European Vertical Reference System
The IAG Subcommission 1.3.a (IAG SC 1.3 Homepage) for Europe EUREF (EUREF Homepage) started in 1994 with its activities for development and establishment of European height systems. The work is based on an excellent cooperation between EUREF, National Mapping Agencies (NMA), Working Group VIII of CERCO (Comité Européen des Responsables de la Cartographie Officielle - now EuroGeographics) and the Governing Board (former Technical Working Group - TWG) of EUREF.
Already in the 1950s and 1970s, several projects aimed at the establishment of a unified European height system, using the combination and common adjustment of national leveling networks. One result of these works was the adjustment of the United European Leveling Network (UELN) of western Europe in 1986. Similar unified networks were measured and adjusted also in Eastern Europe.
In accordance with the Resolution No. 3 of the EUREF symposium 1994 in Warsaw, the work at the UELN was resumed in 1995. Its objective is to provide unified heights for Europe at the one-decimeter level. In the following years, the network has been step by step enlarged, especially due to the inclusion of leveling networks of the Eastern European countries. First results of adjusted European heights were handed over to each participating country in 1999 (EVRF2000).
Simultaneously to the UELN adjustment, definitions and standards of the European Vertical Reference System (EVRS) were developed. At the EUREF symposium 2000 in Tromsø, a first definition of the EVRS was adopted. In the "Conventions for the Definition and Realization of a European Vertical Reference System (EVRS)" – EVRS Conventions 2007 – the IAG Subcommision 1.3a EUREF passed a revised definition of EVRS. Subsequently the solutions of the UELN were considered as realizations of the EVRS and were named as European Vertical Reference Frame.
In the meantime, the importance of harmonization of the vertical reference of spatial coordinates increased on the one hand and the extension, density and topicality of the available data were improved on the other hand. Half of the participating countries provided new national leveling data to the UELN data centre after the release of the solution EVRF2000. Therefore, a new realization of the EVRS was computed and published under the name EVRF2007.
At the EUREF symposium in Brussels (June 2008), Resolution No. 3 was adopted, which proposes to the European Commission that EVRF2007 shall be used as the vertical reference for pan-European geo-information. Accordingly EVRS has been included in the INSPIRE directive.
After another 11 years, a lot of new leveling data were available again. Already in Leipzig 2015, the EUREF resolution No. 4 was adopted, which considered the need for a new realization and noted the role of the quasigeoid for future height system realization. According to this resolution, in 2019 the new realization EVRF2019 was computed.
The European Vertical Reference Network (EUVN) was prepared in parallel to the UELN. It is an integrated network of GNSS, leveling and tide gauge observations.