On mercredi 25 septembre 2019 15:53:50 CEST Bo Victor Thomsen wrote: > Thanks to Kristian and Even for some very thorough answers. That was > somewhat heavy reading (for me at least) on such an ordinary Wednesday :-) > > I'll guess that QGIS (or the underlying transformation library) is using > some of the "earlier" realizations for both ETR89 and WGS84 datums since > the ETR89/UTM32N and WGS84/UTM32N coordinates of a given location is so > close to each other (0.1 mm)
It doesn't use any particular realization. It just uses the generic datums for both, and thus get from the EPSG database, a null transformation between those. $ projinfo -s EPSG:25832 -t EPSG:32632 Candidate operations found: 1 ------------------------------------- Operation n°1: unknown id, Inverse of UTM zone 32N + ETRS89 to WGS 84 (1) + UTM zone 32N, 1 m, Europe - ETRS89 PROJ string: +proj=pipeline +step +inv +proj=utm +zone=32 +ellps=GRS80 +step +proj=utm +zone=32 +ellps=WGS84 The 0.1 mm you see comes from the fact that ETRS89/UTM32N uses the GRS80 ellipsoid and WGS84/UTM32N the WGS84 ellipsoid, which differ by a tiny amount on their inverse flattenin. Given that we use a null transform between both datums, it is not significant at all. -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ QGIS-Developer mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
