1. A registration method for detecting the position and alignment of an object or body part in relation to a position detection system, wherein the method comprises the following steps: arranging a reference sensor on the object or body part and/or on an image sensor unit, detecting the position of the reference sensor by means of the position detection system, photogrammetrically detecting a surface of the object or body part and of the reference sensor by means of the image sensor unit, producing a surface model of the object or body part based on photogrammetrically detected information, determining the position of the reference sensor in the surface model, correlating the surface model with a coordinate system of the position detection system on the basis of the determined position of the reference sensor in the surface model and on the basis of the position of the reference sensor detected by means of the position detection system.