Navigation device, method, and program

1. A navigation device that identifies a leading candidate point by calculating a cost for candidate points that are set on a road, and matches a vehicle position to the identified leading candidate point, the navigation device comprising:

a controller that:

acquires an estimated position of a vehicle based on dead reckoning navigation;

acquires a GPS position of the vehicle based on GPS;

sets the candidate points for the vehicle position on roads in the vicinity of the estimated position;

calculates for each candidate point a normal cost of the candidate point with respect to the estimated position;

calculates for each candidate point a correction cost that corresponds to a value L 1 , the value L 1 being found by subtracting a width W of the road from a distance d between the GPS position and the candidate point; and

identifies the leading candidate point based on a total cost of the normal cost and the correction cost for each candidate point.

2. The navigation device according to claim 1 , wherein the controller:

sets the correction cost to zero if the value L 1 is negative.

3. The navigation device according to claim 1 , wherein the controller:

acquires a speculative maximum error e that specifies a distance of an error range with respect to the GPS position;

calculates a value L 2 by subtracting the speculative maximum error e from the value L 1 ;

if the value L 2 is negative, sets the correction cost as a value equal to the value L 1 multiplied by a first proportionality constant; and

if the value L 2 is positive, sets the correction cost as a value equal to the sum of:

the value L 2 multiplied by a second proportionality constant larger than the first proportionality constant; and

the speculative maximum error e multiplied by the first proportionality constant.

4. The navigation device according to claim 3 , wherein:

the speculative maximum error e is a radius of an error circle that is based on a dilution of precision of the GPS.

5. The navigation device according to claim 3 , wherein:

the speculative maximum error e is a distance that corresponds to a reliability calculated from:

a dilution of precision;

a distance between the estimated position and the GPS position; and

a difference between a heading according to a trajectory of the estimated position and a heading according to a trajectory of the GPS position.

6. A navigation method that identifies a leading candidate point by calculating a cost for candidate points that are set on a road, and matches a vehicle position to the identified leading candidate point, the navigation method comprising:

acquiring, with a controller, an estimated position of a vehicle based on dead reckoning navigation;

acquiring, with the controller, a GPS position of the vehicle based on GPS;

setting, with the controller, the candidate points for the vehicle position on roads in the vicinity of the estimated position;

calculating, with the controller, for each candidate point a normal cost of the candidate point with respect to the estimated position;

calculating, with the controller, for each candidate point a correction cost that corresponds to a value L 1 , the value L 1 being found by subtracting a width W of the road from a distance d between the GPS position and the candidate point; and

identifying, with the controller, the leading candidate point based on a total cost of the normal cost and the correction cost for each candidate point.

7. The navigation method according to claim 6 , further comprising:

setting the correction cost to zero if the value L 1 is negative.

8. The navigation device according to claim 6 , further comprising:

acquiring, with the controller, a speculative maximum error e that specifies a distance of an error range with respect to the GPS position;

calculating, with the controller, a value L 2 by subtracting the speculative maximum error e from the value L 1 ;

if the value L 2 is negative, setting the correction cost as a value equal to the value L 1 multiplied by a first proportionality constant; and

if the value L 2 is positive, setting the correction cost as a value equal to the sum of:

the value L 2 multiplied by a second proportionality constant larger than the first proportionality constant; and

the speculative maximum error e multiplied by the first proportionality constant.

9. The navigation method according to claim 8 , wherein:

the speculative maximum error e is a radius of an error circle that is based on a dilution of precision of the GPS.

10. The navigation method according to claim 8 , wherein:

the speculative maximum error e is a distance that corresponds to a reliability calculated from:

a dilution of precision;

a distance between the estimated position and the GPS position; and

a difference between a heading according to a trajectory of the estimated position and a heading according to a trajectory of the GPS position.

11. A non-transitory computer-readable storage medium storing a computer-executable program usable to identify a leading candidate point by calculating a cost for candidate points that are set on a road, and matches a vehicle position to the identified leading candidate point, the program comprising:

instructions for acquiring an estimated position of a vehicle based on dead reckoning navigation;

instructions for acquiring a GPS position of the vehicle based on GPS;

instructions for setting the candidate points for the vehicle position on roads in the vicinity of the estimated position;

instructions for calculating for each candidate point a normal cost of the candidate point with respect to the estimated position;

instructions for calculating for each candidate point a correction cost that corresponds to a value L 1 , the value L 1 being found by subtracting a width W of the road from a distance d between the GPS position and the candidate point; and

instructions for identifying the leading candidate point based on a total cost of the normal cost and the correction cost for each candidate point.

12. The non-transitory computer-readable storage medium according to claim 11 , the program further comprising:

instructions for setting the correction cost to zero if the value L 1 is negative.

13. The non-transitory computer-readable storage medium according to claim 11 , the program further comprising:

instructions for acquiring a speculative maximum error e that specifies a distance of an error range with respect to the GPS position;

instructions for calculating a value L 2 by subtracting the speculative maximum error e from the value L 1 ;

instructions for, if the value L 2 is negative, setting the correction cost as a value equal to the value L 1 multiplied by a first proportionality constant; and

instructions for, if the value L 2 is positive, setting the correction cost as a value equal to the sum of:

the value L 2 multiplied by a second proportionality constant larger than the first proportionality constant; and

the speculative maximum error e multiplied by the first proportionality constant.

14. The non-transitory computer-readable storage medium according to claim 13 , wherein:

the speculative maximum error e is a radius of an error circle that is based on a dilution of precision of the GPS.

15. The non-transitory computer-readable storage medium according to claim 13 , wherein:

the speculative maximum error e is a distance that corresponds to a reliability calculated from:

a dilution of precision;

a distance between the estimated position and the GPS position; and

a difference between a heading according to a trajectory of the estimated position and a heading according to a trajectory of the GPS position.