Application of GPS in transmission line survey

Because of the characteristics of transmission line survey and the advantages and characteristics of global positioning system (GPS), it is necessary to apply GPS to transmission line survey The introduction of GPS improves the quality and efficiency of transmission line survey, which is a major technological leap in transmission line survey [Abstract] due to the characteristics of transmission line survey and the advantages and characteristics of global positioning system (GPS), it is necessary to apply GPS to transmission line survey The introduction of GPS improves the quality and efficiency of transmission line survey, which is a major technological leap in transmission line survey [Key words] GPS RTK static measurement transmission line [author] Zhao Chengming Guangdong Electric Power Design and Research Institute 1 Introduction GPS (also known as global positioning system) is established by the U.S Department of defense to meet the requirements of military departments for high-precision navigation and positioning of marine, land and air 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) from the receiving satellite is used to provide meter level navigation and positioning for the U.S military and NATO allies, and the C / a code pseudo range with positioning accuracy of tens of meters is used to provide civil navigation and positioning With the development of technology, the operation mode of GPS has developed from static measurement, fast static measurement, post-processing high-precision dynamic measurement to dynamic initialization (OTF) centimeter level real-time RTK (real-time differential positioning of carrier phase) measurement In terms of accuracy, the static measurement can reach 3mm + 0.5ppm after post-processing, and the RTK Positioning accuracy can reach 10mm + 1ppm Compared with classical surveying, GPS surveying has the following characteristics: (1) there is no intervisibility between stations Intervisibility between stations has always been a difficult problem in surveying The feature of GPS makes the selection of points more flexible and convenient However, the space above the station must be open so that the received GPS satellite signal will not be interfered (2) High positioning accuracy In general, the baseline solution accuracy of dual frequency GPS receiver is 5mm + 1ppm, while the nominal accuracy of infrared instrument is 5mm + 5ppm The GPS measurement accuracy is equivalent to that of infrared instrument, but with the increase of distance, the advantages of GPS measurement are more prominent (3) The observation time is short On a short baseline less than 20km, the fast relative positioning usually takes only 5 minutes to observe (4) Provides 3D coordinates GPS survey can measure the earth elevation of the observation station while measuring the plane position of the observation station (5) Easy to operate GPS measurement is highly automated In the observation, the main task of the surveyor is to install and switch the instrument, measure the height of the instrument and monitor the working state of the instrument, while other observation works such as satellite acquisition, tracking observation, etc are automatically completed by the instrument (6) Work 24 hours a day GPS observation can be carried out continuously at any place and at any time, generally not affected 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 survey in transmission line survey the survey of transmission line is divided into engineering survey and aerial photogrammetry, and no matter which survey method needs the participation of GPS static survey and RTK The first is the static measurement, that is, the layout and observation of control points around the whole transmission line, which is used to control the elevation and plane of the whole line For aerial photogrammetric transmission lines, most of the route maps are about 1:10000 photos The first thing to do is to select the appropriate points on these photos as the static external control points As for the selection of control points, we try to select the places that are easy to distinguish with the naked eye and the surrounding elevation difference is not big, so as to facilitate the matching of photos; but at the same time, we also need to take into account the characteristics of line survey, such as road conditions, whether it is convenient to reach, etc Therefore, we need to pay attention to the following points in the layout of external control points: (1) a power transmission line is divided into several air belts, and each air belt map is composed of multiple air photos We stipulate that each air belt has at least three control points to control, regardless of the length of the air belt (2) Select the location with relatively obvious characteristics and easy to save points on the aerial photos, and the surrounding height difference is small, the vegetation is low, and try to stay away from the buildings (3) When selecting points, it is necessary to select places with convenient traffic as much as possible according to the conditions of the road, and it is not allowed to deviate too far from the middle line of our line (4) Although the survey of the line has relatively low accuracy requirements, so it is not necessary to consider the network 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 the same, and the distance between the two adjacent points is not more than 4km, because it should be within the operation radius of RTK The connecting lines of all adjacent two points are zigzag, and the center line of the line runs through them (5) The total number of selected points of each flight belt can be more than 0.33 points per kilometer as a reference (6) Insert the national control points at appropriate positions at the head and tail of the whole line and in the middle of the line There shall be at least two (within 50km) relatively short lines and at least three to four (above 50km) relatively long lines (7) When selecting points, the baseline between two points may be too long because there is no suitable position In this case, the transition point can be used The transition point participates in adjustment but does not participate in aerial photo matching After the control point is selected, it is the field observation work In the observation process, we need to pay attention to: (1) set up the GPS receiver, especially the receiver in case of emergency, such as the receiver suddenly crashes and the terminal cannot control the receiver due to poor line contact (2) Record the points, antenna height and observation period (3) Mark in the field for future search Because the accuracy