149 
with ITRS at the epoch 1989.0 and fixed to the stable part of the 
Eurasian Plate. The realization of the ETRS 89 is basically 
possible with the established connection with the various 
reference frames, and with the various transformation formulas 
between ETRS 89 and other systems. The system is coincident 
with the World Geodetic System 84 (WGS-84) at one meter 
level, what means that the coordinates, for most applications, 
have no time variation. 
ASTROGEODETIC NETWORK OF SLOVENIA 
Traditional geodetic coordinate systems were local coordinate 
systems, covering the part of the Earth surface, mainly the 
territory of a single country. These coordinate systems were 
established with the satisfactory accordance of the Earth surface 
and geometry of the choosen reference ellipsoid. Reference 
ellipsoid plays the role of the mathematical reference surface, 
where all the computations are performed and points positions 
are given. 
The astrogeodetic network of Slovenia covers the territory of 
the Republic of Slovenia. As regards its shape, it is a standard 
trigonometric network (Fig.l) Due to the requirements of 
classical geodesy, trigonometric points are located on hills and 
stabilized by concrete pillars. The network comprises 34 first 
order trigonometric points. For the needs of this paper, it was 
assumed that the 375 Gorjanci trigonometric point is also part of 
the national geodetic network of Slovenia. For this reason, the 
astrogeodetic network of Slovenia is discussed in this paper as a 
network of 35 points which forms 46 triangles. The network 
covers the area of app. 230km* 140km. 
For historical reasons, the position of the astrogeodetic network 
on the reference elliposid is wrong, the network has large scale 
deformations ant its accuracy is not homogenous. Activities for 
the improvement the Slovenian astrogeodetic network began 
after 1974. The greatest emphasis was put on the measurements 
of distances in the network and to the determination of the scale 
of the national geodetic network. In addition to distance 
measurements, the orthometric heights were determined anew 
for many points, such that they have been determined for all 
points. 
THE GEOID IN SLOVENIA 
First geoid determination which covers the territory of Slovenia 
was performed in early seventies and was done by prof. 
Muminagic from Sarajevo. This astrogeodetic solution was 
determined for the whole former Yugoslavia and includes 
astronomic measurements on 170 points. It was a relative 
solution and is only of scientific importance. 
In 1991 was determined the astrogeodetic geoid for Slovenia 
and parts of Croatia (Colic et al., 1992a). It was based on very 
accurate astronomic measurements performed on 32 first order 
trigonometric points. Later on, aditional astronomic 
measurements were carried out, so at the moment there is 43 
astrogeodetic points in Slovenia. This first computation was 
followed by improved solution in 1992 (Colic et ah, 1992b). 
Finally in 1999 it was determined completely new solution 
based on all available astrogeodetic measurements together with 
new density data of the Earth's crust (Pribicevic, 1999). 
All astronomical observations were performed with Zeiss Ni-2 
astrolabe apparatus. The summary of the observation 
innaccuaracies shows very good internal accuracy of an average 
of 0,2" in latitude and 0,3" in longitude. The external accuracy, 
very much depending on topographic conditions, was 
determined according to the method of double measurements, 
and it can be assumed to be: a<j>= 0,4", o A = 0,5". 
In order to take the effect of Earth topography into account, two 
different digital terrain models (DTM) were employed. The 
detailed model consists of mean height and depths for 12"xl5" 
elements. The coarse DTM contains 5'x5' mean heights. 
In all threee solutions the determination of the geoid was 
performed using well known remove-restore technique.