There are at least four atomic clocks in each GPS satellite. The atomic clock is currently a well -known Z accurate equipment. It is more than a second slow every 30,000 to 1 million years. In order to make them more accurate, they regularly adjust and synchronize from different points on the earth. Each satellite sends its own accurate location signals and accurate time signals to the earth at a frequency of 1575.42MHz. These times spread 300,000km/s at a speed of light, and the signal reached nearly 67.3ms when the signal reached the surface of the earth directly below the satellite. The signal is 3.33 microseconds per kilometer. If you want to determine your location in land, sea, or air, what you need is the accurate time, the time for the time for the satellite signal and the launch time of the satellite, so that the transmission time may be determined.

　　Car GPS manufacturer information shows that the distance S of the positioning point to the satellite can be determined by transmission time τ: S = τ × C type C is the speed of light. The measuring signal transmission time and the distance from the satellite are not enough to calculate the three -dimensional space position, which requires four independent equations, so it is necessary to calculate exact positions with four different satellites.

　　In fact, to determine the location of the three -dimensional space, three satellites are required. If the distance from the three satellites is known, the coordinates of the three satellites are known, then the three -dimensional space position can be known. All points in the space can fall on the surface of the ball with a radius with a radius of the three satellites, and the point to be determined is the intersection of the three ball surfaces.

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