[GRASS-dev] PROJ6 support in GRASS

[Markus Metz]

PROJ 6 support is not yet finished in GRASS. Currently it sort of works in
master and relbr78, but I expect troubles because GRASS is heavily relying
on deprecated proj strings as CRS definitions. This is becoming problematic
e.g. when creating locations from GDAL/OGR datasets because GRASS goes from
OGR spatialreference through proj string to GRASS definition.

For GDAL 3 + PROJ 6, GRASS should switch to WKT as main CRS definition
format, ideally also storing a WKT definition next to PROJ_INFO. When
creating locations from GDAL/OGR datasets, GRASS should go from OGR
spatialreference through WKT to GRASS definition, and probably use the new
PROJ6+ methods as much as possible.

When getting the projection info of a GRASS location, GRASS should then
check in that order 1) WKT, 2) EPSG or other SRID, 3) GRASS native
definition (which deviated from proj definition some decades ago).

That means, g.proj, r.in.gdal, r.external, v.in.ogr, v.external need
updates, and the mechanism of conversion between different formats of CRS
definitions in lib/proj needs to be largely rewritten.

Markus M
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