1. A method for geometrical calibration of a volumetric imaging system, the method comprising: computing a projection error between estimated locations of a set of markers of a phantom based on an estimated imaging geometry and observed locations of the respective markers for at least one projection image; decomposing the computed projection error into two or more different, specific error components corresponding to respective parameters of the estimated imaging geometry, wherein the two or more different, specific error components are independent of each other; and updating at least one parameter of the estimated imaging geometry based on at least one of the two or more error components.