On lundi 20 avril 2020 01:08:15 CEST jratike80 wrote: > Hi, > > When it comes to gdalwarp I believe that this part of the documentation > https://gdal.org/programs/gdalwarp.html is essential > > "Starting with GDAL 2.2, if the SRS has an explicit vertical datum that > points to a PROJ.4 geoidgrids, and the input dataset is a single band > dataset, a vertical correction will be applied to the values of the > dataset." > > Both EPSG:4326 and EPSG:2056 are 2D systems without explicit vertical datum. > EPSG:4979 is explicit 3D > http://www.epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::4979 and > the compound crs syntax that you used (-s_srs EPSG:2056+5728) is explicit as > well. > > I do not know how gdaltransform knows to do the conversion in Z coordinate
As this is with GDAL 2, and likely PROJ 4 or 5, this was a change in ellipsoidal height between the WGS84 and Bessel 1841 ellipsoids, but this was highly questionable, and is no longer done in GDAL 3 / PROJ >= 6, at least when using 2D codes. > and how to give the -s_srs and -t_srs right for gdalwarp but I would try > next with > -s_srs EPSG:2056+5728 -t_srs epsg:4979 The change in Z done in gdalwarp requires: - single band dataset - input CRS is a geographic 3D CRS and output CRS is compound CRS (horizontal CRS + vertical CRS) with an explicit +geoidgrids term (or the reverse). The key here would be to have a vertical grid for EPSG:5728. I don't see any mentionned in EPSG. So provided that such grids is available, EPSG:2056+5728 would have to be replaced by "+init=epsg:2056 +geoidgrids=XXXXXX.gtx" Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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