[PROJ] [gdal-dev] GDAL 2 + PROJ 6 does not work

[Even Rouault]

> I tried gdalinfo (GDAL 2.4.2 + PROJ 6.2.1) on a raster with a CRS that does
> not contain an authority code, and it failed to find any CRS. Recompiling
> with configure --with-proj5-api=no solved the problem for me. That makes
> sense to me because the new PROJ API produces quite different results when
> used on PROJ5 or PROJ6.

ok, a bit weird still but I trust you. GDAL 2 hardly uses PROJ for CRS 
building as it has self-contained logic to deal with EPSG, WKT and import/
export PROJ strings.

> I have seen the combination of GDAL 2 + PROJ 6 on Debian and it might occur
> also on EPEL for RHEL 8.

For Debian, I believe this combination is just a transitional state to deploy 
first PROJ 6 and then GDAL 3.

> 
> > Indeed, GDAL 2 is best used with PROJ 5.2.
> 
> And if I want to use PROJ 6 + GDAL, I should use GDAL 3, right?

yes, the recommended combinations are :
- GDAL 2.x with PROJ 5.2
- GDAL 3.x requires PROJ >= 6


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