A unified and continuous national vertical network is the back-bone for geodesy, cartography, civil engineering and global positioning. International institutions are working to reach homogenous and unified vertical datum all around the globe. Levelling evaluation on the border between Latvia and Lithuania is of particular interest. Connection between vertical networks is made in three places, so connecting lines construct the two first order levelling loops. A joined loop adjustment produces a good basis for analysis and evaluation of height connection between Latvia and Lithuania not only as neighbouring countries but also as parties to the EVRS.

As European Union member states -Latvia and Lithuania have changed their national height systems from Baltic Normal Height System 1977 to European Vertical Reference System realizations. Performing practical Global Navigation Satellite System (GNSS) measurements and obtained data mathematical processing, there is a possibility to calculate point height difference between GNSS data and data of 1 st order levelling networks. The aim of the research is to gain insight for methodology development of geodetic point height testing using GNSS measurements. To achieve the goal following tasks are set: 1) perform GNSS measurements of first order levelling network in Latvia and Lithuania; 2) do data processing to get point ellipsoidal height and compare with the point normal height; 3) detect technically feasible accuracy of geoid model for precise height measurements with GNSS method within research area. Performing GNSS measurements at the same time in the territory of Latvia and Lithuania, the experience of mutual cross-border cooperation was accumulated. The results were adjusted with academic software package Bernese and were obtained point ellipsoidal and normal heights. The height measurement accuracy using GNSS method depends on geoid model accuracy and more precise results can be obtained increasing used geoid model accuracy to 1.5 to 2 cm.

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During the last years, the European and the Nordic quasi-geoid models and existing national q-geoid models covered the territory of Latvia. There are many ways for comparison and tests of results achieved. Scientists and professionals can compare models directly at some special geodetic co-location stations or use GNSS/levelling sites. The results of this research can be used by scientists and specialists in the fundamental geodetic observations for independent monitoring of existing q-geoid models and evaluation of accuracy. The research aims at evaluating the transition to the best updated regional q-geoid model. The research objectives are the following: 1) to investigate and analyse the development of q-geoid model LV14; 2) to conduct precision research; 3) to assess the challenges of the European Vertical Reference System; 4) to draw conclusions that allow for further research in this area for development and improvement. Within the framework of the research, the authors have used a variety of research methods. Historical and logical approaches, comparative analysis and synthesis methods, as well as inductive – deductive data analysis methods have been selected for the research. A conclusion for such kind of studies is to implement the most appropriate q-geoid solution and to develop new astrogeodetic methods for unification, monitoring and for reliability of a geodetic reference network.

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