In flight simulation, a need exists for a display that represents the outside world as seen from the cockpit of a flying aircraft. Such a display is difficult to produce because (1) it must cover a large field of view, (2) it must simultaneously reproduce those terrain details that are very close to the simulated aircraft as well as those that are very far away, (3) it must exhibit high resolution over the entire field of view, and (4) it must respond smoothly and rapidly to all motions of the simulated aircraft over wide ranges of positions and attitudes. Many devices (visual simulators) have been constructed that attempt to produce such a display; examples include film-based devices, computed displays, direct optical viewers, and various television systems. Each type of visual simulator has its own characteristic advantages and limitations.
Charles A. Wagner,
"The Flying-Spot Scanner Applied To Visual Simulation", Proc. SPIE 0017, Photo-Optical Techniques in Simulators I, (28 October 1969); doi: 10.1117/12.946819; https://doi.org/10.1117/12.946819