A method includes, identifying, in a three-dimensional (3D) anatomical imageof apatient organ, multiple anatomical points corresponding to respectivepredefined locations on askin of the patient organ in a first coordinate system. Multiple positions ina second coordinatesystem, measured by a position sensor of a position-tracking system at therespectivepredefined locations on the skin of the patient organ, are received. At eachpredefined location,a distance is calculated between a respective anatomical point and closestbone tissue of thepatient organ. Weights are assigned to the predefined locations based onrespective distancesbetween the anatomical points and the closest bone tissue. The first andsecond coordinatesystems are registered, by correlating between the positions and therespective anatomicalpoints using the assigned weights.
