Application of the hottest GPS in engineering surv

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The application of GPS in engineering survey Abstract: This paper briefly describes the basic structure and measurement principle of global positioning system (GPS), summarizes the characteristics of GPS in engineering survey, and introduces the application examples of GPS in engineering survey

key words: GPS; Engineering survey; Application example

global positioning system (GPS) is a new generation of satellite navigation and positioning system developed by the United States for military departments since the 1970s. It took 20 years and cost more than US $20 billion. It was developed in three stages and put into use successively. It was fully completed in 1994. GPS is a satellite based radio satellite navigation and positioning system. It has the functions of all-round, global, all-weather, continuous and real-time precision three-dimensional navigation and positioning, and has good anti-interference and confidentiality. Therefore, GPS technology has been applied in geodesy, engineering surveying, aerial photogrammetry, oceanography, urban surveying and other surveying and mapping fields [1], and has been studied and widely used in military, transportation, communication, resources, management and other fields. This paper introduces the application of GPS in engineering survey in mountainous areas, and puts forward some experiences

1 introduction to GPS

1.1 composition of GPS

gps is mainly composed of three parts: space satellite constellation, ground monitoring station and user equipment

(1) the GPS space satellite constellation consists of 21 working satellites and 3 on orbit standby satellites. The 24 satellites are evenly distributed in six orbital planes. The inclination of the orbital plane is 55 °, the average height of the satellites is 20200 km, and the operation period is 11 h 58 min. The satellite uses two L-band radio carriers to continuously send navigation and positioning signals to the majority of users. The navigation and positioning signals contain the position information of the satellite, making the satellite a dynamic known point. At any point on the earth, at any time, at an altitude angle of more than 15 °, an average of 6 satellites can be observed at the same time, up to 9 satellites

(2) GPS ground monitoring stations are mainly composed of one master control station, three injection stations and five monitoring stations distributed all over the world. The master control station calculates the orbit parameters, clock error parameters, etc. of each satellite according to the observation data of each monitoring station on the GPS satellite, and compiles these data into navigation messages, which are transmitted to the injection station, and then the injection station injects the navigation messages sent by the master control station into the memory of the corresponding satellite

(3) GPS user equipment consists of GPS receiver, data processing software and its terminal equipment (such as computer). The GPS receiver can capture the signal of the satellite to be measured selected according to a certain satellite height cut-off angle, track the operation of the satellite, exchange, amplify and process the signal, and then calculate the three-dimensional coordinates of the GPS receiver Center (measuring station) through baseline calculation and adjustment through the computer and corresponding software

1.2 GPS positioning principle

gps positioning is realized according to the distance intersection point principle in measurement [2]. The GPS receiver is set at the point to be measured Q, and at a certain time TK receives the signals sent by three (or more) satellites S1, S2 and S3 at the same time. Through data processing and calculation, the distance from the receiver antenna center (measuring station) to the satellite at that time can be obtained ρ 1、 ρ 2、 ρ 3。 According to the satellite ephemeris, the three-dimensional coordinates (XJ, YJ, ZJ) of the three satellites at that time can be found, j = 1, 2, 3, so the three-dimensional coordinates (x, y, z) of point Q can be calculated from the following formula:

1.3 characteristics of GPS measurement

compared with conventional measurement, GPS measurement mainly has the following characteristics:

① high measurement accuracy. The accuracy of GPS observation is significantly higher than that of general conventional measurement. On the baseline less than 50 km, the relative positioning accuracy can reach 1 × 10-6, up to 1 on baselines greater than 1000 km × 10-8。

② intervisibility is not required between stations. GPS measurement does not require intervisibility between stations, but can determine the point location according to the actual needs, making the point selection more flexible and convenient

③ the observation time is short. With the continuous improvement of GPS measurement technology and the continuous updating of software, during GPS measurement, the static relative positioning takes only about 20 minutes per station and the dynamic relative positioning takes only a few seconds

④ the instrument is easy to operate. At present, the GPS receiver is becoming more and more automatic and the operation is intelligent. The observer only needs to center, level, measure the antenna height and set parameters after starting up, and the receiver can automatically observe and record

⑤ all-weather operation. The number of GPS satellites is large and the distribution is uniform, which can ensure continuous observation at any time and at any place. Generally, it is not affected by weather conditions

⑥ provide three-dimensional coordinates. GPS survey can accurately measure the three-dimensional coordinates of survey stations at the same time, and its elevation accuracy can meet the requirements of fourth-order leveling

