Support for PROJ 6.0.0

[sebastic]

SUMO still uses proj_api.h which is deprecated in PROJ 6.0.0 and will be removed in PROJ 7.0.0 (scheduled for March 2020).

When using proj_api.h with PROJ 6.0.0 -DACCEPT_USE_OF_DEPRECATED_PROJ_API_H=1 needs to be added to CFLAGS to prevent a compiler error.

SUMO should be updated to (also) support the proj.h API.

[behrisch]

@sebastic So the correct way would be to first check for the presence of proj.h and if this is not there use proj_api.h?

[sebastic]

Yes. Ideally your code is compatible with all major PROJ releases used by users.

PROJ 6 is a major change, and many projects will take significant time to become compatible, so PROJ 5.x will be included in distributions for quite some time.

PROJ 4.x is also still widely used, but will slowly be phased out.