Patent ID: 8666661

Claim:
A method of navigation for an aircraft, the method comprising: during a period when a primary GPS navigation system is operating: (a) capturing a first image frame and subsequent second image frame of ground features from a video camera mounted on the aircraft, (b) identifying a set of feature points in the first and second image frames by dividing each image frame into grid cells each having a plurality of points, selecting from each grid cell a single point with a largest gradient as the largest gradient point for the corresponding grid cell, and identifying the set of feature points as those largest gradient points that exceed a threshold gradient, (c) determining a change of position of the feature points by how they are mapped from the first image frame to the second image frame including identifying feature points that are moving with respect to a background of the first image frame by determining expected positions of the feature points on the second image frame based upon a position of the feature points in the first image frame and based upon a predetermined motion of the aircraft, wherein moving feature points are removed from the set of identified feature points, (d) within a processor, translating the change of position for the feature points into a video-determined change of position for the aircraft, and estimating bias errors in the video-determined change of position using a GPS-derived change of position to obtain an on-line calibration of the bias errors; and during a period of loss of a primary GPS navigation solution: repeating acts (a) through (d) to obtain the video-determined change of position, correcting the video-determined change of position according to the bias errors to provide a corrected video-determined change of position, periodically determining position fixes to update the corrected video-determined change of position, and navigating the aircraft by dead reckoning based upon the aircraft's corrected video-determined change of position.