Abstract

A navigation system on an automobile has a GPS receiver for producing first positional data indicating the automobile position based on radio waves from GPS satellites, and a self-operating sensor for producing second positional data indicating the automobile position based on speed and orientation sensor signals. A data processor compares previous and present first positional data to determine whether the difference therebetween is equal to or smaller than a first predetermined value, and also determines whether a PDOP value of the present first positional data is equal to or smaller than a second predetermined value. The present first positional data and the second positional data are compared to determine whether the distance between the present position of the automobile as indicated by the present first positional data and the present position of the automobile as indicated by the second positional data is equal to or greater than a third predetermined value. The data processor outputs the first positional data as present positional data if the difference between the previous and present first positional data is equal to or smaller than the first predetermined value, if the PDOP value is equal to or smaller than the second predetermined value, and also if the distance is equal to or greater than the third predetermined value.