计算的距离映射到一组点，使用快速行进算法。 解决了2-D恒定速度T= 1程函PDE。 这是不是很一般，但非常适合学习。-Compute the distance map to a set of points using the fast marching algorithm. Solves the 2-D eikonal PDE with constant speed T=1. It is not very general but well suited for learni