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RTK Standards

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FundamentalsFundamentals
Title RTK Standards
Edited by GMV
Level Basic
Year of Publication 2011
Logo GMV.png

With origin dating back to the mid-1990s, Real Time Kinematics (RTK) is a differential GNSS technique which provides high positioning performance in the vicinity of a base station. The technique is based on the use of carrier measurements and the transmission of corrections from the base station, whose location is well known, to the rover, so that the main errors that drive the stand-alone positioning cancel out. A RTK base station covers a service area spreading about 10 or 20 kilometres, and a real time communication channel is needed connecting base and rover. RTK, which achieves performances in the range of a few centimetres, is a technique commonly used in surveying applications.[1][2][3]

The standards applying to RTK systems are the same of classical DGNSS systems, i.e. the ones of data transmission standards defined by the Special Committee 104 on DGNSS of the Radio Technical Commission for Maritime Services (RTCM). Besides RTCM, there exist other proprietary DGPS/RTK standards, such as Trimble Compact Measurement Record (CMR).[4]

RTCM Standards

The internationally accepted data transmission standards for DGNSS are defined by the Radio Technical Commission for Maritime Services organization (RTCM), particularly by its Special Committee SC-104.[4] The protocol is a binary one designed to optimize the communication throughput.[5]

The applicable documents to DGNSS systems are listed in the following table and constitute the current version of the core set of documents to be used for the development of a new DGNSS system.


Document Item Reference Issue Comments
Recommended Standards for Differential GNSS (Global Navigation Satellite Systems) Service RTCM 10402.3 2.3 This standard is used around the world for differential satellite navigation systems, both maritime and terrestrial.
Differential GNSS (Global Navigation Satellite Systems) Services RTCM 10403.1 3.1 A more efficient alternative to RTCM 10402.3
Standard for Networked Transport of RTCM via Internet Protocol (Ntrip) RTCM 10410.0 1 An application-level protocol that supports streaming Global Navigation Satellite System (GNSS) data over the Internet
Standard for Differential Navstar GPS Reference Stations and Integrity Monitors (RSIM) RTCM 10401.2 2 A companion to RTCM 10402.3, this standard addresses the performance requirements for the equipment which broadcasts DGNSS corrections

The RTCM 10402.3 standards defined the messages for differential correction information. The messages 1 to 17 are available in older RTCM versions, while messages 18-21 have been added in version 2.3 to make the standard applicable to RTK corrections. The releases of RTCM versions 3.0 and 3.1 focus on the optimization of the use of bandwidth,[6] on higher integrity[7] and on the management of RTK networks. More information about RTCM messages can be found in article DGNSS Standards.

Other Standards

The Compact Measurement Record (CMR) was developed by and initially used by Trimble in 1992. The format was developed as a method of transmitting code and carrier phase correction data in a compact format from GPS base stations to GPS rovers for RTK GPS surveying. In 2009, Trimble has introduced a new broadcast observation format called CMRx, this has been developed to support significant changes to GNSS constellations which are currently underway. The purpose of CMRx is to improve the initialization time, to cover additional GNSS core constellations, to deal with new GNSS signals and to improve performance in urban environments and user under canopy.[8]

According to the company Septentrio, another RTK standard widely used in Europe is FKP,[4] named after the German Flaechen-Korrektur-Parameter, or spatial correction parameter.[9] As RTCM 3.0 and 3.1, FKP covers networks of base RTK stations, and, because of the broadcast of ionospheric corrections, allows fixing ambiguities for longer baselines than when a single base station is used.[4] In order to provide corrections, FKP makes use of the RTCM proprietary message type 59.[10]

Notes


References

  1. ^ International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK
  2. ^ RTK in Wikipedia
  3. ^ Remote Sensing 2009, A. Rietdorf et al., Precise Positioning in Real-Time using Navigation Satellites and Telecommunication, Proceedings of the 3rd Workshop on Positioning, Navigation and Communication (WPNC’06)
  4. ^ a b c d DGPS vs RTK, Septentrio
  5. ^ RTCM SC-104 Protocol, in Hemisphere GPS homepage
  6. ^ RTCM SC-104 transmission protocols, by TEKMON Geomatics
  7. ^ Lin Minmin (2006). RTCM 3.0 Implementation in Network RTK and Performance Analysis. Msc Thesis, University of Calgary, Dept of Geomatic Engineering.
  8. ^ GPS/GNSS Related Terminology, www.alabamaprecisionagonline.com.
  9. ^ Wubenna G., Bagge A., Seeber G., Volker B., Hankemeier P. (1996). Reducing Distance Dependent Errors for Real Time Precise DGPS Applications by Establishing Reference Station Networks. In Proc. Institute of Navigation National GPS 1996 Kansas, 17-20 September, Vol 2, 1845-1852.
  10. ^ Gerhard Wübbena, Andreas Bagge, RTCM proprietary message type 59, Geo++® White Paper, Nr. 2006.01, 2006.