METHOD AND APPARATUS FOR DETERMINING THE POSITION OF A RETROREFLECTIVE ELEMENT

A method and system for determining the position of at least one position retroreflective element in a predetermined frame of reference using two benchmark positions of known coordinates. A light transmitting and detecting means and a reference retroreflective element are oppositely positioned at a primary benchmark position located at known first coordinates and a secondary benchmark position located at known second coordinates. The light transmitting and detecting means takes angular measurements by sensing a reflected light beam from the position and reference retroreflective elements. After taking angular measurements in the above configuration, the light transmitting and detecting means and the reference retroreflective element are transposed and additional angular measurements are taken. From the angular measurements, the position of the position retroreflective element is determined in the coordinate frame of reference. In addition, the light transmitting and detecting means may be further positioned at an intermediate benchmark position having unknown coordinates. After determining the coordinates of the intermediate benchmark position, angular measurements taken at the intermediate benchmark position are compared with the angular measurements from the primary and secondary benchmark positions and the most accurate measurements are used to determine the position of at least one position retroreflective element.