1.GPS system composition
GPS gloabal Positioning System, which was built in the United States. Mainly divided into three blocks, the control station on the ground, the satellites flying in the sky, and the receivers in our hands.
First talk about equipment, satellites are ready for the United States, as for the main control station, of course, in the homeland of the United States, in Colorado. Three ground antennas, five monitoring stations, distributed throughout the world. It is mainly collecting data, calculating navigation information, diagnosing system status, and scheduling satellites. In the sky, there are 27 satellites, 20,200 kilometers above the ground. There are 24 satellites running on 27 satellites and 3 spares. These satellites have been updated three generations of five models. The satellite transmits two signals: L1 and L2. L1:1575.42 MHz, L2: 1227.60 MHz. The clock on the satellite uses a cesium atomic clock or a helium atomic clock and plans to use a hydrogen atomic clock in the future. The receiver is the receiver. Large and small, varied, there are pocket-sized, piggyback, car, ship, airborne or something. The common handset receives the L1 signal and has a dual-frequency receiver for precise positioning.
2. About GPS receiver
GPS is now generally 12-channel and can receive 12 satellites at the same time. Earlier models, such as the GARMIN 45C, were 8 channels. The GPS receiver can receive 3 satellite signals and can output 2D (that is, 2D) data. Only longitude and latitude, no height, if more than 4 satellites are received, 3D data will be output to provide altitude. But because of the earth's own problems, it is not too standard circle, so the height data has some errors. Some GPS receivers now have built-in barometers, such as etrex's SUMMIT and VISTA. These machines synthesize the final altitude based on the altitude data from the two channels and should be accurate.
The GPS receiver turned on for the first time, or more than 800 km from the last shutdown point in the power-on distance, because the ephemeris stored in the receiver could not be matched, so it should be repositioned on the receiver.
The use of GPS receivers should be in the open visible sky, so the room cannot be used. The accuracy of hand-held GPS is generally about 10 meters in error, that is to say a road can see left or right. The accuracy mainly depends on the signal reception of satellites and the distribution of satellites that can receive signals in the sky. If the distribution of several satellites is relatively dispersed, the positioning accuracy provided by GPS receivers will be relatively high.