通过计算方差，确定划分坐标轴，最后，将点云划分到一个个格子中，这样的好处在于可以将噪点和有效点分别存储于不同的格子中，方便进行去噪。(k-d tree create;By calculating the variance, the coordinate axis is determined. Finally, the point cloud is divided into a number of lattices. The advantage is that the noise and the effective points can be stored in the different lattice, so that the noise can be de-noised conveniently.)