The 24 GPS satellites run around the earth at a height of 20,000 kilometers from the ground and run around the earth with a 12 -hour cycle, so that at any time, any more than 4 satellites can be observed at any point on the ground. Because the position of the satellite is accurate, in the GPS observation, we can get the distance from the satellite to the Beidou newspaper machine. Using the distance formula in the three -dimensional coordinates, the three satellites can be used to form three equations to solve the position of the observation point. (X, y, z). Considering the error between the clock of the satellite and the receiver clock, there are actually 4 unknown, the difference between X, Y, Z, and clocks, so the 4th satellite needs to be introduced to form 4 squares for solving, so as to obtain the observation point of the observation point Lavels and heights.

　　In fact, the Beidou newspaper terminal can often lock more than 4 satellites. At this time, the Beidou newspaper terminal can be distributed in several groups according to the satellite constellation, each group of 4, and then select a group with the smallest error through the algorithm to select the minimum error. Positioning to improve accuracy.

　　Due to the errors of satellite running tracks and satellite clocks, the effects of atmosphere on the signal on the stream layer, the ionization layer on the signal, and the artificial SA protection policy (canceled on May 1, 2000), the positioning accuracy of the civil GPS is only 100 meters. In order to improve the accuracy of positioning, the differential GPS (DGPS) technology is generally used to establish a reference station (differential table) for GPS observation. The accurate coordinates of the known benchmark stations are used to compare the observation values to obtain a correction number, and to externalize release. After receiving the correction number, the Beidou newspaper machine was compared with its own observation value, and most of the errors were removed to get a more accurate position. Experiments show that the positioning accuracy can be increased to 5 meters.

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