title: Obtain Rotation Axis from Rotation Matrix and translation vector in OpenCV
body: <p>I have a chessboard in two images with some angle of rotation. Lets find the rotation angle of second image with reference of first image. </p>
  
  <p>For that I found the Rotation Matrix (3x3) and translation matrix (3x1) of those objects. </p>
  
  <p>How can I find the <strong>Rotation Angle</strong> and <strong>Rotation Axis</strong> of object using those matrices?</p>