Polygon获取中心点坐标

/**
* Author:Wu Yongfeng
* MSN/Email:[e-mail]
*/
package wuyf
{
import com.esri.ags.geometry.Extent;
import com.esri.ags.geometry.MapPoint;
import com.esri.ags.geometry.Polygon;

public class GeometryUtil
{
     /**
      * 获取多边形的重心
* @param polygon 多边形
* @return 重心点
*
      */
static public function getGravityCenter(polygon polygon):MapPoint
     {
         var ext:Extent = polygon.extent;       
         var p0:MapPoint = new MapPoint(ext.xmin, ext.ymin);

         var momentX:Number = 0;
         var momentY:Number = 0;
         var weight:Number = 0;
         for (var i:int=0; i<polygon.rings.length; )
         {
             var pts:Array = polygon.rings as Array;
for ( var j:int=0; j<pts.length; )
             {
                 var p1:MapPoint = polygon.getPoint(i, j);
                 var p2:MapPoint;
                 if( j==pts.length-1 )
                 {
                     p2 = polygon.getPoint(i, 0);
                 }
                 else
                 {
                     p2 = polygon.getPoint(i, j+1);
                 }

                 var dWeight:Number = (p1.x-p0.x)*(p2.y-p1.y)
                 - (p1.x-p0.x)*(p0.y-p1.y)/2
                 - (p2.x-p0.x)*(p2.y-p0.y)/2
                 - (p1.x-p2.x)*(p2.y-p1.y)/2;
                 weight += dWeight;

                 var pTmp:MapPoint = new MapPoint((p1.x+p2.x)/2, (p1.y+p2.y)/2);
                 var gravityX:Number = p0.x + (pTmp.x-p0.x)*2/3;
                 var gravityY:Number = p0.y + (pTmp.y-p0.y)*2/3;
                 momentX += gravityX*dWeight;
                 momentY += gravityY*dWeight;               
             }
         }

         return new MapPoint(momentX/weight, momentY/weight);
     }

}
}