A method for removing ghost markers from a measured set of medical markers, wherein the measured set of markers represents the positions of real markers and the positions of ghost markers, comprising the steps of: —；calculating all possible minimal marker sets, wherein a minimal marker set is a subset of the measured set and a minimal marker set consists of the smallest possible number of markers which would cause the measured set to be measured； —；calculating the smallest extent of each minimal marker set, wherein the smallest extent is the smallest extent among the extents in three orthogonal directions； and —；selecting the minimal marker set having the smallest out of the smallest extents as a marker set without ghost markers.
