title: understanding opencv stereoCalibrate function output
body: <p>I have a dual camera set up and trying to make AR things on it. after stereo calibration and rectification, left and right image works great, epipolar line align well. </p>
  
  <p>I detect the AR marker with one image and would like to render it on the other image with proper camera shift. </p>
  
  <p>stereoCalibration gives the relation between two camera like: </p>
  
  <pre><code>R: !!opencv-matrix
     rows: 3
     cols: 3
     dt: d
     data: [ 9.9922768917754268e-001, 2.4924911359451081e-002,
         3.0377194976358678e-002, -2.4063699016973375e-002,
         9.9930712233274999e-001, -2.8393901539922377e-002,
         -3.1063862775397383e-002, 2.7640984945580323e-002,
         9.9913513219219230e-001 ]
  T: !!opencv-matrix
     rows: 3
     cols: 1
     dt: d
     data: [ -5.5054479009004126e+001, -7.1894766441986058e-001,
         -2.8661303301073544e+000 ]
  </code></pre>
  
  <p>how should I understand this? particularly the translation vector[-55.05,-0.718, -2.866]? is this in pixel unit?</p>
  
  <p>in the rendering part, I use Ogre and makes a customized projection matrix(obtained from the camera calibration matrix). I make a translation matrix with vector[x,y,z], and multiple it to the customized projection matrix. In what unit would these correlated? snap of my code works like: </p>
  
  <pre><code>double pMatrix[16];
      camParams.OgreGetProjectionMatrix(camParams.CamSize,camParams.CamSize, pMatrix, 0.05,50, false);
      Ogre::Matrix4 PM(pMatrix[0], pMatrix[1], pMatrix[2] , pMatrix[3],
              pMatrix[4], pMatrix[5], pMatrix[6] , pMatrix[7],
              pMatrix[8], pMatrix[9], pMatrix[10], pMatrix[11],
              pMatrix[12], pMatrix[13], pMatrix[14], pMatrix[15]);    
  
  .....
  
  //translate the camera a little for the right display
      Ogre::Matrix4 matrix_translate;
      matrix_translate.makeTrans(Ogre::Vector3(-0.3,0.0,0.0));
      Ogre::Matrix3 matrix_rotate;
  
      camera_right-&gt;setCustomProjectionMatrix(true, matrix_translate*PM);
      camera_right-&gt;setCustomViewMatrix(true, Ogre::Matrix4::IDENTITY);   
  </code></pre>