German Combined QuasiGeoid 2016 (GCG2016)

The German Combined QuasiGeoid 2016 (GCG2016) is Germany's official height reference surface, published by the Bundesamt für Kartographie und Geodäsie (BKG). Surveys with satellite navigation systems such as GPS and Galileo produce ellipsoidal heights on the GRS80 ellipsoid, while official heights in Germany are normal heights in the DHHN2016 system, referenced to the Amsterdam tide gauge (NAP). GCG2016 gives the separation between the two surfaces, so ellipsoidal heights in ETRS89/DREF91 (realisation 2016) can be converted directly into DHHN2016 heights. BKG states that the model is compatible with SAPOS, the satellite positioning service of the German federal states.

BKG and the Institut für Erdmessung of Leibniz Universität Hannover modelled GCG2016 in cooperation with the AdV, the working committee of the federal states' surveying authorities. The calculation combines detailed gravity measurements supplied by the AdV, improved digital terrain models and global gravity field models that include satellite gravity missions, tied to points where both GNSS ellipsoidal and levelled heights are known. It is the AdV's official height reference surface and is registered in the EPSG geodetic dataset.

BKG gives the accuracy as 1 cm in lowland areas, 2 cm in high mountains and 2–6 cm at sea. The model covers Germany including its 200-nautical-mile Exclusive Economic Zone; its Baltic Sea part was updated in 2023 for the introduction of the Baltic Sea Chart Datum 2000. The grid is a free download under a CC BY 4.0 licence, in eight formats (including Leica and Trimble grid formats), BKG also offers an online calculator for single points, and serves the model as queryable layers in its OGC web map service WMS Schwere.