Pseudo range measurement is to measure the distance from the satellite to the receiver, that is, the distance obtained by multiplying the propagation time of the ranging code signal transmitted by the satellite to the GPS receiver by the speed of light. The pseudo range method of single point positioning is to use the GPS receiver to measure the pseudo range with more than 4 GPS satellites at a certain time and the satellite instantaneous coordinates obtained from the satellite navigation message, and use the range intersection method to calculate the three-dimensional coordinates of the antenna in the WGS-84 coordinate system .
2. Carrier phase measurement and carrier phase positioning（GPS)
Carrier phase measurement is to measure the phase delay between GPS satellite carrier signal and receiver antenna. The ranging code and navigation message are modulated on the GPS satellite carrier. After receiving the satellite signal, the receiver first removes the ranging code and satellite message on the carrier and obtains the carrier again, which is called reconstruction carrier. The GPS receiver compares the satellite reconstructed carrier with the local oscillator signal generated by the oscillator in the receiver through the phase meter to obtain the phase difference .
3. Real time differential positioning(GPS)
The principle of GPS real-time differential positioning is to place GPS receiver (called reference station) on the existing accurate geocentric coordinate points, calculate the correction value of GPS observation value by using the known geocentric coordinates and ephemeris, and send the correction value to the moving GPS receiver (called mobile station) through radio communication equipment (called data link). The mobile station uses the correction value to correct its own GPS observation value to eliminate the above errors, so as to improve the real-time positioning accuracy. There are many kinds of GPS dynamic difference methods, mainly including position difference, pseudo range difference (RTD), carrier phase real-time difference (RTK) and wide area difference