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|Editors=GMV
|Authors=GMV
|Level=Basic
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|YearOfPublication=2011
|YearOfPublication=2011
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There are DGNSS techniques used by high-precision navigation/surveying applications, based on the use of carrier phase measurements. This is the case of the Real Time Kinematics (RTK), where the differential GNSS measurements are computed in real-time by specific GNSS receivers if they receive a correction signal using a separate radio receiver. When referring to GPS in particular, the system is also commonly referred to as Carrier-Phase Enhancement, CPGPS.<ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref>  
With origin dating back to the mid-1990s, [[Real Time Kinematics]] (RTK) is a [[Differential GNSS|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.<ref name="RTKIAG">[http://www.wasoft.de/e/iagwg451/ International Association of Geodesy (IAG) Working Group 4.5.1: Network RTK ] </ref><ref name="RTK_WIKI">[http://en.wikipedia.org/wiki/Real_Time_Kinematic RTK in Wikipedia]</ref><ref name="RTKWPNC06">[http://www.wpnc.net/fileadmin/WPNC06/Proceedings/34_Precise_Positioning_in_Real-Time_using_Navigation_Satellites_and.pdf 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) ]</ref>


When using RTK dual-frequency systems the rover position accuracy is typically 1 centimeter ± 2 ppm (horizontal) and 2 centimeters ± 2 ppm (vertical) <ref name="GPS_WORLD_LAMBDA">[http://chromatographyonline.findanalytichem.com/lcgc/article/articleDetail.jsp?id=584852&sk=&date=&pageID=3 Bernd Eissfeller, Thomas Pany, Günter Heinrichs, Christian Tiberius, ''Real-Time Kinematic in the Light of GPS Modernization and Galileo'', Oct. 1, 2002, GPS Word]</ref>. As it was seen in article [[RTK Fundamentals]], this accuracy decreases if ambiguity resolution is not correctely solved, and this happens due to error decorrelation that increases proportionately with baseline distance. This decorrelation error can be of the order of one meter, contrary to other error sources ( atmospheric effects, multipath, orbit errors, or noise) that are of the order of several millimeters up to a few centimeters <ref name="GPS_WORLD_LAMBDA"/>. To solve this issue, around 2004 the ''Network RTK'' Systems were developed, mainly in areas of great GPS surveying activity.
There is a big amount of different receiver manufacturers including RTK in their products. With the purpose of solving the limitation that the rover needs to be at a range of a few kilometres from the base station, the technique has evolved from stand-alone base stations to RTK networks.


==RTK Systems==
==RTK Receiver Manufacturers==
[[File:RTK-intro3.jpg|300px|thumb|Network RTK]]
[[File:RTK-intro3.jpg|300px|thumb|Network RTK]]


When the RTK systems began to operate (around 2000), they used a '''single base station''' receiver and a number of mobile units. The base station re-broadcasts the phase of the carrier that it measured, and the mobile units compare their own phase measurements with the ones received from the base station,<ref name="RTK_WIKI"/> following the [[RTK Standards|RTK Standards]]. This allows the mobile units to calculate their relative position to millimeters, although their absolute position is accurate only to the same accuracy as the position of the base station.<ref name="RTK_WIKI"/>


When referring to RTK technique, the key is the [[RTK Fundamentals|"Ambiguity Resolution"]]. Once ambiguity is fixed by LAMBDA Method, the problem of RTK Systems is that accuracy and reliability is degraded when one single base station is in a distance larger than a few tens of kms. To overcome this problem, the ''Network RTK'' Systems have been used over the last years.<ref name=EULER>[http://www.wasoft.de/e/iagwg451/euler/euler.html Reference Station Network Information Distribution, by Hans-Jürgen Euler, IAG Working Group 4.5.1: Network RTK (2003-2007)]</ref>
RTK is a ubiquitous technique used in geodetic receivers provided by  manufacturers targeting the high precision market. In a product survey performed by the company [http://www.hydro-international.com/ Hydro International] in the hydrographical field, the following RTK receiver brands were identified:<ref>[http://www.hydro-international.com/files/productsurvey_v_pdfdocument_18.pdf RTK DGPS Receivers, Product Survey, Hydro International, October 2007]</ref>
*[http://www.adnavigation.com/ AD Navigation AS]
*[http://www.cctechnol.com C&C Technologies]
*[http://www.fugro.com/ Fugro]
*[http://www.hemispheregps.com/ Hemisphere GPS]
*[http://www.leica-geosystems.com/ Leica Geosystems AG]
*[http://www.magellangps.com/ Magellan Navigation]
*[http://www.septentrio.com/ Septentrio NV]
*[http://www.topcon.eu/ Topcon Europe Positioning]
*[http://www.trimble.com/ Trimble]


