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Application of GPS RTK technology in cadastral survey
1, preface
GPS RTK measurement technology is a real-time dynamic positioning system based on carrier phase observation. This paper introduces the application of this new technology in cadastral survey for reference.
2. Basic characteristics of 2.GPS RTK technology.
The instrument used by our unit is a 9800 dual-frequency receiver produced by south surveying and mapping Instruments Company, and its accuracy index is:
Real-time RTK plane accuracy 2 cm+2 ppm? Elevation accuracy 5cm+ 1ppm? The working distance is as high as 15KM. The instrument has good integration performance, the host, power supply and data transmission radio are integrated, and the power of the whole machine is low. 17AH base station is equipped with two lithium batteries, which can work continuously 12 hours. RTK base station is set automatically and intelligently, and the mobile station can fly with one button.
GPS RTK technology system configuration includes the following three parts: 1, reference station receiver; 2. Mobile station receiver; 3. Data link. The receiver of the reference station is set at the reference point with known coordinates (or without known coordinates, with high terrain), and continuously receives all visible GPS satellite signals, and sends out the coordinates, observation values, satellite tracking status and receiver working status of the station through the data link. The receiver of the mobile station receives the data from the reference station while tracking the GPS satellite signal. The carrier phase ambiguity is quickly solved by OTF(On The FLY) algorithm, and the coordinates of the point relative to the reference point are obtained by the relative positioning model.
3.GPS RTK is applied to cadastral survey.
Because Songyuan area is located in the plain, it can give full play to the advantages of RTK technology. This investigation task is mainly based on Jilin Oilfield, which has a large number of oil production wells and is widely distributed. It is necessary to complete all the cadastral maps in a short time, which is difficult to complete without RTK technology. RTK technology can be used to determine the ownership boundary point and the position of some characteristic points of each oil well, and the accuracy can reach centimeter level.
3. 1. Selection and establishment of reference stations
The placement of the reference station is the key to the smooth RTK survey, so the following points should be paid attention to when selecting the site:
(1), avoid choosing areas with strong radio interference;
(2) The site of the reference station and the transmitting antenna of the data link radio station must have a certain height;
(3) In order to prevent data link loss and multipath effect, there is no GPS signal reflector (large water area, large building, etc.). ) around.
3.2, field measurement
Field workers can start the measurement by setting up instruments at the reference station, usually in groups of two, one at the reference station and the other with instruments to set up posts at each boundary and record data. Generally, a recording unit is 3 seconds. When recording data, the surveyors are required to stand accurately, try to hold the centering rod steady, and draw a sketch at the same time to provide reference for the whole map of the industry.
3.3, operation methods and steps
(1), choose a good coordinate system: at present, what coordinate system can be used, but it is not clear that the national basic coordinate system can be used.
(2) Setting projection parameters: if the central meridian of point coordinates is known, use the actual central meridian; If you don't know, choose the local longitude as the central meridian, with 0 for the X constant, 500,000 for the Y constant and 65,438+0 for the projection scale.
(3) Turn off all seven parameters and conversion parameters.
(4), set the reference station, there are two situations:
A, the base station is located at an unknown point:
When the base station has been set up and single point positioning has started, press the Tab key to obtain the coordinates of single point positioning as the coordinates of the base station. If the height difference is too large, you can use the estimated value to input.
B, the base station is located at a known point:
When the base station is erected and the single point positioning starts, enter the breakpoint measurement, press the Tab key to save a coordinate, and set the point as Pr 1. Enter the reference station coordinate input. When inputting the reference station coordinates, press the R key to obtain the measuring point coordinates Pr 1 as the reference station coordinates.
After setting RTK working mode and launch interval, set it as reference station working mode.
(5) In case A, to two known points in the survey area (the distance between the two known points should be as far as possible, and the known points should have enough accuracy), input the breaking point for measurement, and store them in the roll call Pr 1 and Pr2 respectively under the fixed RTK (pay attention to input the antenna height).
In case B, go to another known point in the survey area (these two known points should have enough accuracy), input the breakpoint for measurement, and store it in the named Pr2 under RTK Fixed.
(6) Enter "Find Transformation Parameters", press T to take out the coordinates of Prt 1, press R to take out the coordinates of Pt 1, press Enter to take out the coordinates of the second point, press T to take out the coordinates of Pt2, press R to take out the coordinates of R2, press Enter to complete the calculation of transformation parameters, and automatically store them in "Transformation Parameters", then enter the transformation parameters and view them.
(7) Re-measure the coordinates of P 1 or P2, and check whether the coordinates of each point are consistent with the known points (the error is within 2cm). If possible, you can go to the third known point to check the correctness of the conversion parameters.
3.4, indoor processing
The RAT file stored in field survey is a special database file, which cannot be directly called by surveying and mapping software. The RAT file can be converted into the format required by users through the function of "output of measurement results". The converted format is consistent with our software CASS5.0. Combined with field sketch, digital indoor mapping can be completed quickly.
4. Application experience
4. 1, GPS is being applied in more and more surveying work, and its application in cadastral surveying is an example. RTK technology has incomparable advantages over other measuring instruments and methods.
4.2. Don't start measuring immediately after RTK mode appears. Wait until the GPS is stable for about 20 minutes, otherwise there will be a big error. After replacing the recorded data, the recording mode will not be affected if it works normally.
4.3. The radio signal should not be too far away. According to our working experience for several years, the range of RTK cannot exceed 10KM, otherwise the calculation speed and accuracy will be greatly affected.
4.4. Using RTK to carry out cadastral survey is not limited by weather, terrain, visibility and other conditions, and the working efficiency is 3-4 times higher than that of traditional methods.
4.5. Using RTK technology can greatly save manpower compared with traditional methods.