title: How to calculate the rotated angle from OpenCV rvecs
body: <p>I am using aruco markers to get the location of a robot. After getting the pose from the estimatePoseSingleMarkers i obtain the rvecs and tvecs for a given marker. From this how could i obtain the rotated angle of the marker about each axis. </p>
  
  <p>i used the code below to detect and draw the aruco markers along with its axis</p>
  
  <pre><code>while(true)
  {
      vector&lt; vector&lt;Point2f&gt;&gt; corners; //All the Marker corners 
      vector&lt;int&gt; ids;
  
      cap &gt;&gt; frame;
      cvtColor(frame, gray, CV_BGR2GRAY);
  
      aruco::detectMarkers(gray, dictionary, corners, ids);
      aruco::drawDetectedMarkers(frame,corners,ids);
      aruco::estimatePoseSingleMarkers(corners, arucoMarkerLength, cameraMatrix, distanceCoefficients, rvecs, tvecs);
  
      for(int i = 0; i &lt; ids.size(); i++)
      {
          aruco::drawAxis(frame, cameraMatrix, distanceCoefficients, rvecs[i], tvecs[i], 0.1f);
      }
  
      imshow("Markers", frame);
      int key = waitKey(10);
      if((char)key == 'q')
          break;
  }
  </code></pre>