title: Aruco markers with openCv, get the 3d corner coordinates?
body: <p>I am detecting a printed Aruco marker using opencv 3.2:</p>
  
  <pre><code>aruco::estimatePoseSingleMarkers(corners, markerLength, camMatrix, distCoeffs, rvecs,tvecs);
  </code></pre>
  
  <p>this returns a translation and rotation vector for the marker. What I need, is the 3d coordinates for each corner of the marker.</p>
  
  <p>As i know the marker length, i could do something like</p>
  
  <pre><code>corner1 = tvecs[0] - markerlength /2;
  corner2 = tvecs[0] + markerlength /2;
  </code></pre>
  
  <p>....</p>
  
  <p>But is there an better way? Or an existing function?
  To sum up, I have:</p>
  
  <p>a 3d point in the center of a 2d square.</p>
  
  <p>the length of the sides of that square.</p>
  
  <p>the rotation value of the square.</p>
  
  <p>How can I find the 3d coordinates of the corners?</p>