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NATIONAL AND MODERN GEODETIC COORDINATE SYSTEMS IN SLOVENIA 
Bojan Stopar, Miran Kuhar 
University of Ljubljana, Faculty of Civil and Geodetic Engineering - Geodetic Department, 
Jamova 2, Ljubljana, Slovenia 
1SPRS WG VI/3 and WG IV/3 
KEYWORDS: reference frame, reference system, astrogeodetic network, geoid, transformation, collocation 
ABSTRACT 
The paper presents the condition of the official coordinate system in Slovenia. The inherent errors and distorsions in the astrogeodetic 
network of Slovenia make it unsuitable for today's requirements which not only include national mapping and cadastral purposes, but 
also scientific and safety purposes such as earthquake prediction, crustal dynamics and land subsidence. The results of different 
transformation procedures between the astrogeodetic network and global coordinate system (ETRS89) shows all the drawbacks of 
existing coordinate frame. Now with the advent of new technologies such as GPS, it is becoming of increasing importance that such 
accurate surveying measurements could be incorporated into an existing coordinate frame without degrading the measurements itself. 
It is obvious that such control network must be realized in terms of a stable and consistent coordinate frame which is of a global 
nature. In order to implement such a modern threedimensional coordinate system country should have all reference system (height 
and horizontal position) well defined and up-to-date. One of the prerequisites for that is also an accurate geoid - the reference 
surface for height determination. 
COORDINATE SYSTEMS AND COORDINATE 
FRAMES 
The purpose of a reference frame is to provide the means to 
materialize a reference system so that it can be used for the 
quantitative description of positions and motions on the Earth 
(terrestrial frames), or of celestial bodies, including the Earth, in 
space (celestial frames). 
In geodesy and astronomy only two basic coordinate systems 
are needed: a Conventional Inertial System (CIS), which in 
some 'prescribed' way is attached to extragalactic celestial radio 
sources, to serve as a reference for the motion of a Conventional 
Terrestrial System (CTS). It moves and rotates with the Earth 
and is also attached in some 'prescribed' way to a number of 
dedicated observatories operating on the Earth's surface. Both of 
above mentioned basic coordinates systems are defined and 
maintained by International Earth Rotation Service (IERS) and 
are known as: 
• International Celestial Reference System (ICRS), 
• International Terrestrial Reference System (ITRS). 
At its 23rd General Assembly in August 1997, the IAU decided 
that, as from 1 January 1998, the IAU celestial reference system 
shall be the International Celestial Reference System (ICRS), in 
replacement of the FK5 (Fundamental Katalog 5). The origin of 
the ICRS is at the barycentre of the solar system. The directions 
of its axes are fixed with respect to the distant quasars to better 
than 0.02 mas (milliarc of second). The ICRS is realized by 
estimates of the coordinates of a set of quasars, the 
International Celestial Reference Frame (ICRF). The ICRF 
consists of a catalogue of equatorial coordinates of 608 
extragalactic radio sources derived from about 1.6 million 
observations accumulated by a worldwide network over 1979- 
1995. The accuracy of the definition of the ICRF axes is 
estimated to be 0.02 mas. 
The origin of the International Terrestrial Reference System 
(ITRS) is at the centre of mass of the whole Earth, including the 
oceans and the atmosphere. Its length unit is the metre (SI). The 
orientation of its axes is consistent with that of the BIH System 
at 1984.0 within ±3 milliarcseconds. Its time evolution in 
orientation is such that it has no residual rotation relative to the 
Earth's crust. The ITRS is realized by estimates of the 
coordinates and velocities of a set of observing stations. 
Realizations of the ITRS are produced by the Terrestrial Frame 
Section of the IERS Central Bureau under the name 
International Terrestrial Reference Frame (ITRF), which 
consist of lists of coordinates (and velocities) for a selection of 
IERS sites (tracking stations or related ground markers). 
Currently, ITRF-yy is published annually in IERS Technical 
Notes. The numbers (yy) following the designation ITRF 
specify the last year whose data were used in the formation of 
the frame. Hence ITRF97 designates the frame of coordinates 
and velocities constructed in 1997 using all of the IERS data 
available through 1996. 
EUROPEAN TERRESTRIAL REFERENCE SYSTEM 
1989 ETRS 89 
The I AG has established during its Vancouver General 
Assembly (1987) a subcommission called 'EUREF' for the 
European Reference Frame of the Commission X on 
Continental Networks. EUREF took over the works done by the 
RETRIG subcommision which as a final result produced 
combined adjustment of terrestrial data of national's primary 
triangulation and space derived data covering western Europe 
under the name ED87 (European Datum 1987). 
The primary goal of EUREF was to take full advantage of 
available space geodetic techniques to realize a truly 
threedimensional and mostly accurate control network which 
would be the basic realization of a new terrestrial system for 
Europe. The implementation of this goal were possible by 
availability of the ITRS, established by the IERS, which is 
accepted worldwide. The existence of the rather dense network 
of primary sites over the Europe belonging to the IERS network 
assured the possibility for the connection of the new sistem to 
the existing terrestrial system. In such a system station positions 
in Europe have a common motion of the order of one centimeter 
per year. The system adopted by EUREF is the European 
Terrestrial Reference System 89 (ETRS 89) and is coincident