“…The rotation of the cameras makes the external parameters (orientation and position of the cameras in the world reference frame) time-dependent quantities that have then to be carefully calibrated frame by frame to guarantee high accuracy in the reconstruction of the scene. The literature suggests two different calibration approaches [31]: i) 3D methods, which reconstruct key points of calibrated 3D targets and estimate the external parameters as the ones that minimize the 3D reconstruction error [32], [33], [34], [35], [36]; ii) 2D methods, which match features across the cameras, reconstruct the correspondent 3D points that are then projected back on the cameras, and estimate the external parameters as the ones that minimize the reprojection error [37], [38], [39], [40], [41], [42], [43], [44], [45].…”