ENH: Added force_over kwarg to Transformer.from_crs

docs/history.rst

@@ -7,6 +7,7 @@ Latest
 - DEP: Minimum PROJ version 8.2 (issue #1011)
 - BUG: Fix transformer list for 3D transformations in :class:`.TransformerGroup` (discussion #1072)
 - ENH: Added authority, accuracy, and allow_ballpark kwargs to :class:`.TransformerGroup` (pull #1076)
+- ENH: Added ``force_over`` kwarg to :meth:`.Transformer.from_crs` (issue #997)
 - CLN: Remove deprecated ``skip_equivalent`` kwarg from transformers and ``errcheck`` kwarg from :meth:`.CRS.from_cf` (pull #1077)
 - REF: use regex to process PROJ strings in :meth:`.CRS.to_dict` (pull #1086)
 - BUG: :class:`.MercatorAConversion` defined only for lat_0 = 0 (issue #1089)

pyproj/_transformer.pyi

@@ -81,6 +81,7 @@ class _Transformer(Base):
         authority: Optional[str] = None,
         accuracy: Optional[str] = None,
         allow_ballpark: Optional[bool] = None,
+        force_over: bool = False,
     ) -> "_Transformer": ...
     @staticmethod
     def from_pipeline(proj_pipeline: bytes) -> "_Transformer": ...

pyproj/_transformer.pyx

@@ -242,7 +242,8 @@ cdef PJ* proj_create_crs_to_crs(
     str authority,
     str accuracy,
     allow_ballpark,
-):
+    bint force_over,
+) except NULL:
     """
     This is the same as proj_create_crs_to_crs in proj.h
     with the options added. It is a hack for stabilily
@@ -272,6 +273,7 @@ cdef PJ* proj_create_crs_to_crs(
     options[1] = NULL
     options[2] = NULL
     options[3] = NULL
+    options[4] = NULL
     if authority is not None:
         b_authority = cstrencode(f"AUTHORITY={authority}")
         options[options_index] = b_authority
@@ -283,6 +285,12 @@ cdef PJ* proj_create_crs_to_crs(
     if allow_ballpark is not None:
         if not allow_ballpark:
             options[options_index] = b"ALLOW_BALLPARK=NO"
+        options_index += 1
+    if force_over:
+        IF CTE_PROJ_VERSION_MAJOR >= 9:
+            options[options_index] = b"FORCE_OVER=YES"
+        ELSE:
+            raise NotImplementedError("force_over requires PROJ 9+.")
 
     cdef PJ* transform = proj_create_crs_to_crs_from_pj(
         ctx,
@@ -293,6 +301,8 @@ cdef PJ* proj_create_crs_to_crs(
     )
     proj_destroy(source_crs)
     proj_destroy(target_crs)
+    if transform == NULL:
+        raise ProjError("Error creating Transformer from CRS.")
     return transform
 
 
@@ -455,6 +465,7 @@ cdef class _Transformer(Base):
         str authority=None,
         str accuracy=None,
         allow_ballpark=None,
+        bint force_over=False,
     ):
         """
         Create a transformer from CRS objects
@@ -493,14 +504,12 @@ cdef class _Transformer(Base):
                 authority=authority,
                 accuracy=accuracy,
                 allow_ballpark=allow_ballpark,
+                force_over=force_over,
             )
         finally:
             if pj_area_of_interest != NULL:
                 proj_area_destroy(pj_area_of_interest)
 
-        if transformer.projobj == NULL:
-            raise ProjError("Error creating Transformer from CRS.")
-
         transformer._init_from_crs(always_xy)
         return transformer
 

pyproj/transformer.py

@@ -77,6 +77,8 @@ class TransformerFromCRS(TransformerMaker):
     """
     .. versionadded:: 3.1.0
 
+    .. versionadded:: 3.4.0 force_over
+
     Generates a Cython _Transformer class from input CRS data.
     """
 
