University of Ljubljana Faculty of Civil and Geodetic Engineering

Contact information

Faculty of Civil and Geodetic Engineering, University of Ljubljana
Jamova cesta 2, Ljubljana, SI-1000; Slovenia


Bojan Stopar (
Klemen Ritlop (

The University of Ljubljana Faculty of Civil and Geodetic Engineering (UL FGG) is part of EPOS Slovenia since 2011. Today, UL FGG contributes to EPOS ERIC through TCS10 – GNSS data and products. As part of this project, UL FGG has updated some GNSS equipment in the national GNSS Network SIGNAL and the Combined Geodetic Network. Now, those GNSS stations can track Galileo signal, while GNSS network monitoring software was upgraded to process Galileo observations. For local stability monitoring purposes of GNSS reference stations UL FGG obtained precise terrestrial geodetic instrumentation.


The main research goals of UL FGG within EPOS (European Plate Observing System) infrastructure and project are:

1. permanent tectonic movement monitoring in Slovenian territory
2. setting up a geokinematic model of Slovenia
3. contribute to realization of modern geodetic coordinate system of Slovenia

Slovenia lies on the convergent boundary of two lithospheric plates, the Adriatic microplate, and the Eurasian plate. Therefore, the active tectonic processes lead to significant seismic activity, classifying Slovenia as one of the most earthquake-prone countries in the EU. The goal of our research is to get a better understanding of the distribution of regional tectonic deformation based on GNSS data and to combine them with geological and geophysical data.

GNSS observations acquired with the SIGNAL CORS network were in the past used to determine the velocity of the geodetic reference points in Slovenian territory which can reach up to 5 mm/year relative to stable Eurasia due to active tectonics.In this respect is our contribution to perform high end permanent GNSS observations data which enable us the
coordinates at the Slovenian territory.

Our second goal is to set up a geokinematic model of active tectonic deformations which is a key component of the modern geodetic reference system. The purpose of the geokinematic model is analytically represent recent tectonic movements in the area. The input to geokinematic model are vectors of velocity changes of coordinates.

Modern geodetic coordinates systems are nowadays realized on the basis of permanent GNSS observations performed on continuously operated GNSS stations. GNSS station coordinates, estimated velocity vectors of GNSS stations and geokinematic model are used to establish modern geodetic coordinate system. Our third goal is to establish mid- to long-term realization of the geodetic coordinate system where the impact of velocity vectors of coordinates on the stability of coordinate system realization will be investigated.

RI-SI-EPOS project

UL FGG is part of the EPOS since 2011 and contributes to EPOS ERIC through its National Distributed Center in the TCS10 – GNSS Data and Products. As part of the RI-SI-EPOS project, UL FGG has replaced GNSS equipment of the following permanent GNSS stations:
– CELJ00SVN, LEND00SVN, MRBR00SVN and PTUJ00SVN (part of the Slovenian national GNSS network SIGNAL),
– PZA100SVN (part of Slovenian Combined Geodetic Network (CGN)),
– FGG300SVN (used for research purposes and QC monitoring of the SIGNAL network).

GNSS data, provided by the whole SIGNAL network, all ten GNSS stations of the Slovenian CGN and station FGG300SVN are used for various scientific and research purposes:
– Acquired GNSS observations are periodically processed to obtain daily coordinates time series and velocity vectors needed to explain the geotectonic of Slovenia and develop a 3D Geokinematic Model of the Slovenian Territory.
– A continuous real-time monitoring system was developed at the station FGG300SVN that can be used to monitor the local stability of the station GSR100SVN (SIGNAL network, EPN), or the local quality of the VRS network product form the SIGNAL network. In the future the developed concept can be used for real-time monitoring of local stability of multiple SIGNAL network stations using GNSS stations of the Slovenian CGN.
– GNSS station FGG300SVN was used as a test station for the development of methodologies and strategies for setting up new CORS stations with high positioning quality which is required for GNSS stations used for realization of the national coordinate system.
– Model of double differencing of phase GNSS observations in kinematic mode was developed to determine temporal changes of the baseline’s vector between SIGNAL stations. It was found that temporal and long-term deformations of Earth’s crust could be detected and monitored using GNSS data from permanent GNSS stations. The developed methodology was tested in monitoring the propagation of the seismic wave of the Petrinje earthquake through the Slovenian territory.

To get quality daily coordinate time series and velocity vectors, the GNSS stations should not be affected by local tectonics and other local Earth surface deformations. Therefore, stability of the main pillars of all geodetic points of the Slovenian CGN is monitored with precise geodetic terrestrial measurements. For this purpose, both RI-SI-EPOS total stations and accessories for precise geodetic survey, are used. Also, the possibility of detecting daily displacements of the antenna pole of the station KOPE00SVN (SIGNAL network), was analysed by combining TPS and TLS data, collected with RI-SI-EPOS equipment.

