title: How to derive camera rotation from 2d point
body: <p>I have a camera mounted on a tripod its motion is restricted to pan and tilt rotation.  It is looking at dot that is at a known location directly in front of the camera.  If the camera looks at the dot and gets the 2d coordinate of it, is it possible to deduce the camera's rotation so that I can overlay some 3d models properly aligned to the scene.</p>
  
  <p>I was thinking that it could be solved by reversing the formula that you would use to plot the 2d point you could derive a formula to take a 2d point and give back the camera rotation.</p>
  
  <p>I am thinking that the 2d plot would be something like
  Dot's 3d Target World Position * Camera Position Matrix * Camera Rotation Matrix * Perspective Matrix = 2d point</p>
  
  <p>Is it possible to derive the camera's rotation from the 2d point given that the camera and dot's position are known as well as the perspective matrix (I am assuming I should be able to guess at this and get close by tweaking the field of vision value)?</p>