A method for extrinsic calibration of cameras in a monitoring system, performed by a calibration device, includes obtaining preliminary calibration data of the cameras, obtaining a preliminary pose for an object observed by the cameras, and determining calibration data that results in an optimization of an objective function using the preliminary calibration data and the preliminary pose as starting values for the optimization. The method further includes defining the objective function with calibration data and pose as unknown variables and including a first function yielding aggregated reprojection error, and a second function yielding pose quality based on relative orientation and relative distance between 3D points of the pose. The second function enables improved accuracy of the calibration data and may be configured to yield pose quality for individual poses or motion quality for a time sequence of poses.