How does GPS work?
The basic principle of GPS positioning is to determine the position of the point to be measured by using the method of spatial distance resection, based on the satellite's instantaneous position of high-speed motion as known starting data. According to the positioning method, GPS positioning is divided into single point positioning and relative positioning. Single point positioning is based on a receiver's observation data to determine the location of the receiver, it can only use the pseudo-range view measurement, can be used for the general navigation and positioning of vehicles and ships. Relative positioning is a method of determining the relative position between observation points based on the observation data of two or more receivers. It can use both pseudo-range and phase-view measurements. Geodetic or engineering measurements should use phase observations. Relative positioning.
GPS observations include satellite and receiver clock errors, atmospheric propagation delays, multipath effects, and other errors. They also suffer from satellite broadcast ephemeris errors in positioning calculations. Most of the common errors are caused by relative positioning. Offset or weakened, so the positioning accuracy will be greatly improved, dual-frequency receiver can be based on the observation of the two frequencies to offset the main part of the ionospheric error in the atmosphere, in the high precision requirements, the distance between the receiver is far, you should use dual-frequency Receiver.