The application of GPS technology in highway survey is an important technical revolution in highway field survey, and its application and development prospect are very broad. In particular, real-time dynamic (RTK) positioning technology has great technical potential in highway survey. This paper mainly introduces the application of RTK technology in GPS in highway survey and its great promotion to highway survey.
1, development status of GPS technology
GPS (GlobalPositioningSystem) is a satellite navigation system jointly developed by the US Army, Navy and Air Force. It has global, all-weather, continuous and real-time navigation and positioning functions, and can provide accurate three-dimensional coordinates, speed and time for all kinds of users. Single point navigation and relative geodesic positioning are two aspects of GPS application; Relative geodesic positioning is the main application mode of conventional survey.
Relative geodesic positioning is to realize high-precision measurement by using L 1 and L2 carrier phase observations. Its principle is to adopt the local difference method of carrier phase measurement: find the first difference between receivers and the second difference between receivers and satellite observation epochs, and calculate the length of the baseline to be determined through two differential calculations; Solving integer ambiguity is one of the key technologies. According to the algorithm model, static, fast static and RTK operation modes are designed. Static operation mode is mainly used for high-precision measurement such as crustal deformation observation, national geodesy and dam deformation observation; Fast static measurement is widely used in general engineering survey because of its high efficiency and centimeter-level accuracy. RTK survey is widely used in data acquisition (such as detail survey) and engineering lofting because of its fast, real-time and centimeter-level accuracy. RTK technology represents the mainstream of GPS relative geodesic positioning application.
GPS geodesic receiving equipment is the basic condition to realize geodesic positioning. The receiver is divided into single-frequency and dual-frequency. The dual-frequency can be used to correct ionospheric refraction effect by L2 observation, which is most suitable for medium and long baseline (above 20km) measurement. It has the function of fast static measurement and can be upgraded to RTK function. Single-frequency machine is suitable for short baseline measurement less than 20km, and has good cost performance for general engineering measurement. RTK system consists of GPS receiving equipment, radio communication equipment, electronic notebook and supporting equipment. The whole set of equipment has the characteristics of light weight, simple operation, real-time reliability and centimeter-level accuracy, which can completely meet the requirements of data acquisition and engineering lofting. In view of the limited number of satellites in orbit of GPS system, normal calculation cannot be guaranteed when the visibility to the air is blocked, which affects the accuracy and reliability of positioning. Practice shows that single-frequency GPS system has great limitations due to various environmental constraints. With the continuous improvement of Russian Global Navigation Satellite System (CLONASS), American Ashtech Company has successfully developed a dual constellation system (GLONASSGPS) which uses GLONASS to improve GPS performance. This all-weather, all-region, high-precision system provides users with more perfect receiving equipment, and the receiving equipment of the dual constellation system has reached a new level.
2. The application prospect of 2.GPS technology in highway survey.
With the rapid growth of China's national economy and the implementation of the western development, the construction of high-grade highways in our province has ushered in unprecedented development opportunities, which puts forward higher requirements for survey and design. With the development of software technology and hardware equipment in highway design industry, highway design has been mainly based on CAD, and some software itself needs the support of ground digital surveying and mapping products; Establishing an integrated data link of survey, design, construction and post-management and reducing intermediate links such as data copying and input are the requirements of "integration of indoor and outdoor work" of highway survey and design, and also the "bottleneck" that affects the development of high-grade highway design technology. 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. The progress of measurement technology lies in the introduction of equipment and technical transformation, and the introduction of GPS technology should be the first choice under the current technical conditions. At present, the GPS static or fast static method is used to establish the general control survey along the line, which provides the basis for surveying and mapping the strip topographic map and measuring the plane and longitudinal plane of the route in the survey stage. The establishment of bridge and tunnel construction control network in the construction stage is only the initial stage of GPS application in highway survey. In fact, 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. The following briefly introduces the application of RTK technology in highway survey.
3. Application of 3.RTK technology in highway survey.
3. Brief introduction of1RTK positioning technology
Real-time dynamic (RTK) positioning technology is a real-time differential GPS(RTDGPS) 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 quasi-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.
