各种(空间)角度的计算方法以前自己的立体几何学的不好，各种计算方法全都忘记的差不多了，在这里整理与总结一下，便于以后查询和分享吧
1.两向量间夹角Calculate the 3D angle between two vectors
The angle between two three-element vectors, P1 and P2, can be calculated using matlab in the following way:
a = atan2(norm(cross(P1,P2)),dot(P1,P2)); % Angle in radians
The angle will lie between 0 and pi radians. To get degrees use ‘atan2d’.
Note: However, the cosine of such an angle can be calculated as:
cosine of the angle = dot(P1,P2)/(norm(P1)*norm(P2))
No need to compute the angle itself.