Application of GPS technology in highway field survey?

Global Positioning System (GPS) is a satellite navigation system jointly developed by the US Army, Navy and Air Force. As a new generation of satellite navigation and positioning system, GPS not only has good anti-interference and confidentiality, but also has global, all-weather, continuous and real-time precision three-dimensional navigation and positioning capabilities, which can provide accurate three-dimensional coordinates, speed and time for various users.

Keywords: GPS；; RTK highway survey

With the development of science and technology, GPS technology has entered the industry in expressway. Six years later, I made the following comments on the use of GPS measurement:

Brief introduction of GPS measurement

Global positioning system is a satellite navigation and positioning system developed and put into use in the United States. In the field of survey, GPS system has been widely used in geodesy, engineering survey, topographic survey and so on, especially the real-time dynamic (RTK) positioning technology has great technical potential in highway survey.

Second, the application prospect of GPS technology in highway survey

At present, although advanced instruments and equipment such as electronic total station are used in highway survey, the conventional survey method is limited by lateral visibility and working conditions, with high work intensity and low efficiency, which greatly prolongs the design cycle. Using GPS survey can overcome the above shortcomings, improve working efficiency, reduce labor intensity and ensure the quality of highway survey and design at all levels. Compared with previous surveys, GPS surveys mainly have the following characteristics:

① Interstation intervisibility is not required. Interstation intervisibility is always a difficult problem in measurement. This feature of GPS makes the point selection more flexible and convenient.

② High positioning accuracy. Generally, the baseline accuracy of dual-frequency GPS receiver is 5mm 1ppm, while the nominal accuracy of infrared instrument is 5mm 5ppm. The accuracy of GPS measurement is equivalent to that of infrared instrument, but with the increase of distance, the advantages of GPS measurement become more and more prominent.

③ The observation time is short. On the short baseline less than 20km, the rapid relative positioning generally takes only 5min observation time.

(4) Provide three-dimensional coordinates. GPS survey can accurately determine the plane position of the observation station and the geodetic elevation of the observation station.

⑤ Simple operation. The degree of automation of GPS measurement is very high. In observation, the main task of surveyors is to install and switch instruments, measure the height of instruments and monitor the working state of instruments, while other observation work, such as satellite capture and tracking observation, is automatically completed by instruments.

At present, the technical potential of highway survey lies in the application of RTK (real-time dynamic positioning) technology, which has a very broad application prospect in highway engineering.

Third, the application of RTK technology in highway survey

3. Introduction of1RTK positioning technology: It is a real-time differential GPS(RTK) technology based on carrier phase observations. It is a new breakthrough in the development of GPS measurement technology and has a broad application prospect in highway engineering. As we all know, whether static positioning or dynamic positioning, due to the lag of data processing, it is impossible to calculate the positioning results in real time and check the observation data, so it is difficult to ensure the quality of the observation data. In practical work, the unqualified observation results caused by gross errors often need to be reworked and re-measured. The main method to solve this problem is to extend the observation time to ensure the reliability of measurement data, which reduces the working efficiency of GPS measurement. Real-time dynamic positioning system consists of reference station and mobile station, and the establishment of wireless data communication is the guarantee of real-time dynamic measurement. There are two measurement modes for real-time dynamic (RTK) positioning: static positioning and dynamic positioning. The combination of the two positioning modes can cover highway survey, construction lofting, supervision and GIS (Geographic Information System) front-end data collection.

3.2 Application. The latest RTK technology has the following functions and functions in highway survey and design:

① Drawing large-scale topographic maps. Route selection of high-grade highways is mostly carried out on large-scale (1: 1000 or 1: 2000) strip topographic maps. In traditional surveying and mapping, control points should be established first, and then detailed investigation should be carried out to draw large-scale topographic maps. This method has the advantages of heavy workload, slow speed and long time consuming. This shortcoming can be completely overcome by using real-time GPS dynamic measurement. You only need to stay for a minute or two at each breakpoint along the line to get the coordinates and elevation of each point. Combined with the input point element code and attribute information, the data with all breakpoints in the band can be drawn indoors with drawing software. Because it only needs to collect the coordinates of breakpoint and input its attribute information, and the collection speed is fast, the difficulty of surveying and mapping is greatly reduced, which saves time and effort and is very practical.

(2) Road centerline lofting. After the alignment is determined on the large-scale strip topographic map, the designer needs to mark the highway center line on the ground. Using real-time GPS survey, as long as the coordinates of the middle pile point are input into the GPS electronic manual, the system software will automatically determine the position of the lofting point. Because the measurement of each point is completed independently, there will be no accumulated error, and the lofting accuracy of each point tends to be consistent.

(3) Layout of transverse and longitudinal sections of roads and calculation of earthwork. When setting out vertically, firstly, the data to be set out are input into the electronic manual, and the setting-out point file of the construction plane is generated and stored for setting out at any time; When setting out the cross section, first determine the cross section form (filling, digging, half filling and half digging), then input the cross section design data into the electronic notebook (such as slope gradient, shoulder width, road width, superelevation, widening and design height), generate the construction lofting point file, save it, and set out at the site at any time. At the same time, the software can automatically connect with the ground line, carry out the work of "wearing a hat" and use the "section method" to calculate the earthwork. Through the drawing software, the longitudinal section along the line and the cross-sectional map of each point can be drawn. Because all the data used are collected during topographic mapping, there is no need to go to the site for longitudinal and cross-sectional measurement, which greatly reduces the workload in the field. In addition, dynamic GPS can be used to detect compounds on site when necessary, which is economical and practical compared with traditional methods.

3.3 Advantages of RTK technology:

① Real-time dynamic display of centimeter-level accuracy measurement results (including elevation) tested by reliability. ② Completely get rid of the rework caused by gross error and improve the efficiency of GPS operation.

(3) The operation efficiency is high, each lofting point only needs to stay at 1-2s, and the mobile stations work in groups, and each group (3-4 people) can complete the centerline measurement of 5- 10km, which is incomparable in accuracy and efficiency to conventional measurement.

(4) Finish the pile leveling work at the same time of setting out the centerline.

⑤ The application scope is wide, which can cover many aspects such as highway survey (including horizontal, vertical and horizontal), construction lofting, supervision, completion survey, maintenance survey, GIS front-end data acquisition and so on.

⑥ RTK can be combined with total station, and their respective advantages can be brought into full play with corresponding software assistance.

References:

[1] Xu Shaoquan. Principle and application of GPS measurement [M]. Wuhan Technical University of Surveying and Mapping Press. 1998

[2] Gao Deci, Wen. Surveying [M]. Beijing University of Technology Press. 1996

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