title: How to calculate the angle from rotation matrix
body: <p>I am using two image of the single object the object is roated certain degree from its first image.  </p>
  
  <p>I have calculated the POSE of each image and converted the rotational vector to Matrix using Rodergues().  Now how do I calculate and see how much it is rotated from its first position?</p>
  
  <p>I have tried many ways but answers was no were close</p>
  
  <p>EDIT: My camera is fixed only the object is moving.</p>