A method includes transmitting electrical signalsbetween one or more pairs of body-surface electrodesattached to a body of a patient. Electrical potentialsresulting from the transmitted electrical signals areacquired by an outer-facing electrode and an inner-facingelectrode of a medical probe inserted in an organ of thepatient. A proximity of the medical probe to surface tissueof the organ is estimated based on the electricalpotentials acquired by the outer-facing electrode. Aposition of the medical probe within the organ is estimatedbased on the electrical potentials acquired by the inner-facingelectrode.
