(1) Observation error. In addition to the distinguishing error, it also includes the resettlement error of receiving an antenna relative to measure. The resolution error is generally considered to be about 1%of the signal wavelength. The resettlement error mainly includes the level of the antenna and the medium error and the height of the center of the antenna phase of the antenna. For example, the antenna is 1.6 m and the flat error is 0.10, and the middle error is 2.10 mm.

　　(2) The receiver is poor. The GPS receiver generally has high-precision quartz clock with a daily frequency stability of 10-11. If the synchronization difference between the receiver clock and the satellite clock is 1S, the equivalent distance error is 300 m. The method of processing the difference in the receiving machine is used as an unknown, and it is solved in the data processing; the method of poor observation value is used to weaken the impact of the receiving machine bell; Improve the time standard accuracy of the receiver.

　　(3) The carrier phase observation is unknown throughout the week. It is impossible to directly determine that the carrier phase starts to change the entire week of the transmission path. At the same time, the signal tracking was interrupted and the whole week was caused by the satellite signal being blocked and disturbed by the satellite signal.

　　(4) The position of the center of the antenna phase. In the GPS positioning, the observation values are based on the center position of the phase of the receiving machine antenna. In theory, the center of the antenna phase and the geometric center of the instrument should be consistent. The change, which is related to the quality of the antenna, can reach several millimeters to several centimeters. How to reduce the offset of the phase center is an urgent issue of antenna design.

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