Details on GNRT

Types of receivers

GNRT is designed to be receiver-independent. Thus, in principle, all major receiver types, including Ashtech, Leica, Trimble and Zeiss among others, are supported by GNRT. This includes both dual and single frequency receivers, and all available information (code or carrier phase) can be processed. As well as GPS, GNRT also supports both GLONASS and hybrid GPS/GLONASS receivers.

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Standard data formats

GNRT operates with standard data formats. Correction data are RTCM-compatible. The results, in real time or otherwise, are provided in a variety of NMEA formats. The raw receiver data can also be stored in RINEX format for post-processing.

Präzises DGPS mit GNRT-K

By means of the GNRT-K module, the high precision carrier-phase solution will be activated at the GNRT mobile station. With its fast ambiguity resolution, which can be applied to both static and mobile antennae on-the-fly (OTF4), an accuracy down to one centimetre or better can be achieved within a few seconds. A rapid initialisation of the ambiguities at a known point is also possible.

4 OTF: Ambiguity resolution on-the-fly, also known as on-the-way (OTW) or on-the-track (OTT).

Dual and single frequency receivers, GLONASS

GNRT may be used with both single and dual frequency receivers. The main advantages of the considerably more expensive dual frequency receivers are their higher accuracy over longer distances as well as faster initialisation for ambiguities using carrier phase measurements. Networked reference stations also allow single frequency receivers to achieve good accuracies. The initialisation time for ambiguity resolution can be drastically reduced by the use of hybrid GPS/GLONASS equipment, so that here too single frequency receivers can yield good results.

Coordinate transformation

GNRT handles coordinate transformations from the global WGS845 to DHDN6, STN42/837 or to any desired local coordinate system.

5 WGS84: World Geodetic System of 1984, the global coordinate system in which all internal GPS observations and computations are carried out
6 DHDN (Deutsches Hauptdreiecknetz): German primary triangulation, the reference frame for the coordinate systems of the states of the former West Germany
7 STN (Staatl. Trigonometrisches Netz ): Government trigonometric network, the reference frame for several of the former East German states

Computer platform

GNRT runs on a standard PC under a graphic multi-tasking operating system. In accordance with the application environment, desktop, notebook or pen computers may be used for GNRT. The possibility of outdoor use of a graphic user interface has allowed the GNRT system to be designed specifically for field activities such as setting out, position fixing and GIS applications. Acoustic support can also in many cases allow work to continue without constant visual checking of displays. For unmanned applications such as deformation monitoring , GNRT can also be configured for automatic operation.

Graphic fieldbook

All coordinates from GNRT can be input to onward processing in real time on the same computer platform, which is in effect a graphic fieldbook. This allows simple and rapid orientation on an existing cartographic background , or even easy capture and processing of spatial data directly onto the map. For special application areas such as GIS, specific attributes may be defined which may be stored, together with the coordinates, as layers in a database.

System integration

GNRT is modular and can be expanded using new or current program modules at any time. With its standard interfaces and formats GNRT can easily be integrated with other systems (for example, navigation or railway track measurement systems), or can itself import information from other systems (such as inertial systems and other sensors). Thanks to the underlying multi-tasking operating system, users’ own or external software can also run alongside GNRT and can communicate directly with GNRT using the internal architecture (pipes and shared memory).8.

8 For examle, the graphic fieldbook note system ver/pro of Schwarz + Partner in Hildesheim, the HYMAS hydrographic measurement and analyysis system of the Bundesanstalt für Gewässerkunde (BfG) in Koblenz, or the SEADAT software of HPC in Hamburg.

Accuracy range

GNRT covers a very wide range of accuracies depending on the configuration. In its simplest configuration GNRT delivers DGPS accuracy of about one metre. By activating the RTCM++ format, with carrier phase smoothing of code observations the accuracy can be improved to about 0.5m. With the GNRT-K carrier phase module, the system accuracy reaches about one centimetre. Even more accurate coordinates can be achieved with a real time multi-station solution using several reference and mobile stations together with the GNNET module. For applications with the highest accuracy requirements, special calibration procedures allow accuracy-limiting error effects such as multi-path mitigation techniques and antenna phase eccentricities to be determined and corrected. By these means GPS will for the first time become suitable for the most precise engineering surveying tasks with tolerances of the order of one millimeter.

Remote Tracking

With the supplementary “Remote Tracking” module, GNRT is able to receive and process signals from one or more GNRT mobile stations at the base station, and compute their positions.

Multi-station solution

GNRT-K is at present the only RTK system which operates in a multi-station environment. Multiple reference stations and multiple mobile stations can be analysed in one process. Thus the accuracy, reliability and availability of precise RTK solutions can all be further increased.

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