US Patent 7711480 Differential GPS corrections using virtual stations

Method and apparatus for providing GPS pseudorange correction and carrier phase correction information for navigation or surveying activities over a selected geographic region S of arbitrary size. In a navigation mode, a virtual reference station (VRS), positioned near a selected location L, receives differential GPS (DGPS) correction signals, translates these signals into a selected format, and broadcasts this DGPS information in this format for use by a local user. In a survey mode, the VRS receives corrected GPS information, translates this information into a selected format and broadcasts this translated and corrected GPS information and the VRS location, for use by a mobile station in forming a baseline vector from the GPS mobile station to the VRS location.