Originally originated from military equipment to explain to you what GPS is

Global Positioning System (GPS) is a new generation of space satellite navigation and positioning system jointly developed by the US Army, Navy and Air Force in the 1970s. Its main purpose is to provide real-time, all-weather and global navigation services for the three major areas of land, sea, and air. It is also used for military purposes such as intelligence collection, nuclear explosion monitoring, and emergency communications. It is an important component of the US's monopoly on global strategy. After more than 20 years of research and experiments, which cost US $ 30 billion, by March 1994, 24 GPS satellite constellations with a global coverage of 98% had been deployed.

The global positioning system is composed of three parts: (1) the ground control part, which is composed of the main control station (responsible for managing and coordinating the work of the entire ground control system), the ground antenna (under the control of the main control station, injecting telegrams into the satellite), Monitoring station (automatic data collection center) and communication auxiliary system (data transmission); (2) Space part, composed of 24 satellites, distributed on 6 track planes; (3) User device part, mainly by GPS receiver And satellite dish.

The main features of the global positioning system: (1) all-weather; (2) global coverage; (3) three-dimensional fixed-speed timing and high precision; (4) fast time-saving and high efficiency: (5) widely used multi-function.

The main uses of the global positioning system: (1) land applications, mainly including vehicle navigation, emergency response, atmospheric physical observation, geophysical resource exploration, engineering survey, deformation monitoring, crustal movement monitoring, municipal planning control, etc .; (2) marine applications , Including the determination of the best voyage route of ocean-going ships, real-time scheduling and navigation of ships, marine rescue, ocean exploration, hydrogeological survey, positioning of offshore platforms, and monitoring of sea level rise and fall; Attitude control, low-orbit satellite orbit determination, missile guidance, aviation rescue and manned spacecraft protection detection, etc.

There are many types of GPS satellite receivers, which are divided into geodesic type, total station type, timing type, handheld type and integrated type according to the model; according to the use, they are divided into vehicle type, ship type, airborne type, satellite type and bomb type .

After more than 20 years of practice, GPS system is a multi-functional system with high precision, all-weather and global radio navigation, positioning and timing. GPS technology has developed into an international high-tech industry with multiple fields, multiple modes, multiple uses, and multiple models.

   GPS principle

The 24 GPS satellites orbit the earth in a 12-hour period at an altitude of 12,000 kilometers above the ground, so that at any time, at any point on the ground, more than 4 satellites can be simultaneously observed.

Because the position of the satellite is accurately known, in GPS observation, we can obtain the distance from the satellite to the receiver. Using the distance formula in three-dimensional coordinates and using three satellites, three equations can be formed to solve the position of the observation point (X , Y, Z). Considering the error between the satellite's clock and the receiver's clock, there are actually 4 unknowns, X, Y, Z and clock difference, so the fourth satellite needs to be introduced to form 4 equations to solve, so as to obtain the observation point Latitude, longitude and elevation.

In fact, the receiver can often lock more than 4 satellites. At this time, the receiver can be divided into several groups according to the constellation of satellites. Each group has 4 satellites. Then, the group with the smallest error is selected by the algorithm for positioning. Improve accuracy.

Due to errors in satellite orbits, satellite clocks, the influence of the atmospheric troposphere and ionosphere on signals, and man-made SA protection policies, the positioning accuracy of civilian GPS is only 100 meters. In order to improve the positioning accuracy, the differential GPS (DGPS) technology is generally used to establish a reference station (differential station) for GPS observations. The known coordinates of the reference station are used to compare with the observed values ​​to obtain a correction number and release it to the outside world. . After receiving the correction number, the receiver compares it with its own observation value to eliminate most errors and obtain a more accurate position. Experiments show that using differential GPS, the positioning accuracy can be increased to 5 meters.

GPS prospects

Because of the all-weather, high-precision and automatic measurement characteristics of GPS technology, as advanced measurement methods and new productivity, it has been integrated into various application fields of national economic construction, national defense construction and social development.

With the end of the Cold War and the vigorous development of the global economy, the US government announced that from 2000 to 2006, under the premise of ensuring that the US national security is not threatened, the SA policy will be cancelled, and the accuracy of GPS civilian signals will be improved globally. The accuracy of A code for single-point positioning is increased from 100 meters to 20 meters, which will further promote the application of GPS technology, improve productivity, operating efficiency, scientific level and people's quality of life, and stimulate the growth of the GPS market. According to the prediction of relevant experts, in the United States, the car GPS navigation system alone will have a market of 3 billion US dollars after 2000, while in China, the market for car navigation will also reach 5 billion yuan. It can be seen that the application prospect of the GPS technology market is very impressive.