Due to the characteristics of
transmission line survey work and the advantages and characteristics of Global Positioning System (
GPS ),
GPS is inevitable for
transmission line surveys.
GPS makes the introduction of quality
power transmission line survey, are given to improve efficiency, is a major
transmission line survey technology leap.
Abstract: Due to the characteristics of
transmission line survey work and the advantages and characteristics of Global Positioning System (
GPS ), it is inevitable that
GPS will be applied to
transmission line survey.
GPS makes the introduction of quality
power transmission line survey, are given to improve efficiency, is a major
transmission line survey technology leap.
Key words
GPS RTK static measurement
transmission line [Author] Zhao Chengming Guangdong Electric Power Design Institute
1 Introduction
GPS (also known as Global Positioning System) is established by the US Department of Defense to meet the military's requirements for high-precision navigation and positioning of offshore, land, and airborne facilities. The system has been designed and developed since the early 1970s. According to Zui's initial design idea, the pseudo-random noise code (P code) transmitted by the receiving satellite is used to provide the m-level navigation positioning for the US and North Atlantic allied forces, and the C/A code pseudo-range with the positioning accuracy of several tens of meters is provided. Civil navigation positioning. With the development of technology,
GPS operation mode has evolved from static measurement, fast static measurement, post-processing high-precision dynamic measurement, to dynamic initialization (OTF) centimeter-level real-time RTK (carrier phase real-time dynamic differential positioning (Real-TimeKinematic) Measurement work. In terms of accuracy, the static measurement can be up to 3mm + 0.5ppm after post-processing, and the RTK positioning accuracy can reach 10mm +1ppm.
GPS measurement Compared to classical measurement,
GPS measurement has the following characteristics:
(1) There is no need to look through the stations. Inter-station inter-viewing has always been a problem in measurement. This feature of
GPS makes the selection point more flexible and convenient. However, the station must be wide open so that the receiving
GPS satellite signals are not disturbed.
(2) High positioning accuracy. The baseline resolution of the general dual-frequency
GPS receiver is 5mm+1ppm, while the infrared instrument has a nominal accuracy of 5mm +5ppm. The
GPS measurement accuracy is comparable to that of the infrared, but as the distance increases, the
GPS measurement superiority becomes more prominent.
(3) The observation time is short. On a short baseline of less than 20 km, fast relative positioning typically takes only 5 minutes of observation time.
(4) Provide three-dimensional coordinates.
GPS measurements accurately determine the earth's elevation of the observatory while accurately measuring the plane position of the observatory.
(5) Easy to operate.
GPS measurements are highly automated.
In the observation, the surveyor's main task is to install and switch the instrument, measure the instrument height and monitor the working state of the instrument, while other observations such as satellite capture, tracking observation, etc. are automatically completed by the instrument.
(6) All-weather operation.
GPS observations can be performed continuously, at any time, anywhere, and are generally unaffected by weather conditions.
It is the above characteristics that determine that
GPS must be widely used in the survey of
transmission lines .
2 Application of
GPS static measurement in
transmission line survey
Surveys of
transmission lines are divided into industrial surveys and aerial photogrammetry, and any measurement method requires
GPS static measurement and RTK participation. The first to participate is static measurement, that is, the arrangement and observation of control points around the entire
transmission line , used to carry out elevation and plane control of the entire line.
For the aerial photogrammetric
transmission line , most of the taken road maps are photos of about 1:10000. The first thing to do is to select the appropriate points on these aerial photographs as the control points for static external control. In the choice of control points, we refer to aerial photographs. We try to use the naked eye to distinguish them, and the surrounding height difference is not big, to facilitate the matching of photos; but at the same time we must take into account the characteristics of the
line survey , such as road conditions, whether it can Easy to arrive and more. Therefore, we need to pay attention to the following points when laying out the external control points:
(1) A
transmission line is divided into several navigation belts. Each belt map consists of multiple aerial photographs. We stipulate that each belt has at least three control points to control, regardless of the length of the belt.
(2) Select a location on the aerial film where the features are relatively obvious and the points are easy to preserve, and the surrounding height difference is small, the vegetation is low, and as far as possible away from the building.
(3) When selecting a point, according to the situation of the road, try to choose a convenient place, and can not deviate too far from the center line of our line.
