GPS performance is good, high precision, is the best navigation and positioning system to date. GPS technology is used to measure the non-visual requirements between measuring points, convenient to select, can greatly reduce the cost of building high standards, save the cost of marking, can be observed all day, short observation time, fast data processing speed, high precision of results, etc. The completion and development will lead to a profound technological revolution in the surveying and mapping industry. GPS can be used to establish high-precision geodetic control points and engineering control points. GPS uses the L-band with two carrier frequencies: the center frequency of L1 is 1 575.42 MHz, and the center frequency of L2 is 1 227.6 MHz. There are many types of receivers, which can be divided into single-frequency coarse code receiver and dual-frequency fine code receiver according to the required accuracy. The real-time positioning accuracy of the coarse code receiver is about 25 m, and the real-time positioning accuracy of the fine code receiver is accurate. Better than 10 m, using a phase receiver, the relative positioning of the data processing (three-dimensional determination of the baseline) can be as high as one in a million, the baseline length can be from a few kilometers to 1 000 km, and the typical 15 km baseline is 3 The coordinate difference can be up to centimeter level, and the measurement time used is up to several hours.
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Application in urban surveying
With the acceleration of urbanization, urban measurement has developed greatly. Urban measurement results and mapping are important basic materials necessary for urban planning and construction management. Geodetic survey is the basis of other surveying and mapping work. Topographic maps and high-level control points for engineering construction, while providing accurate and basic data for geophysics. Combined with the actual control measurement (or geodetic survey) of each city, it is important to use GPS technology to establish and expand the urban control network. At present, many cities such as Guangzhou, Shenzhen, Beijing, and Shanghai have conducted explorations in this area and have achieved good results. From April to August 2005, the author led a team to establish the GPS-C/D network of Jiangmen City Control Network in Jiangmen area.
(1) Instruments and equipment 4 sets of 5650 dual-frequency receivers of Trimble Company of USA, equipped with small disk antennas, the nominal accuracy of the instrument is (10+2×10-6 mm)·D, and the receiver is long. Short baseline tests, as well as comparisons with standard baseline tests and other items to be tested, met the nominal accuracy criteria.
(2) The application situation began in April, and the GPS city network was measured in more than 280 points in 6 county-level cities of Jiangmen City, Xinhui, Heshan, Taishan, Kaiping and Enping. The principle of network deployment in various cities is to expand the control area and improve the accuracy based on the old network. The field measurement plan and data processing are arranged by the GPS operation group according to the specific conditions and requirements of each city. Such as the number of stations, the connection expansion of the network, the selection of the necessary coincidence points, and so on. The operating technology is based on the requirements of the Global Positioning System Measurement Specification (GB/T18314-2001) and the technical design book. According to the time of the satellite passing through the region, develop the operation plan, select the best satellite group, observe the two time periods every day for safety as much as possible during the daytime operation, at least 6 satellites can be tracked during observation, PDOP≤6 (Position Dilution of Precision position accuracy) Weakness), at least two stations per point, the duration is controlled at 30 to 60 minutes, and the edge-connected expansion is used to increase the redundant observation.
(3) Field baseline pretreatment and results selection A field portable computer is used to carry out baseline pre-processing on daily observation data. Retesting is performed on any baseline, closed loop overrun or full-circumference ambiguity. .
There are several reasons for this:
1) The instrument is unstable and may be related to meteorological conditions. One receiver is repaired and used on the first day. The baseline related to the instrument is completely unusable and the operation is improved.
2) If the temperature is too high, the accuracy of the result will be affected. If the temperature of a certain place reaches 36~38 °C, the results cannot be used. After adjusting the observation time, it can be solved;
3) After the lightning storm, the shutdown phenomenon occurred several times;
4) Inaccurate antenna measurement does not affect the baseline length.
Through several cities' application of results and comparison with old coordinates, GPS positioning technology is used in urban control networks and engineering networks, and has the advantages of high precision, high speed, high efficiency, low cost, and uniform and reliable results.
