A method for determining a transformation of a three-dimensional pre-operative image data set to obtain a registration of the three-dimensional image data with an X-ray imaging system. In one aspect of the present invention, the method comprises the steps of the user identifying a center point and extreme contour points of the object from an X-ray image, obtaining a set of contour points for the image object in each of a plurality of section-planes, and selecting from a sampling of section-planes the points projecting nearest to the user-identified extreme points. The method then defines a grid having a predetermined number of intervals at a predetermined interval spacing with the grid center at the user-identified center of the pre-operative image, and performs a projection of the center point of the three-dimensional image data set onto each grid point for evaluation and selection of the grid point projecting nearest to the user-identified center. Registration of a three dimensional image data will allow, among other things, overlay of a visual representation of a pre-operative image object onto an X-ray image plane that can serve as a visual tool and a surgical navigation aid.