title: How to calculate the focal length in mm by the result of camera calibration?
body: <p>The focal length in the camera-calibration result is in pixels,but i need the value in mm.How to calculate?</p>
  
  <p>I used OpenCV to calibrate the camera and got the internal parameter matrix.I also get the camera sensor size in the logitech community.</p>
  
  <pre><code>the camera matrix is
  [1432.379199223981, 0, 949.4032591833937;
   0, 1432.97806149025, 518.5291260500587;
   0, 0, 1]
  and the size of sensor is 6.00mm, width of 4.80mm and height of 3.60mm (16:9 format).
  </code></pre>
  
  <p>I want to get the focal length in mm ,how to calculate?</p>