2025. február 11.
Colleagues at our department have registered several geodetic datums and transformations into the international EPSG system and have gotten their codes over the recent months. In addition, they uploaded their VITEL-like grid shift files into the PROJ database with a CC BY license.
EPSG Geodetic Parameter Dataset (also EPSG registry) is a public registry of geodetic datums, spatial reference systems, Earth ellipsoids, coordinate transformations and related units of measurement, originated by a member of the European Petroleum Survey Group (EPSG) in 1985. Hungarian users must have the EPSG code 23700 in mind, which contains the HD72 (Hungarian Datum 1972) and the Hungarian national map projection (EOV). The transformation from the ETRS89 (European Terrestrial Reference System 1989) to the HD72 can be carried out using different methods and parameters. In the first approximation, a spatial similarity transformation with constant parameters to the whole country is widely used but with limited, typically decimeter accuracy. Another solution is to apply a grid shift, officially the VITEL one, to reach cm accuracy. The 9.5.1 version of PROJ and its PROJ-data 1.20 dataset contains the horizontal and vertical grid shift, which was developed at our department about 10 years ago, and their metadata was slightly updated recently. Applying these VITEL-like grid shifts, you can have practically the same results as with the VITEL one. The most recent versions of GIS software applying PROJ, like QGIS 3.34.15 and 3.40, contain our grid shifts. Using them is worth choosing the 10660 EPS code. Another option is to keep the 23700 code but select the transformation containing the transformation containing our grid shift files (https://epsg.io/10668). For further details, please visit our GitHub page or PROJ-data GitHub page.