Patent US 5,155,684

A vehicle primarily for unmanned operation is equipped with a video camera pointed up, and progressively records in an on-board computer memory the observed locations of points derived from overhead features such as pre-existing overhead lights in a building during a manually driven teaching mode trip along a desired course. On subsequent unmanned trips, the vehicle directs itself along the chosen course by again observing the overhead features, deriving points from them and comparing the locations of those points to the locations of the points that were recorded during the teaching mode trip. It then corrects its steering to bring the errors between the observed locations and the recorded locations to zero, thereby directing the vehicle to automatically follow the course that was followed during the teaching mode trip.