Method for improving vehicle positioning in a navigation system

• US 6,597,987 B1
• Filed: 05/15/2001
• Issued: 07/22/2003
• Est. Priority Date: 05/15/2001
• Status: Expired due to Term

• Current Assignee: HERE Global B.V. (HERE Holding Corporation)
• Original Assignee: Navigation Technologies Corp. (Nokia Corporation)
• Inventors: Barton, Mark
• Primary Examiner(s): Nguyen, Tan Q.
• Assistant Examiner(s): Tran, Dalena
• Application Number:
  US09/855,381
• Time in Patent Office: 798 Days
• Field of Search: 701/200, 701/208, 701/201, 701/207, 701/213, 701/224, 701/300, 340/988, 340/990, 340/995, 731/78.R
• US Class Current: 701/213
• CPC Class Codes: G01C 21/30 Map- or contour-matching
• CPC Class Codes: G01S 19/40 Correcting position, velocity or attitude
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial

Abstract

A method implemented on a navigation system in a vehicle for determining the position of the vehicle relative to a road network. The navigation system uses a geographic database that contains data that represent positions of roads upon which the vehicle travels. Using the output from a GPS system, and optionally outputs from other sensors, the navigation system matches the positions of the vehicle to the locations of the roads represented by the data contained in the geographic database. Upon detecting an event from which the position of the vehicle with respect to the roads represented by the data contained in the geographic database can be determined with a relatively high degree of accuracy, a correction factor is determined. The correction factor is an offset (i.e., a distance and direction) of the GPS position reported during the event to the known-to-be-highly-accurate position. The correction factor is then used to adjust subsequently obtained GPS readings for a limited period of time, i.e., while the same atmospheric conditions apply. This period of time may be 10-20 minutes.

Claims

1. A method for determining a position of a vehicle relative to a road network, the method comprising:

matching a position of the vehicle to locations of roads represented by data contained in a geographic database;

detecting an event pattern by which the position of the vehicle with respect to the roads represented by data contained in the geographic database can be determined with a relatively high degree of accuracy;

determining a correction factor by which an output from a GPS system varied from the position of the vehicle during the event pattern;

storing multiple correction factors during a limited period of time;

using said stored multiple correction factors to continuously determine a new correction factor; and

thereafter, applying the new correction factor to subsequent outputs of the GPS system.

2. The method of claim 1 wherein the limited period of time is approximately 10-20 minutes.

3. The method of claim 1 further comprising:

after applying the new correction factor, determining another new correction factor by performing the steps of matching, detecting, and determining again.

4. The method of claim 1 wherein the correction factor is a latitude and longitude offset.

5. The method of claim 1 wherein the event pattern is a well-defined turn.

6. The method of claim 1 wherein the event pattern is traveling in a straight line for a defined distance.

7. The method of claim 1 wherein the event pattern is traveling on a road that extends in a direct east-west or direct north-south direction.

8. The method of claim 1 further comprising:

upon detecting that the GPS system is obtaining signals from a different collection of satellites than those whose signals were being used when the new correction factor was determined, determining another new correction factor.

9. The method of claim 1 further comprising:

storing data that indicate a corrected position of the vehicle when the vehicle is parked; and

when the vehicle is started again, using the data that indicate the corrected vehicle position to adjust a GPS reading obtained when the vehicle is started.

10. The method of claim 1 wherein the event pattern comprises traveling in a straight line in a first direction and then traveling in a straight line in a second direction, wherein the first direction and the second direction are not parallel to each other.

11. The method of claim 1 further comprising:

weighting those more recently obtained of said multiple correction factors relative to those less recently obtained of said multiple correction factors.

12. The method of claim 1 further comprising:

averaging the multiple correction factors.

13. The method of claim 1 wherein said GPS system receives signals without the Selective Availability error.

14. A method implemented with a navigation system in a vehicle for determining a position of the vehicle relative to a road network, wherein the navigation system uses a GPS system and a geographic database containing data that represent positions of roads upon which the vehicle travels, and wherein the method is implemented in the absence of Selective Availability error, the method comprising:

matching a position of the vehicle to locations of roads represented by data contained in the geographic database;

detecting an event by which the position of the vehicle with respect to the roads represented by data contained in the geographic database can be determined with a relatively high degree of accuracy;

determining a correction factor by which an output from the GPS system varied from the position of the vehicle during the event pattern;

storing multiple correction factors during a limited period of time;

using said stored multiple correction factors to continuously determine a new correction factor; and

thereafter, applying the new correction factor to subsequent outputs of the GPS system.

15. The method of claim 14 wherein the limited period of time is approximately 10-20 minutes.

16. A feature implemented by a software application on a navigation system installed in a vehicle comprising:

a first program routine that monitors roads upon which the vehicle is traveling for an event at which a position of the vehicle can be accurately matched to a specific location along a road represented by data contained in a geographic database used by the navigation system;

a second program routine that determines a difference between a GPS reading obtained when the event occurred and the specific location along a road and stores multiple correction factors during a period of time;

a third program routine that uses said multiple correction factors to continuously determine a new correction factor; and

a fourth routine that applies the new correction factor to subsequently obtained GPS readings.

17. The invention of claim 16 further comprising:

a fifth routine that stores data indicative of a corrected vehicle position upon parking of the vehicle.

18. The invention of claim 17 wherein the fifth routine determines a second new correction factor upon the vehicle being restarted, wherein the second new correction factor represents a difference between the corrected vehicle position when the vehicle was parked and a new GPS reading obtained when the vehicle was restarted.

19. The invention of claim 17 wherein the fifth routine checks, when the vehicle is restarted, whether the vehicle has been moved since being parked.