merge datum and ellipsoid modules for clarity

docs/api/crs/datum.rst

@@ -27,10 +27,20 @@ CustomDatum
 
 
 Ellipsoid
----------
+----------
+
+.. autoclass:: pyproj.crs.Ellipsoid
+    :members:
+    :inherited-members:
+
 
-- :class:`pyproj.crs.Ellipsoid`
-- :class:`pyproj.crs.ellipsoid.CustomEllipsoid`
+CustomEllipsoid
+----------------
+
+.. autoclass:: pyproj.crs.datum.CustomEllipsoid
+    :members:
+    :show-inheritance:
+    :special-members: __new__
 
 
 Prime Meridian

docs/build_crs.rst

@@ -30,7 +30,6 @@ Here are links to the API docs for the pieces you need to get started:
 - :ref:`crs`
 - :ref:`coordinate_operation`
 - :ref:`datum`
-- :ref:`ellipsoid`
 - :ref:`coordinate_system`
 
 
@@ -100,8 +99,7 @@ PROJ string::
 
     from pyproj.crs import GeographicCRS, ProjectedCRS
     from pyproj.crs.coordinate_operation import UTMConversion
-    from pyproj.crs.datum import CustomDatum
-    from pyproj.crs.ellipsoid import CustomEllipsoid
+    from pyproj.crs.datum import CustomDatum, CustomEllipsoid
 
     ell = CustomEllipsoid(
         semi_major_axis=6378137,
@@ -142,15 +140,7 @@ PROJ string::
             scale_factor_natural_origin=0.9996,
         ),
         geodetic_crs=GeographicCRS(
-            datum=CustomDatum(
-                ellipsoid={
-                    "$schema": "https://proj.org/schemas/v0.2/projjson.schema.json",
-                    "type": "Ellipsoid",
-                    "name": "International 1909 (Hayford)",
-                    "semi_major_axis": 6378388,
-                    "inverse_flattening": 297,
-                }
-            )
+            datum=CustomDatum(ellipsoid="International 1909 (Hayford)")
         ),
     )
     bound_crs = BoundCRS(

pyproj/_crs.pyx

@@ -5,7 +5,7 @@ from collections import OrderedDict
 
 from pyproj._datadir cimport pyproj_context_initialize
 from pyproj.compat import cstrencode, pystrdecode
-from pyproj.crs.ellipsoid import CustomEllipsoid
+from pyproj.crs.datum import CustomEllipsoid
 from pyproj.crs.enums import CoordinateOperationType, DatumType
 from pyproj.enums import ProjVersion, WktVersion
 from pyproj.exceptions import CRSError

pyproj/crs/datum.py

@@ -14,7 +14,7 @@ def __new__(cls, ellipsoid="WGS 84", prime_meridian="Greenwich"):
         ----------
         ellipsoid: Any, optional
             Anything accepted by :meth:`pyproj.crs.Ellipsoid.from_user_input`
-            or a :class:`pyproj.crs.ellipsoid.CustomEllipsoid`.
+            or a :class:`pyproj.crs.datum.CustomEllipsoid`.
         prime_meridian: Any, optional
             Anything accepted by :meth:`pyproj.crs.PrimeMeridian.from_user_input`.
         """
@@ -27,3 +27,51 @@ def __new__(cls, ellipsoid="WGS 84", prime_meridian="Greenwich"):
             ).to_json_dict(),
         }
         return cls.from_json_dict(datum_json)
+
+
+class CustomEllipsoid(Ellipsoid):
+    """
+    .. versionadded:: 2.5.0
+
+    Class to build a custom ellipsoid.
+    """
+
+    def __new__(
+        cls,
+        name="undefined",
+        semi_major_axis=None,
+        inverse_flattening=None,
+        semi_minor_axis=None,
+        radius=None,
+    ):
+        """
+        Parameters
+        ----------
+        name: str, optional
+            Name of the ellipsoid. Default is 'undefined'.
+        semi_major_axis: float, optional
+            The semi major axis in meters. Required if missing radius.
+        inverse_flattening: float, optional
+            The inverse flattening in meters.
+            Required if missing semi_minor_axis and radius.
+        semi_minor_axis: float, optional
+            The semi minor axis in meters.
+            Required if missing inverse_flattening and radius.
+        radius: float, optional
+            The radius in meters. Can only be used alone.
+            Cannot be mixed with other parameters.
+        """
+        ellipsoid_json = {
+            "$schema": "https://proj.org/schemas/v0.2/projjson.schema.json",
+            "type": "Ellipsoid",
+            "name": name,
+        }
+        if semi_major_axis is not None:
+            ellipsoid_json["semi_major_axis"] = semi_major_axis
+        if inverse_flattening is not None:
+            ellipsoid_json["inverse_flattening"] = inverse_flattening
+        if semi_minor_axis is not None:
+            ellipsoid_json["semi_minor_axis"] = semi_minor_axis
+        if radius is not None:
+            ellipsoid_json["radius"] = radius
+        return cls.from_json_dict(ellipsoid_json)

