An apparatus includes a shaft, a flexible distal-end assembly, two or more sensing-electrodes, and a fiber-optic shape sensor. The shaft is configured for insertion into a body of a patient. The flexible distal-end assembly is fitted at a distal end of the shaft. The two or more sensing-electrodes are disposed over the distal-end assembly and are configured to generate signals indicative of positions of the sensing-electrodes in the body. The fiber-optic shape sensor is coupled to a portion of the distal-end assembly, wherein the two or more sensing-electrodes have α-priori known distances from a known location over the fiber-optic shape sensor, and wherein the fiber-optic shape sensor is configured to provide an indication of a spatial deformation of the flexible distal-end assembly.
