根据协变矩阵和求最小特征值的方法求出三维点云数据的法向，根据OpenGL实现可视化,程序实用.-Noraml directions of 3D points can be obtained by calculating the smallest eigenvalue of covariance matrix, also, the method can be visualized by OpenGL, which is practical.

l1-magic，快速求解l1最小化的算法-l1-magic，fast l1 minisize matlab code