GPS (Global Positioning System, Global Positioning System) is the United States in 1994 and fully completed, with full range of real-time three-dimensional navigation and positioning capabilities of the new generation of satellite navigation and positioning system. Surveying and mapping and other departments in China after nearly 10 years of use shows that, GPS with all-weather, high precision, automation, high efficiency and other salient features to win the trust of workers in the general mapping, and successfully applied to land surveying, engineering surveying, aerial photography measurements, vehicle navigation, crustal movement monitoring, engineering deformation monitoring, resource exploration, Geodynamics and other disciplines, surveying and mapping fields to bring about a profound technological revolution.
GPS RTK (Real Time Kinematic, RTK) GPS technology is developed on the basis, capable of real-time mobile stations in the specified coordinates in three-dimensional positioning results, and within a certain range to achieve centimeter-level precision of a new GPS position measurement, is a major milestone in GPS application, which loft the emergence of engineering, topographic mapping, measurement of various control has brought a new light, greatly enhancing the efficiency of foreign trade operations.
At present, the routine use of GPS measurements are mainly static, rapid static method to create two or more horizontal control network, GPS in the Cadastral Survey of the applications are limited to this; GPSRTK technique is mainly used for the Department of Ordnance Survey's broken point of acquisition, construction layout, etc. and used in place of one, two encryption control surveying, Figure Root Control measurements, cadastral survey of the boundary point of measurement is still in the pilot study stage. In this paper, examples on the application of RTK techniques to measure the encryption a cadastral control points, boundary points of the pilot study obtained some useful conclusions for the revision of cadastral survey reference standard, while it in the Cadastral Survey of scientific and standardized.
2, GPS RTK technology, the basic principle and measurement method
2.1 RTK basic principle of
RTK technology uses three types of differential GPS (location differential, pseudo-range differential and phase difference) in the phase difference. These three differential manner by the number of base stations to send corrected by the mobile stations to receive and make corrections to their measurements in order to obtain accurate positioning results, the difference is sent to correct the specific content is not the same as the number of their differential positioning accuracy are also different. The first two categories would be the relevance of positioning errors with the base station and mobile station to increase its spatial distance from the positioning accuracy rapidly decreased, so RTK using the third method.
RTK works is a receiver placed on the base station, another station or several receivers placed on mobile stations, the base station and mobile stations at the same time receiving the same GPS satellite launch at the same time the signal received by base station The observed value compared with the known location information received differential GPS corrections. And then the corrections in a timely manner through the radio data link radios to the mobile stations in order to refine the GPS observations, to be corrected by the difference a more accurate real-time location of mobile station. Mobile stations could be in a quiescent state, but also in motion.
RTK sub Amendment Act and the difference method. Amendment Act is the base station will send the amount of carrier phase-corrected mobile stations in order to correct the carrier phase, and then solve the coordinates. Difference method is the base station carrier phase collected sent to the mobile station is evaluated difference solver coordinates. RTK technology, whichever is earlier, the latter for real RTK technology.
2.2GPS RTK system components
The United States Tianbao (Trimble) 5700 dual-frequency RTK receivers as an example to illustrate the composition of the system.
2.3RTK measurements
(1) "No projection / no conversion" method. Directly in the base station and mobile station receiver receives WGS-84 coordinates, and then use observations of known points of WGS-84 coordinates and the corresponding local coordinates of the mathematical model according to certain conversion. This approach need not be placed in the base station known point, but according to different conversion method needs to observe a certain number of known points.
(2) "type parameter" method. The observations obtained with the static of the WGS-84 coordinates and local coordinates of type hand book, the conversion can also be placed in a static observation of the transformation parameters adjustment when the strike. The method to be mounted on a known reference station point, but can not observe other known point (in order to check, suggested at a convenient time, or a certain amount of a known observation point).
Set a GPS receiver as the base station, and some of the necessary data, such as base station coordinates, elevation, GPS coordinates transformation parameters such as input control of hand-book, one or several GPS receivers set to the mobile station. Base station and mobile stations to receive satellite signals at the same time, base station will receive the satellite signal through the radio base station sent to the mobile stations, mobile stations will receive satellite signals and base station transmit the signal sent to the control hand-book for real-time differential and the adjustment processing, real-time to be site of the coordinates and elevation and its accuracy indicators, and to keep the measurement accuracy and precision of indicators to compare the default, if the default precision index measurement accuracy requirements, hand book will be prompted to measure whether the staff to accept the results, to accept flac book will be the measured coordinates, elevation and precision hand book store at the same time.
2.4 The mobile station distance from the base station
RTK data link radio transmitter operating frequency UHF band currently used, when the power is constant, firing range with the antenna height increases.

3 Applications
Use Trimble5700 dual-frequency GPS receiver, its nominal precision of RTK, horizontal: ± (10mm +1 ppm × baseline length), vertical: ± (20mm +1 ppm × baseline length), select three or more with a standard height and evenly distributed in RTK measurement range of the three or four other GPS points as the public points, seven parameters to strike a WGS-84 coordinate system to the local coordinate system conversion.
