The application concerns a method of determining in a three-dimensional operating space a measure of super-imposition M between an object or a portion thereof, referred to as object, and a spatial representation of the object, referred to as object representation, in an object representation pose, a pose comprising position and orientation in operating space, the method comprising:a) obtaining a similarity measure S (350) between the first imaging data (320) taken in first respective imaging poses of the object and second imaging data (310) comparable to the first imaging data taken in second respective imaging poses which are digitally reconstructed (340) from the object representation in the object representation pose,b) locating in operating space at least one point on the surface of the object (330) andc) obtaining a distance measure D (355) between the at least one point in operating space and a surface of the object representation in the object representation pose, characterized in that the method further comprises obtaining a measure of superimposition M (360) by a combination of the similarity measure S and the distance measure D and an apparatus for performing the method.