GNSS observations from all Slovenian CGN GNSS stations are available through the EPOS-GNSS Pan-European Node. GNSS observations from station FGG300SVN is available through the OGS EPOS data node. GNSS observations from the SIGNAL network are available through the SIGNAL network web portal.

SLOKIN – Geokinematic Model of Slovenian Territory

Slovenia and the surrounding areas lie on the convergent boundary of two lithospheric plates, the Adriatic microplate and the Eurasian plate, which have been converging at a rate of several mm/year for tens of millions of years. Although the ongoing deformation rates in Slovenia are relatively low from a global point of view, the active tectonic processes nevertheless lead to significant seismic activity, making Slovenia one of the most earthquake-prone countries in the EU.

Active tectonic processes also cause deformations of the Earth’s surface, although the spatial distribution of tectonic deformations is usually very inhomogeneous. The extent of these movements can now be measured using sophisticated geodetic techniques. Reference points used to define Slovenia’s national reference system move by up to 7 mm/year, meaning that reference points used to define the national reference system 20 years ago may now be displaced by up to 15 cm relative to stable Eurasia. These movements are inhomogeneous in direction and magnitude. It is therefore clear that without the introduction of a geokinematic model that accurately predicts coordinate change over time, the realization of the national coordinate system cannot provide sufficient quality to meet current and future accuracy requirements for positioning within the national and global coordinate systems.

The Slovenian territory is an ideal case for the study of active tectonics and geodynamic influences on the geodetic coordinate/reference system. The existing Slovenian network of passive (periodically occupied) GNSS stations is among the densest in Europe and in the world. For most of these locations, the time series of campaign-type GNSS measurements are over 15 years long. The passive GNSS network is complemented by more than 40 continuously operating GNSS stations distributed throughout the region, including cross-border areas of neighbouring countries. The vertical movement of points can be additionally constrained by precise levelling data repeatedly collected over the last 50 years and by gravimetric observations.

The proposed project will connect our previous activities of determining the horizontal geokinematic model. With this project, we want to achieve:
– to update and significantly improve the horizontal geokinematic model,
– to establish a new vertical geokinematic model,
– to integrate both components into a coherent 3D geokinematic model of the Slovenian territory.

The main goal of the proposed project is to create a unified 3D-geokinematic model of active tectonic deformation in the north-eastern zone of the collision zone between the Adriatic and Eurasian plates.

Among other data, GNSS observations from the Slovenian national GNSS network SIGNAL and the Slovenian national Combined Geodetic Network (CGN) are used within the project. GNSS stations CELJ00SVN, LEND00SVN, MRBR00SVN and PTUJ00SVN (part of the SIGNAL network), PZA100SVN (part of the Slovenian CGN) and FGG300SVN are all equipped with RI-SI-EPOS equipment from 2022 onwards. Stability monitoring of the main pillars for all geodetic points of the national Combined Geodetic Network is conducted with both RI-SI-EPOS total stations (Leica Nova MS60 SmartStation and Trimble S5 Total Station) and equipment for a precise geodetic survey.

RI-SI-EPOS third project

These are GNSS stations, networks, and geodetic points, set up by private companies that are used for positioning with adequate relative precision, but with questionable precision and accuracy within the national coordinate system.

Currently, private CORSes and CORS networks are established based on the needs of the private sector and without any standardised procedures and criteria to ensure high-quality compliance with a national coordinate system. Due to the lack of knowledge of the situation, we can also only speculate about the quality and reliability of the establishment and maintenance of private GNSS stations.

On a basis of our own research and good practice examples, at home and abroad, we proposed a methodology for the establishment of CORS, namely:
– location selection and the impact of the location surrounding on GNSS observation over a longer period of time,
– equipment of CORS that must be of high quality to ensure continuous operation and
GNSS observations from several frequencies,
– determined coordinates that represent the origin for positioning of new geodetic points and should be determined in the national coordinate system with high quality in the long term and
– methods of CORS data distribution that are used for positioning new points in
national coordinate system.

The main objective of the project was to provide a methodology for the establishment of CORS or CORS network that will ensure the positioning of new geodetic points in a national coordinate system with the same quality as in the case of the SIGNAL network. Some aspects of the project were focused on the determination of the protocol for dissemination of CORS metadata for the owner/manager of CORS to easily assure the quality and reliability of CORS data and their products.

Among all data, GNSS observations from stations CELJ00SVN, LEND00SVN, MRBR00SVN and PTUJ00SVN, which are part of the SIGNAL network, station PZA100SVN, which is part of the national Combined Geodetic Network and FGG300SVN station, which was our experimentally established CORS, were also used within the project. All mentioned GNSS stations were and still are equipped with the RI-SI-EPOS equipment. Additionally, SIGNAL network products, produced by Trimble RTXNet Processor, which is also part of the RI-SI-EPOS equipment were also used. Trimble R12i GNSS receiver was used for field testing.

RI-SI-EPOS equipment


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Stopar, B. (2021). Državni koordinatni sistem, temelj vseh dejavnosti v prostoru. Slovenski inženirski dan. Online presentation, March 4, 2021.

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