photographic land surveying technique used by airport management to document obstructions or possible obstructions located at each runway end The technique is the first of its kind to provide a pictorial record of the approach and takeoff zones located at the end of every runway The photograph, along with a specially designed overlay, illustrates and aids in the location of all clear zone obstructions An obstruction is defined as any building, sign, utility pole, or tree which breaks through the imaginary plane called the approach surface A survey crew sets control points at the end of each runway being analyzed The terrestrial land camera is then mounted on top of the survey instrument and three photographs are taken across the end of the runway The photographs are then processed, and analyzed by means of a computer program The results identify possible obstructions which break the imaginary approach surface