title: How can I convert cordinates from rectified stereo to original coordinates in opencv?
body: <p>I am using this code to rectify stereo pair of images:</p>
  
  <pre><code>stereoRectify(cm, Mat(), cm, Mat(),imageSize,
      RT_d,tt,R1,R2,P1,P2,Q,CALIB_ZERO_DISPARITY,
      0.9, imageSize, &amp;validROI[0], &amp;validROI[1]);
  
  initUndistortRectifyMap(cm, Mat(), R1, P1, imageSize, CV_16SC2, rmap[0][0], rmap[0][1]);
  initUndistortRectifyMap(cm, Mat(), R2, P2, imageSize, CV_16SC2, rmap[1][0], rmap[1][1]);
  remap(v1.img, rimg1, rmap[0][0], rmap[0][1], INTER_LINEAR);
  remap(v2.img, rimg2, rmap[1][0], rmap[1][1], INTER_LINEAR);
  </code></pre>
  
  <p>Rectification works successfully.</p>
  
  <p>Now I need to match each pixel (x,y) in rectified image rimg1 to initial pixel (x0,y0) in v1.img. How can I do it? Where can I get formulae, how to use P1 and R1? Thanx!</p>