title: How to verify the correctness of calibration of a webcam?
body: <p>I am totally new to camera calibration techniques... I am using OpenCV chessboard technique... I am using a webcam from Quantum...</p>
  
  <p>Here are my observations and steps..</p>
  
  <ol>
  <li>I have kept each chess square side = 3.5 cm. It is a 7 x 5 chessboard with <strong>6 x 4</strong> internal corners. I am taking total of 10 images in different views/poses at a distance of 1 to 1.5 m from the webcam.</li>
  <li><p>I am following the C code in <strong>Learning OpenCV</strong> by <strong>Bradski</strong> for the calibration.
  my code for calibration is </p>
  
  <pre><code>cvCalibrateCamera2(object_points,image_points,point_counts,cvSize(640,480),intrinsic_matrix,distortion_coeffs,NULL,NULL,CV_CALIB_FIX_ASPECT_RATIO);
  </code></pre></li>
  <li><p>Before calling this function I am making the first and 2nd element along the diagonal of the intrinsic matrix as one to keep the ratio of focal lengths constant and using <code>CV_CALIB_FIX_ASPECT_RATIO</code></p></li>
  <li><p>With the change in distance of the chess board the <code>fx</code> and <code>fy</code> are changing with <code>fx:fy</code> almost equal to 1. there are <code>cx</code> and <code>cy</code> values in order of 200 to 400.  the <code>fx</code> and <code>fy</code> are in the order of 300 - 700 when I change the distance.</p></li>
  <li><p>Presently I have put all the distortion coefficients to zero because I did not get good result including distortion coefficients. My original image looked handsome than the undistorted one!!</p></li>
  </ol>
  
  <p>Am I doing the calibration correctly?. Should I use any other option than <code>CV_CALIB_FIX_ASPECT_RATIO</code>?. If yes, which one?</p>