Support PROJ >= 6.0.0

[tina-junold]

Currently the build failed if proj >= 6.0.0 is used. The Flag ACCEPT_USE_OF_DEPRECATED_PROJ_API_H has to be defined.

see: https://github.com/postgis/postgis/pull/354/files#r242068366

[jmckenna]

I agree that this flag is required now (as PROJ 6 was released on 2019-03-01).

Note that PROJ 7 release next year will drop proj_api.h completely.

[pnorman]

Do we use proj directly or only via libosmium?

[jmckenna]

Ah, it seems through libosmium only.

[jmckenna]

libosmium's associated ticket: osmcode/libosmium#277

[jmckenna]

You can close this ticket, but I bet this will be an FAQ.

[jmckenna]

related PROJ 7.0 discussion happening at osmcode/libosmium#295

[lonvia]

Reopening this. We are going to need osmium-independent proj >= 6 support.

[kennykb]

Thanks for reopening. I was going to grumble that I produce some paper maps projected to UTM zone 18 and therefore maintain a small subset of OSM in PostGIS in that projection, so losing support for everything but plate carree and spherical Mercator would be a problem.

[lonvia]

#1066 reorders the code so that it becomes fairly easy to implement a generic projection using the proj6 variant and then have cmake detect which one to use. Just add a reprojection-generic-proj6.cpp similar to the existing reprojection-generic-proj4.cpp implementation.

PRs would be most welcome.