This Network RTK Systems have had a great success in areas with a lot of GPS surveying activity, such as Europe. In these areas there are many permanent reference stations, allowing to users to share infrastructure and costs. <ref name=EULER/>
It is noted that this is not an exhaustive list of RTK product providers, as some well-known manufacturers are missed, such as:
*[http://www.ashtech.com/ ashtech]
According to H-J Euler:<ref name=EULER/>
*[http://www.javad.com/ JAVAD]
*[http://www.navcomtech.com/ NAVCOM]
*[http://www.novatel.com/ NovAtel].


''The integration of several reference stations into a combined network provides benefits for the user by improving the accuracy and increasing the overall user system performance. For the reference station operator, networking reduces the number of stations that are needed to provide a given level of accuracy to the rover users. These permanent reference station networks are requiring real-time communication to a networking computation center and real-time estimation of biases between reference stations.''
==RTK Networks==
In its origin, RTK was designed to broadcast corrections from one base station to a set of rovers in its vicinity. Due to the difficulties to [[RTK Fundamentals|fix the carrier phase ambiguities]] as the distance between base and rover increases, and to the spatial de-correlation of the errors corrected, the practical range of RTK is around 10 to 20 kilometres.<ref name="RTKIAG"/>


The way of distributing the information generated in the computing center to the user in the field is a very important question, because having the capability to supply the RTK service for a lot of types of rover equipment is essential to service providers. Therefore, the supplied information by the network computation centers and the way of processing the data must be completely understood. Nowadays, the information is supplied in two ways:  
In order to cope with this limitation, several [[RTK Standards|standards]] have recently been developed to provide corrections for a network of base stations. In this way, the rover can use the nearest base station from the network without the need of reinitialising the ambiguity fixing filters. This is only possible if a common processing is done for the base stations, so that the carrier measurements broadcast for the different receivers in the network have consistent phase ambiguities.<ref name="RTKIAG"/><ref name=EULER>[http://www.wasoft.de/e/iagwg451/euler/euler.html Reference Station Network Information Distribution, by Hans-Jürgen Euler, IAG Working Group 4.5.1: Network RTK (2003-2007)]</ref> RTK network solutions are particularly successful in regions with dense deployment of permanent base receivers, as it is the case in Europe.<ref name=EULER/>
* the FKP-approach  (FKP stands for the German word of spatial correction parameter)<ref>[http://www.geopp.de/download/seeb60_wuebbena_e.pdf On the modeling of GNSS observations for high−precision position determination, Gerhard Wübbena, Translation of Wübbena, G. (2001). Zur Modellierung von GNSS−Beobachtungen für die hochgenaue Positionsbestimmung. Wissenschaftliche Arbeiten Fachrichtung Vermessungswesen an der Universität Hannover, Festschrift Prof. G. Seeber zum 60. Geburtstag, Nr. 239, Hannover, 143−155.]</ref>, property of [http://www.geopp.de/ Geo++]  
* Virtual Reference Station (VRS) approach, property of [http://www.trimble.com Trimble].
The list of standards that handle with RTK networks includes:
 
*RTMC v3.0<ref>[[http://www.rtcm.org Radio Technical Commission for Maritime Services]</ref> and higher versions.
As it is noted in H-J Euler:<ref name=EULER/> ''Both approaches deliver observations that are supposed to be operational with modern RTK equipment. However, as noted above, the ways the computational algorithms running at the networking computation center are proprietary. Optimal interoperability is not guaranteed, since the definition and an interface mechanism is missing. While the roving user equipment might work optimally with one vendor's networking software providing a service, it might have degraded performance with another vendor's software.''
*FKP<ref>[http://www.geopp.de/download/seeb60_wuebbena_e.pdf On the modeling of GNSS observations for high−precision position determination, Gerhard Wübbena, Translation of Wübbena, G. (2001). Zur Modellierung von GNSS−Beobachtungen für die hochgenaue Positionsbestimmung. Wissenschaftliche Arbeiten Fachrichtung Vermessungswesen an der Universität Hannover, Festschrift Prof. G. Seeber zum 60. Geburtstag, Nr. 239, Hannover, 143−155.]</ref> by [http://www.geopp.de/ Geo++].
 