Application in terrain, cadastre and real estate measurement
Topographic maps provide topographic maps of cities, mines, and different scales for various projects to meet the needs of urban planning and various economic construction. Cadastral and real estate surveys are the precise location of land tenure boundaries, while mapping large-scale cadastral plans and property maps used by land and property management departments, and measuring land and floor space. GPS appears to accurately and quickly determine the coordinates of the control points at each level. In particular, the application of RTK (Real Time Kinematic real-time dynamic measurement) new technology, even without the control points at all levels, based on a certain number of reference control points, can accurately and quickly determine the boundary points, topographic points, features The coordinates of the points can be mapped into electronic maps in the field by using mapping software, and then output various scales of drawings through computers and plotters and printers.
When using RTK technology for positioning, the base station receiver is required to transmit observation data (such as pseudorange or phase observation) and known data (such as reference station coordinates) to the rover GPS receiver in real time, and the rover can quickly solve the whole week. The ambiguity, after observing 6 satellites (at least 4), can solve the dynamic position of the centimeter-level rover in real time. This is much better than the GPS static, fast static positioning needs to be processed afterwards. Therefore, as soon as the RTK technology appeared, its application in measurement immediately received attention.
(1) RTK technology for various control measurements
Conventional control measurements such as triangulation and traverse measurement require inter-point visibility, time-consuming and labor-intensive, and the accuracy is not uniform, and the accuracy of the measurement results is not known in the field. GPS static and fast static relative positioning measurement can perform various control measurements with high precision without the need for inter-point communication. However, data processing is time-consuming, and it is impossible to locate and know the positioning accuracy in real time. After the internal processing, the accuracy is not required to be reworked. The control measurement with RTK technology can not only know the positioning result in real time, but also know the positioning accuracy in real time, which can greatly improve the working efficiency. Real-time positioning with RTK technology can achieve centimeter-level accuracy. Therefore, in addition to high-precision control measurements, GPS static relative positioning technology is used. Control measurement in cadastral surveys, cadastral and real estate measurements, and control points are used. Bit measurement can be done using RTK technology. Using RTK technology to map, only one person carrying the instrument to observe the broken points on the point to be measured for 1 or 2 seconds and input the feature code at the same time, using electronic handbook or portable microcomputer to record, the position accuracy is satisfactory. Next, the terrain features in an area are measured and returned to the room or in the field, and the required topographic map can be output by professional mapping software. The use of RTK technology to measure points does not require point-to-point viewing. Only one person is required to complete the mapping work, which greatly improves the working efficiency of the mapping.
(2) Application of RTK technology in cadastre and real estate measurement
In the cadastre and real estate surveys, the RTK technology is used to determine the ownership boundary points of each land, as well as the surveying and mapping cadastre and real estate maps. As with the above surveyed topographic maps, the location of the relevant boundary points and some feature points can be measured in real time and can be achieved. The required centimeter accuracy. After the data obtained by the GPS is processed and directly recorded into the GPS, the cadastre and real estate map can be accurately obtained in time. However, in the shadow zone that affects the reception of GPS satellite signals, measurement tools such as total stations, range finder, and theodolite should be used, and detailed measurements should be made by analytical or graphical methods. In the measurement of the construction survey, the RTK technology can measure the position of the boundary pile in real time, determine the land use limit range, and calculate the land area. The use of RTK technology for surveying and setting out is the direct stakeout of coordinates. The area measurement in the construction surveying boundary is actually calculated and checked by the area calculation function in GPS software. The complexity of the conventional analytical method lofting is avoided, and the working procedure of the construction surveying and measuring industry is simplified.
Application in engineering deformation monitoring
Since it was put into civilian use in the mid-1980s, GPS has been widely used in various fields such as navigation and positioning, especially in the measurement and measurement of measurement circles. Because of its high precision, high efficiency, all-weather, and no need to look at the static relative positioning, it is widely used to gradually replace the conventional triangle, three sides, corners and other methods, and has achieved great success in theory and practice. The result. However, there are still few applications in the monitoring of precision engineering deformation, which is still in the theoretical research and practice. In the following, the author will analyze the benchmark design, graphic structure strength design, observation period design and monitoring period design of GPS in (engineering) deformation monitoring, and explore new ideas for using GPS technology to observe engineering deformation.
