1. A system for monitoring the position and orientation of non-visible structure of a body, the system comprising: a fiducial reference adapted to be rigidly attached to the body, the fiducial reference having at least one pattern segment; a three-dimensional tracking marker rigidly attached at a predetermined location in a predetermined orientation on an implement proximate the body; a tracker arranged to obtain image information about an area encompassing the fiducial reference and the marker; a computer system coupled to the tracker and having a previously obtained scan data of the body including internal structure of the body with the fiducial reference fixed to the body and including a processor with memory and a software program having a series of instructions for execution by the processor to determine the relative position and orientation of the marker and the fiducial reference relative to the internal structure of the body based on the image information and the scan data scan data; and a display system in communication with the computer system; wherein the system is characterized by at least one of the marker and the tracker being connected to the fiducial reference in a fixed relative position and orientation.