Abstract: A hybrid positioning system for locating an object using a combination of a GPS pseudoranges and local radio pseudoranges. The system includes one or more receptors coupled to a base station, and one or more location markers. The location markers are located with an object whose location is to be determined. Each of the location markers includes a GPS receiver for determining GPS pseudoranges and a radio transmitter for transmitting a radio signal including the GPS pseudoranges and information about the object. Each of the receptors passes the radio signal to the base station as an interface signal. The base station includes a radio pseudorange detector, a base GPS receiver, and a hybrid pseudorange processor. The radio pseudorange detector uses the times-of-arrival of the interface signals and the known interface signal transit times for determining radio pseudoranges from the location marker to the receptors. The base GPS receiver determines the locations-in-space of GPS satellites.