At the moment all three Baltic countries – Estonia, Latvia and Lithuania – use Baltic Normal Height System 1977 as a national height system. But the European Union regulations declared the European Vertical Reference System as a national height system. For height transformation there is a transformation formula for each European country. After calculations it is seen that height difference between Baltic Normal Height System 1977 and the European Vertical Reference System depends on point location in the territory (coordinates). This unequal height difference between both height systems will cause unequal height values on border connection points between the Baltic countries.

Along with the development of the technological possibilities, the Global Positioning Satellite System (GNSS) is increasingly used in geodetic measurements. Using GNSS, measurements are performed in horizontal plane as well as for point elevation determination. The aim of the article is to demonstrate that the GNSS measurements’ static mode has a high accuracy. To achieve the aim the following objectives were set: 1) to perform global positioning measurements in Class I national leveling network, 2) to calculate the elevation above the sea level, 3) to evaluate the accuracy of performed GNSS measurements. The following research methods were used: static measurement method and analytical method for comparison of the obtained data.

Geoportal.lt is a Lithuanian state information system whose scope is to allow all data users to freely access geographic data, maps and e-services. The portal also allows drawing relief altitude profile and set the altitude of point on location. It is performed by applying the tool “Set altitude of point on location”. It is one of the newest tools of geoportal.lt website, whose accuracy has not been analysed, and which, according to the information provided by GIS Centre, complies with the requirements set for 1:50000 scale maps. This tool is selected as an object of research, while the aim of the research is to analyse the accuracy of data provided by Lithuanian spatial information portal tool “Set altitude of point on location” in case of different land covers. The following methods of investigation have been employed: literary analysis; the analysis of cartographic material; field measurements and data processing; comparative analysis of data. The data is processed using Geomap and Microsoft Excel programmes. After the analysis has been carried out, it was established that the most common errors in all types of land covers are from 0.5 m to 1.5 m. Such errors comprise 70 per cent in forest areas, 35 per cent in built-up territory, and 53 per cent in thin land cover. Taking into consideration that the website geoportal.lt operates on the basis of orthographic map whose accuracy is 1 meter and the discussed tool shows the altitude of the nearest known point, it can be stated that the obtained presumptions are permissible. To summarise the obtained data, the tool is reliable. The reliability of the data is 91 per cent in thin land cover, 86 per cent in forest area, 75 per cent in built-up area. To compare it with topographic maps of analogous format, where the errors of altitudes may reach up to 10 meters, the tool is reliable even in case of major errors.