基于南方CASS工程之星RTK在地籍调查中的精度分析.doc

译文：
基于南方CASS工程之星RTK在地籍调查中的精度分析

摘要：当前，随着GPS技术的发展，GPS RTK被迅速的应用于地籍调查。GPS RTK技术不但提高了工作效率、加快了成图率，而且提高了经济效益。作者介绍了GPS RTK快速定向的方法，通过连续运行参考站（CORS）作为基准站来获得边界点的实时三维坐标，从而改善早先的绘图方法。同时需要利用全站仪统计分析这些实时的三维坐标点，从而获得GPS RTK 实时坐标点的精度。应用GPS RTK 参与实际测量工作还有许多问题有待讨论，尤其是在数据链丢失时的问题。但一般情况下，利用工程之星RTK 进行三维坐标点采集完全可愿意取代全站仪。
关键词：CORS 数据处理 统计分析 补偿 数据连接
引言
随着数字地籍的迅速发展，DPS实时定向技术被充分的应用于这一领域。早先通过平板仪或经纬仪绘制地图，不仅需要知道地理特征点的平面方向（涉及到分散点和测量点），还需要表明测量点的属性和四至关系。当遇到地图较大或表面属性复杂的情况时，运用早先的方法不仅耗费时间，而且结果会出现边界点的大量错误，导致争议。伴随着大量新技术的诞生，如全站仪联合GPS RTK技术和其他的技术应用于地籍测量，同时显著提高了速度和效率。这项研究即是使用CORS基站和GPS RTK实时定向来获得边界点的实时三维坐标。其结果与用全站仪获得的边界点三维坐标作比较。方向偏差后获得∆X,∆Y,∆Z，统计分析即计算利用CORS采集的三维坐标点的精度。
一、 载波相位动态差分定向原则
涉及到定时导航卫星和测距定向系统，如GPS，已经广泛应用于地面坐标的测量。GPS有着高精度、全天候、高效率、多功能、易操作，广为80后所知；但它对工作情况有些要求，如果无法满足，它将无法工作。
相比GPS静态测量，GPS同步观测需要两台或两台以上的接收机。数据在现场记录后用软件处理。WGS-84的精度基线矢量可在两站间获得。然后通过调整，坐标转换等方法，最终获得未知坐标。坐标无法在野外直接获得而且没有事实性，因此静态GPS设备对特定工程的地图应用要素的直接测量是十分困难的。近几年来，载波相位差分技术迅速发展，它可以再明确坐标系中提供实时测量点，在20公里的范围内精度为厘米级。
在GPS RTK测量模式中，基站和流动站之间用必要的无线电通信连接。然而在野外情况下，无线电信号会由于地势的屏障或其他原因无法成功接收，导致测量数据无法获取。这需要测量员们等待很长时间或者采取其他措施来实现测量工作，甚至有时候不得不暂时放弃无法测量的测量点，分离基站或填充的方法。如果这些无法获得的点因为通信连接可以在第一时间获得，测量时间、劳动量和测量费用会大大减少。这项工作的目的是在南方CORS站中使用实时动态卫星实现GPS定向，使无线电信号无法到达的区域可以进行测量和可靠的三维坐标分析。这种方法在经济技术方面有着十分重要的意义。在经济上，它使野外工作更顺利，减少了在设置基站时花费的时间，包括交通工具的燃料消耗和劳动，还有各种消耗。在技术上，这种测量方法是一种实力尝试的技术革新，它联合了南方CORS、工程之星RTK和测量的后处理，表现了一种联合创新的方法。
另外，约束GPS RTK野外观测的卫星信号很容易被阻塞；建筑、高达树木和其他特殊地物无法直接测量；在水中设置点；电缆和蓝牙都无法连接等问题。这些问题可以灵活运用测量只是和仪器功能来解决。
二、 数据连接功能和影像数据连接的原因
（一） 数据连接功能
数据连接可以被基站发出的任务准确控制并实时的将信息传输给流动站。正如以上描述，一台GPS接收机安置在基站并通过明显的GPS卫星连续观测，观测数据实时通过无线电传输设备发射给用户。在用户端，一台GPS接收机通过无线电接收设备获得观测数据，按照相应的GPS卫星信号接收定向原则来计算并显示三维坐标精度。用这种方法，通过实时定向计算出结果，基站观测结果的质量和用户的调制集合将可被监控。如果没有数据连接，实时的动态定向将无法完成。此时，接收机的定向是独立的点位定向，坐标精度是“默认值”最大误差精确至10米。
（二）数据无法连接的原因
有许多原因可以引起数据无法连接。
基站无线电传输的能量很低。基站无线电传输的能量在基站建立时已被设定，通常由无线电传输生产厂家设置。如果一个极小的零件被遗漏，发送信号的能量会很弱。无线电站将无法接收到信号。
无线电能量不足。为了维持无线电传输能量，需要维持高频率电流。通常基站需要较为耐用的铅酸电池或碱性蓄电池。如果电池严重损坏或工作环境太热、太冷、太湿，又或电池使用时间过长，电池剩余的能量或电压过低，都会导致无线电能量不足。
离基站过远。地球是一个表面封闭的椭球体。在一定的高度，可视距离是有限的。为满足测量精度，无线电设备制造商通常选用无线电频率大约400 MHZ左右。此波段衍射的破洞不是很强，因此主要延直线传播。当接收机离基站过远的时候，无线电信号无法达到接收机。