*Virtual Reference Station (VRS) approach, property of [http://www.trimble.com Trimble]. According to Trimble, VRS is the network solution used in more than 95% of the installations.<ref name=RTK_TRIMBLE>[http://www.trimble.com/survey_wp_scalable.asp?Nav=Collection-33413 Support of Network Formats by Trimble GPSNet Network RTK Solution, Trimble, 2005]</ref>
According to Trimble, VRS is the network solution used in more than 95% of the installations.<ref name=RTK_TRIMBLE>[http://www.trimble.com/survey_wp_scalable.asp?Nav=Collection-33413 Support of Network Formats by Trimble GPSNet Network RTK Solution, Trimble, 2005]</ref>
 
==Credits==
This article has been edited by GMV, including and adapting text from the following sources, as indicated with the corresponding references:
* RTK in Wikipedia<ref name="RTK_WIKI"/>, provided under [http://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike License]
* ''Real-Time Kinematic in the Light of GPS Modernization and Galileo'', by Bernd Eissfeller et al.<ref name="GPS_WORLD_LAMBDA"/>
* ''Reference Station Network Information Distribution'', by Hans-Jürgen Euler<ref name=EULER/>


==Notes==
==Notes==

Revision as of 19:32, 5 December 2011


FundamentalsFundamentals
Title RTK Systems
Author(s) 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]

There is a big amount of different receiver manufacturers including RTK in their products. With the purpose of solving the limitation that the rover needs to be at a range of a few kilometres from the base station, the technique has evolved from stand-alone base stations to RTK networks.

RTK Receiver Manufacturers

Network RTK


RTK is a ubiquitous technique used in geodetic receivers provided by manufacturers targeting the high precision market. In a product survey performed by the company Hydro International in the hydrographical field, the following RTK receiver brands were identified:[4]

It is noted that this is not an exhaustive list of RTK product providers, as some well-known manufacturers are missed, such as:

RTK Networks

In its origin, RTK was designed to broadcast corrections from one base station to a set of rovers in its vicinity. Due to the difficulties to fix the carrier phase ambiguities as the distance between base and rover increases, and to the spatial de-correlation of the errors corrected, the practical range of RTK is around 10 to 20 kilometres.[1]

In order to cope with this limitation, several standards have recently been developed to provide corrections for a network of base stations. In this way, the rover can use the nearest base station from the network without the need of reinitialising the ambiguity fixing filters. This is only possible if a common processing is done for the base stations, so that the carrier measurements broadcast for the different receivers in the network have consistent phase ambiguities.[1][5] RTK network solutions are particularly successful in regions with dense deployment of permanent base receivers, as it is the case in Europe.[5]

The list of standards that handle with RTK networks includes:

  • RTMC v3.0[6] and higher versions.
  • FKP[7] by Geo++.
  • Virtual Reference Station (VRS) approach, property of Trimble. According to Trimble, VRS is the network solution used in more than 95% of the installations.[8]

Notes


References

  1. ^ a b c 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. ^ RTK DGPS Receivers, Product Survey, Hydro International, October 2007
  5. ^ a b Reference Station Network Information Distribution, by Hans-Jürgen Euler, IAG Working Group 4.5.1: Network RTK (2003-2007)
  6. ^ [Radio Technical Commission for Maritime Services
  7. ^ On the modeling of GNSS observations for high−precision position determination, Gerhard Wübbena, Translation of Wübbena, G. (2001). Zur Modellierung von GNSS−Beobachtungen für die hochgenaue Positionsbestimmung. Wissenschaftliche Arbeiten Fachrichtung Vermessungswesen an der Universität Hannover, Festschrift Prof. G. Seeber zum 60. Geburtstag, Nr. 239, Hannover, 143−155.
  8. ^ Support of Network Formats by Trimble GPSNet Network RTK Solution, Trimble, 2005
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