Function getPolygonCenterOfGravity

mapprimitive.c:1215–1245

** Computes the center of gravity for a polygon based on it's largest outer ring only. */

** Computes the center of gravity for a polygon based on it's largest outer ring only.
*/
static int getPolygonCenterOfGravity(shapeObj *p, pointObj *lp) 
{
  int i, j;
  double area=0;
  double sx=0, sy=0, tsx, tsy, s; /* sums */
  double a;

  double largestArea=0;

  for(i=0; i<p->numlines; i++) {
    tsx = tsy = s = 0; /* reset the ring sums */
    for(j=0; j<p->line[i].numpoints-1; j++) {
      a = p->line[i].point[j].x*p->line[i].point[j+1].y - p->line[i].point[j+1].x*p->line[i].point[j].y;
      s += a;
      tsx += (p->line[i].point[j].x + p->line[i].point[j+1].x)*a;
      tsy += (p->line[i].point[j].y + p->line[i].point[j+1].y)*a;
    }
    area = MS_ABS(s/2);

    if(area > largestArea) {
      largestArea = area;
      sx = s>0?tsx:-tsx;
      sy = s>0?tsy:-tsy;
    }
  }

  lp->x = sx/(6*largestArea);
  lp->y = sy/(6*largestArea);

  return MS_SUCCESS;
}

int msGetPolygonCentroid(shapeObj *p, pointObj *lp, double *miny, double *maxy)
{