calibration transformation matrices

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Hi all,

I am using the OpenCV calibration code from this tutorial: http://docs.opencv.org/doc/tutorials/calib3d/camera_calibration/camera_calibration.html#cameracalibrationopencv

Here is the arguments list for the calibration function: runCalibration(s,imageSize, cameraMatrix, distCoeffs, imagePoints, rvecs, tvecs, reprojErrs, totalAvgErr);

rvecs and tvecs are essentially the rotational and transnational components of the Homogeneous transformation matrix.

My question is the following:

does the transformation matrix( using rvecs, tvecs) take us from:

calibration grid coordinate system to the camera coordinate system

or

from camera coordinate system to the calibration grid coordinate system.

Thanks,

Paul