horizontal_datum_name missing from the CF version of a CRS, breaking conformity with CF ≥ 1.7

[gerritholl]

Code Sample, a copy-pastable example if possible

import pyproj
pyproj.CRS(4326).to_cf()

Problem description

According to the documentation, to_cf should return a description conforming to CF version ≥1.8. However, the resulting dictionary does not contain any key for "horizontal_datum_name". According to the CF Convenions, Appendix F, version 1.7 or greater:

reference_ellipsoid_name, prime_meridian_name, horizontal_datum_name and geographic_crs_name must be all defined if any one is defined.

The resulting dictionary does not contain horizontal_datum_name:

{'crs_wkt': 'GEOGCRS["WGS 84",ENSEMBLE["World Geodetic System 1984 ensemble",MEMBER["World Geodetic System 1984 (Transit)"],MEMBER["World Geodetic System 1984 (G730)"],MEMBER["World Geodetic System 1984 (G873)"],MEMBER["World Geodetic System 1984 (G1150)"],MEMBER["World Geodetic System 1984 (G1674)"],MEMBER["World Geodetic System 1984 (G1762)"],MEMBER["World Geodetic System 1984 (G2139)"],ELLIPSOID["WGS 84",6378137,298.257223563,LENGTHUNIT["metre",1]],ENSEMBLEACCURACY[2.0]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,2],AXIS["geodetic latitude (Lat)",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["geodetic longitude (Lon)",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]],USAGE[SCOPE["Horizontal component of 3D system."],AREA["World."],BBOX[-90,-180,90,180]],ID["EPSG",4326]]',
 'semi_major_axis': 6378137.0,
 'semi_minor_axis': 6356752.314245179,
 'inverse_flattening': 298.257223563,
 'reference_ellipsoid_name': 'WGS 84',
 'longitude_of_prime_meridian': 0.0,
 'prime_meridian_name': 'Greenwich',
 'geographic_crs_name': 'WGS 84',
 'grid_mapping_name': 'latitude_longitude'}

Therefore, the description is not conforming with CF 1.8 or greater, despite the documentation claiming so. However, it is conform CF 1.6.

Expected Output

I expect a dictionary that includes a definition for horizontal_datum_name.

Environment Information

pyproj info:
    pyproj: 3.4.1
      PROJ: 9.1.1
  data dir: /data/gholl/mambaforge/envs/py311/share/proj
user_data_dir: /home/gholl/.local/share/proj
PROJ DATA (recommended version): 1.12
PROJ Database: 1.2
EPSG Database: v10.076 [2022-08-31]
ESRI Database: ArcGIS Pro 3.0 [2022-07-09]
IGNF Database: 3.1.0 [2019-05-24]

System:
    python: 3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:27:40) [GCC 11.3.0]
executable: /data/gholl/mambaforge/envs/py311/bin/python
   machine: Linux-5.3.18-150300.59.76-default-x86_64-with-glibc2.31

Python deps:
   certifi: 2022.12.7
    Cython: 0.29.33
setuptools: 67.4.0
       pip: 23.0.1

Installation method

• mamba

Conda environment information (if you installed with conda):

Environment (mamba list):

$ mamba list proj
# packages in environment at /data/gholl/mambaforge/envs/py311:
#
# Name                    Version                   Build  Channel
proj                      9.1.1                h8ffa02c_2    conda-forge
pyproj                    3.4.1           py311h945b3ca_1    conda-forge

Details about mamba and system ( mamba info ):

$ mamba info


                  __    __    __    __
                 /  \  /  \  /  \  /  \
                /    \/    \/    \/    \
███████████████/  /██/  /██/  /██/  /████████████████████████
              /  / \   / \   / \   / \  \____
             /  /   \_/   \_/   \_/   \    o \__,
            / _/                       \_____/  `
            |/
        ███╗   ███╗ █████╗ ███╗   ███╗██████╗  █████╗
        ████╗ ████║██╔══██╗████╗ ████║██╔══██╗██╔══██╗
        ██╔████╔██║███████║██╔████╔██║██████╔╝███████║
        ██║╚██╔╝██║██╔══██║██║╚██╔╝██║██╔══██╗██╔══██║
        ██║ ╚═╝ ██║██║  ██║██║ ╚═╝ ██║██████╔╝██║  ██║
        ╚═╝     ╚═╝╚═╝  ╚═╝╚═╝     ╚═╝╚═════╝ ╚═╝  ╚═╝

        mamba (1.0.0) supported by @QuantStack

        GitHub:  https://github.com/mamba-org/mamba
        Twitter: https://twitter.com/QuantStack

█████████████████████████████████████████████████████████████


     active environment : py311
    active env location : /data/gholl/mambaforge/envs/py311
            shell level : 2
       user config file : /home/gholl/.condarc
 populated config files : /data/gholl/mambaforge/.condarc
                          /home/gholl/.condarc
          conda version : 22.9.0
    conda-build version : not installed
         python version : 3.9.13.final.0
       virtual packages : __cuda=11.4=0
                          __linux=5.3.18=0
                          __glibc=2.31=0
                          __unix=0=0
                          __archspec=1=x86_64
       base environment : /data/gholl/mambaforge  (writable)
      conda av data dir : /data/gholl/mambaforge/etc/conda
  conda av metadata url : None
           channel URLs : https://conda.anaconda.org/conda-forge/linux-64
                          https://conda.anaconda.org/conda-forge/noarch
                          https://conda.anaconda.org/torch/linux-64
                          https://conda.anaconda.org/torch/noarch
          package cache : /data/gholl/mambaforge/pkgs
                          /home/gholl/.conda/pkgs
       envs directories : /data/gholl/mambaforge/envs
                          /home/gholl/.conda/envs
               platform : linux-64
             user-agent : conda/22.9.0 requests/2.28.1 CPython/3.9.13 Linux/5.3.18-150300.59.76-default opensuse-leap/15.3 glibc/2.31
                UID:GID : 16209:16217
             netrc file : None
           offline mode : False

[snowman2]

pyproj/pyproj/crs/crs.py

Lines 714 to 722 in 8109fc4

	if self.datum:
	cf_dict["horizontal_datum_name"] = self.datum.name
	else:
	cf_dict["grid_mapping_name"] = "latitude_longitude"
	return cf_dict
	# handle projected CRS
	if self.is_projected and self.datum:
	cf_dict["horizontal_datum_name"] = self.datum.name

[djhoese]

So just above that snippet it looks like crs.coordinate_operation is None so it never enters this if statement. The coordinate_operation is None because:

pyproj/pyproj/_crs.pyx

Lines 2563 to 2567 in 8109fc4

	if not (
	self.is_bound or self.is_derived
	):
	self._coordinate_operation = False
	return None

where is_bound and is_derived are both False. I'm not sure I understand that since EPSG 4326 definitely has bounds...right?

[snowman2]

I'm not sure I understand that since EPSG 4326 definitely has bounds...right?

is_bound tells you whether the CRS is a BoundCRS or not. Not necessarily if it has bounds.

[snowman2]

There is definitely a chance that something is off in the logic here, the code there is just a pointer to where to start digging.