有关2D凸包的算法，1. 排序更简单，只是简单的比较，没有运算. 2. 起始点更好找，就是排序后的第一个点. 3. 可以很好地处理特殊情况(共线).-The 2D convex hull algorithm, 1. Sorting easier, just a simple comparison, there is no operation. 2. To find a better starting point, that is sort of a point after the fir