Abstract: In a preferred embodiment, a vehicle position uncertainty area correction method and a corresponding apparatus are detailed. This method is preferably executed on a hardware platform 400. This method includes provision of an initial position envelope (307) associated with a vehicle position. Then, a corrected position envelope (307"") is derived from the initial position envelope (307) and bounded within a predetermined fixed area (313, 315) surrounding an outermost pair (305, 309) of road segments. The outermost pair (305, 309) of road segments are extracted from a map database (415) positioned within boundaries delimited by the position envelope (307).

Abstract: A differential odometer includes a left wheel sensor (503) coupled to a left wheel (103), and a right wheel sensor (513) coupled to a right wheel (105). The left wheel sensor (503) provides a left wheel pulse count (505) as the left wheel (103) rotates. A left wheel distance traversed is determined by a product of the left wheel pulse count and a left distance per pulse coefficient. The right wheel sensor (513) provides a right wheel pulse count (515) as the right wheel rotates. A right wheel distance traversed is determined by a product of the right wheel pulse count and a right distance per pulse coefficient. A vehicle heading (601'), and vehicle distance traversed (1201), are determined using the left wheel distance traversed and the right wheel distance traversed. A correction value (901, 1001) is provided corresponding to a measured relationship between the left wheel pulse count and the right wheel pulse count.

Abstract: An electronic compass (10) having at least two sense windings (11, 12) is mounted in a vehicle. The outputs (x(h), y(h)) of the windings are measured for a number of compass directions (headings). From this data an error difference angle (.phi.), from a nominal angle, which actually exists between the output windings is calculated. Preferably a look-up table (21, 39) is created relating actual compass heading (h) to measured sense winding outputs by utilizing the calculated error difference angle (.phi.). This table is then utilized for calculating actual compass heading based on actual measured sense winding outputs. The calculated error angle (.phi.) can also be used to calibrate the compass without creating a look-up table. The calibrated compass compensates for misalignment of the sense windings and provides a more accurate electronic compass without requiring creating a calibration table by orienting the compass in a very large number of exactly known directions.

Abstract: A method for calibrating a differential odometer in a vehicle (10) having a pair of wheels (14, 16) and a pair of associated wheel sensors (18, 24) which generate output pulses as their associated wheels rotate. The method includes driving the vehicle (10) around a path (12) in a first direction (counterclockwise or clockwise), measuring the vehicle's heading change (preferably 360 degrees), and counting the number of pulses generated by each wheel sensor (18, 24) while the path is traversed. Then the vehicle is driven around the same, or a different, path in the opposite direction, again measuring the vehicle's heading change, and counting the number of pulses generated by each wheel sensor (18, 24). The pulse counts, the measured heading changes, and the known distance between the vehicle's wheels, are used to calculate the distance traveled by each wheel per output pulse from its associated wheel sensor.

Abstract: Vehicle position determining apparatus (10) uses dead reckoning to calculate new vehicle position and heading (A2, H2) based on prior position and heading (A1, H1). Computer (11) separately calculates heading changes (.DELTA.H.sub.od, .DELTA.H.sub.c) as measured by a pair of differential wheel sensors (16, 17) and a magnetic compass (15) and uses these heading changes to calculate assoicated lateral accelerations of the vehicle (LA.sub.od, LA.sub.c) over a time and/or distance interval (.DELTA.t, .DELTA.d). If calculated lateral acceleration, or rate of vehicle turn, exceeds a maximum predetermined limit value, and this is therefore indicative of unstable or improbable vehicle operation, heading change data which resulted in calculation of excessive lateral acceleration is probably erroneous and will not be substantially utilized to calculate new vehicle position and heading.