What's the difference between using EPSG:4326 and +init=EPSG:4326 for transformer?

[zxdawn]

I'm trying to transform 4326 location to EPSG:32722:

from pyproj import Transformer

transformer_wrong = Transformer.from_crs("EPSG:4326", "EPSG:32722")
wrong_coords = transformer_wrong.transform(-48.15, -15.85)

transformer_correct = Transformer.from_crs("+init=EPSG:4326", "EPSG:32722")
correct_coords = transformer_correct.transform(-48.15, -15.85)

I see the results are different for EPSG:4326 and +init=EPSG:4326:

print('wrong: ', wrong_coords, 'correct: ', correct_coords)

wrong:  (3086209.1874748142, 4038854.4578049984) correct:  (805260.2679547772, 8245581.8793749055)

Any ideas are welcome ;)

[djhoese]

+init= syntax is deprecated. You should get a FutureWarning when using that that looks like this:

/home/davidh/miniconda3/envs/satpy_py312/lib/python3.12/site-packages/pyproj/crs/crs.py:141: FutureWarning: '+init=<authority>:<code>' syntax is deprecated. '<authority>:<code>' is the preferred initialization method. When making the change, be mindful of axis order changes: https://pyproj4.github.io/pyproj/stable/gotchas.html#axis-order-changes-in-proj-6
  in_crs_string = _prepare_from_proj_string(in_crs_string)

So flipping the order of the parameters:

In [7]: transformer_wrong.transform(-15.85, -48.15)
Out[7]: (805260.2679547772, 8245581.8793749055)

Or:

In [8]: transformer_better = Transformer.from_crs("EPSG:4326", "EPSG:32722", always_xy=True)

In [9]: transformer_better.transform(-48.15, -15.85)
Out[9]: (805260.2679547772, 8245581.8793749055)

In summary, EPSG 4326 is defined as (lat, lon) so you need to take extra care in modern PROJ/pyproj, where special care has been taken to follow CRS axis order definitions, to make sure your arguments/axes are in the right order.

[zxdawn]

Ha, thanks! I don't realize the order is different.