Use always_xy option in the pyproj Transformer

[jorisvandenbossche]

Related to pyproj4/pyproj#355 (comment), and another short term fix to ensure compatibility with recent pyproj versions (xref #1003).

We should use the always_xy option in Transformer.from_proj (https://pyproj4.github.io/pyproj/stable/api/transformer.html#pyproj.transformer.Transformer.from_proj), if available (depending on the pyproj version), to ensure we always transform the coordinates in the expected order.

[snowman2]

Addressed in #998.

[jorisvandenbossche]

About switching to the new pyproj CRS class -> I would like to do that fully at once (meaning: requiring pyproj > 2.1, so that the geopandas user has an consistent interface for .crs, not depending on the pyproj version). That was at least my initial idea, maybe I should let that go ..

And for fully requiring PROJ 6 / pyproj 2, I think we should wait a bit longer (last time I checked fiona / gdal was not yet compatible with the latest PROJ on conda-forge, that might be fixed in the meantime, but it's all still very recent)

[snowman2]

If you are not ready to have the CRS class returned, I could modify the PR to always return a dict.

[mullenkamp]

Hi there. I just ran into this problem.
Lines 403 and 406 of geoseries.py need to have always_xy=True for the to_crs method to work properly...as far as I have tested.
Thanks.

[snowman2]

@jorisvandenbossche, I think this is a must for the 0.6 release. Would it be helpful for me to dissect #998 and focus it to address this without the CRS class?