The real-time dynamic positioning system consists of a reference station and a mobile station. Establishing wireless data communication is the guarantee of real-time dynamic measurement. Its principle is to take the first control point with high accuracy as the reference point, and place a receiver as the reference station to continuously observe the satellite. The receiver on the mobile station receives the satellite signal and the observation data on the reference station through the radio transmission equipment, and the random computer calculates and displays the three-dimensional coordinates and measurement accuracy of the mobile station in real time according to the relative positioning principle. In this way, users can monitor the data observation quality of the points to be measured and the convergence of the baseline calculation results in real time, and determine the observation time according to the accuracy index of the points to be measured, thus reducing redundant observation and improving work efficiency.
3.2 Application
There are two measurement modes for real-time dynamic (RTK) positioning: fast 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. 1 Fast static positioning mode. The GPS receiver needs static observation at each mobile station. During observation, the synchronous observation data of reference station and satellite are received at the same time, and the whole unknown and the three-dimensional coordinates of user station are calculated in real time. If the change of calculation results tends to be stable and the accuracy meets the design requirements, the real-time observation can be ended. Generally used for control measurement, such as control network encryption; If conventional survey methods (such as total station survey) are used, they are greatly influenced by objective factors, and it is difficult to implement them in areas with harsh natural conditions, while RTK rapid static survey can get twice the result with half the effort. Single point positioning only takes 5- 10min (with the continuous development of technology, the positioning time will be shortened), which is less than one-fifth of the time required for static measurement. In highway survey, it can replace total station to complete the encryption of control points such as traverse survey.
3.2.2 Before dynamic positioning measurement, it is necessary to observe at a control point for a few minutes (some instruments only need 2 ~ 10s) for initialization, and then the rover station can automatically observe at a predetermined sampling interval to determine the spatial position of the sampling point in real time together with the synchronous observation data of the reference station. At present, its positioning accuracy can reach centimeter level.
Dynamic positioning mode has a broad application prospect in highway survey stage, which can complete topographic mapping, middle pile survey, cross-section survey, vertical section ground line survey and so on. After measuring for 2 ~ 4 s, the accuracy can reach 1 ~ 3 cm, and the whole measurement process does not need intervisibility, which has incomparable advantages over conventional measuring instruments (such as total station).
3.3 advantages of RTK technology
3.3. 1 Real-time dynamic display of centimeter-level accuracy measurement results (including elevation) after reliability test.
3.3.2 Completely get rid of rework caused by gross error, and improve the efficiency of GPS operation.
3.3.3 The operation efficiency is high, and each lofting point only needs to stay at 1 ~ 2s. Mobile stations work in groups, and each group (3 ~ 4 people) can complete the 5 ~ 10km centerline survey. If it is used in topographic survey, each group can complete topographic mapping of 0.8 ~ 1.5km3 every day, with normal accuracy and efficiency.
3.3.4 At the same time of setting out the center line, the leveling of the intermediate pile is completed.
3.3.5 Wide application range-it 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.
3.3.6 RTK can cooperate with total station to give full play to their respective advantages if there is corresponding software assistance.
3.4 Promotion suggestions
3.4. 1GPS static positioning technology combined with dynamic positioning technology can complete highway plane control survey efficiently and accurately.
3.4.2 The production process combining conventional methods with GPS technology can greatly improve the production efficiency.
3.4.3 With the development of GPS technology characterized by RTK technology, various manufacturers have successively introduced instruments with independent patent technology, which have shorter initialization time, stronger tracking ability, higher accuracy, stronger reliability and better cost performance. Survey and design units tend to replace total station, and this factor should be considered when updating unit equipment.
3.4.4GPS The application of GPS technology in highway survey is a revolutionary technical innovation in highway survey, which will update the traditional operation concept.
4. Conclusion
The application of GPS in highway survey has revolutionized the survey methods and working methods of high-grade highways, and greatly improved the survey accuracy and efficiency. In particular, real-time dynamic (RTK) positioning technology will have broad application prospects in highway survey, construction, post-maintenance and management.
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