title: How to convert camera extrinsic matrix to SCNCamera position and rotation
body: <p>I'm trying to achieve Augmented Reality with <code>SceneKit</code>.</p>
  
  <p>I got a intrinsic camera matrix and a extrinsic matrix by estimating pose of a marker, using ARuco (OpenCV augmented reality library).</p>
  
  <p>And I set up the <code>SCNCamera</code>'s <code>projectionTransform</code> with parameters of the intrinsic matrix (fovy, aspect, zNear, zFar).</p>
  
  <p>Normally in <code>OpenGL</code>, <strong>world coordinate relative to camera coordinate</strong> is calculated with ModelView but in SceneKit, there is no things such as modelView.</p>
  
  <p>So I calculated inverse matrix of the extrinsic matrix to get <strong>the camera coordinate relative to the world coordinate</strong>(the marker coordinate).</p>
  
  <p>And I think I've got correct camera's position by the inverse matrix which contains rotation and translate matrix.</p>
  
  <p>However I cannot get camera's <strong>rotation</strong> from that.</p>
  
  <p>Do you have any ideas?</p>