网上说的好多都错了，opencv里的pointPolygonTest()函数确实可以判断点相对于轮廓的位置关系，
但关于参数measureDist的作用却说错了，官方文档解释如下：
Performs a point-in-contour test.
The function determines whether the point is inside a contour, outside, or lies on an edge (or coincides with a vertex). It returns positive (inside), negative (outside), or zero (on an edge) value, correspondingly. When measureDist=false , the return value is +1, -1, and 0, respectively. Otherwise, the return value is a signed distance between the point and the nearest contour edge.
翻译过来就是：measureDist为false时才能判断位置关系，返回值+1（在轮廓里面）、-1（在轮廓外面）、0（在轮廓上）
官方文档说是Test的函数，可能是说判断结果不太准确，慎用。