Precise positioning system for mobile GPS users

A differential positioning method for at least one mobile GPS user comprising the steps of:

• determining known geographic locations or positions of a plurality of reference stations with,
• inputting the known geographical locations to a central processing facility,
• receiving GPS signal data at each reference station,
• communicating between each reference station and the central processing facility, wherein measurement data is sent from each reference station to the central processing facility,
• calculating differences between the received measurement data and the the known locations of the reference stations,
• generating an error model from the calculated differences, the error model covering at least the area including the central processor and all the reference stations,
• two way communicating between the at least one mobile user and the central processing facility, and
• receiving GPS signal data locally at the at least one mobile user,
• sending measurement data to the central processing facility, wherein the central processor uses the error model to calculate the corrected positional data for the mobile user, and
• receiving corrected positional data for the at least one mobile user from the central processing facility, and
• generating a local error or offset at the at least one mobile user from the last corrected position received as compared to its received GPS signals, and
• using the offset when the mobile user is calculating its own position from the locally received GPS signals.