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, countries in order to promote economic development, vigorously promote the construction of railways and other infrastructure. Followed by increasingly heavy task of survey and design, becoming shorter and shorter period, and the field of complex terrain conditions, with conventional instruments can not improve efficiency. Hand-held high-precision GPS technology and applications, in order to line the historic survey work changes.
     1. The traditional handheld GPS in the line of the limitations of survey
     The past, hand-held GPS is mainly used after a single point positioning and differential positioning mode. Single point positioning accuracy of the low, generally around 10m; differential positioning in the post-operation called for the establishment of the base stations, base station within the industry, handheld GPS synchronized data acquisition for joint processing. Single point positioning accuracy and low differential manner after the non-real-time, making the traditional handheld GPS line does not apply to investigations.
     II. Handheld GPS function of the realization of real-time differential
     Today, CORS as satellite positioning technology, the vigorous development of the new trend, it can provide accurate mobile devices for real-time differential correction of stability information. Mapping the South especially in the wake of international standards to develop their own network of CORS technology (NRS), breaking the monopoly of the import manufacturers of high-priced domestic set off an upsurge of CORS, in order to have real-time differential GPS enabled handsets to create a more extensive and realistic application prospects.
     For example, with real-time differential function yami level handheld GPS "South S750", its built-in mobile phone modules, only one common mobile phone card inserted, you can access the Internet through mobile phones connect to a server or network CORS base stations, access Real-time differential correction data calculated yami-class solution accuracy.
     And, when at a railway survey, such as often encountered in mountainous areas without mobile phone signal, the South S750 motherboard can also use automatic support differential access Star Station (SBAS) function. When the S750 users have SBAS services in the region (the Americas for the WAAS, Europe EGNOS, Asia, MSAS), you can search for differential signal, to achieve even yami-level meter-scale real-time differential positioning. This fundamental breakthrough in the traditional limitations of GPS, the S750 south railway survey and design work to become an effective solution.
     III. South S750 to hang a long investigation of high-speed rail help
     Ready to start construction this year, to Changsha, Hangzhou high-speed passenger rail line more than nine hundred kilometers in length, line by most of the hilly mountain terrain, the use of circuit design bridges and culverts more can be said that the environment is very difficult investigation. Commitment to this survey and design work of the Fourth Survey and Design Institute of China Railway, according to the urgency of the task of investigation, procurement of the S750 handset 60 South, applied to geological prospecting and crude lines measured, and achieved very good results.
     1. Construction of Coordinate Transformation
     In初勘work, based on high-precision GPS control network information (CPI), the use of S750 of the coordinate transformation software features, sub-strike WGS84 coordinate system with the construction of the conversion relationship between the different railway lines yami-class section coordinates the construction of the data acquisition system.
     2. Lofting line
     Prior to the application of S750 is not mainly rely on paper maps the field investigation, the accuracy, efficiency is very low. After the introduction of S750, only the standard linear design documents through the SD card or USB data cable into the S750, make lofting lines can accurately indicate the location of lines in the field, but also in the setting-out data interface Acquisition of high-precision.
     3. Data compatible with the operation
     S750 collected from the industry, its data formats, not only with the South the same RTK data formats, also supported the South CASS, DXF mainstream software, such as import and export data formats, is very convenient for designers to make use of field survey data and processing.
     South S750 is a high-precision smart handheld GPS, real-time differential allows the measurement accuracy yami. Intel 520M and 128M processor large memory, Windows operating system, with independent research and development company of the South railway survey and design software professional, you can achieve line curve at the scene design, bridge design, setting-out lines and cross-sectional and a number of coordinate transformation to calculate the relevant operation. High-end hardware configuration and software professional investigation, particularly in hilly terrain for the mountain, and the investigation task, the urgency of the railway construction and surveying tasks Geological Survey.