| 摘要 |
PURPOSE:To measure a position with high accuracy in spite of the of reception of a reflection wave of a navigation radio wave, by detecting the reception of the reflected wave of the navigation radio wave by monitoring a difference between an absolute position and a relative position in case when a receiving state of the navigation radio wave is good, and regarding the relative position in that case as the present position of a moving body. CONSTITUTION:A loran signal is received by a receiving circuit 12 and absolute position coordinates (XL, YL) of a moving body such as a vehicle, etc. are calculated by a receiving position arithmetic circuit 14. On the other hand, by an integrating operation from an azimuth by an earth magnetism sensor 16, a distance by a distance sensor 18, etc., an estimated position arithmetic circuit 20 calculates relative position coordinates (X0, Y0), and one of the coordinates (XL, YL), (X0, Y0) is selected by an arithmetic position selecting circuit 24. S/N, etc. at the time of reception of this circuit 12 are monitored by a receiving state monitoring circuit 22, and when the S/N is low, and also, a difference between the coordinates (XL, YL), (X0, Y0) is larger then a prescribed value by a reflected wave receiving and detecting circuit 26, it is decided that a loran reflected wave of a crest, etc. is detected, and the circuit 24, selects the coordinates (X0, Y0). Accordingly, a position is measured with high accuracy irrespective of reception of a reflected wave of a navigation radio wave.
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