Abstract: A vehicle navigation system computes an optimal route for a journey. When the system detects that a vehicle has deviated from the optimal route, information that tells the driver of the deviation of the vehicle is displayed. When the driver turns on a recomputation command switch after reading the information, a new optimal route is computed, with the vehicle's present location as the new starting point. If the vehicle deviates again after computation of the new optimal route, another new optimal route is automatically recomputed, again with the vehicle's present location as the new starting point. The driver is thus freed from having to initiate the recomputation manually.

Abstract: An angular rate sensor for a vehicle navigation system stores an environmental temperature and a related null voltage each time the vehicle stops. The pairs of data points are stored in a non-volatile look-up table for use during vehicle motion. During vehicle motion, the environmental temperature is measured, and a null voltage is selected from the look-up table corresponding to the measured temperature. The null voltage is used to correct drift offset. Interpolation is used when data keyed to the measured temperature cannot be found in the look-up table.

Abstract: A navigation system prevents a vehicle from deviating from a new optimal route immediately after the new optimal route has been computed following the first deviation of the vehicle from an original optimal route. The system does this by determining the present location of the vehicle and searching road network data in a map database for a plurality of locations that are farther away from the present location than a distance travelled by the vehicle during recomputation of a new optimal route. These locations are selected as candidate new starting points. Then the system recomputes an optimal route from each of the candidate starting points to the destination. After the recomputation, the present location of the vehicle is read into the system, and an optimal route from the present location to each candidate starting point is computed.