1. How does the GPS
positioning system locate
24 GPS satellites are located at an altitude of 12,000 kilometers above the ground. The 12-hour cycle orbits the earth, making it possible to observe more than 4 satellites simultaneously from any point on the ground at any time.
Because of the precise position of the satellites, we can get the distance from the satellite to the receiver in GPS observation. Using the distance formula in the three-dimensional coordinates and using 3 satellites, we can form 3 equations. The position of the observation point (X, Y, Z). Considering the error between the satellite’s clock and the receiver’s clock, there are actually 4 unknowns, X, Y, Z and the clock difference, so it is necessary to introduce a fourth satellite to form 4 equations to solve, so as to obtain the observation point’s Latitude and longitude and elevation.
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 of 4, and then the algorithm with the smallest error is selected. One set is used for positioning, which improves accuracy.
Due to the errors in satellite orbits and satellite clocks, the influence of atmospheric troposphere and ionosphere on signals, and the artificial SA protection policy, the positioning accuracy of civilian GPS is only 100 meters. In order to improve the positioning accuracy, the differential GPS (DGPS) technology is generally used to establish a base station (differential station) for GPS observation, and use the known precise coordinates of the base station to compare with the observed value to obtain a correction number and publish 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 relatively accurate position. Experiments show that using differential GPS, the positioning accuracy can be improved to 5 meters.
The main car navigation system It consists of a navigation host and a navigation display terminal. The built-in GPS antenna will receive data information from at least 3 of the 24 GPS satellites orbiting the earth to determine the current position of the car. By matching the position coordinates determined by the GPS satellite signal with the electronic map data, the navigation host can determine the exact position of the car in the electronic map.
On this basis, various functions such as driving navigation, route recommendation, information inquiry, and AV/TV playback will be realized. The driver only needs to watch the picture on the display, listen to the voice prompt, and operate the remote control in his hand to realize the above functions, so as to drive easily and freely.
Global Positioning System (Global Positioning System) is the second-generation satellite navigation system in the United States. It is developed on the basis of the Meridian satellite navigation system, and it adopts the successful experience of the Meridian system. Like the meridian system, the global positioning system consists of three parts: the space part, the ground monitoring part and the user receiver.
According to the current plan, the space part of the global positioning system uses 24 satellites with an altitude of about 20,200 kilometers to form a satellite constellation. The 21+3 satellites all have near-circular orbits, with an operating period of about 11 hours and 58 minutes, and are distributed on six orbital planes (four per orbital plane) with an orbital inclination of 55 degrees. The distribution of satellites enables more than four satellites to be observed anywhere in the world at any time, and maintains a geometric figure (DOP) with good positioning accuracy. This provides continuous global navigation capability in time.
The ground monitoring section includes four monitoring stations, an upstream injection station and a master control station. The monitoring station is equipped with GPS user receivers, atomic clocks, sensors for collecting local meteorological data and computers for preliminary data processing. The main task of the monitoring station is to obtain satellite observation data and transmit these data to the main control station. The main control station is located at Vandenberg Air Force Base. It exercises full control over the Ground Surveillance Department. The main task of the main control station is to collect all the observation data of GPS satellites from each monitoring station, and use these data to calculate the orbit and satellite clock correction value of each GPS satellite. Upstream injection stations are also located at Vandenberg Air Force Base. Its main task is to inject this kind of navigation data and the command of the main control station into the satellite when each satellite moves to the sky. This injection is performed once a day for each GPS satellite, with a final injection before the satellite leaves the range of the injection station.
Global positioning system has the characteristics of good performance, high precision and wide application, and is the best navigation and positioning system so far. With the continuous improvement of global positioning system and the continuous improvement of hardware and software, the application fields are constantly being developed. At present, it has spread to various sectors of the national economy, and has begun to gradually penetrate into people’s daily life.
Second, the positioning principle of GPS navigation
d2=[ (x2-x)^2+(y2-y)^2+(z2-z)^2]^1/2+c(Vt2-Vt0)
d4=[(x4-x)^2+(y4-y)^2+(z4-z)^2]^1/2+c(Vt4-Vt0)
above The coordinates x, y, z and Vto of the point to be measured in the four equations are unknown parameters, where di=c??ti (i=1, 2, 3, 4).
di(i=1, 2, 3, 4) are the distances from satellite 1, satellite 2, satellite 3, and satellite 4 to the receiver, respectively.
??ti (i=1, 2, 3, 4) is the time it takes for the signals from satellite 1, satellite 2, satellite 3, and satellite 4 to arrive at the receiver, respectively.
c is the propagation speed of the GPS signal (ie the speed of light).
The meanings of the parameters in the four equations are as follows:
x, y, z are the space rectangular coordinates of the coordinates of the point to be measured.
xi, yi, zi (i=1, 2, 3, 4) are the rectangular space coordinates of satellite 1, satellite 2, satellite 3, and satellite 4 at time t, which can be obtained from the satellite navigation message .
Vt i (i=1, 2, 3, 4) are the clock errors of the satellite clocks of satellite 1, satellite 2, satellite 3, and satellite 4, respectively, provided by the satellite ephemeris.
Vto is the clock error of the receiver.
The coordinates x, y, z of the point to be measured and the clock error Vto of the receiver can be calculated from the above four equations.
The basic positioning principle of GPS is: the satellite continuously sends its own ephemeris parameters and time information. After the user receives the information, the three-dimensional position, three-dimensional direction and movement speed of the receiver are calculated and calculated. and time information.
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