SURVEYING INSTRUMENT FOR ESTABLISHING A POINT IN A PLANE AND METHOD OF USE

摘要

A direction finding system is disclosed in which a predetermined horizontal plane is established by the projection from one location of an image having illuminated and unilluminated portions corresponding to the predetermined horizontal plane. A receiver at a remote location detects the image at two spaced points and produces an indication of the center of the transition zone between the illuminated and unilluminated portions of the projected image.