原文
Analysis on accuracy of Engineering Star RTK in cadastral survey based on SOUTH-CORS
SONG Yuanming,LIU Lilong,HU Jiaxing and LIU Jingye
Civil Engineering College,Guilin Institute of Technology,Guilin 541004,China Abstract:Currently,with the fast development of GPS technique,GPS RTK is rapidly being applied to the cadastral survey.GPS RTK technique not only improves efficiency and accelerates the rate of mapping,but also increases economic efficiency.The authors introduced a method for GPS RTK rapid positioning,which uses continuous operational reference system (CORS)as a base station to change the method of previous map drawing by obtaining real-time three-dimensional coordinates of boundary points and statistically analyzing with the three-dimensional coordinates obtained by Total Station to get the accuracy of GPS RTK real-time coordinates.The application of GPS RTK in practical measurement was discussed when the data link had been lost especially.The results show that the three-dimensional coordinates measured by total station can be replaced by real-time three-dimensional coordinates measured by Engineering Star RTK in the CORS. Key words:continuous operational reference system;data processing;statistical analysis;offset;data link Introduction
With the rapid development of digital cadastral(Qiao et al.,2004),GPS real-time positioning
technology
is
fully
utilized
in
that
field
(Qiao
et
a1.,2003).Previously,mapping by plane table method or theodolite method for measuring boundary points not only need to measure the plane position of geographical feature points(referred to as scattered points or measurement points)(Wang et a1.,2003),but also need to identify the property of the measurement points and the connection relationship. When cases encountered in which the area of the map is large and the surface features are complex,the using of the previous
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method would not only be time consuming,but also results larger errors in boundary points causing dispute.Followed by a number of new methods such as Total Station with GPS RTK technique and other applications in the cadastral survey,both the speed and efficiency have improved significantly.This study uses the CORS as the base station and the GPS RTK real-time positioning to obtain the real-time three-dimensional
coordinates
of
boundary
points(Zhang,2005;Zhang,2008;Xu,2007).And the results are compared with the three--dimensional coordinates of the boundary points obtained by the total station.After the deviation of direction of ?X,?Y,?Z gained,Statistical analysis is made to calculate three-dimensional coordinates of the CORS accuracy. 1 Principle of carrier phase difference dynamic positioning
Navigation Satellite Timing and Ranging/Global Position System,referred to as GPS,have now been applied widely to direct measurement of ground point coordinates.GPS
with
high
precision,all-weather,high
efficiency,multi-functional,simple,which are 80 widely known;but it also has some requirements for working conditions.When certain conditions are not required,it can not work(Li& Huang,2005).
Compared to the GPS static measurements,GPS system synchronizing observation needs to two or more of the receiver.The data recorded by the field is post-processed by software,and then WGS-84 precision baseline vector between the two stations can be
obtained(Wei&Huang,2004).And
then
by
the
adjustment,coordinate
transformation,etc.,to finally get the unknown coordinates.The coordinates could not be obtained in the field and do not have real-time ability,so the static type of GPS equipment is difficult to measure directly the basic mapping application to specific projects(Zhang,2006).In recent years,carrier phase difference technique,also known as RTK (Real Time Kinematic)rea1.time dynamic positioning technology is rapidly developing,it can provide real-time measurement points(user stations)of the three-dimensional coordinates in the specified coordinate system,and centimeter 1evel accuracy can be obtained within the 20 km range.
In the GPS RTK measurement mode,wireless communication is necessary between
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the base and rover stations.However,in the field conditions,the radio signal can not successfully reach the station because of the terrain shielding and other reasons measurement data would not be obtained.That requires surveyors to wait for a long time or to take measures to fulfill the survey work,and sometimes they had to temporarily give up the measure points which can not be measured,to take separate base stations and supplementary methods.If these points which cannot be obtained because of data communication link can be obtained at one time,measuring time will be greatly reduced,as well as labor and measurement costs.The purpose of this work is to use real-time the dynamic star of RTK positioning method in the South CORS ,making region in which wireless communication link cannot be achieved can be measured and the reliability of three-dimensional coordinates is analyzed.And this method has significance of both the economy technology.Economically,it makes field work more smoothly,reducing the time spent setting up base stations,including vehicle fuel consumption and labor,and the other losses;technically,measurement methods can bring new attempt to give an example of innovative thinking,i.e.the combination of the South CORS,engineering Star RTK and post-processing measurements which indicates a combination of innovative approaches.
