javascript实现计算多边形的质心

最近要基于百度地图显示多边形的标注，所以就研究了下计算Polygon的质心，代码如下：

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);
}

标注文字的效果如下：