Method and system to determine the position of a land vehicle during movement over a predetermined path

In a vehicular navigation system,

• a method of indicating to a vehicle operator, from a known initial position, the current position of a land vehicle during movement over a predetermined path, and of navigating the vehicle, said system having
• a first, differential odometer, sensor (10) measuring direction and distance of movement, in any specific direction, of the vehicle, and providing first vehicle operating output signals having comparatively high short-term accuracy;
• a second, geomagnetic field, sensor (12) measuring directional orientation of the vehicle, and change thereof, with respect to a surrounding geomagnetic field, during movement of the vehicle over its predetermined path, and providing second, magnetic field, signals having comparatively high long-term accuracy;
• and
• a vehicle navigation computer (14),
• said method comprising the steps of
• storing said known initial vehicle position in said computer,
• differentiating, with respect to distance, said first output signals from the first sensor;
• integrating, with respect to distance, said second magnetic field output signals;
• combining said differentiated first signals and said integrated second signals to provide a third output signal of comparatively high accuracy both short-term and long-term;
• applying said third output signal, at regular intervals during travel by said vehicle, to said navigation computer (14), for updating of said stored initial vehicle position, thereby permitting regular mid-course correction of vehicle position data stored in said computer and keeping errors in said stored vehicle position data within predetermined acceptable tolerances;
• indicating the updated vehicle position to said vehicle operator;
• and steering the vehicle in accordance with said updated vehicle position indication.