1. A method for calibrating a three-dimensional optical measurement system, said method comprising the steps of: mechanically measuring three-dimensional coordinates at each of a plurality of points on a surface of a three-dimensional test calibration fixture; placing said test calibration fixture into the field of view of said optical measurement system; optically acquiring a set of data representing the phase at each of a plurality of pixels corresponding to said optical measurement system's view of the surface of said test calibration fixture; for both the mechanically measuring step and the optically acquiring step, calculating the intersection point of three faces on said surface to uniquely define an accurate correlation between three-dimensional coordinate position and measured phase at that location; and using an optimization procedure, calculating parameters of said three-dimensional optical measurement system, so as to minimize the difference between intersection point coordinates calculated from the mechanically measuring step and intersection point coordinates calculated from the optically acquiring step; and fixing said parameters based upon the results of the optimization procedure.