Abstract: A system for tracking motion of an object comprises at least a first magnetic source configured to generate a static magnetic field, with the magnetic source fixed in a first coordinate frame, and a plurality of magnetic sensors configured to be located on the object and to detect the static magnetic field. The magnetic sensors are located in a second coordinate frame that is movable relative to the first coordinate frame. A processor is operative to receive magnetic field data from the magnetic sensors. A memory unit coupled to the processor stores a magnetic field model or a magnetic field database defined for the first coordinate frame, and a magnetic sensor measurement model with uncertainties defined for the second coordinate frame. The processor computes and outputs an estimated position and orientation of the object based on the magnetic field data and other information stored in the memory unit.