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A new approach to the informational processing in a terrain-following control system uses a cubic-spline curve to provide a very smooth reference path for the aircraft to follow. The spline is optimally computed to lie as close as possible to the terrain and yet to satisfy the practical constraints. Since the computed optimal path is smoother than those of other systems, the path and its derivatives can be used in a simple tracking system to provide precise control over the aircraft path. The scheme has onboard potential for advanced terrain-following systems, since splines allow consideration of fewer computational data points.
James E. Funk (Tue,) studied this question.