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

Richard Greenwood richard.greenwood at gmail.com
Wed Mar 18 08:14:53 EST 2015

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

> 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
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.

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