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EUREF Working Group "European Unified Height Reference"

The working group was established at the EUREF Symposium 2021 by resolution 2021/1. Its goals comprise

  • to complement EVRS with an official height reference surface (hybrid quasigeoid model),
  • to improve information about national height coordinate frames and their transformations to the EVRS, and
  • to enhance the usability of the unified European height reference.

An official height reference surface will be an essential element to promote the EVRS for scientific and practical applications in the future. This is in line with the EUREF activities and tasks (e.g., EUREF “Mission & Objectives”, Resolutions 2009/5, 2011/4, 2015/4, 2018/2).

Background and motivation

ETRS89 is the European standard for spatial reference systems and is realized across national borders by means of global measurement techniques (GNSS). ETRS89 is stipulated in the national geodetic standards in all countries and is implemented by means of the different ETRF realizations. Every country provides respective satellite positioning services that enable to determine coordinates with centimeter accuracy in real-time. By that, the incompatibility of the national coordinate reference frames that lasted until the 1990ies could be practically resolved.

To date, this function is still not fulfilled by the European Height Reference System (EVRS). National height reference frames are computed based on the national leveling networks applying different standards. Likewise, national mapping agencies provide official models of the height reference surface that establish the transformation between ellipsoidal heights and heights in these national height reference frames with centimeter accuracy. At the borders, height coordinates of adjacent national leveling networks differ by more or less large amounts. The EVRS realizations are based on the common adjustment of the national networks (UELN) in terms of geopotential numbers and normal heights, latest 2019 (EVRF2019). Most of the European countries have not adopted EVRF solutions for their national height reference frames directly, they are rather used to derive transformation parameters for individual cross-border applications.

Despite the demands acknowledged by Resolution 2009/5, to date there is still not available

  • an official model of the height reference surface associated with a respective EVRS realization that readily enables GNSS-based height determination across borders,
  • a complete and maintained list of national height reference surfaces (i.e., hybrid geoid or quasigeoid models) and their metadata in Europe.

The national implementation of unified European standards for height determination is a process that is not yet foreseeable. Information about transformations should be improved in order to facilitate working with the unified European height reference system, and, by that, to conform to the growing demands of surveyors and to better promote the EVRS.

Tasks and actions

  • Establish a continuously updated inventory of official national height reference surfaces (and national reference frames for positions and heights including transformation parameters to ETRS89 or ITRS realizations) in order to facilitate, first, comparisons and consistent use of the height reference surfaces along borders and, second, unification of height systems in general.
  • Develop a new and homogenized GNSS/leveling dataset for Europe as a key basis for the European Height Reference Surface (EHRS, see next item). Consequently, the working title for this dataset is EHRS Control Points (EHRS_CP). It shall replace the previous and now outdated EUVN_DA dataset. The EUVN_DA project started in 2003 and was preliminary finished in 2009. One of the major limitations of the EUVN-DA dataset from today’s perspective is the insufficient homogenization of the differing national ETRS89 realizations and epochs, which implies potential inconsistencies in the ellipsoidal heights up to several centimeters. In the meantime, a new realization of EVRS has been computed, which includes additional countries, especially in Eastern Europe. On the other hand, new sets of GNSS/leveling have become available in several countries. In the EUVN_DA project, the EVRF2007 heights of some countries (Spain, Italy, Latvia) were determined by transformation only. With the updated leveling data set of EVRF2019, it may be possible to link the GNSS heights of these countries with the leveling heights directly.
  • Compute a European quasigeoid model as an official height reference surface for the EVRS, which is consistent with the latest EVRS and ETRS89 realizations (currently EVRF2019 and ETRF2020). Consequently, this model shall have the name European Height Reference Surface (EHRS).

Further information

Further information about the goals, objectives and tasks can be found in the WG Charter.

Download EUREF-WG “European Unified Height Reference Charter” (Version 1.6, 17 May 2024)

Preliminary products

Inventory of the national integrated geodetic reference in Europe

For the moment, provisional results are available in static form (PDF) here. This also includes an overview of current national ETRS89 realizations for many European countries.

The incorporation of this information into the database interface of the CRS-EU website will be realized at a later stage.

EHRS_CP

Data collection and analysis for the EHRS_CP is still ongoing.

Report of activities

  • Call to national authorities to fill questionnaire about national integrated geodetic reference
    Status:
    • Questionnaire sent out 2022
    • Processing of the response, reminders and/or updates ever since
    • First static version of inventory to be published (estimated July 2024)

  • Call to national authorities to provide up-to-date GNSS observations with connection to the UELN for the EHRS_CP dataset, also updated/first-time leveling data for the UELN (if applicable)
    Status:
    • Call sent out 2022
    • Reminders and/or updates ever since
    • Analysis of preliminary results
    • Ongoing investigations to improve the quality of UELN solution towards a new EVRF version, to harmonize the national GNSS coordinates with respect to ETRF2020, and to improve agreement with gravimetric quasigeoid models
    • Highlights of UELN developments: Moldova included in UELN, major revision of dataset from France, additional cross-border leveling connections

  • WG meetings and status reports at EUREF Symposia
    • 2021-05-26 EUREF Symposium 2021 (online from Ljubljana, Slovenia)
      Installation and initial presentation of WG
    • 2021-10-01 Online meeting WG EUHR1
    • 2022-01-21 Invited report of Albania about geodetic works
    • 2022-06-01 EUREF Symposium 2022 (online from Zagreb, Croatia)
      with WG Splinter Meeting (online)
    • 2022-10-27 Online meeting WG EUHR3
    • 2023-05-24 EUREF Symposium 2023 (Gothenburg, Sweden)
    • 2024-04-12 Online meeting WG EUHR4
    • 2024-06-06 EUREF Symposium 2024 (Barcelona, Spain)
      with WG Splinter Meeting (hybrid)
    • Participation in the regular EUREF Governing Board meetings

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