| 摘要 |
PROBLEM TO BE SOLVED: To prevent erroneous correction due to map matching by making a decision whether the field strength of a radio wave received by a satellite receiving means is higher than a predetermined level. SOLUTION: At first, moving distance and moving direction of a vehicle are received from a self-contained navigator 15 and a surveying data is received from a satellite receiving unit 14. The moving distance and moving direction of the vehicle are accumulated on the previous data of the vehicle in order to determine an estimated position of the vehicle and then a map data in the vicinity of the estimated position is received from an external reader 16. A CPU 11 makes a decision whether the field strength of a received radio wave is lower than a predetermined level. If it is higher than the predetermined level, a decision is made whether the estimated position of the vehicle is within an error range. If it deviates from the error range, the estimated position of the vehicle is corrected to an absolute position and subjected to map matching. If it is within an error range, the estimated position of the vehicle is determined as the position of the vehicle. |
