A medical data processing method for determining the spatial relationship of a first medical device relative to a second medical device, the method being constituted to be executed by a computer and comprising the following steps: d) acquiring first medical device position data comprising first medical device position information describing the position of the first medical device, wherein the first medical device position data is acquired based on reading, from a marker device having for example a fixed spatial relationship relative to the first medical device, the first medical device position information or information which allows access to the first medical device position information; e) acquiring second medical device position data comprising second medical position information describing the position of the second medical device; f) determining, based on the first medical device position data and the second medical device position data, relative position data comprising relative position information describing the spatial relationship of the second medical device relative to the first medical device.