Although the indoor positioning market is growing, due to the differences in indoor space design and planning, there is no set of application solutions that can be directly incorporated. Therefore, the current outdoor positioning market potential is still the largest, and the development is more mature . With the gradual maturity of my country's Beidou technology and industrial chain, a large number of market spaces will emerge, such as location tracking and vehicle information service projects combining intelligent transportation and new smart cities, urban public investment management, logistics tracking management methods, agricultural and animal husbandry precise positioning, geological disaster monitoring and meteorological monitoring, etc.
What is a GPS module
The GPS module is a GPS signal receiver, which can be connected to a computer or mobile phone by wireless bluetooth or plug-in, and transmits the GPS signal it receives to the GPS software in the notebook or mobile phone for resolution. The GPS positioning module that people often say is called the client part. It accepts and modulates the live C/A code data signal of the satellite like a "radio", and its working frequency is 1575.42MHz. The GPS module does not play data signals, but belongs to passive positioning.
The application focus of the GPS module lies in the establishment of the serial port communication protocol, which is actually the relevant output protocol format of the module. It includes basic data types and message formats, among which basic data types mainly include binary data and NMEA deep-sea electronic association data information. These two kinds of information can communicate with the GPS receiver through the serial port communication.
The GPS module calculates the four main parameters of the receiver, namely latitude and longitude, layer, altitude and duration adjustment, based on the pseudo-distance calculation with each satellite, using the distance intersection method. The characteristic is that the positioning point speed is faster, but the deviation is large. The first positioning module requires at least 4 satellites to participate in the calculation, which is called 3D positioning. 3 satellites can achieve 2D positioning, but the accuracy is not good. The GPS module continuously exports NMEA format positioning information and assistance information through the serial communication port for the receiver to choose and use.
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The basic principle of GPS module positioning
24 GPS satellites orbit the earth in 12 hours at an altitude of 12,000 kilometers above the ground, so that at any moment, more than 4 satellites can be observed at any point on the ground at the same time.
Because the satellite position is accurately known, in GPS measurement, the distance between the satellite and the receiver, using the distance formula in the three-dimensional coordinates, using 3 satellites, can form 3 expressions to solve the position of the observation point (X ,Y,Z). Fully consider the deviation between the digital clock of the satellite and the receiver clock, in fact there are 4 unknowns, X, Y, Z and the clock difference, so the fourth satellite must be introduced, and 4 expressions must be established to obtain it, so as to obtain The geographic coordinates and elevation of the observatory.
In fact, the receiver can often lock more than 4 satellites. At this time, the receiver can be divided into several groups according to the constellation distribution of the satellites, each group has 4 satellites, and then the group with the least deviation is screened out through the optimization algorithm as the positioning, and then Improve precision.
Due to errors in satellite orbits and satellite clocks, and the influence of the atmospheric troposphere and ionosphere on signals, the positioning accuracy of civilian GPS is only 10 meters. In order to improve the positioning accuracy, differential GPS (DGPS) technology is commonly used to establish a reference station (difference station) for GPS observation, and use the known precise coordinates of the reference station to compare with the observed value to obtain a correction number and release it to the outside world . After receiving the correction number, the receiver compares it with its own observation value, eliminates most of the errors, and obtains a more accurate position. Experiments show that using differential GPS, the positioning accuracy can be increased to 5 meters.