Fix setting geography on non-geo field

src/earthkit/data/field/component/geography.py

@@ -659,6 +659,19 @@ def area(self) -> tuple:
     def grid_type(self) -> str | None:
         return None
 
+    def set(self, *args, shape_hint=None, **kwargs) -> "GeographyBase":
+        """Return a new GeographyBase object with updated values."""
+        kwargs = self._normalise_set_kwargs(*args, **kwargs)
+        keys = set(kwargs.keys())
+
+        if keys == {"shape"}:
+            return self.from_dict(**kwargs)
+
+        if keys == {"grid_spec"} or keys == {"latitudes", "longitudes"}:
+            return super().from_dict(kwargs, shape_hint=shape_hint)
+
+        raise ValueError(f"Invalid {keys=} for Geography specification")
+
     @classmethod
     def from_dict(cls, d) -> "EmptyGeography":
         if not isinstance(d, dict):

tests/list_of_dicts/test_lod_geography.py

@@ -153,6 +153,34 @@ def test_lod_no_latlon(
     assert ds[0].geography.latlons() == (None, None)
 
 
+def test_lod_geo_set_on_nongeo_1():
+    from earthkit.data import Field
+
+    f = Field.from_dict({"parameter": {"variable": "t", "units": "K"}, "values": np.array([1.0, 2.0, 3.0])})
+
+    lats = np.array([10.0, 20.0, 30.0])
+    lons = np.array([100.0, 110.0, 120.0])
+
+    f_new = f.set({"geography.latitudes": lats, "geography.longitudes": lons})
+
+    assert np.allclose(f_new.geography.latitudes(), lats)
+    assert np.allclose(f_new.geography.longitudes(), lons)
+
+
+def test_lod_geo_set_on_nongeo_2():
+    from earthkit.data import Field
+
+    f = Field.from_dict({"parameter": {"variable": "t", "units": "K"}, "values": np.array([1.0, 2.0, 3.0])})
+
+    lats = np.array([10.0, 20.0, 30.0])
+    lons = np.array([100.0, 110.0, 120.0])
+
+    f_new = f.set(geography={"latitudes": np.array([10.0, 20.0, 30.0]), "longitudes": np.array([100.0, 110.0, 120.0])})
+
+    assert np.allclose(f_new.geography.latitudes(), lats)
+    assert np.allclose(f_new.geography.longitudes(), lons)
+
+
 if __name__ == "__main__":
     from earthkit.data.utils.testing import main