接收机和基站之间的障碍物。正如手机信号存在盲区一样，当有山体，建筑群，密集植被在接收机和基站之间时，接收机或许接收不到基站信号。此时，升高接收机或基站的天线可以改善这种反应。
接收机或基站的天线脱离或接触不良。当天线连接不正确时，也会引起数据无法连接传输。
（三） 数据连接传输失败的一般解决方案
以上提到的原因按顺序解决。当传播能量较弱时，能量需要被增加。对于电量不足的问题，应当定期更换电池或消除电池接口处的腐蚀。当接收机与基站距离过远，应当放弃首次测量结果，更换基站位置进行另外的测量。如果接收机和基站之间存在障碍物，更换基站位置是一种较好的方法，或者改用其它测量方法作业，如全站仪测量。
当使用工程之星RTK时，有时长时间显示“单点解”或“浮点解”。此时，我们应当改变天线方向直到“固定解”出现在卫星图上；在测量房屋时，我们可以通过两个已知点引出两条直线交会出房屋的第三点；在城市中，建筑物错综复杂，致使接收机在建筑物下无法接受信号，这种情况下我们可以首先测量出建筑物外的两个点，获得两个点到实际测量点的距离。作图过程中，我们用CASS软件将两点连接，将两点的连线作为基线做一条平行线即可得到建筑物的规则形状。
三、原理
以Liao yuan市国土资源局对shanty towns土地调查及绘图技术革新工作为例，应用南方CASS工程之星设备。与传统的GPS相比，CORS的连续运行参考站在广泛和高精度中担任重要角色，在独立操作和野外作业方面有许多优势。一般地说，一些比较大的城市、省份和工程，正在体验着高端CORS站网络建设。工程之星测量软件是一款简单、高效、功能强大的绘图测量软件。它可以用来很好的解决大地测量学、工程测量学、建筑领域的问题。工程之星系统集软件集合能使用南方RTK获得测量系统的最优成果。是极好的野外测量管理工具。
在本次实验中，有三组住户在调查区域，这些农民家中总共有有10个green-houses(GH1-GH10)，图1为调查区域。在试测区域有71个边界点。首先，用GPS RTK获得71个边界点的三维坐标，然后用全站仪进行测量。

图1.调查区域略图
四、结论
在CORS中，工程之星GPS RTK采集三维坐标测量取代了全站仪三维坐标测量。这不仅使野外工作效率大大提高，而且降低了测量时间、测量工作量和测量成本消耗。X方向的精度误差为0-15mm；Y方向的精度误差为0-15mm；Z方向的精度误差为0-10mm，精度满足城市测量规范。我们可以完全使用工程之星来完成地籍测量、地籍调查和地籍变更等城市地籍测量工作。
参考文献

【1】Qiao Y W,Wu W B,Zhao G,et a1.2004.Digital cadastral survey.Northeastern University Press,260-264.(in Chinese)
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【3】Wang J K,Wang P X,Pei L,et a1.2003.Fundamentals of surveying and mapping Education Science and Technology Press,78-104.(in Chinese)
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【7】Zhang Q,Hu S Y.2008.Discussion on the application of GPS—RTK Technology in land consolidation and mapping.Geomatics & Spatial Information Technology,31(2):20-22.(in Chinese with English abstract) Xu R X.2007.The application of GPS RTK technology in city surveying.Urban Geotechnical Investigation & Surveying.(6):66-68.(in Chinese with English abstract)
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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 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 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 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.
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 base