add warning for GeostationarySatelliteConversion where latitude_natur…

…al_origin is nonzero (#546)

pyproj/crs/coordinate_operation.py

@@ -1,3 +1,4 @@
+import warnings
 from distutils.version import LooseVersion
 
 from pyproj._crs import CoordinateOperation
@@ -204,6 +205,13 @@ def __new__(
         if sweep_angle_axis not in valid_sweep_axis:
             raise CRSError("sweep_angle_axis only supports {}".format(valid_sweep_axis))
 
+        if latitude_natural_origin != 0:
+            warnings.warn(
+                "The latitude of natural origin (lat_0) is not used "
+                "within PROJ. It is only supported for exporting to "
+                "the WKT or PROJ JSON formats."
+            )
+
         geos_json = {
             "$schema": "https://proj.org/schemas/v0.2/projjson.schema.json",
             "type": "Conversion",

test/crs/test_crs_coordinate_operation.py

@@ -120,14 +120,15 @@ def test_geostationary_operation__defaults():
 
 
 def test_geostationary_operation():
-    geop = GeostationarySatelliteConversion(
-        sweep_angle_axis="y",
-        satellite_height=11,
-        latitude_natural_origin=1,
-        longitude_natural_origin=2,
-        false_easting=3,
-        false_northing=4,
-    )
+    with pytest.warns(UserWarning):
+        geop = GeostationarySatelliteConversion(
+            sweep_angle_axis="y",
+            satellite_height=11,
+            latitude_natural_origin=1,
+            longitude_natural_origin=2,
+            false_easting=3,
+            false_northing=4,
+        )
     assert geop.name == "unknown"
     assert geop.method_name == "Geostationary Satellite (Sweep Y)"
     assert _to_dict(geop) == {