described is an automatic control system for land vehicles based on carrier phase differential gps . the system relies on cpgps to determine vehicle position and attitude very precisely . a system incorporates a technique to calculate and compensate for antenna motion due to vehicle roll and pitch . one aspect of the system utilizes an intelligent vehicle controller that recognizes and adapts to changing conditions , such as vehicle speed , implements towed by the vehicle , soil conditions , and disturbance level . the system provides the capability to control the vehicle on various paths , including straight lines and arbitrary curves . also described is a technique for initialization and vehicle control using only a single pseudolite .