Paul wrote: > This is not correct, and indeed seems to be a clue as to > what is going on. The GRASS default parameters for > rome40/Monte_Mario are +towgs84=-225.000,-65.000,9.000 > However the location is being created with the parameters > +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68 > i.e. the parameters with the description "Used in Italy > (Peninsular Part)" from datumtransform.table. > > This set of parameters is not being put there by GRASS; it > is coming through from GDAL when it is used to look up the > EPSG code. ... > This is true, and as there have been very minimal changes > in general/g.proj and lib/proj between RC5 and now I was > initially very baffled. My latest hunch is to do with the > CSV tables in lib/proj. I notice Markus has updated them at > least a couple of times since RC5 - the latest change two > weeks ago in r41248 with the description "backport from > GDAL: big upgrade to EPSG 7.4.1 with improved datum logic" > sounds particularly suspicious ;) I would hazard a guess > that GDAL is now attempting to make a "best guess" at which > are the most appropriate transformation parameters for a > particular datum. Previously if there was a choice it left > them unspecified, and GRASS prompted the user. However GRASS > (i.e. g.proj) trusts the co-ordinate system it gets back > from GDAL and if the datum transformation parameters are > already there, then it doesn't query GDAL's decision! I > don't subscribe to the GDAL developers list any more as > there was too much traffic, so it's likely I've missed some > discussion or announcement from Frank over there. > > I haven't had time to test reverting the CSV files yet but > if that works I would suggest doing it, as if that is going > to be the way GDAL works from now on it will require quite a > few changes to how g.proj works, and it is much too late in > the release cycle of 6.4.0 to go changing things there...
hmmm +file lib/proj/datum_shift.csv in https://trac.osgeo.org/grass/changeset/41248 see also r41223. Hamish _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
