Current position calculating system for a vehicle having a function for correcting a vehicle direction

Claim 1

A current position calculating system being installed on a vehicle for calculating a current position of the vehicle, comprising: direction detecting means for successively detecting a vehicle direction which changes as the vehicle travels; distance calculating means for successively calculating a travelled distance of the vehicle; road data storing means for storing road data which contain line segments connected together; map matching means for estimating a vehicle current position as a virtual current position according to a previously determined vehicle current position and a relative displacement with respect to said previously determined vehicle current position, said relative displacement having been obtained on the basis of said vehicle direction and said travelled distance, and for determining a most probable latest current position on a road on the basis of distances from the virtual current position to line segments of said road data respectively and angular differences between each of line segment directions and a vehicle direction; and direction modification means for holding a plural number of angular differences between road and vehicle directions, which are differences between the vehicle directions for a predetermined plural number of previously obtained positions having been determined by the map matching means, and said line segment directions at each of the previously obtained positions respectively, for obtaining an averaged value of the previously obtained plural number of angular differences between road and vehicle directions, and for modifying a latest vehicle direction detected by said direction detecting means on the basis of the averaged value, wherein said map matching means performs a map matching process on the basis of the vehicle direction having been modified.