What is the gps/Global Positioning System

Global Positioning System (GPS) is a new generation of space satellite navigation and positioning system developed by the United States armed forces in the 70 's. Its main purpose is to provide real-time, all-weather and global navigation services for the three major areas of land, sea and air, and for some military purposes, such as intelligence collection, nuclear explosion monitoring and emergency communications, and is an important component of the United States ' global strategy of domination. After more than 20 years of research experiments, costing 30 billion U.S. dollars, by March 1994, the global coverage of up to 98% of the 24 GPS satellite constellation has been laid out.

The Global Positioning system is composed of three parts: (1) The ground control part, the main control station (responsible for the management, coordination of the entire ground control system work), the ground antenna (under the control of the main control station to the satellite into the search for messages), monitoring stations (data Automatic Collection Center) and Communication Assistance system (transmission) composition; (2) Space part, Composed of 24 satellites, distributed on 6 road plane, (3) User device part, mainly consists of GPS receiver and satellite antenna.

The main features of the Global Positioning System are: (1) All-weather, (2) global coverage, (3) Three-dimensional fixed-speed timing high-precision, (4) Fast time-saving Efficiency: (5) wide range of applications.

The main uses of the Global Positioning System: (1) land applications, mainly including vehicle navigation, emergency response, atmospheric physical observation, geophysical resource exploration, engineering surveying, deformation monitoring, crustal movement monitoring, municipal planning control, etc. (2) marine applications, including the best voyage route determination of ocean ships, real-time ship scheduling and navigation, Marine Rescue, Marine exploration, hydrogeological survey and offshore platform positioning, sea level fluctuation monitoring, (3) aerospace applications, including aircraft navigation, remote sensing attitude control, low orbit satellite orbit, missile guidance, aviation rescue and manned spacecraft protection detection.

There are many kinds of GPS satellite receivers, according to the model is divided into geodesic type, total station type, timing type, hand-held type, integrated type, according to the use of vehicle-mounted, ship-mounted, airborne, on-board, missile-loaded.

After more than 20 years of practice, the GPS system is a high-precision, All-weather and Global radio navigation, positioning and timing of the multi-functional system. GPS technology has developed into many fields, multimodal, multi-purpose, many models of international High-tech industries.

GPS principle

With 24 GPS satellites orbiting the Earth at a height of 12,000 kilometres from the ground, a 12-hour cycle makes it possible to observe more than 4 satellites at any point on the ground at any given time.

Because the position of the satellite is accurate, we can get the distance from the satellite to the receiver in the GPS observation, using the distance formula in the three-dimensional coordinate, using 3 satellites, we can compose 3 equations, and solve the position of the observation Point (X,Y,Z). Considering the error between the satellite clock and the receiver clock, there are actually 4 unknowns, X, Y, z and clock difference, so we need to introduce the 4th satellite to form 4 equations for solving, thus obtaining the latitude and longitude of the observation point and elevation.

In fact, the receiver can often lock more than 4 satellites, at this time, the receiver can be divided into several groups by satellite constellation Distribution, each group of 4, and then through the algorithm to select the smallest error set for positioning, so as to improve accuracy.

Due to the error of satellite orbit, satellite clock, atmospheric troposphere, ionospheric influence on signal, and artificial SA protection policy, the positioning accuracy of GPS is only 100 meters. In order to improve the positioning accuracy, the differential GPS (DGPS) technique is adopted to establish the Datum station (difference station) for GPS observation, and the precise coordinates of the datum stations are used to compare with the observed values, so as to obtain an amendment number and release the external. After receiving the correction number, the receiver compares with its own observation value, eliminating most of the errors and getting a more accurate position. The experiment shows that the positioning accuracy can be increased to 5 meters by using differential GPS.

GPS foreground

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

With the end of the cold war and the booming global economy, the United States government announced from 2000 to No. 2006, in order to ensure that U.S. national security is not threatened, the cancellation of SA policy, GPS civil signal accuracy in the global scope of improvement, the use of C/A code for the single point of positioning accuracy from 100 meters to 20 meters, This will further promote the application of GPS technology, improve productivity, operational efficiency, scientific level and people's quality of life, stimulate the growth of the GPS market. According to experts predict, in the United States, the car GPS navigation system alone, 2000 years after the market will reach 3 billion U.S. dollars, and in China, auto navigation market will reach 5 billion yuan. It can be seen that the application prospect of GPS technology is very considerable.