Basic Concept of Satellite Positioning
Generally, satellite positioning means that a satellite signal receiver receives the electromagnetic wave signals from different positioning satellites in space. After data processing and calculation, the position of the receiver in space is determined. Relevant positioning methods include:
Single-point positioning
The basic principle lies in that a receiver simultaneously receives the positioning signals from different positioning satellites to estimate the distance among them and, through the distance intersection method, obtain the coordinates. In practice, as the satellite positioning signal is an electromagnetic wave signal, in order to determine the position of the receiver, it is only necessary to calculate the frequency of the electromagnetic wave and the time of signal transmission from the satellite to the receiver to estimate the distance between the satellite and the receiver. However, as the clock of the satellite may not be accurately synchronized with that of the receiver, a time error (t) will occur. Consequently, the time of signal transmission from the satellite to the receiver cannot be accurately calculated, which directly affects the calculation of the distance between the satellite and the receiver. Thus, in order to accurately calculate the coordinate values (X, Y, Z) of the receiver and the time error (t), the positioning signals from at least four different satellites must be received simultaneously during positioning to determine the exact coordinate position of the receiver.
Relative positioning
It is also known as differential positioning. It is a positioning method in which two or more receivers are used for simultaneous observation to determine the vector relationship among the receivers. For the simplest application in practice, two receivers are used to simultaneously receive the signals from over four identical positioning satellites. As the simultaneous observation modes of the two receivers are the same, we can suppose that, in an adjacent area, the environmental impacts and error factors are roughly the same. After post-processing and calculation, the relative relationship of the positions of the two receivers, i.e. the difference in coordinates, can be obtained. Therefore, when the coordinates of one receiver are known, the coordinates of the other receiver can be calculated based on the difference between two coordinates.
Real-time kinematic positioning
Real-time kinematic (RTK) satellite positioning mode is a relative positioning technology integrating the modern mobile telecommunication technology and advanced calculation methods. In practice, a receiver on a known point sends satellite positioning correction messages to a receiver on an unknown point via telecommunication devices such as a radio or a mobile. The latter utilizes the correction message and the signals sent by positioning satellites to eliminate environmental impacts and error factors to obtain the precise coordinates.