(4) Although the accuracy of the line survey is relatively low, it is not necessary to consider the mesh shape when selecting points, but it should be noted that the distribution of the number of control points on the left and right sides of the line is basically equal, and the distance between two adjacent points is not more than 4km. Because it is guaranteed to be within the operating radius of the RTK. All adjacent two-point lines are zigzag, and the line center line runs through it.
(5) The total number of points selected for each voyage can be greater than 0.33 points per kilometer as a reference.
(6) Insert the national control points appropriately at the appropriate positions at the beginning and the middle of the entire line. The entire line is at least two (fifty kilometers) and relatively long at least three to four (fifty kilometers or more). .
(7) When selecting a point, the baseline between the two points may be too long because there is no suitable position. In this case, the transition point can be used, and the transition point participates in the adjustment but does not participate in the matching of the aerial survey photos.
After the control point is selected, it is the observation work in the field. In the observation process, it is necessary to pay attention to:
(1) Set up the
GPS receiver, especially for the receiver's sudden situation, such as: the receiver suddenly crashes and the line contact is bad, the terminal can not control the receiver.
(2) Make a good point and record the antenna height and observation period.
(3) Make a mark on the spot to facilitate future search.
Since the accuracy requirements of the
transmission line are relatively low, we only guarantee a joint common point between the two observations in the field static observation, not the common side. The length of the observation period depends on the length of the side. Since most of it is about 3km, most of the time is twenty to forty minutes.
After the field observation is done, the next step is the post-processing of the data, which should pay attention to the antenna height and point number of the data. The data post-processing work includes data adjustment and the establishment of a coordinate transformation system, which is divided into a one-step method and a classical three-dimensional method. Since the
transmission lines are generally long, the classical three-dimensional method is used to find the conversion parameters, and the static operation ends.
For the circuit of the test, there is no need to match the photos, and the other basic work is basically the same.
3 RTK measurement in
transmission line survey
RTK refers to carrier phase real-time dynamic differential positioning (Real-TimeKinematic), which is a new form of zui developed by
GPS . Static
GPS measurements can achieve centimeter or even millimeter accuracy with phase difference, but the disadvantage is that the results are known after the process. And RTK can achieve centimeter-level accuracy through real-time processing.
The application of RTK in
transmission lines is mainly used for alignment, positioning, stakeout of straight piles and towers, and measurement of flat sections.
The form of data that
GPS can provide directly is the coordinates. The two main functions of RTKzui are real-time mapping and engineering lofting. The basic functions we use are the lofting function. For the flat section measurement, the point coordinates of each feature are also recorded by the lofting function, and the different landmarks are distinguished by the previously agreed point markers; the tower topographic map can also be measured by the same method.
RTK requires a base station and at least one rover and associated data communication chain. The base station transmits the station information and all observations to the rover through the data link in real time. The rover uses advanced processing techniques to instantaneously determine the three-dimensional coordinates of the rover.
The application of RTK technology to transmission circuits is inevitably related to its characteristics:
(1) High work efficiency. Under the general topographical terrain, the high-quality RTK station can measure the measuring area of ​​4km radius once, only one person is required to operate. In the general electromagnetic wave environment, a little coordinate is obtained in a few seconds, the working speed is fast, and the labor intensity is low. , saving the cost of the field and improving labor efficiency.
(2) High positioning accuracy, safe and reliable data, no error accumulation. As long as the basic working conditions of the RTK are met, the plane accuracy and elevation accuracy of the RTK can reach centimeter level within a certain working radius (generally 4km).
(3) Reduced working condition requirements. RTK technology does not require optical communication between two points, and only requires "electromagnetic wave viewing". Therefore, compared with traditional measurement, RTK technology is less affected and restricted by factors such as visibility conditions, visibility, climate, and seasons. In the traditional measurement, it is difficult to see through the complex terrain and obstacles. As long as the basic working conditions of the RTK are met, it can easily perform fast high-precision positioning.
(4) RTK operations are highly automated and integrated, and the mapping function is powerful. RTK is suitable for a variety of mapping inside and outside the industry. The rover utilizes a built-in software control system to automatically implement multiple surveying and mapping functions without manual intervention, which greatly reduces auxiliary measurement work, reduces human error, and ensures job accuracy.
