Route guidance on/off-route state filter

A route guidance module in a vehicle navigation system for determining whether a vehicle is following a predetermined route on a map of roadways, said route comprising a selected portion of said roadways, said navigation system calculating a dead-reckoned position of said vehicle and further generating a set of position possibilities of said vehicle on said roadways, said route guidance module comprising:

• means for receiving said set of position possibilities;
• means for verifying that each of said position possibilities is a valid possibility, thereby generating a first subset of position possibilities;
• means for filtering the first subset of position possibilities without reference to said predetermined route to remove those least likely to correspond to an actual position of the vehicle, thereby generating a second subset of position possibilities;
• means for filtering the second subset of position possibilities with reference to said predetermined route, thereby generating a set of remaining position possibilities;
• means for selecting a current position from the remaining position possibilities;
• and
• means for determining a route status of the vehicle based on said current position and said predetermined route.

A route guidance system for determining whether a vehicle is following a predetermined route on a map of roadways, said route guidance system comprising:

• means for storing said map of roadways;
• means for reading a heading sensor and a distance sensor;
• means for calculating a dead-reckoned position using heading and distance readings;
• means for comparing said dead-reckoned position to said map of roadways;
• means for deriving a set of position possibilities, said position possibilities comprising positions on said roadways within an error region having said dead-reckoned position as its center;
• means for verifying that each of said position possibilities is a valid possibility, thereby generating a first subset of position possibilities;
• means for filtering the first subset of position possibilities without reference to said predetermined route to remove those least likely to correspond to actual position of the vehicle, thereby generating a second subset of position possibilities
• means for filtering the second subset of position possibilities with reference to said predetermined route, thereby generating a set of remaining position possibilities;
• means for selecting a current position from the remaining position possibilities;
• means for comparing said current position to said predetermined route to determine a route status of the vehicle, said route status comprising an ON ROUTE status or an OFF ROUTE status;
• and
• means for communicating said route status to a user of the route guidance system.