Navigation system

A navigation system for use on a mobile object, comprising:

• GPS positioning means for receiving radio waves from GPS satellites, determining a present position of the mobile object based on the received radio waves, and outputting first positional data indicative of the determined position;
• self-operating positioning means having a sensor on the mobile object for determining a present position of the mobile object and outputting second positional data indicative of the determined position;
• first positional data comparing means for comparing previous first positional data and the present first positional data to determine whether the difference between the previous and present first positional data is equal to or smaller than a first predetermined value;
• PDOP value determining means for determining whether a PDOP value of the present first positional data is equal to or smaller than a second predetermined value;
• distance determining means for comparing the present first positional data and the second positional data to determine whether the distance between the present position of the mobile object as indicated by the present first positional data and the present position of the mobile object as indicated by the second positional data is equal to or greater than a third predetermined value;
• and
• selecting means for outputting the first positional data as present positional data if the difference between the previous first positional data and the 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.