If the general differential GPS technology is used, each vehicle shall receive the differential correction number, which will cause the system to be too complex, so the centralized differential technology is often used in practical applications. Working principle: Each vehicle is equipped with GPS receiver and communication radio. The monitoring center is located at the base station, and the coordinates are known accurately. GPS receiver is installed on the reference point, and communication radio, computer, electronic map, large screen display and other equipment are installed at the same time. When working, the GPS receiver on each vehicle sends its position, time, vehicle number and other information to the monitoring center. The monitoring center calculates the difference between the vehicle position and the GPS positioning result of the reference station, corrects the vehicle position, calculates the precise coordinates, and displays them on the large screen after coordinate conversion.

　　This centralized difference technology can simplify the equipment on the vehicle. The on-board part only receives GPS signals, and does not need to consider the reception of differential signals. The monitoring center centralizes differential processing, display, record and storage. The original vehicle communication equipment can be used for data communication, as long as the communication conversion interface is added. As the differential GPS equipment can provide accurate position, speed, heading and other information in real time, the on-board GPS differential equipment can also calibrate various sensors on the vehicle (such as log, speedometer, magnetic compass, etc.).

　　Automobile is the most closely related means of transportation to everyone in modern civilized society. According to statistics, only a few developed countries have tens of millions of automobiles. Therefore, vehicle navigation will become one of the largest potential markets for GPS applications in the next 20 years. It is estimated that by 2000, 1/3 of the world's total investment in vehicle navigation will be made.

　　In China, there are hundreds of thousands of special vehicles. Relevant departments require that special vehicles such as overtaking vehicles, first aid vehicles, fire engines, patrol vehicles and greeting vehicles be monitored, guided and commanded in the whole process. At present, there are few vehicles using vehicle GPS receivers for autonomous positioning, and a large number of development and application hotspots are in the monitoring and scheduling system. The development direction of vehicle GPS navigation equipment in application should focus on multi satellite system, remote monitoring and multi-function display.

　　Multi satellite systems, such as GNSS (which will become an integrated navigation and positioning system after 2000), are used to ensure the accuracy and reliability of real-time vehicle positioning due to the large number of satellites. For the monitoring system used for dispatching and command, the operating distance between the monitoring center and the vehicles under its jurisdiction is only tens of kilometers due to the limited power of the communication radio. To increase the monitoring distance, the problem of long-distance communication should be solved. For example, increase the communication relay station, extend the operating distance, and use broadcast or satellite communication to make the monitoring range cover a larger area. The functions of the monitoring system should be multifaceted. For example, voice transmission, visual image transmission, as well as various commands and vehicle surrounding environment input and storage, etc.

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