GPS stands for "Global Positioning System", which means "Global Positioning System" in Chinese. It is a high-precision radio navigation positioning system based on artificial earth satellites. It can be used anywhere in the world and near the earth. The space can provide accurate geographical location, vehicle speed and precise time information; it is a new generation satellite navigation and positioning system with all-round real-time three-dimensional navigation and positioning functions on sea, land and air.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Global Positioning System (GPS) is a high-precision radio navigation positioning system based on artificial earth satellites. It can provide accurate geographical information anywhere in the world and in near-Earth space. Location, vehicle speed and precise time information.
Since its inception, GPS has attracted many users with its high accuracy, all-weather, global coverage, convenience and flexibility.
GPS is not only the patron saint of cars, but also the smart star of logistics industry management. With the rapid development of the logistics industry, GPS plays a decisive role and has become the second largest major consumer group after the automobile market.
GPS was developed by the United States starting in the 1970s. It took 20 years and cost 20 billion U.S. dollars. It was fully completed in 1994 and has the ability to conduct all-round operations on sea, land and air. A new generation satellite navigation and positioning system with real-time three-dimensional navigation and positioning functions. The use of my country's surveying and mapping departments in the past 10 years has shown that GPS has won the trust of the majority of surveying and mapping workers with its outstanding features such as all-weather, high precision, automation, and high efficiency, and has been successfully used in geodetic surveying, engineering surveying, and aerial photogrammetry. , vehicle navigation and control, crustal movement monitoring, engineering deformation monitoring, resource survey, geodynamics and other disciplines, thus bringing a profound technological revolution to the field of surveying and mapping.
GPS is the second generation satellite navigation system in the United States. It is developed on the basis of the meridian satellite navigation system and adopts the successful experience of the meridian system. According to the current plan, the space part of GPS uses 24 satellites with an altitude of approximately 20,200 kilometers to form a satellite constellation. The 24 satellites are all in a near-circular orbit with an operating period of approximately 11 hours and 58 minutes. They are distributed on 6 orbital planes (4 satellites per orbital plane) with an orbital inclination of 55 degrees. The distribution of satellites allows more than 4 satellites to be observed anywhere in the world at any time, and maintains geometry with good positioning solution accuracy. This provides a temporally continuous global navigation capability.
GPS mainly consists of three major components: space part, ground monitoring part and user equipment part. The GPS system has the characteristics of high accuracy, all-weather, and wide use.
Positioning principle
GPS positioning includes pseudo-range single point positioning, carrier phase positioning and real-time differential positioning.
1. Pseudorange measurement and pseudorange single point positioning
Pseudorange measurement is to measure the distance from the satellite to the receiver, which is the propagation time of the ranging code signal transmitted by the satellite to the GPS receiver multiplied by the speed of light. distance. Pseudo-range method single-point positioning is to use the GPS receiver to measure the pseudo-range with more than 4 GPS satellites at a certain time, and the instantaneous coordinates of the satellites obtained from the satellite navigation messages, and use the distance intersection method to calculate the WGS-84 position of the antenna. Three-dimensional coordinates in a coordinate system.
2. Carrier phase measurement and carrier phase positioning
Carrier phase measurement is to measure the phase delay between the GPS satellite carrier signal and the receiver antenna. The ranging code and navigation message are modulated on the GPS satellite carrier. After receiving the satellite signal, the receiver first removes the ranging code and satellite message on the carrier to regain the carrier, which is called reconstructed carrier. The GPS receiver compares the satellite reconstructed carrier wave with the local oscillator signal generated by the oscillator in the receiver through a phase meter to obtain the phase difference.
3. Real-time differential positioning
The principle of real-time differential positioning of GPS is to place a GPS receiver (called a base station) on an existing precise geocentric coordinate point, and use the known geocentric coordinates and ephemeris Corrections to GPS observations are calculated and sent to a moving GPS receiver (called a rover) via a radio communications device (called a data link). The rover uses the correction value to correct its own GPS observations to eliminate the above errors and thereby improve real-time positioning accuracy. There are many GPS dynamic difference methods, including position difference, pseudorange difference (RTD), carrier phase real-time difference (RTK), and wide-area difference.
GPS Features
GPS is currently the most successful satellite positioning system in use and is known as A milestone in human positioning technology. To sum up, the system has the following characteristics:
(1) Global, all-weather continuous navigation and positioning capabilities.GPS can provide continuous, all-weather navigation and positioning capabilities for various users anywhere in the world or in near-Earth space. Users do not need to transmit signals, so it can satisfy multiple users.
(2) Real-time navigation, high positioning accuracy and short observation time.When using GPS positioning, position data can be obtained several times within 1 second. This near-real-time navigation capability is of great significance to highly dynamic users. It can also provide users with continuous three-dimensional position, three-dimensional speed and accurate time information. At present, the real-time positioning accuracy using C/A code can reach 20-50m, the speed accuracy is 0.1m/s, using special processing it can reach 0.005m/s, and the relative positioning accuracy can reach millimeter level.
With the continuous improvement of the GPS system and the continuous updating of software, relative static positioning within 20km currently only takes 15-20 minutes. During fast static relative positioning measurements, when each rover is within 15km of the base station At this time, the observation time of the rover only takes 1-2 minutes, and then it can be positioned at any time, and the observation of each station only takes a few seconds.
(3) The measuring station does not require a clear view: GPS measurement only requires the sky above the measuring station to be open, and does not require the measuring stations to be visible to each other, so it can save a lot of standard building costs (generally The cost of standardization accounts for 30% and 50% of the total funds). Since there is no need to see between points, the point positions can be sparse or dense as needed, which makes the point selection work very flexible, and can also save the measurement work of transfer points and transition points in classic measurement.
(4) It can provide globally unified three-dimensional geocentric coordinates: GPS measurement can accurately determine the plane position and earth elevation of the station at the same time. The current GPS level can meet the accuracy of fourth-class leveling. In addition, GPS positioning is calculated in the globally unified WGS-84 coordinate system, so the measurement results at different locations around the world are interrelated.
(5) The instrument is easy to operate: With the continuous improvement of GPS receivers, the degree of automation of GPS measurements is getting higher and higher. During the observation, the surveyor only needs to install the instrument, connect the cables, measure the height of the antenna, and monitor the working status of the instrument. Other observation tasks, such as satellite capture, tracking, observation and recording, are automatically completed by the instrument. When the measurement is completed, , just turn off the power and put away the receiver to complete the field data collection task.
If long-term continuous observation is required at a measuring station, the collected data can also be transmitted to the data processing center through data communication to achieve fully automated data collection and processing. In addition, the size of the receiver is getting smaller and smaller, and the corresponding weight is getting lighter, which greatly reduces the labor intensity of the measurement author and makes field work easier.
(6) Strong anti-interference abilityand good confidentiality: GPS uses spread spectrum technology and pseudo code technology. Users only need to receive GPS signals and will not transmit signals themselves. It will be interfered by other external signal sources.
(7) Multiple functions and wide application: GPS is a dual-use system for both military and civilian use, and its application range is very wide. Specific application examples include: car navigation and traffic management, line patrol vehicle management, road engineering, personal positioning and navigators, etc.
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