A system comprising: a catheter configured to be inserted into a body-part of a living subject, and comprising: an insertion tube including a distal end, and a first coil-based position sensor disposed at the distal end; a pusher including a second coil-based position sensor disposed thereon and a distal portion, and being configured to be advanced and retracted through the insertion tube; and an expandable assembly comprising a plurality of flexible strips disposed circumferentially around the 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 being configured to bow radially outward when the pusher is retracted; at least one magnetic field radiator configured to transmit alternating magnetic fields into a region where the body-part is located, the first and second position sensors being configured to output respective first and second position signals in response to the transmitted alternating magnetic fields; and processing circuitry configured to: receive the first and second position signals from the first and second position sensors; compute location and orientation coordinates for the first and second position sensors using a position computation in which the location and orientation coordinates of each of the position sensors are interdependently computed in an iterative manner responsively to the respective received position signals, and subject to a constraint that the first and second position sensors are coaxial; compute a distance between the computed location coordinates of the first position sensor and the computed location coordinates of the second position sensor; and estimate respective positions of the flexible strips responsively to at least the computed distance. a catheter configured to be inserted into a body-part of a living subject, and comprising: an insertion tube including a distal end, and a first coil-based position sensor disposed at the distal end; a pusher including a second coil-based position sensor disposed thereon and a distal portion, and being configured to be advanced and retracted through the insertion tube; and an expandable assembly comprising a plurality of flexible strips disposed circumferentially around the 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 being configured to bow radially outward when the pusher is retracted; an insertion tube including a distal end, and a first coil-based position sensor disposed at the distal end; a pusher including a second coil-based position sensor disposed thereon and a distal portion, and being configured to be advanced and retracted through the insertion tube; and an expandable assembly comprising a plurality of flexible strips disposed circumferentially around the 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 being configured to bow radially outward when the pusher is retracted; at least one magnetic field radiator configured to transmit alternating magnetic fields into a region where the body-part is located, the first and second position sensors being configured to output respective first and second position signals in response to the transmitted alternating magnetic fields; and processing circuitry configured to: receive the first and second position signals from the first and second position sensors; compute location and orientation coordinates for the first and second position sensors using a position computation in which the location and orientation coordinates of each of the position sensors are interdependently computed in an iterative manner responsively to the respective received position signals, and subject to a constraint that the first and second position sensors are coaxial; compute a distance between the computed location coordinates of the first position sensor and the computed location coordinates of the second position sensor; and estimate respective positions of the flexible strips responsively to at least the computed distance. receive the first and second position signals from the first and second position sensors; compute location and orientation coordinates for the first and second position sensors using a position computation in which the location and orientation coordinates of each of the position sensors are interdependently computed in an iterative manner responsively to the respective received position signals, and subject to a constraint that the first and second position sensors are coaxial; compute a distance between the computed location coordinates of the first position sensor and the computed location coordinates of the second position sensor; and estimate respective positions of the flexible strips responsively to at least the computed distance.