@@ -87,6 +89,7 @@ class TransformerFromCRS(TransformerMaker):
     authority: Optional[str]
     accuracy: Optional[str]
     allow_ballpark: Optional[bool]
+    force_over: bool = False
 
     def __call__(self) -> _Transformer:
         """
@@ -102,6 +105,7 @@ def __call__(self) -> _Transformer:
             authority=self.authority,
             accuracy=self.accuracy,
             allow_ballpark=self.allow_ballpark,
+            force_over=self.force_over,
         )
 
 
@@ -520,12 +524,14 @@ def from_crs(
         authority: Optional[str] = None,
         accuracy: Optional[float] = None,
         allow_ballpark: Optional[bool] = None,
+        force_over: bool = False,
     ) -> "Transformer":
         """Make a Transformer from a :obj:`pyproj.crs.CRS` or input used to create one.
 
         .. versionadded:: 2.2.0 always_xy
         .. versionadded:: 2.3.0 area_of_interest
         .. versionadded:: 3.1.0 authority, accuracy, allow_ballpark
+        .. versionadded:: 3.4.0 force_over
 
         Parameters
         ----------
@@ -554,6 +560,9 @@ def from_crs(
         allow_ballpark: bool, optional
             Set to False to disallow the use of Ballpark transformation
             in the candidate coordinate operations. Default is to allow.
+        force_over: bool, default=False
+            If True, it will to force the +over flag on the transformation.
+            Requires PROJ 9+.
 
         Returns
         -------
@@ -569,6 +578,7 @@ def from_crs(
                 authority=authority,
                 accuracy=accuracy if accuracy is None else str(accuracy),
                 allow_ballpark=allow_ballpark,
+                force_over=force_over,
             )
         )
 

test/conftest.py

@@ -10,6 +10,7 @@
 
 _NETWORK_ENABLED = pyproj.network.is_network_enabled()
 PROJ_LOOSE_VERSION = version.parse(pyproj.__proj_version__)
+PROJ_GTE_9 = PROJ_LOOSE_VERSION >= version.parse("9.0.0")
 PROJ_GTE_901 = PROJ_LOOSE_VERSION >= version.parse("9.0.1")
 PROJ_GTE_91 = PROJ_LOOSE_VERSION >= version.parse("9.1")
 

test/test_transformer.py

@@ -18,7 +18,13 @@
 from pyproj.enums import TransformDirection
 from pyproj.exceptions import ProjError
 from pyproj.transformer import AreaOfInterest, TransformerGroup
-from test.conftest import PROJ_GTE_91, grids_available, proj_env, proj_network_env
+from test.conftest import (
+    PROJ_GTE_9,
+    PROJ_GTE_91,
+    grids_available,
+    proj_env,
+    proj_network_env,
+)
 
 
 def test_tranform_wgs84_to_custom():
@@ -1541,3 +1547,30 @@ def test_transformer_group_authority_filter():
         group.transformers[0].description
         == "Ballpark geographic offset from WGS 84 to ETRS89"
     )
+
+
+def test_transformer_force_over():
+    if PROJ_GTE_9:
+        transformer = Transformer.from_crs("EPSG:4326", "EPSG:3857", force_over=True)
+        # Test a point along the equator.
+        # The same point, but in two different representations.
+        xxx, yyy = transformer.transform(0, 140)
+        xxx_over, yyy_over = transformer.transform(0, -220)
+        # Web Mercator x's between 0 and 180 longitude come out positive.
+        # But when forcing the over flag, the -220 calculation makes it flip.
+        assert xxx > 0
+        assert xxx_over < 0
+        # check it works in both directions
+        xxx_inverse, yyy_inverse = transformer.transform(
+            xxx, yyy, direction=TransformDirection.INVERSE
+        )
+        xxx_over_inverse, yyy_over_inverse = transformer.transform(
+            xxx_over, yyy_over, direction=TransformDirection.INVERSE
+        )
+        assert_almost_equal(xxx_inverse, 0)
+        assert_almost_equal(xxx_over_inverse, 0)
+        assert_almost_equal(yyy_inverse, 140)
+        assert_almost_equal(yyy_over_inverse, -220)
+    else:
+        with pytest.raises(NotImplementedError, match="force_over requires PROJ 9"):
+            Transformer.from_crs("EPSG:4326", "EPSG:3857", force_over=True)