A system for tracking a catheter in a patient. The system including a plurality of surface electrodes and a surface patch attached to the patient and a processor coupled to the plurality of surface electrodes and the surface patch. The processor determines a location of at least one of the plurality of surface electrodes, stores locations of the surface patch and the at least one of the plurality of surface electrodes, determines a three-dimensional shell shape that corresponds to a portion of the patient, determines a model of an impedance tracking field in at least a portion of the three-dimensional shell shape, injects current through one or more of the plurality of surface electrodes, fits measured voltages from the catheter to the model of the impedance tracking field to determine locations of the catheter, and provides therapy to the patient based on the locations of the catheter.