In addition,the constraints GPS RTK observations in the field condition,the satellite signals are a1so easily blocked;buildings and tall trees and other surface features cannot be measured directly;setting out points falls into the water;cable and Bluetooth does not connect and other problems.These problems can be resolved through the flexible use of knowledge in surveying and functions of instrumentation. 2 Function of data link and the cause of data link loss 2.1 Function of data link
Data link will be charged with the mission of issuing the correct number of base stations and other information transmitted in real-time to the rover.As mentioned above,a GPS receiver is placed in base station with all visible GPS satellites for continuous observation,and the observation data in real-time via radio transmission equipment is sent to the user stations.On the user stations,a GPS receiver obtains observation data from base station via wireless receiving equipment and calculates
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and displays the three-dimensional coordinates with accuracy according relative positioning principle while receiving GPS satellite signals.In this way,through real-time positioning calculation results,the quality of the results of observing of base station and user station along with the convergence of reconciliation can be monitored.If there is no data link,real-time kinematic positioning cannot be completed.At this point,the rover’s position is a single point positioning,and coordinate accuracy is “automatic”precision with large error which may reach ten meters.
2.2 Cause of data link loss
Chain of a variety of reasons can result in loss of data.
Base station Radio transmit power is too low.Base station transmit power can be set to change when setting the base station,usually the manufacturers of the radio transmission power has a number of stalls can be set. If the minimum gear is selected,the transmitted signal will be weak.Radio station may not be received. Radio base station power is shortage.In order to maintain the radio base station transmit power,high current is required. Usually surveying units of each base station is equipped with a large lead-acid batteries or nickel-cadmium batteries. If the batteries are badly charged,or the working environment is too hot,too cold,too wet,or the batteries have been working a long while,the battery’s remaining capacity and the voltage will drop,resulting in lack of radio transmission power.
It’s too far away from the base station. The earth is a spheroid,the surface of which is curved.A certain height,the visual distance is limited.To ensure surveying accuracy,the radio equipment manufacturers usually choose radio frequency as 400 MHZ or so.The diffraction wave energy is not strong,so that the transmission is basically straight-line.When the rover is too far from the base station,the radio signal cannot reach the rover.
There are barriers between the rover and base station.Just like mobile phone signals have blind districts,when there are mountains,blocks of buildings,or a wide range of vegetation between the rover and base stations,the rover may not receive base station signal.At this point,raising the rover or base station’s antenna may improve reception.
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Antennas of rover or base station are off or have bad connection.The data link connection failure also occurs when cable which attaches to the antenna goes wrong. 2.3 Usual solutions for data link connection failure
The causes mentioned above are to be solved in sequence.When the transmission power is too low,the power will be increased.The lack of battery power problem can be fixed by replacing the battery or removing corrosion on the power connections and battery contacts.When rover is too far from the base station,the first surveying will be abandoned and another surveying will be made after changing the station.When there are barriers between the rover and base station,changing for another station is advisable,or using other measuring devices such as total station.
When using Star of the project RTK,sometimes long and stable“single-point solutions”or“float solution”may appear. At this time,we can change the direction of the antenna are fixed solution according to the star map;on the house condition,we can use the approach of extending the line between the two known points and the known points of the room,the intersection of is the third known point of the room;in the city,buildings are as densely many wires, resulting in the receiver under the building can not receive signals,in that case we can measure the first two points outside the building,then obtain the distance between two outside points and the actual point.Within the industry,we use CASS software to connect these two points,using the connection line between these two points as the baseline to draw a parallel line of the building entity easily due to the regular shape of most buildings. 3 Principle
This experiment is caried out by Liaoyuan Municipal Bureau of Land and Resources on land survey and mapping for reformation of shanty towns. South CORS Star Project RTK is used as the equipment.Compared with traditional GPS,CORS’S continuously operating reference station operating with a role in a wide range of high precision,stand-alone operation and many other advantages of the field.Currently,a large number of cities,provinces and industries are experiencing a continuously operating reference station network construction climax.Engineering Star mapping software is a simple, efficient and powerful graphical field measurement software.It
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