title: Camera pose estimation: How do I interpret rotation and translation matrices?
body: <p>Assume I have good correspondences between two images and attempt to recover the camera motion between them.
  I can use OpenCV 3's new facilities for this, like this:</p>
  
  <pre><code> Mat E = findEssentialMat(imgpts1, imgpts2, focal, principalPoint, RANSAC, 0.999, 1, mask);
  
   int inliers = recoverPose(E, imgpts1, imgpts2, R, t, focal, principalPoint, mask);
  
   Mat mtxR, mtxQ;
   Mat Qx, Qy, Qz;
   Vec3d angles = RQDecomp3x3(R, mtxR, mtxQ, Qx, Qy, Qz);
  
   cout &lt;&lt; "Translation: " &lt;&lt; t.t() &lt;&lt; endl;
   cout &lt;&lt; "Euler angles [x y z] in degrees: " &lt;&lt; angles.t() &lt;&lt; endl;
  </code></pre>
  
  <p>Now, I have trouble wrapping my head around what <code>R</code> and <code>t</code> actually mean. Are they the transform needed to map coordinates from camera space 1 to camera space two, as in <code>p_2 = R * p_1 + t</code>? </p>
  
  <p>Consider this example, with ground-truth manually labeled correspondences</p>
  
  <p><img src="https://i.stack.imgur.com/LY3MN.jpg" alt="enter image description here"></p>
  
  <p>The output I get is this:</p>
  
  <pre><code>Translation: [-0.9661243151855488, -0.04921320381132761, 0.253341406362796]
  Euler angles [x y z] in degrees: [9.780449804801876, 46.49315494782735, 15.66510133665445]
  </code></pre>
  
  <p>I try to match this to what I see in the image and come up with the interpretation, that <code>[-0.96,-0.04,0.25]</code> tells me, I have moved to the right, as the coordinates have moved along the negative x-Axis, but it would also tell me, I have moved further away, as the coordinates have moved along the positive z-Axis. </p>
  
  <p>I have also rotated the camera around the y-Axis (to the left, which I think would be a counter-clockwise rotation around the negative y-Axis because in OpenCV, the y-Axis points downwards, does it not?)</p>
  
  <p><strong>Question:</strong> Is my interpretation correct and if no, what is the correct one?</p>