Nearest_Orthonormal_Matrix

代码说明：

  Finding the Nearest Orthonormal Matrix In some appoaches to photogrammetric problems (perhaps inspired by projective geometry), an estimate M of an orthonormal matrix R representing rotation is recovered. It is then desired to find the “nearest’’ orthonormal matrix. While this two step approach — first finding a “best fit’’ matrix without enforcing orthonormality,and then finding the nearest orthonormal matrix — is not to be recommended, it may be of interest to find a solution to this problem nevertheless.