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COMPARISON OF SINGLE BASELINE RTK and NETWORK RTK GNSS METHODS

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In this study, the static accuracy performances of the Single Baseline and Network RTK positioning techniques were analysed. Accuracies of the RTK-based positioning were assessed based on field test in City of Çorum district, Turkey. For this purpose, several geodetic points with different distances from Single Baseline RTK base station in City of Çorum were established. The coordinates of these points were calculated with Single Baseline RTK and Network RTK methods. According to the obtained results, it can be stated that the method allows cm to dm level of accuracy in positioning without having the need of an additional user’s own reference station(s) or any other data, thus reduces the field operational costs. The obtained level of accuracy is perceived acceptable for different surveying and mapping applications such as general surveying projects, cadastral surveying, topographic detailed plans, general detailed site plans, as-built maps and GIS applications.
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INTERNATIONAL SYMPOSIUM ON
MODERN TECHNOLOGIES, EDUCATION AND PROFESSIONAL PRACTICE
IN GEODESY AND RELATED FIELDS
910 November 2017, Sofia
________________________________________________________________________________
COMPARISON OF SINGLE BASELINE RTK and NETWORK
RTK GNSS METHODS
R. M. ALKAN, İ. M. OZULU and V. İLÇİ
TURKIYE
SUMMARY
In this study, the static accuracy performances of the Single Baseline and Network RTK
positioning techniques were analysed. Accuracies of the RTK-based positioning were assessed
based on field test in City of Çorum district, Turkey. For this purpose, several geodetic points
with different distances from Single Baseline RTK base station in City of Çorum were
established. The coordinates of these points were calculated with Single Baseline RTK and
Network RTK methods. According to the obtained results, it can be stated that the method allows
cm to dm level of accuracy in positioning without having the need of an additional user’s own
reference station(s) or any other data, thus reduces the field operational costs. The obtained level
of accuracy is perceived acceptable for different surveying and mapping applications such as
general surveying projects, cadastral surveying, topographic detailed plans, general detailed site
plans, as-built maps and GIS applications.
1. INTRODUCTION
With origin dating back to the mid-1990s, Real-Time Kinematic (RTK) Positioning has become
common practice. RTK is a relative positioning technique that used at least two GNSS receivers;
one is setup on a point as base stations with known coordinates while the other(s) as rover(s).
The usability of this method and attainable accuracy is highly dependent on the distance between
the user receiver and its base station due to distance-dependent biases i.e. orbital, ionospheric
and tropospheric biases that deteriorate the positioning accuracy (El-Mowafy, 2012). Thus, it
works best when short baselines are issued as the precision of RTK measurements decreases
since the baseline length increases. In general, this conventional RTK, i.e. Single Baseline RTK,
has been limited to the distance of 10 to 20 km from the base station and is extended to 50 km
with long-range RTK.
Within a couple of decades, many administrative entities and private organizations have
established and operated Continuously Operating Reference Stations (CORSs) Networks for
achieving different purposes not only academic but also professional studies. In early 2000, a
method called as Network RTK Positioning have been started to be commonly used by adding
real-time capability to CORS networks. In this method, the distance-dependent errors mentioned
above are modelled accurately and reliably for long baselines i.e. several tens of kilometres. The
Network RTK provides more convenient, cost-effective and real-time precise positioning. The
most accurate real-time kinematic positioning method makes GNSS a very efficient tool for land,
air, marine and numerous different applications where reliable, accurate and precise real-time
positioning is required. More information can be found in Fotopoulos and Cannon (2001);
Lachapelle and Alves (2002); Rizos (2002); Rizos, (2007); El-Mowafy (2012) and Cina et al.
(2015).
The main objective of this study is to assess accuracy performances of the Single Baseline RTK
and Network RTK techniques. For this purpose, a number of static experiments were conducted.
In this study, the test procedure and obtained results with some recommendations are given.
2. CASE STUDY
In this study, a Single Baseline RTK operated by Çorum Local Municipality and a Network RTK
named as TUSAGA-Aktif operated by Republic of Turkey, the General Directorate of Land
Registry and Cadastre of Turkey were compared to each other in terms of accuracy performance
in static mode. For this purpose, a field test was carried out in City of Çorum district, Turkey on
May 2017 (GPS Day of Year 145 and 147). 9 Groups of points (3 points in each group) were
established at the different distances from the base station of Single Baseline RTK (i.e.
approximately 11 km, 20 km, 30 km, 41 km, 45 km, 50 km, 62 km, 75 km and 89 km) from Çorum
City centre (Figure 1).
