[GRASS-dev] [GRASS GIS] #2456: read CSV from GDAL data directory

Paul Kelly paul-grass at stjohnspoint.co.uk
Mon Apr 25 14:15:53 PDT 2016

On 04/25/2016 09:47 PM, Markus Neteler wrote:
> Paul, still struggling with "SIRGAS2000"
> https://trac.osgeo.org/grass/ticket/2456#comment:15
> (g.proj versus testepsg output). Needs a different trick?

Hi Markus,
It looks to me like the canonical and equivalent names are the wrong way 
round. I will attempt a brief summary.

datum.table is the oldest file, going back to the earliest days of 
datums in GRASS. It should contain:

1. Short code for datum, used only in GRASS
2. Full EPSG name of datum, in quotation marks
3. ellipsoid used with this datum (GRASS ellipsoid code, from ellipse.table)
4. A single 3-parameter datum transformation that should cover the whole 
area the datum is used in

datumtransform.table is newer and allows multiple different sets of 
datum transformation parameters to be supplied for any datum. These can 
be in any format accepted by PROJ.4, so towgs84= 3 parameters or 7 
parameters, or nadgrids=
A datum does not have to have an entry in datumtransform.table, and 
there can be multiple entries for each datum if necessary.

Some datums have different names (i.e. different from the EPSG name) 
that are used in WKT descriptions. These should be added as a pair of 
names in the papszDatumEquiv[] array lib/proj/convert.c. The equivalent 
name comes first in the pair and the EPSG name (as used in the GRASS 
datum.table file) comes second.

So for the SIRGAS2000 datum, according to the testepsg program 
"Sistema_de_Referencia_Geocentrico_para_las_AmericaS_2000" is the EPSG 
name, so this is what should go in datum.table. I don't think you even 
need the equivalent 
"Sistema_de_Referencia_Geocentrico_para_America_del_Sur_2000" in 
convert.c, unless there have been problems with this?

I would suggest the attached patch to solve both problems (taking into 
account Helena's comments that NAD83 HARN should be separate).

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