title: Wide angle lenses calibration with Opencv
body: <p>I'm using a wide-angle lens (178º Diagonal FOV ) and I'm trying to calibrate it properly using Opencv Calibration module. All the detection and calibration process are working fine, but the result is very poor.</p>
  
  <p>I have tried many different configurations:</p>
  
  <ul>
  <li>Different set of images</li>
  <li>Different radial coefficient numbers: 2,3,4,5 even 6.(CV_CALIB_FIX_K1,...,CV_CALIB_FIX_K6 )</li>
  <li>Fixing principal point and tangential disortion to 0 (CV_CALIB_FIX_ASPECT_RATIO,  CV_CALIB_FIX_PRINCIPAL_POINT)</li>
  <li>Using expected focal length as initial camera matrix. (CV_CALIB_USE_INTRINSIC_GUESS)</li>
  </ul>
  
  <p>The best I can get is something like:<img src="https://i.stack.imgur.com/fiMKm.png" alt="Bad calibration"></p>
  
  <p>Any ideas about how could I get a good calibration?
  Do you think using two calibrattion patterns at the same time, or using a circles grid as calibration pattern would help?</p>
  
  <p>I've seen in opencv 3.0 thin prism coeffs are added. I haven't tried it, but I don't think there will make a difference, right? Edit: Checked it... Nothing</p>