What is the established geodetic datum for SPSLux?

The national GNSS reference stations do not only provide GNSS correction data, but also establish an accurate network to realize the national reference system called LURES / LUREF (Luxembourg Reference System / Frame). The station’s coordinates are managed in a European reference system, the ETRS89, more specifically in the ETRF2000 realization @ 2013-01-27. By doing so, the SPSLux network provides a linkage between the local reference system and the European reference system.

The broadcasted RTCM formats do not supply information about the local reference frame LUREF. Therefore, if local coordinates are required, a transformation from the European ETRS89 datum to the local LURES datum, as well as the Gauss Luxemburg projection has to be implemented within the user’s rover. The datum transformation is regularly evaluated and published by the Luxemburgish cadastre and mapping authority. Parameters for datum transition and Gauss Luxemburg projection can be downloaded below. If neither the ETRF2000toLUREF transformation nor any other transformation is applied, coordinates will be obtained in ETRF2000 frame. 

Some applications may require WGS84 coordinates. Contrary to the ETRS89 reference system, the WGS84 is not stable over time but is tied to the tectonic plate shifts.  As of January 2021, positional difference between both systems is about half a meter, increasing about 2cm a year. An official WGS84toLUREF transformation does not exist. The ETRF2000toLUREF transformation can be used for approximate WGS84 positions leading to accuracy of about half a meter.

Please note that no official geoid model of Luxembourg is available. The offset between the GNSS ellipsoidal height and the physical national official NG-95 height system is only modeled as part of the seven parameter transformation within the geodetic datum transformation. As a result, using SPSLux services in combination with the ETRF2000toLUREF transformation leads to local LUREF coordinates with horizontal accuracies of 2-3cm and vertical NG-95 accuracies of 5-15cm, good GNSS conditions and measurement conducted in a professional manner assumed.

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