[Proj] why doesn't the epsg file reference the hpgn grids?

[Richard Greenwood]

On Tue, Mar 17, 2015 at 9:53 PM, Even Rouault <even.rouault at spatialys.com>
wrote:


> As most of the "heavy" grids are not directly distributed with proj, it
> might be
> tricky to propose a reasonable +nadgrids parameter. Although we could use
> the @
> syntax to make their presence optional.


What is the "@ syntax"?


> But there's currently no way of doing
> the association between a datum and corresponding grids when the "raw" CSV
> files
> are processed in the gcs.csv/pcs.csv. Perhaps something similar to
>
> http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/datum_shift_pref.csv
> could be used.
>

I'm still unclear as to how epsg.org addresses grid shifts. I randomly
surfed thru the files in
http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/
<http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/datum_shift_pref.csv>
and
found no clues. It seems like it would be nice to enhance the processing of
the epsg.org source definitions to reference grid shift files if possible.
By "if possible" I mean if there is sufficient information in the epsg.org
source definitions to do that. If not, then I agree that something
like datum_shift_pref.csv would be good.

Thanks,
Rich
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