requirement of transmission line is relatively low, we only guarantee a common point, not a common side, between the two periods of observation in the field static observation The length of observation period depends on the side length Most of the time is about 3km, so most of the time is 20 to 40 minutes After field observation, the next step is data post-processing, in which pay attention to the antenna height and point number of the data Data post-processing includes data adjustment, establishment of coordinate conversion system, which is divided into one-step method and classical three-dimensional method Because the transmission lines are generally long, the classical three-dimensional method is used to calculate the conversion parameters, and the static work is finished For the engineering test line, only no photo matching is needed, and other basic work is basically the same The application of RTK in transmission line survey RTK refers to real-time kinematic positioning of carrier phase, which is a new form of Zui developed by GPS The static GPS measurement can achieve centimeter or even millimeter accuracy by phase difference, but the disadvantage is that the result is known only after the post-processing RTK can achieve centimeter level accuracy through real-time processing The application of RTK in transmission line is mainly used for setting out, positioning, setting out of linear pile position and tower position, as well as the measurement of plane section The data form that GPs can directly provide is coordinates Rtkzui's main two functions are real-time mapping and engineering lofting We basically use lofting functions For the plane section survey, it also uses the lofting function to record the point coordinates of each figure, and uses the pre agreed point identification to distinguish different figures; it can also use the same method to measure the tower position topographic map RTK requires one reference station, at least one mobile station and corresponding data communication link The datum station transmits the information of the station and all the observation values to the mobile station through the data link in real time The mobile station uses advanced processing technology to calculate the three-dimensional coordinates of the mobile station instantaneously The application of RTK technology to transmission circuit is closely related to its characteristics: (1) high efficiency In general terrain, high-quality RTK can complete the measurement area with a radius of 4km by setting up a station once It only needs one person to operate In general electromagnetic wave environment, a point of coordinates can be obtained in a few seconds The operation speed is fast, the labor intensity is low, the field cost is saved, and the labor efficiency is improved (2) High positioning accuracy, safe and reliable data, no error accumulation As long as the basic working conditions of RTK are met, the plane accuracy and elevation accuracy of RTK can reach centimeter level within a certain working radius (generally 4km) (3) The requirements of working conditions are reduced RTK technology does not require optical intervisibility between two points, but only "electromagnetic wave intervisibility" Therefore, compared with traditional measurement, RTK technology is less affected and limited by intervisibility conditions, visibility, climate, season and other factors In traditional measurement, as long as the basic working conditions of RTK are met, it can also easily be used in difficult intervisibility areas caused by terrain complexity and ground obstacles Carry out fast and high-precision positioning operation (4) RTK has a high degree of automation, integration and powerful mapping function RTK is competent for all kinds of Surveying and mapping The mobile station uses the built-in software control system, which can automatically realize a variety of mapping functions without manual intervention, greatly reducing the auxiliary measurement work, reducing the human error, and ensuring the operation accuracy (5) Easy to operate, easy to use, strong data processing ability As long as a simple setting is made in setting up the station, the coordinates of the measurement results can be obtained while walking or setting out the coordinates The ability of data input, storage, processing, conversion and output is strong, and it can communicate with computers and other measuring instruments conveniently and quickly The application of RTK Technology in the survey of transmission lines is a qualitative leap compared with the traditional survey: the engineering characteristics of transmission lines: (1) most of the transmission lines are located in the mountains and hills, with complex vegetation and poor visibility conditions; on the contrary, the transmission lines located in the plain area may also have poor visibility due to too many features (2) The complexity of the mountainous terrain may cause the surveyors to get lost, take the wrong route, take the wrong position, etc., which not only has no personal safety but also affects the work efficiency (3) The distribution of the survey area is belt like and long, stretching for tens or even hundreds of kilometers Therefore, it is easy to accumulate large errors, and the elevation is greatly affected by the curvature of the earth (4) The sight distance of the instrument is long, which can be as long as 1km or longer In order to ensure the accuracy, long-distance back-up is needed, and the target is small, which is not easy to find (5) It is often difficult for a line to pass through a survey completely, and the route should be modified repeatedly (6) Surveyors pay more for physical strength The traditional survey can not avoid these situations at all, and the introduction of RTK technology can avoid some limitations In practical application, we use the combination of 1 + 2 in most cases, that is, one reference station with two mobile stations, of course, the conditions allow more mobile stations In order to save the trouble of manual input and avoid errors, we can import our external control results and transformation coordinate system into GPS in advance Although RTK technology is convenient, it has its disadvantages: (1) it is limited by satellite conditions When the position of satellite system is Zui good for the United States, some countries in the world can not be covered by the satellite well in a certain period of time, which is easy to generate false values In addition, in the deep mountains and canyons, dense forest areas and densely populated urban high-rise areas, the satellite signal is blocked for a long time, making the working time of the day available