(5) Easy to operate, easy to use, and powerful in data processing. As long as you make a simple setup when you set up the station, you can get the coordinates of the measurement results or coordinate the stakes while walking. The ability to input, store, process, convert, and output data is fast and easy to communicate with computers and other measuring instruments.
The application of RTK technology to
transmission lines is a qualitative jump over traditional surveys:
Engineering features of
transmission lines :
(1) Most of the
transmission lines are located in mountainous hills with complex vegetation and poor visibility conditions. Conversely, in the plain area, the visibility may be poor due to too many features.
(2) The complexity of mountainous terrain may cause the surveyor to get lost, take the wrong route, go wrong, etc., not only without personal safety and affecting work efficiency.
(3) The distribution of the survey area is band-shaped and long, stretching for several tens of kilometers or even hundreds of kilometers. Therefore, large error accumulation is likely to occur, and the elevation is greatly affected by the curvature of the earth.
(4) The instrument has a long viewing distance and can be as long as 1km or longer. In order to ensure accuracy, long-distance rear view is required, and the target is small and not easy to find.
(5) A line is often difficult to pass completely through a survey, and it is necessary to repeatedly modify the line.
(6) The survey personnel pay a lot of physical strength.
The traditional survey can not avoid these situations at all, and the introduction of RTK technology can better avoid some restrictions. In practical applications, most of our cases use a combination of 1+2, that is, one reference station cooperates with two mobile stations, of course, the conditions allow the number of mobile stations to be more. We can introduce our external control control results and conversion coordinate system into the
GPS at one time in order to save the trouble of manual entry and avoid errors.
Although RTK technology is convenient, it also has its drawbacks:
(1) Limited by satellite conditions. When the position of the satellite system is good for the United States, some countries in the world are still not well covered by satellites for a certain period of time, which is prone to false values. In addition, in the depths of the alpine valleys and dense forest areas, the high-rise buildings in the city, the satellite signal is blocked for a long time, so that the working hours of the day are limited.
(2) Sky environmental impact. At noon during the day, the ionospheric interference is large, the number of shared satellites is small, and less than 5 satellites are often accepted. Therefore, the initialization time is too long or even initialized, and measurement cannot be performed.
(3) The problem of data link transmission being disturbed and limited, and the working radius is smaller than the nominal distance. RTK data link transmission is susceptible to obstacles such as tall mountains, tall buildings and various high-frequency signal sources, which are seriously attenuated during transmission, seriously affecting the accuracy of the field and the operating radius. Signal transmission signals in mountainous areas and urban densely populated areas with large terrain fluctuations are limited. In addition, when the RTK operating radius exceeds a certain distance (generally several kilometers, each model is different in different environments), the measurement error exceeds the limit, so the actual working radius of the RTK is smaller than its nominal radius. A lot, engineering practice and specialized research have proved this.
(4) Initialization capability and time required. When operating in mountainous areas, general forest areas, urban densely populated areas, etc.,
GPS satellite signals are blocked more often, which is likely to cause loss of lock. Sometimes RTK operations require frequent reinitialization. The accuracy and efficiency of such measurements are affected.
(5) Elevation anomaly problem. The RTK operation mode requires that the conversion of elevation must be accurate, because in some areas of China, especially in mountainous areas, elevation anomalies are prone to occur.
Of course, for the survey of the line, there are certain ways to overcome these shortcomings. Try to choose a better measurement period, and the position of the reference station should be as high as possible. In addition, the control point can be appropriately encrypted with the rover to solve the problem of insufficient working radius. For densely populated areas, trees must be cut down. Although there is no cumulative error in RTK, due to some problems such as elevation anomalies and data link transmission error factors, RTK quality control must be carried out. It is effective and convenient for
transmission line surveys. The method is known to check the nuclear comparison method. Before each work, check the known points and compare the two differences. The general situation will not exceed 5cm.
In addition, it is worth mentioning that: Due to the introduction of
GPS technology, the cumbersome line rerouting work has become very fast.
4 Conclusion
The GPS technology is applied to the
transmission line measurement, which makes the efficiency and quality of the
line survey greatly improved, and saves the physical strength of the survey personnel. In addition, the deforestation of trees has been reduced, which has played a certain environmental protection role.
GPS technology has become an important part of
transmission line survey. With the continuous improvement of
GPS technology and the continuous exploration of surveying and mapping workers,
GPS will gradually deepen to more specific work and meet the needs of more special projects.
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