Reference Structure For A Tracking System

A method of determining a position of an instrument within a volume of a patient with a reference member, comprising:

• injecting a current into the patient with a set of axis electrodes connected to the patient;
• evaluating an electrical property relative to the patient based on an input of a first reference electrode that is positioned on the patient, wherein the input includes measuring a voltage drop at an interface between the patient and at least one of the axis electrodes;
• evaluating the electrical property within the patient based at least in part on sensing with a position element on an instrument positioned within the patient;
• and
• determining a position of the instrument based on the evaluated electrical property;
• generating a map based on the plurality of determined positions of the instrument;
• displaying the map;
• determining a position of the first reference electrode relative to the displayed map based on the evaluated electrical property at the first reference electrode;
• and
• displaying the determined position of the first reference electrode relative to the displayed map.

A method of determining the position of an instrument within a volume of a patient, comprising:

• operating a position sensing unit to drive at least three sets of electrodes positioned on the patient to inject a current along three substantially orthogonal axes into the volume of the patient between each set of the at least three sets of electrodes;
• fixedly positioning a first reference electrode on a ventral surface of the patient at a directly over the xiphoid process at a first reference position;
• fixedly positioning a second reference electrode on a dorsal surface of the patient second reference position across from the first reference position;
• and
• operating the position sensing unit to evaluate an electrical property sensed with both the first reference electrode and the second reference electrode based on the injected current into the volume of the patient along the three substantially orthogonal axes;
• and
• automatically determining a first reference electrical property at a first reference position defined by a first reference electrode and a second reference electrical property at a second reference position defined by a second reference electrode to at least one of determine a respiratory cycle based on the evaluated electrical property with both of the first reference electrode and the second reference electrode or monitor a cardiac cycle based on the evaluated electrical property with both of the first reference electrode and the second reference electrode.