Apparatus for mapping and/or ablation of cardiac tissue, comprising: a catheter body, shaped to define a lumen thereof, a distal end of the catheter body comprising one or more electrodes (29, 31); and a catheter shaft that comprises an electromagnetic sensor, the shaft being configured to be placed inside the lumen of the catheter body; the apparatus further comprising: an electrical interface; and a processor, configured to: ascertain a position and an orientation of a distal end of the catheter body with respect to the sensor (DE_S), based on: (a) an indication of the distal end of the catheter body shown in a calibration image taken by an imaging system, and (b) a signal from the electromagnetic sensor, but not based on any indication of the electromagnetic sensor shown in the calibration image; and using the ascertained position and orientation of the distal end of the catheter body with respect to the electromagnetic sensor, drive a display to generate a visual output, wherein the processor is configured to drive the display to generate the visual output by driving the display to superimpose a visual representation of the distal end of the catheter body on an image of a portion of the body of the subject and wherein the visual representation of the distal end of the catheter body includes a visual representation of the one or more electrodes. a catheter body, shaped to define a lumen thereof, a distal end of the catheter body comprising one or more electrodes (29, 31); and a catheter shaft that comprises an electromagnetic sensor, the shaft being configured to be placed inside the lumen of the catheter body; an electrical interface; and a processor, configured to: ascertain a position and an orientation of a distal end of the catheter body with respect to the sensor (DE_S), based on: (a) an indication of the distal end of the catheter body shown in a calibration image taken by an imaging system, and (b) a signal from the electromagnetic sensor, but not based on any indication of the electromagnetic sensor shown in the calibration image; and using the ascertained position and orientation of the distal end of the catheter body with respect to the electromagnetic sensor, drive a display to generate a visual output, wherein the processor is configured to drive the display to generate the visual output by driving the display to superimpose a visual representation of the distal end of the catheter body on an image of a portion of the body of the subject and wherein the visual representation of the distal end of the catheter body includes a visual representation of the one or more electrodes. ascertain a position and an orientation of a distal end of the catheter body with respect to the sensor (DE_S), based on: (a) an indication of the distal end of the catheter body shown in a calibration image taken by an imaging system, and (b) a signal from the electromagnetic sensor, but not based on any indication of the electromagnetic sensor shown in the calibration image; and (a) an indication of the distal end of the catheter body shown in a calibration image taken by an imaging system, and (b) a signal from the electromagnetic sensor, but not based on any indication of the electromagnetic sensor shown in the calibration image; and using the ascertained position and orientation of the distal end of the catheter body with respect to the electromagnetic sensor, drive a display to generate a visual output, wherein the processor is configured to drive the display to generate the visual output by driving the display to superimpose a visual representation of the distal end of the catheter body on an image of a portion of the body of the subject and wherein the visual representation of the distal end of the catheter body includes a visual representation of the one or more electrodes.