a method of steering a laser beam from an instrument toward a point on a retroreflector , including : intercepting with the retroreflector a cone of light from the instrument ; obtaining a first image of retroreflected light on a photosensitive array and transmitting an electrical data signal in response ; determining a position on the photosensitive array of the first image ; calculating first and second angular increments to steer the laser beam to the point ; rotating the first and second motors to intercept with the position detector the retroreflected laser beam and to place the laser beam at a preferred location on the position detector ; measuring fifth and sixth angles with first and second angle transducers ; measuring a distance with a distance meter ; and determining three - dimensional coordinates of the point based at least in part on the fifth angle , the sixth angle , and the distance .