithm for computing the area based on a variable number of points?

This is C code but really easy to read :

points[] is an array of vectors, the first is the origin of the polygon, and the other are vectors relatives to the first point. To have the area, the first point is not needed.



  double surface=0;
  long   idx;
  if (is_closed() && point_nb>2)
  {
    // all points are delta from first -> don't need first
    for (idx=2;idx<point_nb;idx++)
      surface+= // det 2d
        (points[idx-1] || points[idx])/2.0 ;
  }
  return(fabs(surface));


det 2d is computed with the following method:

	x*v.y-y*v.x



-- 
Riccardo Cohen

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