1. Method for registering a Medical Positioning System (MPS) coordinate system, and with a two dimensional (2D) coordinate system, the method comprising: acquiring at least one 2D image of a volume of interest, said volume of interest including an organ within the body of a patient, said 2D image being associated with said 2D coordinate system; acquiring a plurality of MPS points, within said organ, said MPS points being associated with said MPS coordinate system, said MPS coordinate system being registered with said 2D coordinate system; and estimating a volumetric model of said organ according to acquired MPS points.