A medical probe tracking system, comprising: a plurality of body surface electrodes configured to be applied to a skin surface of a living subject; a first probe configured to be inserted into a body of the living subject and comprising first probe electrodes; a second probe configured to be inserted into the body of the living subject and comprising second probe electrodes (52a, 52b) and a magnetic field sensor; a magnetic field generator configured to generate a magnetic field within the body of the living subject; a display; and processing circuitry configured to: measure (102, 122) first and second electrical currents between the body surface electrodes and the first and second probe electrodes within the body, respectively; compute first position coordinates of the first probe in a first coordinate frame responsively to a distribution of the first electrical currents; receive magnetic position signals from the magnetic field sensor in response to the magnetic field; render to the display an initial three-dimensional representation of the first probe in the first coordinate frame and then compute a current-position map between a distribution of the second electrical currents and the magnetic position signals with respect to a second coordinate frame defined by the magnetic field generator; find a transformation between the first and second coordinate frames; apply the transformation to the first position coordinates yielding second position coordinates of the first probe in the second coordinate frame; and render to the display a modified 3D representation of the first probe according to the second position coordinates in the second coordinate frame. a plurality of body surface electrodes configured to be applied to a skin surface of a living subject; a first probe configured to be inserted into a body of the living subject and comprising first probe electrodes; a second probe configured to be inserted into the body of the living subject and comprising second probe electrodes (52a, 52b) and a magnetic field sensor; a magnetic field generator configured to generate a magnetic field within the body of the living subject; a display; and processing circuitry configured to: measure (102, 122) first and second electrical currents between the body surface electrodes and the first and second probe electrodes within the body, respectively; compute first position coordinates of the first probe in a first coordinate frame responsively to a distribution of the first electrical currents; receive magnetic position signals from the magnetic field sensor in response to the magnetic field; render to the display an initial three-dimensional representation of the first probe in the first coordinate frame and then compute a current-position map between a distribution of the second electrical currents and the magnetic position signals with respect to a second coordinate frame defined by the magnetic field generator; find a transformation between the first and second coordinate frames; apply the transformation to the first position coordinates yielding second position coordinates of the first probe in the second coordinate frame; and render to the display a modified 3D representation of the first probe according to the second position coordinates in the second coordinate frame. measure (102, 122) first and second electrical currents between the body surface electrodes and the first and second probe electrodes within the body, respectively; compute first position coordinates of the first probe in a first coordinate frame responsively to a distribution of the first electrical currents; receive magnetic position signals from the magnetic field sensor in response to the magnetic field; render to the display an initial three-dimensional representation of the first probe in the first coordinate frame and then compute a current-position map between a distribution of the second electrical currents and the magnetic position signals with respect to a second coordinate frame defined by the magnetic field generator; find a transformation between the first and second coordinate frames; apply the transformation to the first position coordinates yielding second position coordinates of the first probe in the second coordinate frame; and render to the display a modified 3D representation of the first probe according to the second position coordinates in the second coordinate frame.