1. A method of determining in a three-dimensional operating space a measure of super-imposition M between at least a portion of an object and a spatial representation of the object or part thereof in an object representation pose, a pose comprising position and orientation in operating space, the method comprising: a) obtaining a similarity measure S between a first imaging data taken in first respective imaging poses of the object or part thereof and second imaging data comparable to the first imaging data taken in second respective imaging poses that are digitally reconstructed from the spatial representation of the object or part thereof in the object representation pose; b) locating in operating space at least one point on the surface of the object or part thereof; c) obtaining a distance measure D between the at least one point in operating space and a surface of the spatial representation of the object or part thereof in the object representation pose; and d) obtaining a measure of superimposition M by a combination of the similarity measure S and the distance measure D.