// Taken from http://docs.opencv.org/3.0-beta/doc/tutorials/calib3d/camera_calibration/camera_calibration.html
float computeReprojectionErrors(List <Mat> objectPoints, List <Mat> imagePoints, List <Mat> rvecs, List <Mat> tvecs, Mat cameraMatrix, Mat distCoeffs, List <float> perViewErrors)
{
MatOfPoint2f imagePoints2 = new MatOfPoint2f();
int i, totalPoints = 0;
float totalErr = 0, err;
int numItems = objectPoints.Count;
for (i = 0; i < numItems; ++i)
{
MatOfPoint3f objectPointsi = new MatOfPoint3f(objectPoints[i]);
MatOfPoint2f imagePointsi = new MatOfPoint2f(imagePoints[i]);
MatOfDouble distCoeffsv2 = new MatOfDouble(distCoeffs);
Calib3d.projectPoints(objectPointsi, rvecs[i], tvecs[i], cameraMatrix, distCoeffsv2, imagePoints2);
err = norml2(imagePointsi, imagePoints2); // difference
Size temp = objectPoints[i].size();
int n = (int)temp.height;
perViewErrors.Add(Mathf.Sqrt(err * err / (n))); // save for this view
totalErr += err * err; // sum it up
totalPoints += (int)n;
}
return(Mathf.Sqrt(totalErr / totalPoints)); // calculate the arithmetical mean
}