[GRASS-dev] nasty gotcha in alternate ogr2ogr solution comment

[Markus Neteler]

On Mon, Nov 3, 2008 at 12:18 PM, Hamish <hamish_b at yahoo.com> wrote:
>> > Author: hamish
>> > Date: 2008-11-02 06:54:33 -0500 (Sun, 02 Nov 2008)
>> > New Revision: 34139
>> >
>> > Modified:
>> >   grass/trunk/scripts/v.out.gps/v.out.gps
>> > Log:
>> > comments about nasty gotcha in alternate ogr2ogr
>> solution (merge from devbr6)
>> ...
>> > +#     lossy. Also that would allow ogr2ogr -a_srs $IN_PROJ -t_srs EPSG:4326
>> > +#     so skip m.proj pains.. if that is done ogr2ogr -a_srs MUST HAVE +wktext
>> > +#     with PROJ.4 terms or else the +nadgrids will be ignored! (best to feed
>> > +#     it g.proj -wf) in that case.
>>
>> hi Hamish,
>>
>> curious - what does that mean? To use ogr2ogr in
>> conjunction with
>> g.proj -wf is one of my favourites... but is
>>
>> GRASS 6.4.svn (latlong_tbe_climate):~ > g.proj -wf
>> GEOGCS["wgs84",DATUM["WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563],
>> TOWGS84[0.000,0.000,0.000]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]]
>>
>> sufficient to work around the indicated '+nadgrids will be ignored'
>> problem?
>
>
> If ogr2ogr is given PROJ.4 +terms the OGR srs reading FN ignores anything
> it can't parse, which includes +nadgrids with filename. so ogr2ogr skips
> +nadgrids file unless the +wktext param is added then it doesn't try to
> match terms and passes literally.. FW says it better:
>  http://trac.osgeo.org/gdal/changeset/15681
>  (google: nadgrids+ogr2ogr for ML)
>
> AFAICT `g.proj -wf` doesn't include grid file, while `g.proj -jf` does.
> So I think my "best use `g.proj -wf` in that case" might be wrong as it
> drops the grid file, so really best to use:
>
> IN_PROJ="`g.proj -jf` +wktext"
>
> http://trac.osgeo.org/gdal/ticket/2638#comment:6
> http://trac.osgeo.org/gdal/changeset/15681

Mhh, that's fairly bad. Perhaps we need a note on
the g.proj and g.region manual pages?

However. I feel that 'g.proj -jf' is a poor representation
compared to 'g.proj -wf', at least it doesn't help to
maintain metadata in a reasonable way.

Markus