2 application examples

2.1 project overview

the project involved in this paper is invested and constructed by a group company. It is a comprehensive project integrating leisure, entertainment, tourism, vacation and other functions. The project is located in the outskirts of the city, covering an area of more than 66.7 hm2. It belongs to the terrain of two mountains and one ditch, and the mountainous area accounts for about two-thirds. About 90 m at the highest point. The mountains are lush with trees, complex terrain, difficult intervisibility and inconvenient walking. For the design and construction of the project, the primary control shall be established. Considering the complexity of the project, tight construction period, difficult intervisibility in the survey area, large topographic relief and other factors, it is decided to adopt GPS survey

2.2 technical design of GPS surveying

(1) the technical design of GPS surveying is mainly based on the industrial standard code for urban surveying issued by the Ministry of construction in 1999, the industrial standard technical specification for GPS urban surveying issued by the Ministry of construction in 1997 and the relevant requirements of the engineering surveying contract

(2) according to the project needs and the situation of the survey area, the urban or engineering secondary GPS is selected as the primary control of the survey area. It is required that the average side length is less than 1 km, the relative mean square error of the weakest side is less than 1/10000, the fixed error a of the nominal accuracy of the GPS receiver is ≤ 15 mm, and the proportional error coefficient B is ≤ 20 × 10-6。

(3) the design basis and shape are shown in Fig. 2. A total of 12 points are controlled, including 2 known horizontal control points (i12, i13) and 5 elevation control points (i12, i13105109110, whose elevation is measured by the fourth-order leveling). Three GPS receivers are used for observation, which are arranged in a side connected manner

(4) the observation plan selects the best observation period (more than 4 satellites, clean inside and outside, uniform distribution without corrosion, and PDOP value less than 6) according to the visual prediction map and geometric figure intensity (spatial position factor PDOP) of more than 2000 GPS satellites of the mold manufacturer, and prepares the operation schedule

2.3 field practice of GPS surveying

(1) there is no need for intervisibility between GPS surveying stations, and the graphic structure is flexible. Therefore, it is convenient to select points. However, in consideration of the particularity of GPS measurement and the subsequent measurement, the following points should be taken into account when selecting points: ① each point should be intervisibility with a certain point to facilitate the use of subsequent measurement; ② There shall be no obstacle above the height angle of 15 ° around the point to prevent the signal from being blocked or absorbed; ③ The points shall be far away from high-power radio emission sources, high-voltage wires, etc. to avoid the interference of electromagnetic fields on signals; ④ The point shall be selected in the field of vision. The mission has completed the final flight test at NASA's Marshall Space Flight Center in Huntsville, Alabama. It is an open, convenient, easy to expand and easy to preserve place for observation and future use; ⑤ After the point selection, mark stones shall be buried as required and the points shall be filled in

(2) observation shall be carried out according to the arrangement of GPS operation schedule. Static relative positioning shall be adopted. The satellite altitude angle is 15 °, the period length is 45min, and the sampling interval is 10 s. Three receiver antennas (centering, leveling and orientation) shall be installed at three points at the same time. The antenna height shall be measured, meteorological data shall be measured, and the machine shall be started for observation. When all indicators meet the requirements, the receiver shall input relevant data according to the prompts of the receiver, and the receiver shall automatically record, and the observer shall fill in the measurement manual

2.4 data processing of GPS measurement

gps data processing is divided into two stages: baseline solution and adjustment, which are completed by random software. After baseline calculation, quality check, field survey and adjustment, the three-dimensional coordinates of GPS control points are obtained, and each accuracy index meets the technical design requirements

3 conclusion

through the application of GPS in surveying, the following experiences are obtained

(1) GPS control is flexible in point selection, convenient in layout, and is basically not limited by intervisibility and shape, especially in survey areas with complex terrain and difficult intervisibility. However, due to the poor conditions in the survey area, the side length is short (the average side length is less than 300 m), the relative accuracy of baseline is low, and the relative accuracy of individual side length is greater than 1/10000. Therefore, when the accuracy requirements are high, the short side should be avoided, and when it is unavoidable, the observation should be cautious

(2) GPS receiver observation has basically realized automation and intelligence, and the observation time is decreasing, which greatly reduces the operation intensity. The observation quality is mainly affected by the spatial distribution of satellites and the quality of satellite signals. However, as the selection of each point is limited by the terrain conditions, trees block it, affecting the observation of the satellite and the quality of the signal. It passes after re measurement. Therefore, the observation points shall be selected in strict accordance with the relevant requirements, the best time period shall be selected for observation, and attention shall be paid to the use of walkie talkie and other equipment

(3) the data transmission and processing of GPS measurement are completed by random software. As long as the quality of the received satellite signal and the quantity and accuracy of the known data are guaranteed, customers are also requested to pay more attention to the knowledge of other experimental machines of our company, and the three-dimensional coordinates of the control points that meet the accuracy requirements can be easily obtained. However, because there are few known elevation points (only 5) in the joint survey, the elevation accuracy of the control points is low. Therefore, to ensure the accuracy of the elevation of control points, it is necessary to measure enough known elevation points

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