Figure 1. The Location of Measured Points
As the first step, the coordinates of these points were determined with TUSAGA-Aktif network
by using Network RTK technique. The coordinates of the same points were then determined
again with Single Baseline RTK. In order to determine the known coordinates of established
points, static measurements were also occupied lasting 45 minutes to 1 hour time period (Figure
2).
Figure 2. Field Test Measurement
During the test measurements, multi-frequency and multi-constellation Trimble R10 GNSS
receivers were used. The provided accuracy level for the receiver is given in Table 1.
Table 1. Accuracy Specifications of Trimble R10 GNSS Receiver (URL 1)
Method
Accuracy
Static GNSS surveying
High-Precision Static
Horizontal ............................................... 3 mm + 0.1 ppm RMS
Vertical ................................................ 3.5 mm + 0.4 ppm RMS
Real Time Kinematic
Surveying
Single Baseline <30 km
Horizontal .................................................. 8 mm + 1 ppm RMS
Vertical .................................................... 15 mm + 1 ppm RMS
Network RTK
Horizontal ............................................... 8 mm + 0.5 ppm RMS
Vertical .................................................. 15 mm + 0.5 ppm RMS
Trimble CenterPoint RTX
Horizontal ............................................................... 4 cm
Vertical ................................................................... 9 cm
More information about the receivers used in this study can be found in URL 1.
During the post-processing stage, TUSAGA-Aktif stations which are the closest to the study area
were used as reference stations. The static data of these reference stations were downloaded from
TUSAGA-Aktif website (http://rinex.tusaga-aktif.gov.tr). The coordinates of the points were
calculated with differential method by using observations of reference stations and newly
established points within a few cm accuracies with Leica Geo Office integrated office processing
software. Then, the RTK-derived coordinates were compared to their known values and
differences in 2D position and ellipsoidal height components were calculated. The differences
between the known and RTK-derived coordinates are given in Figure 3.
Figure 3. Differences between Differential and RTK Positioning
3. CONCLUSION
The obtained results showed that cm to dm level accurate point positioning for both 2D positions
and height components is possible via Single Baseline and Network RTK approaches performing
very short (typically few minutes or even shorter) real-time measurements. Both of the systems
do not require conventional GNSS measurement as well as post-processing of the collected data.
The result implies that, both RTK users can determine their position fast, easily, and cost-
effectively at any time and all year round in real-time within a few cm-level of accuracy.
However, after the results from Single Baseline RTK were examined, it was realized that the
accuracy slightly decreased compared to Network RTK by getting distant from the reference
point. This provides slightly worse results than the Network RTK. This case was not observed
for the results of Network-RTK. Unlike Single Baseline RTK, the distance-dependent errors (e.g.
atmospheric and orbit) were modelled more conveniently in Network RTK and depending on
this fact, this technique provides more homogenous accuracy and in general, better positioning.
Generally, the obtained accuracies from the both Single Baseline RTK and Network RTK
approaches are good enough for many surveying applications while reducing the surveying costs
and labour.
REFERENCES
Cina, A., Dabove, P., Manzino, A. M. & Piras, M. (2015). Network real time kinematic (NRTK)
positioningdescription, architectures and performances. In: Prof. Shuanggen Jin (Editor).
Satellite Positioning-Methods, Models and Applications, InTech Publishing, 23-45.
El-Mowafy, A. (2012). Precise real-time positioning using network RTK. In: Prof. Shuanggen
Jin (Editor). Global navigation satellite systems: signal, theory and applications. InTech
Publishing, 161-188.
Fotopoulos, G. & Cannon, M. E. (2001). An overview of multi-reference station methods for
cm-level positioning. GPS Solutions, 4(3), 1-10.
Lachapelle, G. & Alves, P. (2002). Multiple reference station approach: overview and current
research. Journal of Global Positioning Systems, 1(2), 133-136.
Rizos, C. (2002). Network RTK research and implementation - A geodetic perspective. Journal
of Global Positioning Systems, 1(2), 144-150.
Rizos, C. (2007). Alternatives to current GPS-RTK services and some implications for CORS
infrastructure and operations. GPS Solutions, 11(3), 151-158.
URL 1: Trimble R10 GNSS System.
Available from: http://trl.trimble.com/docushare/dsweb/Get/Document-781669/022543-
544H_TrimbleR10_DS_A4_0517_LR.pdf [accessed 29/07/2017].
CONTACT
Prof. Dr. Reha Metin ALKAN
Hitit Üniversitesi Rektörlüğü
Kuzey Kampüsü, 19030 Çorum / TÜRKİYE
Telephone : +90 364 219 1926
E-mail : alkan@hitit.edu.tr
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