作者：张勇政

近几年，国家为了促进经济发展，大力推行铁路等基础设施建设。随之而来的勘测设计任务越来越重，工期越来越短，而野外复杂的地形条件，以常规仪器根本不能提高效率。高精度手持GPS技术的出现和应用，为线路勘测工作带来了历史性的变革。
    一.传统手持GPS在线路勘测中的局限性
    以往，手持GPS主要是采用单点定位和后差分定位方式。单点定位精度低，一般在10m左右；后差分定位方式在作业时要求建立基准站，内业对基站、手持GPS同步采集的数据进行联合处理。单点定位的低精度和后差分方式的非实时性，使得传统的手持GPS不适用于线路勘测工作。
    二.手持GPS实时差分功能的实现
    现今，CORS作为卫星定位技术的新潮流蓬勃地发展起来，它可以为移动设备提供精准稳定的实时差分改正信息。尤其随着南方测绘自主研发出国际水平的网络CORS技术（NRS），打破了进口厂家的高价垄断，国内掀起了CORS的建站热潮，为具备实时差分功能的手持GPS开创了更广泛及切合实际的应用前景。
    例如具备实时差分亚米级功能的手持GPS“南方S750”，其内置有手机模块，只需在其中插入普通的手机卡，即可通过手机上网的方式连接到CORS服务器或网络基准站，获取实时差分改正数据，解算出亚米级的精度。
    并且，当处于铁路勘测中常遇到的山区等无手机信号的区域，南方S750还可以使用主板自动支持的接入星站差分（SBAS）的功能。当S750的用户处在拥有SBAS服务的区域（美洲为WAAS,欧洲为EGNOS，亚洲为MSAS），就可以搜索到差分信号，实现米级甚至亚米级的实时差分定位。这样就从根本上突破了传统GPS的局限性，使得南方S750成为铁路勘测设计工作行之有效的解决方案。
    三.南方S750为杭长高铁勘测工作助力
    准备在今年开工建设的杭州至长沙高速铁路客运专线全长900多公里，线路所经大部分是山地丘陵地形，线路设计采用桥梁及涵洞较多，可以说勘测环境非常困难。承担本次勘测设计工作的中铁第四勘测设计院，根据紧迫的勘测任务，采购了60台南方S750手持机，应用于线路地质勘查及粗测，取得了很好的效果。
    1.施工坐标转换
    在初勘工作中，依据高精度的GPS控制网资料（CPI）,使用S750软件提供的坐标转换功能，分段求取WGS84与其施工坐标系的转换关系，在铁路线路的不同段进行亚米级的施工坐标系统下的数据采集。
    2.线路放样
    在未应用S750之前，主要依靠纸质地图实地勘察，准确性、效率都非常低。在采用S750后，只需将标准的线型设计文件通过SD卡或USB数据线导入到S750中，进行线路放样，既可精确地指示出线路在实地的位置，还可在放样界面进行数据的高精度采集。
    3.数据的兼容操作
    S750在外业采集时，其数据格式不仅与南方RTK的数据格式相同，还支持南方CASS、DXF等主流软件数据格式导入导出，非常方便设计人员对野外勘测数据的利用和处理。
    南方S750是高精度智能手持GPS，其实时差分的功能可以使测量精度达到亚米。采用英特尔520M处理器及128M大内存，Windows操作系统，配有南方公司自主研发的专业铁路勘测设计软件，可以现场实现线路曲线设计、桥梁设计、线路和横断面放样及一些坐标转换、计算的相关操作。高端的硬件配置及专业的勘测软件，特别适合山地丘陵地形多、勘测任务重、工期紧迫的铁路勘测和地质勘测任务。


 

In recent years, the state in order to promote economic development, and vigorously promote the building of railways and other infrastructure. Followed by survey and design task has become increasingly heavy, shorter and shorter duration, while the field of complex terrain conditions, with conventional instruments can not improve efficiency. The emergence of handheld GPS technology, high accuracy and application of survey work for the line to bring a historic change.
     1. The traditional handheld GPS survey of the limitations of the line
     In the past, hand-held GPS is mainly used single-point positioning and post-differential targeting. Single point positioning accuracy is low, generally around 10m; after the differential positioning method in operations requires the establishment of base stations, base station within the industry, hand-held GPS synchronized data acquisition joint treatment. Single-point positioning accuracy of the low-and post-differential approach of non-real-time, making the traditional handheld GPS does not apply to line investigation.
     2. Handheld GPS to achieve real-time differential function
     Today, CORS, as the new trend of satellite positioning technology developed vigorously, which can provide precise and stability for mobile devices, real-time differential correction information. In particular, as the South mapping out the world-class self-developed network of CORS technology (NRS), breaking the monopoly of importing high-priced manufacturers, the domestic setting off the Jianzhan CORS boom, with real-time differential functions for the handheld GPS to create a more extensive and realistic application prospects.
     For example, differential sub-meter-class functionality with real-time handheld GPS "the South S750", its built-in phone module, which simply plugs into a regular phone card, you can access the Internet through mobile phones connect to a server or network CORS base stations, access to Real-time differential correction data, Xie calculate sub-meter level accuracy.
     And, when in the mountains of railway survey and frequently encountered in areas such as free cell phone signal, the South S750 can also use the motherboard automatically support differential access to satellite stations (SBAS) capabilities. When the S750 has a SBAS service users at the regional (the Americas for the WAAS, Europe EGNOS, Asia MSAS), you can search for differential signals to achieve sub-meter level meter-scale or even real-time differential positioning. This fundamental breakthrough in the traditional limitations of GPS, making the South S750 a railway survey and design work for an effective solution.
     3. Southern S750 to Hang a long high-speed rail investigation help
     Ready to start construction this year, to Changsha, Hangzhou high-speed rail passenger line length of more than 900 kilometers, the line went through the most mountainous and hilly terrain, circuit design bridges and culverts with larger, we can say it very difficult to survey. Undertake this survey and design work of the Fourth Survey and Design Institute of China Railway, according to the urgent task of the investigation, procurement of 60 units south of S750 handset, used in geological prospecting and the coarse lines, and achieved good results.
     1. Construction of coordinate transformation
     In Chukan work, based on high precision GPS control network information (CPI), the use of S750 software provides the coordinate transformation functions, and its construction of section to strike a WGS84 coordinate system transformation between the different railway lines to carry out the sub-meter level Construction of coordinate system under the data collection.
     2. Lofting line
     Before without the application of S750, mainly relying on paper maps to conduct site surveys, accuracy, efficiency is very low. After the introduction of S750, simply a standard linear design documents through the SD card or USB data cable into S750, make line lofting, can accurately indicates the location of lines in the field, but also in the loft data interface high-precision acquisition.
     3. Data interoperability
     S750 gathering outside the industry, its data format not only with the South RTK data format the same, also supports the South CASS, DXF and other mainstream software, data format import and export, is very convenient for field survey data designers use and processing.
     Southern S750 is a high-precision smart handheld GPS, its real-time differential function allows to reach sub-meter accuracy. Intel 520M processor and 128M large memory, Windows operating system, with the South's self-developed specialized railway survey and design software, you can field lines curve to achieve the design, bridge design, lofting and a number of lines and cross-sectional coordinate transformation to calculate the relevant operation. High-end hardware configuration and professional surveying software, especially suitable for hilly terrain and more surveying the arduous tasks, duration and urgent task of railway survey and geological surveys.