The SPSLux network provides GNSS correction data and forms part of the national geodetic reference infrastructure of Luxembourg. Through some of its permanently operating reference stations, SPSLux contributes to the realization of the Luxembourg national reference system LURES (Luxembourg Reference System) and provides a link between national, European and global geodetic reference frames. The coordinates of the SPSLux reference stations are maintained in the European Terrestrial Reference System ETRS89, realized through a national reference frame at a defined national reference epoch. The stations are furthermore connected to the International Terrestrial Reference System (ITRS).
The RTCM correction messages broadcast by SPSLux services contain the coordinates of the reference stations in ETRS89. Users who require coordinates in the national coordinate reference system LURES LTM must apply:
- the official ETRS89-to-LURES transformation
- the Luxembourg Transverse Mercator (LTM) map projection
These transformations are typically implemented within the rover receiver. The Administration of Cadastre and Topography regularly evaluates and publishes the official transformation parameters. Users should always ensure that the currently valid transformation version is used.
Key Features:
- LURES/LUREF: The national reference system of Luxembourg, aligned with ETRS89 via official transformation parameters.
- LTM Projection: The Luxembourg Transverse Mercator projection is used to derive planar coordinates (N/E) coordinates.
WGS84 Considerations:
- Some applications require coordinates in WGS84. Although ETRS89 and WGS84 were originally aligned, they are maintained differently.
- WGS84 follows the global terrestrial reference frame, whereas ETRS89 remains fixed to the Eurasian tectonic plate. Consequently, the difference between both systems increases over time. In 2026, the positional difference is approximately 0.5 m and continues to grow by about 2.5 cm per year.
- No official transformation between WGS84 and LURES exists.
Height System Considerations:
- Luxembourg currently does not provide an official national geoid model for GNSS applications.
- The relationship between GNSS ellipsoidal heights and the national official height system NG95 is modeled within the official ETRS89-to-LURES transformation. When the transformation parameters are applied, SPSLux users can typically achieve heights consistent with NG95 within approximately 5–15 cm.
Current ETRS89-to-LURES transformation parameters - LUREF2025
The Administration of Cadastre and Topography (ACT) is responsible for publishing the official transformation parameters linking ETRS89 to the national reference system LURES. The most recent version is LUREF2025, which replaces LUREF2020 on 31 October 2026. The LUREF2025 parameters define the transformation from ETRS89 (ETRF2000 @ 2025.83) to the national reference system LURES.
On the same date, new ETRS89 coordinates of the SPSLux reference stations are valid. The new transformation parameters and the new reference station coordinates have been derived consistently and are intended to be used together.
Until 31 October 2026, users should continue to use LUREF2020. From 31 October 2026 onwards, users should switch to LUREF2025 at the same time as the updated reference station coordinates become effective.