GPS positioning principle
The GPS receiver can receive time information that can be used for time-tightening to the quarter; for forecasting the forecast of the satellite position in the coming months; a broadcast epicard for satellite coordinates for calculating positioning The accuracy is several meters to dozens of meters (different satellites, change at any time); and GPS system information such as satellite conditions. The measurement of the GPS receiver code can obtain the distance from the satellite to the receiver, since the error and atmospheric propagation error containing the receiver satellite clock is called a pseudo distance. The pseudo-distance measured by 0A code is called a UA code pseudo-distance, and the accuracy is about 20 meters, and the pseudo distance measured by the P code is called the P code pseudo-distance, the accuracy is about 2 meters. The GPS receiver can resume the carrier after decoding or using other techniques for receiving satellite signals. Strictly, the carrier phase should be referred to as a carrier beat frequency phase, which is the difference between the satellite signal carrier phase affected by Doppler frequency transfer and the receiver local oscillation generates signal phase. Generally measured at the long-term time measurement of the receiving machine clock, keep the satellite signals, the change value of the phase can be recorded, but the phase initial value of the receiver and satellite oscillator when the start of the observation is not known. The phase integer of the enclosure is also unknown, that is, the entire circumference is blurred, and can only be used as a parameter solution in the data processing. The accuracy of the phase observation value is as high as millimeter, provided to solve the entire circumference, so only the phase observation value can only be used in relatively positioning, and there is a continuous observation value, but to achieve better positioning accuracy of the meter-scale The phase observation value can be used. According to the positioning method, the GPS positioning is divided into single point positioning and relative positioning (differential positioning). Single point positioning is based on the observation data of a receiver to determine the location of the receiver, which can only be used for a pseudorange view, which can be used for the rough navigation positioning of the vessel vessel. The relative positioning (differential positioning) is a method of determining the relative position between the observation points according to the observation data of two or more receivers. It can also use a pseudo-distance viewing amount or a phase observation amount, earth measurement or engineering measurement. The relative positioning is performed using the phase observation value. In the GPS observation, the clock difference, atmospheric propagation delay, multipath effect, etc. in the GPS observation, the error, and the effect of the satellite broadcast epicardial error is also affected during the positioning calculation, and most of the public championships is performed in the relative positioning. Offset or weaken, the positioning accuracy will greatly increase, the dual-frequency receiver can counteract the main part of the electroplating layer error in the atmosphere according to the two frequencies, and the accuracy requirements are high, the distance between the receiving is far (the atmosphere is significantly different) ), A dual frequency receiver should be selected. When positioning observation, if the receiver is moved relative to the surface of the Earth, it is called dynamic positioning, such as a pseudo-range positioning of 301,100 meters, or for urban vehicle navigation positioning, or for urban vehicle navigation positioning Mi-scale precision pseudorange differential positioning, or centimeter-level phase difference positioning (RTK) for measuring the discharge or the like, real-time differential positioning requires data chains to transfers two or more station observation data in real time to calculate. When positioning observation, if the receiver is stationary relative to the surface of the Earth, it is called a static positioning. When performing the control network observation, it is generally used by several receivers simultaneously, which is the most limited to GPS. Positioning accuracy, a receiver dedicated to this purpose is referred to as a local receiver, which is one of the best performance in the receiver. At present, GPS has been able to achieve the accuracy of the crust-shaped observation, and the IGS's all-year observatory station has enabled the millimeter global coordinate framework.