3.1GPS RTK cadastral encrypt a wire instead of an instance of
District Overview 3.1.1 instance
Examples of areas to a certain town as the center of Chuxiong, 1:500 digital cadastral area of about 40km2, mainly residential areas, plains, hilly, small part is mountainous. Maximum elevation difference of about 200 meters, with an average elevation of 1850 meters, examples near enough three or four other GPS points.
3.1.2 Observation of a wire
RTK sub Amendment Act and the difference method. Amendment Act is the base station will send the amount of carrier phase-corrected mobile stations in order to correct the carrier phase, and then solve the coordinates. Difference method is the base station carrier phase collected sent to the mobile station is evaluated difference solver coordinates. RTK technology, whichever is earlier, the latter for real RTK technology.
In the three or four GPS points, such as laying a cable under the net, wire net horizontal angle using LeicaTC702 and TOPCON GTS322 Total Station observations, horizontal angle measured back to two measurement. Network to measure elevation near the third-class standard of points as the base, laid into a node network, according to fourth-grade wire EDM height requirements and horizontal angle measurement facilities at the same time, the vertical angle in the wire method and from the observation three measurements back, side measured back from a long observation. A wire net total of 274 points, with an average side length of 350m, angle measurement error in mβ = ± 3.0 ", the weakest little bit of adjustment after the error of mX = ± 3.22cm, mY = ± 2.50cm, mXY = ± 4.08cm , the weakest wire routes are closed differential 1:19000; four wire networks such as electro-optical distance Elevation Elevation of the weaknesses of the error mH = ± 1.61cm. more accuracy in line with literature [3] requirements.
3.1.3 GPS RTK Shi test case
RTK were detected in this area with a wire-point 47-point, mobile stations from the base station maximum distance 5.84km, nearest 30m, an average distance of 2.45km. Preset accuracy: Flat 3cm, height 5cm.
3.1.4 RTK measurement results compared with a wire
The outcome will be a conductor as the true value, RTK with the results of the X, Y, H margin are in line with the characteristics of accidental error, the largest margin of dx =- 4.1cm, dy =- 4.7cm, dH =- 12.4cm, by the lower Δ calculated RTK observation error mX = ± = ± 2.05cm, mY = ± 1.78cm, mXY = ± 2.71cm, mH = ± 4.25cm.
In order to further test the accuracy of RTK, simultaneous detection of 32 a side length of wires, compared with the total station observation maximum side length less of 2.3cm, an average of less 5.6mm (average side length of 314m, the relative error of 1 / 56000 ), RTK side length of error of ± 0.98cm.
It can be seen, RTK Cadastral Control Survey can replace the conventional one, two wire measurement and map Root Control Survey.
3.2 GPS RTK collect examples of boundary points
The same region, in the two control points on the wire above, the application GPSRTK technology to some to be able to receive satellite signals were detected boundary points (mobile stations the maximum distance from the base station 2.59Km,, nearest 210m, the average distance of 1.54km) . Boundary points were detected, the region of 28 points, with the polar coordinate method with the total station coordinates of the observed compared to the value of its X, Y, H difference also in line with the characteristics of accidental error, the largest margin of dx =- 5.0cm, dy = 4.2cm, dH =- 8.8cm, calculated by the poor RTK observation error mX = ± 2.80cm, mY = ± 2.14cm, mXY = ± 3.52cm, mH = ± 2.95cm.
Can be seen, RTK technology to collect a boundary-point accuracy in line with literature [3] requirements.
4, Conclusion
By the following examples can be concluded with the GPS RTK technology in the supply of cadastral control surveying, cadastral and revise cadastral standard reference.
(1) GPSRTK technology for high efficiency, flexibility, and the error does not accumulate and centimeter-level surveying and mapping of high-precision more and more persons of all ages. RTK Elevation below the plane precision accuracy, while the cadastral survey of the elevation accuracy requirements are lower. Thus, RTK technology to carry out the cadastral and secondary control and Boundary-point measurements is the ideal method of delimitation in the investigation of edge particularly prominent. In other words, RTK measurement methods can replace the conventional 12 lead measurement and map Root Control, Boundary-point measurement.
(2) and the static, rapid static GPS measurements compared, RTK without adequate vetting of the geometric conditions, I believe that should not be used as a first-stage control. Encrypted using the RTK control points laid to step up checks, if instead of one, two points can be taken at different base stations, respectively, or to set up an independent testing facilities the way pairs of base stations, test facilities, take the number to use, it will not only to avoid gross error, but also point precision is improved.
(3) RTK positioning data processing is mainly between the base station and mobile station a single-baseline processing, while the base station and mobile station observation data quality and the quality of radio signals transmitted a great impact on the positioning accuracy. Therefore, the base station set up in the region to conduct RTK measurement of the higher point, raising the base station and mobile station antenna height erected.
(4) RTK measurement point must be to strike a WGS-84 coordinates to the local coordinate system transformation parameters of the high-level control points within the same time, as even as possible distribution, the highest point of the lowest point for the election as much as possible.
(5) According to (1) calculated the distance without any shelter materials in the open area of the theoretical value, in fact be determined according to conditions on the ground. According to the calculated distance from the range of centimeter-level precision can only be guaranteed, it is necessary to meet the literature [3] the provisions of accuracy, for one, two boundary control points and mobile stations is generally the distance from the base station should not exceed 8 km in ( 1) can be calculated by the scope of the cadastral detailed point measurements.