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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>


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.  
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.


Most of the currently available RTK receiver systems use double-differenced GPS and/or GLONASS carrier phase measurements to determine the position of the roving receiver. The typical nominal accuracy for dual- frequency systems is 1 centimetre ± 2 ppm (horizontal) and 2 centimetres ± 2 ppm (vertical). The latency for position outputs varies from less than 20 ms to 100 ms for different receiver systems. If the receiver works in the synchronised RTK mode, the latency depends, of course, on the latency of the radio data link. The position accuracy drastically decreases if the double-differenced ambiguities are not resolved or are resolved incorrectly. In the latter case, errors in the order of one metre can easily occur. Therefore, reliable ambiguity fixing is probably the most important design aspect for an RTK system. All other error sources - such as unmodeled atmospheric effects, (carrier) multipath, orbital errors, or receiver measurement noise - are of the order of several millimetres up to a few centimetres.
==RTK Receiver Manufacturers==
[[File:RTK-intro3.jpg|300px|thumb|Network RTK]]


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


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, following the [[Work in Progress:RTK Standards|RTK Standards]].  
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 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. A single reference station set-up within up to 20-30 km is typically required if a user is operating in baseline mode. Otherwise the performance, accuracy, and with some systems the reliability of user's RTK is degraded.
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.javad.com/ JAVAD]
*[http://www.navcomtech.com/ NAVCOM]
*[http://www.novatel.com/ NovAtel].


Over the last few years, permanent reference station installations have emerged in many countries. This is quite appealing, since in areas with considerable GPS surveying activity, a number of users might share the infrastructure and the associated costs. Some of the installations are operated by companies and provide a service to the surveying community. Installations can be just :
==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"/>


*single reference stations,
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/>
*a number of single reference stations,
*or networking reference stations.  
 
Then, RTK systems have evolved to the integration of several reference stations into a combined '''network RTK''' that 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.
 
A key factor of success is the distribution of the information generated within the networking computation center to the roving user in the field. Some of the installations are relying on proprietary computation algorithms and possibly formats and restricting themselves with the field equipment. However, in general it is in the interest of service providers to supply the service for more than a single type of RTK field equipment. Therefore, the detailed understanding of the supplied information such as applied corrections or the way of processing is absolutely mandatory.  
   
   
Today, installations are supplying the information basically in two ways:
The list of standards that handle with RTK networks includes:
* the so-called [http://www.geopp.de/download/seeb60_wuebbena_e.pdf FKP-approach] (FKP stands for the German word of spatial correction parameter);
*RTMC v3.0<ref>[http://www.rtcm.org Radio Technical Commission for Maritime Services]</ref> and higher versions.
* the [http://trl.trimble.com/docushare/dsweb/Get/Document-231963/022543-130_NetworkInfras_WP_0605.pdf VRS approach] (Virtual Reference Station).  
*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://trl.trimble.com/docushare/dsweb/Get/Document-231963/022543-130_NetworkInfras_WP_0605.pdf Support of Network Formats by Trimble GPSNet Network RTK Solution, Trimble, 2005]</ref>
Both approaches deliver observations that are supposed to be operational with modern RTK equipment. However, the ways the computational algorithms running at the networking computation center are proprietary, FKP is property of [http://www.geopp.de/ Geo++] and VRS of [http://www.trimble.com Trimble]. The VRS GNSS RTK is the dominant Network RTK technique today (around 95%). 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. Within [http://www.rtcm.org RTCM] Special Committee No. 104 (SC104), a Network RTK working group is developing the future standardized way of interfacing between networking reference stations and roving field users.<ref>[http://www.wasoft.de/e/iagwg451/ IAG Working Group: Network RTK.] </ref>


==Notes==
==Notes==

Latest revision as of 08:09, 27 July 2018


FundamentalsFundamentals
Title RTK Systems
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]

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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