说明：  In point set analysis, it is useful to compare 2 sets of points by computing the distance between each possible point pair. For example, this is a required step in the ICP point set registration algorithm. MATLAB s built in function for computing the distance matrix is pdist2. This function does the same thing, but also returns an angle matrix, which is the angle defined by each possible point pair. The limitations of this function are that it only computes the Euclidean distance and it only works in 2D. This function is useful for excluding hypotheses that don t match distance and orientation constraints for object detection in computer vision.