In one embodiment, a system includes a catheter including an insertion tube and a first position sensor, a pusher including a second position sensor, and an expandable assembly including flexible strips disposed circumferentially around a distal portion of the pusher, with first ends of the strips connected to the distal end of the insertion tube and second ends of the strips connected to the distal portion of the pusher, the flexible strips bowing radially outward when the pusher is retracted, processing circuitry to receive a respective position signal from the first and second position sensors, compute location and orientation coordinates for the position sensors subject to a constraint that the position sensors are coaxial and have a same orientation, compute a distance between the computed location coordinates of the position sensors, and find position coordinates of the flexible strips responsively to at least the computed distance.