Registering method, position detecting system, and scanning instrument

1. A method for assigning position values, detected by means of a position detection system, to a topographic image of an object or body part, the method comprising the following steps:

providing a scanning instrument having a partly spherical scanning tip,

providing a topographic model of an object or body part having a model surface,

calculating from the model surface of said topographic model a virtual model surface that has a distance from the model surface, which equals a radius of the partly spherical scanning tip of the scanning instrument,

scanning a surface of the object or body part by means of said scanning instrument,

detecting position values that are related to the sphere center of the scanning tip during the scanning, and

assigning detected position values to points of said virtual surface of the topographic model.

2. A method according to claim 1 , characterized by the method step:

establishing a transformation prescription for transforming position values and/or coordinates of the position detection system to model position values and/or model coordinates of the topographic model, or vice versa.

3. A method according to claim 1 , wherein a position detection system comprising a field generator for an alternating electromagnetic field and comprising at least two position sensors, each with at least one electrical coil, is used as position detection system, of which position sensors one position sensor is connected to the object or body part in such a way that this position sensor maintains a fixed relative position in relation to the object or body part, while the other position sensor is fastened to the scanning instrument.

4. A method according to claim 1 , wherein the topographic model is recorded by means of a tomographic method.

5. A method according to claim 1 , wherein, when assigning the detected position values to corresponding positions in the topographic model, a plurality of position values recorded at different positions of the object or body part are assigned to points on the virtual model surface in such a way that this results in an error which is as small as possible in the case of linear scaling and rotation.

6. A position detection system, comprising:

a movable scanning instrument, the movable scanning instrument having a scanning tip with a partly spherical external surface and the sphere center of the sphere-shaped scanning tip serving as position reference point; and

a storage medium for a topographic model of an object or body part and being embodied to transfer position values detected by a movable instrument into a model coordinate system, underlying the topographic model, by means of a transformation prescription in such a way that position values detected by means of the scanning instrument with partly spherical scanning tip are assigned to points or positions on a model surface defined by the topographic model by virtue of the position detection system assigning position values, related to the sphere center of the scanning tip as position reference point, to a virtual surface which has a distance from a model surface defined by the topographic model, which distance corresponds precisely to the sphere radius of the partly spherical scanning tip.

7. A position detection system according to claim 6 , wherein the position detection system is furthermore embodied, for establishing the transformation prescription, to carry out an assignment of position values detected by means of the scanning instrument to points on a model surface defined by the topographic model by virtue of the position detection system determining a virtual model surface which has a distance from the model surface which equals the distance of the sphere center of the scanning tip from the sphere-shaped external surface thereof and assigning position values detected by means of the scanning instrument as precisely as possible to the virtual model surface while maintaining the relative position of said position values to one another.

8. The position detection system according to claim 6 , wherein the position detection system is a position detection system comprising a field generator for an alternating electromagnetic field and comprising at least two position sensors, each with at least one electrical coil, of which position sensors one position sensor is to be connected to the object or body part in such a way that this position sensor maintains a fixed relative position in relation to the object or body part, while the other position sensor is fastened to the scanning instrument.

9. The position detection system according to claim 6 , wherein the scanning instrument has a proximal end with a handle and a distal end with a partly spherical scanning tip, which is connected to the handle via a shank, and the position sensor of the scanning instrument is embodied to supply position values which supply a location and alignment of the scanning instrument in relation to a reference sensor, the position sensor having a known, fixed location from the sphere center of the partly spherical scanning tip and the position detection system being embodied to derive, from position values of the position sensor of the scanning instrument, position values of the sphere center of the partly spherical scanning tip as position reference values of the scanning instrument for assigning position values to points on a model surface defined by the topographic model.