The basic principle of GPS positioning is based on the instantaneous calculation data of the instantaneous position of the high -speed movement, and the method of the space distance is used to determine the location of the test point. As shown in the figure, assuming that when T is placed on the ground to be placed on the ground at the ground, the GPS receiver can be measured, and the time for the GPS signal to reach the receiving machine △ T, plus other data such as the satellite star calendar received by the receiver can determine the following four four. Formula:

　　In the above four equations, the measuring point coordinates X, Y, Z, and VTO are unknown parameters, where DI = C △ TI (i = 1, 2, 3, 4).

　　DI (i = 1, 2, 3, 4) is satellite 1. Satellite 2, satellite 3. Satellite 3. Satellite 3, satellite 4 to receiver.

　　△ TI (i = 1, 2, 3, 4) is the time of satellite 1. Satellite 1. Satellite 2, satellite 3, and satellite 4.

　　C is the speed of transmission of GPS signal (ie, the speed of light).

　　The meaning of each parameter in the four equations is as follows:

　　X, Y, Z are the spatial right -angle coordinates of the coordinates to be tested.

　　XI, Yi, Zi (i = 1, 2, 3, 4) are satellite 1. Satellite 2, Satellite 3, Satellite 4 in the right -angle coordinates of the space at the time of T.

　　VT I (i = 1, 2, 3, 4) The bells of satellite clocks with satellite 2, satellite 2, satellite 3, and satellite 4 are provided by the satellite star calendar.

　　VTO is the bell of the receiver.

　　From the above four equations, the clock difference of the coordinates X, Y, Z and the receiver of the coordinates to be measured at the above four equations.

　　GPS satellite sends its own star parameters and time information. Under the independent GPS mode, the positioning terminal receives the information through the antenna from the GPS satellite, and the three -dimensional position, three -dimensional direction and motion speed and time information of the receiving machine are calculated. Because satellites are directly broadcasting from high -altitude, the signal is weak and the transmission rate is slow. This gives the positioning terminal a certain problem.

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