Keywords: RTK survey technology, power line survey, alignment survey
China Library Classification Number: P2 Document Identification Number: A Document Number:1672-3791(2012) 06 (c)-0045-02.
The rise of RTK positioning technology is another major breakthrough of GPS positioning technology. The application of this technology makes it possible to implement route measurement and real-time dynamic positioning measurement in line aerial survey on a large scale. When RKT GPS is applied to tower positioning, it can cancel several procedures, such as colluding straight line and alignment measurement, pile spacing and height difference measurement, which can only be completed by physical strength (such as waving flags and running around repeatedly) in traditional aerial survey positioning, and directly carry out real-time dynamic lofting measurement for each tower position to realize one-step lofting positioning. This simplifies the process, saves a lot of manpower and material resources, and improves the overall work efficiency by 2 ~ 3 times.
Implementation principle and operation flow of 1 GPS RTK
1. 1 Collect data of control points in the survey area.
Firstly, collect the data of control points in the survey area, including coordinates, gradient, central meridian, coordinate system, whether it is a conventional control network or a GPS control network, and whether the terrain and location environment of the control points are suitable as reference stations for dynamic GPS.
1.2 Determination of conversion parameters of survey area
GPS RTK survey is carried out in WGS-84 coordinate system, while power line survey and positioning is carried out in local coordinates or domestic Beijing 54 or Xi 'an 80 coordinates. There is a problem of coordinate transformation between them. In GPS static measurement, coordinate transformation is done afterwards. GPS RTK is used for real-time Australian 4 quantities, which requires local coordinates, which makes coordinate transformation more important.
The necessary condition of coordinate transformation is that at least three large sites have WGS-84 geocentric coordinates and Beijing 54 coordinates or Xi 'an 80 coordinates respectively, and the transformation parameters are solved by using the transformation model. This parameter control line is generally about 30km: a set of conversion parameters control a line, and the corner is the dividing point.
1.3 Selection and establishment of reference stations
The setting of reference station is one of the keys to the smooth implementation of dynamic GPS. Placement of reference stations shall meet the following conditions.
(1) The reference station should have the correct known coordinates. (2) The reference station should be located in a place with high terrain and wide sky, and there is no altitude angle exceeding10 around it. Obstacles, which are favorable for receiving satellite signals and data link transmission. (3) In order to prevent data link loss and multipath effect, there is no GPS signal reflector (large water area, large building, etc.). ) around, and there are no interference sources such as high-voltage lines, TV stations, radio transmitters and microwave stations. (4) The reference station should be selected in a position where the soil is solid and not easy to be damaged.
1.4 interior design and parameter setting of engineering project
(1) Ellipsoid parameters of local coordinate system (such as Beijing 54 coordinate system): long semi-axis and reciprocal of oblateness. (2) Central meridian. (3) Conversion parameters between coordinate systems of survey area.
1.5 field work
Place the GPS receiver of the reference station on the reference point. Turn on the receiver and input the precise Beijing 54 coordinates and antenna height. The reference station's GPS receiver converts Beijing 54 coordinates into WGS-84 coordinates through conversion parameters, continuously receives all visible GPS satellite signals, and sends its station coordinates, observation values, satellite tracking status and receiver working status through the data transmission station. The receiver of the mobile station receives the data of the reference station while tracking the GPS satellite signal, and obtains the three-dimensional WGS-84 coordinates of the mobile station through processing, and finally converts the WGS-84 coordinates into Beijing 54 coordinates through the same coordinate conversion parameters as the reference station. The receiver can also compare the real-time position with the design value to guide the lofting to the correct position.
Realization of RTK online measurement
2. 1 route survey
Alignment measurement is the work of accurately measuring each line segment between the starting point, corner point and end point of the center line of a straight line (that is, writing a series of straight piles between two points). Because GPS alignment does not need intervisibility between main points, RTK can dynamically display the current position in real time, so it is very easy to control the line direction and the geometric relationship of other structures in the survey process (Figure 1).
As shown in Figure 2, J2 and J3 are two corner piles of the line, and a series of straight piles Z 1, Z2, ... will be decided by J2 and J3.
The measurement method is: a reference station is set between J2 and J3, and the coordinates of the corner J2 and J3 are measured by the rover station respectively (if the coordinates of the corner are known, it is not necessary to measure, but can be called directly). After obtaining the coordinate information of the turning point, set the coordinate information of J2 and JBOY3 as two points on a straight line, and then take this straight line as the reference line. According to the field situation, after inputting the interval of lofting linear piles in the electronic notebook, a polyline file containing the coordinates of each linear pile point will be generated. According to the coordinates of the linear pile in the polyline file and RTK real-time navigation instructions, the linear pile Z 1, Z2, ...
2.2 section measurement
Measuring the height and distance of the change points of topographic features along the center line of the line and on both sides of the line or in the vertical direction of the line is called section measurement; Measuring the topographic change state of each point along the center line of the line is called longitudinal profile measurement; Measuring the topographic change state of each point along the vertical direction of the center of the line is called cross-sectional measurement. In the section survey of transmission line, the mileage and elevation of feature points of ground objects and landforms are mainly measured, and the elevation accuracy is not very high, but the relative distance between each feature point and transmission line conductor is mainly measured. Therefore, RTK can be used to quickly measure the cross section.
Cross-sectional survey is generally carried out at the same time as alignment survey, and there is no need to set up another reference station. There are two kinds of measurement methods when RTK carries out section measurement.
(1) You can directly use the data acquisition function to collect the coordinates of feature points, and then output the cross section in office data processing. (2) The section measurement function module in RTK data processing software can be used for section measurement. Different brands of RTK have different performances and uses, and their functions are similar. In the process of cross-section measurement, usually, lines connected to cross-section and profile design files and line files connected to cross-section are transferred to file settings, and designed cross-section files are transferred to profile file names. After setting the file name, enter the cross-section measurement interface. The status display of section measurement interface is the same as that of line lofting. For mobile instruments, if the deviation distance of the current point is within the designed deviation threshold, longitudinal data can be collected according to the fluctuation of the line. After the collection is completed, users can convert the data format according to their own needs, for example, to generate the commonly used weft cross-section data format.
2.3 tower positioning measurement
Tower positioning survey is based on the location of the tower on the horizontal section of the line designed by the line designer to the selected center line of the line, and the center pile of the vertical pole tower position is nailed as a sign.
The method of RTK lofting tower position is similar to alignment survey. Generally, a reference station is set between two adjacent tension towers, and the coordinates of both ends of a straight line are measured by a mobile station (if the coordinates are already available, they can be directly called). After obtaining the coordinate information of the turning point, the coordinate information of the two endpoints is set as two points of a straight line, and then the scheme design is carried out with this straight line as the reference line. After entering the distance between the tower and the end point in the electronic notebook, a polyline file containing the coordinates of the pile points of each tower will be generated. According to the coordinates of tower piles in the broken line file, the real-time navigation instructions of RTK are used to erect and calibrate the tower piles.