Add warning for radians flag with Proj class

pyproj/_transformer.pyx

@@ -424,8 +424,8 @@ cdef class _Transformer(Base):
             return
         if radians and self.is_pipeline:
             warnings.warn(
-                "radian input with pipelines is not supported and may result "
-                "in unexpected transformations."
+                "radian input with pipelines is not supported in pyproj 2. "
+                "support for raidans will be added in pyproj 3."
             )
 
         tmp_pj_direction = _PJ_DIRECTION_MAP[TransformDirection.create(direction)]

pyproj/proj.py

@@ -137,6 +137,7 @@ def __call__(
         latitude: Any,
         inverse: bool = False,
         errcheck: bool = False,
+        radians: bool = False,
     ) -> Tuple[Any, Any]:
         """
         Calling a Proj class instance with the arguments lon, lat will
@@ -158,6 +159,11 @@ def __call__(
         inverse: boolean, optional
             If inverse is True the inverse transformation from x/y to
             lon/lat is performed. Default is False.
+        radians: boolean, optional
+            If True, will expect input data to be in radians and will return radians
+            if the projection is geographic. Default is False (degrees).
+            This does not work with pyproj 2 and is ignored. It will be enabled again
+            in pyproj 3.
         errcheck: boolean, optional
             If True an exception is raised if the errors are found in the process.
             By default errcheck=False and ``inf`` is returned.
@@ -167,6 +173,11 @@ def __call__(
         Tuple[Any, Any]:
             The transformed coordinates.
         """
+        if radians:
+            warnings.warn(
+                "radian input is currently not supported in pyproj 2. "
+                "Support for radian input will be added in pyproj 3."
+            )
         # process inputs, making copies that support buffer API.
         inx, xisfloat, xislist, xistuple = _copytobuffer(longitude)
         iny, yisfloat, yislist, yistuple = _copytobuffer(latitude)

pyproj/transformer.py

@@ -363,7 +363,7 @@ def transform(
         radians: boolean, optional
             If True, will expect input data to be in radians and will return radians
             if the projection is geographic. Default is False (degrees). Ignored for
-            pipeline transformations.
+            pipeline transformations with pyproj 2, but will work in pyproj 3.
         errcheck: boolean, optional
             If True an exception is raised if the transformation is invalid.
             By default errcheck=False and an invalid transformation

test/test_proj.py

@@ -522,3 +522,9 @@ def test_numpy_bool_kwarg_true():
         proj="utm", zone=32, ellipsis="WGS84", datum="WGS84", units="m", south=south
     )
     assert "+south " in proj.srs
+
+
+def test_proj_radians_warning():
+    proj = Proj("epsg:4326")
+    with pytest.warns(UserWarning, match="radian"):
+        proj(1, 2, radians=True)

test/test_transformer.py

@@ -738,5 +738,5 @@ def test_pipeline_itransform(pipeline_str):
 
 def test_pipeline_radian_transform_warning():
     trans = Transformer.from_pipeline("+proj=pipeline +ellps=GRS80 +step +proj=cart")
-    with pytest.warns(UserWarning):
+    with pytest.warns(UserWarning, match="radian"):
         trans.transform(0.1, 0.1, 0, radians=True)