test/crs/test_crs_datum.py

@@ -1,4 +1,6 @@
-from pyproj.crs.datum import CustomDatum, Ellipsoid, PrimeMeridian
+from numpy.testing import assert_almost_equal
+
+from pyproj.crs.datum import CustomDatum, CustomEllipsoid, Ellipsoid, PrimeMeridian
 
 
 def test_custom_datum():
@@ -14,3 +16,44 @@ def test_custom_datum__input():
     )
     assert cd.ellipsoid.name == "Airy 1830"
     assert cd.prime_meridian.name == "Lisbon"
+
+
+def test_custom_ellipsoid():
+    ce = CustomEllipsoid(semi_major_axis=6378137, inverse_flattening=298.257222101)
+    assert ce.name == "undefined"
+    assert ce.semi_major_metre == 6378137
+    assert ce.semi_minor_metre == 6356752.314140356
+    assert_almost_equal(ce.inverse_flattening, 298.257222101)
+    assert sorted(ce.to_json_dict()) == [
+        "$schema",
+        "inverse_flattening",
+        "name",
+        "semi_major_axis",
+        "type",
+    ]
+
+
+def test_custom_ellipsoid__minor():
+    ce = CustomEllipsoid(
+        name="test", semi_major_axis=6378137, semi_minor_axis=6356752.314
+    )
+    assert ce.name == "test"
+    assert ce.semi_major_metre == 6378137
+    assert ce.semi_minor_metre == 6356752.314
+    assert_almost_equal(ce.inverse_flattening, 298.25722014)
+    assert sorted(ce.to_json_dict()) == [
+        "$schema",
+        "name",
+        "semi_major_axis",
+        "semi_minor_axis",
+        "type",
+    ]
+
+
+def test_custom_ellipsoid__radius():
+    ce = CustomEllipsoid(radius=6378137)
+    assert ce.name == "undefined"
+    assert ce.semi_major_metre == 6378137
+    assert ce.semi_minor_metre == 6378137
+    assert ce.inverse_flattening == 0
+    assert sorted(ce.to_json_dict()) == ["$schema", "name", "radius", "type"]

test/crs/test_crs_maker.py

@@ -125,15 +125,7 @@ def test_bound_crs__example():
             scale_factor_natural_origin=0.9996,
         ),
         geodetic_crs=GeographicCRS(
-            datum=CustomDatum(
-                ellipsoid={
-                    "$schema": "https://proj.org/schemas/v0.2/projjson.schema.json",
-                    "type": "Ellipsoid",
-                    "name": "International 1909 (Hayford)",
-                    "semi_major_axis": 6378388,
-                    "inverse_flattening": 297,
-                }
-            )
+            datum=CustomDatum(ellipsoid="International 1909 (Hayford)")
         ),
     )
     bound_crs = BoundCRS(