OpenCV lacks a conversion function from rotation matrix to quaternion. In ROS applications, the rotation of a robot or link is generally described by 4 quaternion numbers. Some people might say that you have "tf" for all such transformations, but it requires your data to be of specific datatype. Here is a small function, that converts opencv Mat…

rotationMat2Quaternion.cpp

void getQuaternion(Mat R, double Q[])
{
    double trace = R.at<double>(0,0) + R.at<double>(1,1) + R.at<double>(2,2);
 
    if (trace > 0.0) 
    {
        double s = sqrt(trace + 1.0);
        Q[3] = (s * 0.5);
        s = 0.5 / s;
        Q[0] = ((R.at<double>(2,1) - R.at<double>(1,2)) * s);
        Q[1] = ((R.at<double>(0,2) - R.at<double>(2,0)) * s);
        Q[2] = ((R.at<double>(1,0) - R.at<double>(0,1)) * s);
    } 
    
    else 
    {
        int i = R.at<double>(0,0) < R.at<double>(1,1) ? (R.at<double>(1,1) < R.at<double>(2,2) ? 2 : 1) : (R.at<double>(0,0) < R.at<double>(2,2) ? 2 : 0); 
        int j = (i + 1) % 3;  
        int k = (i + 2) % 3;

        double s = sqrt(R.at<double>(i, i) - R.at<double>(j,j) - R.at<double>(k,k) + 1.0);
        Q[i] = s * 0.5;
        s = 0.5 / s;

        Q[3] = (R.at<double>(k,j) - R.at<double>(j,k)) * s;
        Q[j] = (R.at<double>(j,i) + R.at<double>(i,j)) * s;
        Q[k] = (R.at<double>(k,i) + R.at<double>(i,k)) * s;
    }
}

Thanks for sharing your code :)

Thank you :-)

My thanks as well! What is the license for this code? Much appreciated!

Thanks for sharing code!