Navigation system using satellite signals

Abstract

The navigation system using GPS signals from satellites first checks whether or not there are four or more satellites in radio range of the moving body. If so, the position calculation section performs an ordinary three-dimensional positioning operation to provide an accurate fix of the moving body. When the number of satellites within the radio range is three or less, the two-dimensional positioning operation is carried out, which comprises reading the previous altitude data from the altitude storage section; calculating the atmospheric pressure deviation from the atmospheric pressure sensor output as caused by the movement of the body; calculating the altitude deviation from the previous altitude data and the atmospheric pressure deviation; calculating the current altitude from the altitude deviation and the previous altitude data; and then calculating the two-dimensional position data from the GPS signals and the current altitude data. This method produces no errors which would otherwise be caused by changes in the altitude of the moving body but provides accurate two-dimensional fix data of the body.

Dependencies are inferred from the claim text.