[GRASS-dev] GRASS GIS + PROJ 6 + GDAL 2.5

[Even Rouault]

On lundi 25 février 2019 15:10:10 CET Markus Metz wrote:
> Hi all,
> 
> GRASS needs some adjustments in order to be compatible with PROJ 6 + GDAL
> 2.5
> 
> The plain text file "share/proj/epsg" no longer exists. This file is
> currently required by the GUI location wizard to retrieve a list of known
> EPSG codes. Now there is a sqlite db "proj.db", and a new PROJ function
> proj_get_codes_from_database(). I suggest to enhance g.proj with a new
> option "list_codes_auth" which will print a list of codes for the given
> autority name (EPSG, IGNF, etc.). This option can be made backwards
> compatible to read "share/proj/epsg" with PROJ versions up to 5. The
> location wizard can then use this new output of g.proj to construct a list
> of known EPSG codes.

If you want to do a nice GUI, proj_get_crs_info_list_from_database() is an
enhanced version of proj_get_codes_from_database(), that will retrieve
more information besides the code: name, area of use, type of CRS (geographic,
projected, compound, etc...)
in a very fast way (you can do the same with proj_get_codes_from_database(),
and constructing a CRS for each code, but this is slower)

> 
> We need to take care of axis order if a CRS is created from EPSG because
> the axis order can now be northing, easting instead of traditional easting,
> northing. Maybe it is enough to enforce +axis=enu, 

You can only use this if you use a PROJ string when invokating
proj_create_crs_to_crs(), and this is the default axis order for PROJ string anyway.

> or to use GDAL's
> SetAxisMappingStrategy(OAMS_TRADITIONAL_GIS_ORDER)

Yes, if you use GDAL OGRSpatialReference this is the way to go.

If you don't use GDAL SRS and just PROJ API, you might also just reuse
https://github.com/pramsey/postgis/blob/svn-trunk-proj/liblwgeom/lwgeom_transform.c#L298

which is called for the source and target CRS of the PJ object created
with proj_create_crs_to_crs()
https://github.com/pramsey/postgis/blob/svn-trunk-proj/liblwgeom/lwgeom_transform.c#L357

Even

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