The SLO-VRP2016/Koper quasi-geoid model is the latest height reference surface for Slovenia, referred to the GRS80 ellipsoid. The acronym means SLOvenska Višinska Referenčna Ploskev iz leta 2016, datum Koper (translated in English, Slovenian Height Reference Surface from the year 2016, datum Koper). It was computed by the Surveying and Mapping Authority of the Republic of Slovenia, in cooperation with the Norwegian Mapping Authority (Kartverket). The model is based on a set of old terrestrial gravity data (origin from Yugoslavia, from 1956-75), a set of new Slovenian gravity data (along levelling lines and regional gravimetric survey, from 2000 to 2015) and sets from neighboring countries (Italy, Austria, Hungary and Croatia), altogether 16.400 points in the mean-tide system. Stokes/Molodensky equations and the Fast Fourier transform technique have been applied with use of global geopotential model EGM2008.

The computed quasi-geoid surface was adapted (fitted) to 66 high quality GNSS/levelling points, which were fairly distributed throughout the territory of Slovenia. Therefore, the resulting quasi geoid model can be used to perform the conversion between ellipsoidal heights (Slovenian realization of ETRS89 - D96, GRS80 ellipsoid) and normal heights (Slovenian Height System 2010 - SVS2010 with Koper tide gauge). The SLO_VRP2016/Koper model is given in the form of a regular grid, with resolution of 30” × 45”, within the limits of 13° < λ < 17° (east of Greenwich) and 45° < φ < 47° (north of the equator). In this area geoid heights range between 42.157 m and 50.608 m, with an average of 46.162 m. The inner accuracy of the calculated geoid heights is 2.6 cm, the outer accuracy (based on 871 control GNSS/levelling measurements along levelling lines) is up to 10 cm.

The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).