Export as WKT1_ESRI or WKT1_GDAL silently returns None for custom CRS

[martinfleis]

Code Sample, a copy-pastable example if possible

import pyproj

crs_wkt = 'PROJCRS["unknown",BASEGEOGCRS["unknown",DATUM["unknown",ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1,ID["EPSG",9001]]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8901]]],CONVERSION["unknown",METHOD["Equidistant Cylindrical",ID["EPSG",1028]],PARAMETER["Latitude of 1st standard parallel",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],PARAMETER["Longitude of natural origin",0,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["False easting",0,LENGTHUNIT["unknown",111319.490793274],ID["EPSG",8806]],PARAMETER["False northing",0,LENGTHUNIT["unknown",111319.490793274],ID["EPSG",8807]]],CS[Cartesian,3],AXIS["(E)",east,ORDER[1],LENGTHUNIT["unknown",111319.490793274]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["unknown",111319.490793274]],AXIS["ellipsoidal height (h)",up,ORDER[3],LENGTHUNIT["metre",1,ID["EPSG",9001]]]]'

crs = pyproj.CRS.from_user_input(crs_wkt)
crs.to_wkt(version="WKT1_ESRI")

Problem description

Export of the custom CRS used above to WKT using version="WKT1_ESRI" returns None. My assumption is that the CRS cannot be expressed as WKT1_ESRI but pyproj does not raise or warn about it but happily returns None instead. The CRS is coming from geopandas/geopandas#2387.

Expected Output

I would expect this to raise or give me some sort of indication that the export did not happen.

Environment Information

pyproj info:
    pyproj: 3.2.1
      PROJ: 8.1.1
  data dir: /Users/martin/mambaforge/envs/geo_dev/share/proj
user_data_dir: /Users/martin/Library/Application Support/proj

System:
    python: 3.9.7 | packaged by conda-forge | (default, Sep 29 2021, 19:24:02)  [Clang 11.1.0 ]
executable: /Users/martin/mambaforge/envs/geo_dev/bin/python
   machine: macOS-12.3-arm64-arm-64bit

Python deps:
   certifi: 2021.10.08
       pip: 21.3.1
setuptools: 58.5.3
    Cython: 0.29.24

Installation method

• conda-forge

Conda environment information (if you installed with conda):

Environment (conda list):

$ conda list proj
# packages in environment at /Users/martin/mambaforge/envs/geo_dev:
#
# Name                    Version                   Build  Channel
proj                      8.1.1                h2d984c1_2    conda-forge
pyproj                    3.2.1            py39had8e633_2    conda-forge

Details about conda and system ( conda info ):

$ conda info

     active environment : geo_dev
    active env location : /Users/martin/mambaforge/envs/geo_dev
            shell level : 2
       user config file : /Users/martin/.condarc
 populated config files : /Users/martin/mambaforge/.condarc
                          /Users/martin/.condarc
          conda version : 4.10.3
    conda-build version : not installed
         python version : 3.9.7.final.0
       virtual packages : __osx=12.3=0
                          __unix=0=0
                          __archspec=1=arm64
       base environment : /Users/martin/mambaforge  (writable)
      conda av data dir : /Users/martin/mambaforge/etc/conda
  conda av metadata url : None
           channel URLs : https://conda.anaconda.org/conda-forge/osx-arm64
                          https://conda.anaconda.org/conda-forge/noarch
          package cache : /Users/martin/mambaforge/pkgs
                          /Users/martin/.conda/pkgs
       envs directories : /Users/martin/mambaforge/envs
                          /Users/martin/.conda/envs
               platform : osx-arm64
             user-agent : conda/4.10.3 requests/2.26.0 CPython/3.9.7 Darwin/21.4.0 OSX/12.3
                UID:GID : 501:20
             netrc file : None
           offline mode : False

[martinfleis]

I just realised that the same happens when trying to export to WKT1_GDAL as well.

[snowman2]

The None return is expected and the behavior is consistent with the to_epsg() method where there isn't always an EPSG code in the response. I think it would make sense for geopandas to check for a None response from to_wkt.

I am seeing that the typing/docstring should be updated for the to_wkt methods for the CRS/_CRS classes to specify that the response is an Optional[str].

To get error more descriptive information from PROJ, see:
https://pyproj4.github.io/pyproj/stable/advanced_examples.html#debugging-internal-proj

[martinfleis]

The None return is expected and the behavior is consistent with the to_epsg() method where there isn't always an EPSG code in the response.

Shouldn't pyproj at least warn about that? In both to_wkt and to_epsg.

[snowman2]

Shouldn't pyproj at least warn about that? In both to_wkt and to_epsg.

Runtime warnings sound like they could be useful. Is this something you are interested in implementing?

[martinfleis]

Is this something you are interested in implementing?

I can make a PR for that, yes. Are there any other methods with the same behaviour that should be treated in the same way?

[snowman2]

Are there any other methods with the same behaviour that should be treated in the same way?

The main one to be concerned about is to_authority. So far I haven't seen to_json or to_proj4 return None, but it is technically possible for them to return None as well.

Thanks 👍

[jorisvandenbossche]

The None return is expected and the behavior is consistent with the to_epsg() method where there isn't always an EPSG code in the response. I think it would make sense for geopandas to check for a None response from to_wkt.

Personally I wouldn't necessarily expect to_epsg and to_wkt to be consistent in this case. For to_epsg I know that not every CRS has a corresponding EPSG number and so this might not always return something. But when doing to_wkt, I want to get a WKT version of the CRS, and generally I would assume that every CRS can be represented in some WKT form (although this assumption thus appears to be wrong depending on the WKT version ...).

[snowman2]

I was thinking about this last night and had the exact same thoughts as @jorisvandenbossche.

Here is an example:
https://github.com/opendatacube/odc-geo/blob/d1e45e366a511cf690d36155daccac73241e52eb/odc/geo/crs.py#L34-38.

I am starting to think that a warning only on to_wkt makes sense. What are your thoughts @martinfleis ?

[jorisvandenbossche]

For to_wkt, I would even consider making it an error (and propagate the actual error message from PROJ).
(although I suppose that's a bigger change)

[martinfleis]

I am starting to think that a warning only on to_wkt makes sense.

While you can reasonably expect to_epsg not to return a code for a custom CRS, the warning doesn't hurt. I think it is better to be explicit about why that happened than implicitly expect people to know why it failed.

For to_wkt, I would even consider making it an error (and propagate the actual error message from PROJ).

I agree with this but that should be probably done with a deprecation period if we decide to go that way.