how to find the rotated angle of aruco marker

edit

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. i used the code below to detect and draw the aruco markers along with its axis.

while(true)
{
vector< vector<Point2f>> corners; //All the Marker corners 
vector<int> ids;

cap >> 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 < 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;
}