A medical tool includes a location sensor at a distal end. While the tool is being maneuvered to a desired region of interest, a control unit records a first location reading obtained according to an output from the sensor when requested by a user, indicative of when a patient's anatomy constrains free movement of the tool in at least one degree of freedom. Once the tool has reached the region of interest, the control unit records a second location reading according to the sensor output indicative of a current location. A relaxation shape of the tool forms a shape constraint on the tool shape reconstruction. The control unit determines a reconstruction representing the current shape of the tool based on the positional constraints and the shape constraint. The reconstruction is graphically superimposed on an image of the region of interest.