1. A method for obtaining a registration of three-dimensional image data with an X-ray imaging system, the method comprising the steps of: obtaining a set of contour points for the image object in each of a plurality of section-planes; the user identifying at least two extreme opposing points on the object in the subject body from at least one X-ray image plane; performing a projection of each contour point on a sampling of the plurality of section-planes for evaluation; selecting the section-plane with the contour point projecting nearest to the user-identified extreme point.