[PROJ] Get PROJ description in PROJ 5?

[Nyall Dawson]

On Sat, 20 Mar 2021 at 03:04, Matthew Woehlke <mwoehlke.floss at gmail.com> wrote:
>
> On 19/03/2021 12.52, Sebastiaan Couwenberg wrote:
> > On 3/19/21 5:36 PM, Matthew Woehlke wrote:
> >> Sigh... looks like I need a pile of version-checking code.
> >
> > Why bother with PROJ 5 support at this point in time, you can just focus
> > on supporting PROJ 6+.
>
> Because PROJ 6 doesn't support the PROJ 4 API (without code changes,
> anyway), and we get PROJ from an external repo. This leads to a
> chicken-and-egg problem; we can't bump to providing PROJ 6 because our
> project will break, and we can't use the PROJ 6 API because we don't
> *have* PROJ 6.
>
> So far, I've bumped us to providing PROJ 5; we can still build against
> that using the PROJ 4 API. Now I'm working on updating our usage to PROJ
> 5, with PROJ 6 support. It's not pretty, but it's not as bad as two
> totally separate implementations, which is what we'd just about have to
> do with PROJ 4 + PROJ 6.
>
> Given how much of a headache this has been, and that we still have other
> projects using PROJ 4, I suspect we may not try to move to PROJ 6 until
> it becomes absolutely necessary. (At which point there is some hope some
> of the other code still on PROJ 4 will be effectively dead.)
>
> It doesn't help that code that works with PROJ 5 is broken with PROJ 6.

Coming from the viewpoint of a maintainer of a large project (QGIS)
which went through the pain of proj 4 -> 6 update, my sincere advice
is that it's a waste of time to support ANY versions earlier than proj
6 today. Your code will end up with so many conditional branches that
it becomes near unmaintainable. Absolutely **no-one** should be using
proj < 6 in 2021, to do so is to subject your users to all sorts of
misleading results.

I'd strongly encourage you to use your effort instead resolving the
packaging and community issues which are preventing you from migrating
completely to proj 6+.

Nyall




>
> --
> Matthew
> _______________________________________________
> PROJ mailing list
> PROJ at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/proj