[GRASS-dev] Location wizard (missed window to select +towgs params)

[Hamish]

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