https://www.cnblogs.com/zzcpy/p/10524348.html

*-鞋带公式：https://en.wikipedia.org/wiki/Shoelace_formula

def polygon_area(points):
    """返回多边形面积
 
    """
    area = 0
    q = points[-1]
    for p in points:
        area += p[0] * q[1] - p[1] * q[0]
        q = p
    return area / 2

最后记得绝对值一下