1. A method for determining the location and orientation of a fiducial reference in three dimensions, the method comprising a. disposing the fiducial reference to render a part of the fiducial reference observable by a tracker; b. obtaining from the tracker scan data of the part of the fiducial reference that is observable by the tracker; c. obtaining predetermined geometric information about location points on the fiducial reference, the geometric information comprising three-dimensional coordinates of the location points relative to the structure of the fiducial reference; d. identifying within the scan data at least three location points having coordinates arranged along at least two non-parallel lines in the predetermined geometric information; and e. determining the three-dimensional location and orientation of the fiducial reference from the scan data and from the coordinates of the at least three identified location points in the predetermined geometric information.