js 矩形（不规则）中心点位置查找

    function getPolygonAreaCenter(points) {
        var sum_x = 0;
        var sum_y = 0;
        var sum_area = 0;
        var p1 = points[1];
        for (var i = 2; i < points.length; i++) {
            p2 = points[i];
            area = Area(points[0], p1, p2);
            sum_area += area;
            sum_x += (points[0].x + p1.x + p2.x) * area;
            sum_y += (points[0].y + p1.y + p2.y) * area;
            p1 = p2;
        }
        var xx = sum_x / sum_area / 3;
        var yy = sum_y / sum_area / 3;
        return { xx, yy };
    }
    function Area(p0, p1, p2) {
        var area = 0.0;
        area =
            p0.x * p1.y +
            p1.x * p2.y +
            p2.x * p0.y -
            p1.x * p0.y -
            p2.x * p1.y -
            p0.x * p2.y;
        return area / 2;
    }