1 benchmark design
In engineering deformation monitoring, the baseline design (including positional reference and internal and external scaled reference design) is a work related to whether the monitoring results reliably and accurately reflect the deformation of the deformed body. Deformation monitoring of structures and structures, due to the constraints of the instrument and other factors, the reference point of the monitoring network can not be too far away from the deformation monitoring area, and too close will be affected by its own deformation, and the deformation value cannot be accurately reflected. So it is more difficult. Due to the continuous improvement of GPS technology and the introduction of high-precision instruments (1 +0.5×10-6 mm), it is easier to solve this problem. It is completely possible to select the reference point outside the deformation zone, thus ensuring the data. Reliability.
2 graphic structure strength design
The graphic intensity design refers to the geometric configuration between the deformation points, the deformation point and the reference point, the number of independent baselines in the network and the interconnection design. First of all, in the graphics selection process, it is necessary to take into account the effective control of the deformation point of the reference point, and the reference points must be able to check each other. Secondly, the design of model identification and parameter identification will guarantee the true deformation model and the real factors causing the deformation, in order to analyze the real factors causing the deformation and take corresponding countermeasures.
(1) Design model of model identification When designing the reference network, it should be able to effectively detect any unstable point in the network; when designing the relative network, it should be able to correctly detect and separate from several possible deformation models. A true deformation model. In order to ensure the correct deformation analysis results, the GPS monitoring network also needs good gross error detection and positioning capability. Studies have shown that when the number of baselines issued by each point in the GPS baseline vector monitoring network is at least three, the network has better reliability.
(2) Design model for parameter identification As can be seen from the above, as long as the distinguishability index satisfies the requirements, the sensitivity must meet the requirements, but the parameters of the optimal deformation model often require more accurate estimation.
3 Design of observation period and period
For the observation period and period, the nature of engineering and engineering deformation (such as drastic changes, continuous rapid changes, long-term slow changes, etc.) can be combined to make the best observations that are beneficial for the analysis results and monitoring intentions. Cycle, and can be combined with the current satellite distribution of the sky, the health of the satellite, for the length of time, day, night, weather and other external factors, the best observation period.
4 Continuous long-term observation, bifurcation metadata processing - a new data processing method describing deformation displacement (horizontal)
The relatively static positioning method usually performed is to use the data observed (synchronized) in a certain period of time, and obtain the coordinate vector between the points by means of difference, etc.; and for continuous engineering deformation, this is obtained. The most mature relationship between points in the time period. However, it is often necessary to know the relationship between the most mature points and points in a small time and even at a certain moment. At present, it is more common to use the synchronized observation data for a long period of time to perform the metadata processing. The method of getting the most mature point-to-point relationship at that time.
The application of GPS technology in engineering deformation monitoring is divided into the following steps:
(1) According to the purpose of monitoring, select points on the map, and then go to the field to ensure that the selected points meet the requirements of the network and the conditions of the field observations, and finally obtain the approximate points to be tested;
(2) According to the principle that three independent baselines are issued at each point and the side length distribution is relatively uniform, and according to the number of receivers and the principle of laying network, the observation pattern of the network is designed, and the route that may be additionally tested is selected;
(3) Calculate the required discriminability index (or accuracy index) until the required requirements are met, and finally obtain the final test plan after adding the independent observation baseline;
(4) Design of observation period and period;
(5) Using continuous observation and divergence metadata processing, or intermittent observation, the entire data processing method is used for data calculation;
(6) Using statistical data of observations, genetic analysis, linear regression of one or more components, stepwise regression, and graphs for data analysis.
It can be known from the above method that the same deformation body can be solved by this monitoring method, and it is directly affected by sunlight, wind power, external factors (such as the influence of vehicles driving on the bridge on the bridge), etc. at a certain moment. The relative relationship (relative displacement and disturbance, etc.) and their absolute displacement relative to the reference datum point. Analyze the significance of their various factors on the deformation body, and provide the most reliable and most intuitive data and analysis data for engineering and design, operation management units.
Conclusion
GPS positioning technology is also controlled by the United States. China's colleges and universities and scientific research departments are actively participating in this high-tech field research, establishing China's high-precision GPS control network, engaged in GPS orbit determination and precision positioning research, which will Let GPS technology show the bright future of application in various fields of national economic construction, national defense construction and scientific research.
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