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As early as the late 1970s, some people began to study vehicle positioning and navigation. At that time, the specific orientation of the vehicle and how to reach this orientation were confirmed through deduction and calculation of the running track and the ratio of the map. The essence of track calculation (DRS) is to regard the vehicle driving as a two-dimensional plane motion, measure the change of vehicle driving length and viewpoint all the time according to its starting orientation and the initial viewpoint, and then use the map matching to calculate and estimate the orientation of the vehicle. However, this method is difficult to complete and the accuracy is not high, but the research on DRS has laid the foundation for future scientific research.

According to the navigation principle of global positioning system (GPS)

In the late 1990s, the field frequency of the IT industry was constantly updated, the satellite skills were gradually sophisticated, and the communication equipment was gradually developed, and then the satellite positioning system was invented. Meanwhile, the global positioning system of the United States is the best.

GPS is composed of 24 operational satellites. It is located 20200km above the earth's surface, evenly distributed on 6 track surfaces (4 for each track surface), and the track inclination is 55 °. In addition, there are four active backup satellites in orbit. The distribution of satellites makes it possible to observe more than four satellites anywhere and at any time in the world, and can maintain a few images with good positioning accuracy. This provides a continuous global navigation ability in time.

Because the azimuth of the satellite is accurate, in GPS observation, we can get the interval from the satellite to the receiver. According to the interval formula in three-dimensional coordinates, using three satellites, we can form three equations to solve the azimuth (x, y, z) of the observation point. Considering the error between the satellite clock and the receiver clock, there are four unknowns in practice, x, y, Z and clock difference. Therefore, it is necessary to introduce the fourth satellite to form four equations for solution, and then obtain the longitude, latitude and elevation of the observation point.

In fact, the receiver can often lock more than four satellites. At this time, the receiver can be divided into several groups according to the constellation distribution of satellites, four in each group, and then select the group with the smallest error through the algorithm for positioning, and then improve the accuracy.

The positioning accuracy of civil GPS is only 100 meters due to errors in satellite operation trajectory and satellite clock, the influence of atmospheric troposphere and ionosphere on signals, and man-made SA protection policy. In order to improve the positioning accuracy, the differential GPS (DGPS) skill is widely used to establish a reference station (differential station) for GPS observation. The known accurate coordinates of the reference station are used to compare with the observed values, and then a correction number is obtained and released to the public. After receiving the correction, the receiver compares it with its own observation value to eliminate most errors and obtain a more accurate azimuth. Experiments show that the positioning accuracy can be improved to 5 meters by using differential GPS.

After the emergence of GPS, it provides accurate position recognition skills support for countries all over the world. Satellite positioning improves the accuracy compared with track calculation. After GPS and track calculation, the positioning accuracy can reach 1 cm, and the accurate positioning is completely completed. Moreover, the EU has also established its own scientific research queue of navigation and positioning system, which is called Galileo plan. Because GPS has high precision and high quality and low price, many parts and governments use this positioning technology. In addition, there are also technologies often used to confirm the specific location according to the mobile communication network and the location according to the human retina. These skills must be used in an orderly way, not alone.

The article comes from Jiangmen vehicle navigatorhttp://www.t2nupai.cn