JavaScript计算多边形质心并用于地图标注

function Area(p0,p1,p2)
{
  var area = 0.0 ;
  area = p0.lng * p1.lat + p1.lng * p2.lat + p2.lng * p0.lat - p1.lng * p0.lat - p2.lng * p1.lat - p0.lng * p2.lat;
  return area / 2 ;
}
//line 249 计算polygon的质心
function getPolygonAreaCenter(points) {
  var sum_x = 0;
  var sum_y = 0;
  var sum_area = 0;
  var p1 = points[1];
  debugger;
  for (var i = 2; i < points.length; i++) {
    p2=points[i];
    area = Area(points[0],p1,p2) ;
    sum_area += area ;
    sum_x += (points[0].lng + p1.lng + p2.lng) * area;
    sum_y += (points[0].lat + p1.lat + p2.lat) * area;
    p1 = p2 ;
  }
  var xx = sum_x / sum_area / 3;
  var yy = sum_y / sum_area / 3;
  return new BMap.Point(xx, yy);
}