add return_back_azimuth: bool = True to fwd()

pyproj/_geod.pyi

@@ -23,7 +23,13 @@ class Geod:
     def __reduce__(self) -> Tuple[Type["Geod"], str]: ...
     def __repr__(self) -> str: ...
     def _fwd(
-        self, lons: Any, lats: Any, az: Any, dist: Any, radians: bool = False
+        self,
+        lons: Any,
+        lats: Any,
+        az: Any,
+        dist: Any,
+        radians: bool = False,
+        return_back_azimuth: bool = True,
     ) -> None: ...
     def _inv(
         self, lons1: Any, lats1: Any, lons2: Any, lats2: Any, radians: bool = False

pyproj/_geod.pyx

@@ -91,12 +91,14 @@ cdef class Geod:
         object az,
         object dist,
         bint radians=False,
+        bint return_back_azimuth=True,
     ):
         """
         forward transformation - determine longitude, latitude and back azimuth
         of a terminus point given an initial point longitude and latitude, plus
         forward azimuth and distance.
         if radians=True, lons/lats are radians instead of degrees.
+        if return_back_azimuth=False, the return azimuth will be the forward azimuth instead of the forward azimuth.
         """
         cdef PyBuffWriteManager lonbuff = PyBuffWriteManager(lons)
         cdef PyBuffWriteManager latbuff = PyBuffWriteManager(lats)
@@ -133,10 +135,11 @@ cdef class Geod:
                 )
                 # back azimuth needs to be flipped 180 degrees
                 # to match what PROJ geod utility produces.
-                if pazi2 > 0:
-                    pazi2 = pazi2 - 180.
-                elif pazi2 <= 0:
-                    pazi2 = pazi2 + 180.
+                if return_back_azimuth:
+                    if pazi2 > 0:
+                        pazi2 = pazi2 - 180.
+                    elif pazi2 <= 0:
+                        pazi2 = pazi2 + 180.
                 if not radians:
                     lonbuff.data[iii] = plon2
                     latbuff.data[iii] = plat2

pyproj/geod.py

@@ -240,9 +240,17 @@ def __init__(self, initstring: Optional[str] = None, **kwargs) -> None:
         )
 
     def fwd(  # pylint: disable=invalid-name
-        self, lons: Any, lats: Any, az: Any, dist: Any, radians: bool = False
+        self,
+        lons: Any,
+        lats: Any,
+        az: Any,
+        dist: Any,
+        radians: bool = False,
+        return_back_azimuth: bool = True,
     ) -> Tuple[Any, Any, Any]:
         """
+        .. versionadded:: 3.5.0 return_back_azimuth
+
         Forward transformation
 
         Determine longitudes, latitudes and back azimuths of terminus
@@ -276,6 +284,9 @@ def fwd(  # pylint: disable=invalid-name
         radians: bool, default=False
             If True, the input data is assumed to be in radians.
             Otherwise, the data is assumed to be in degrees.
+        return_back_azimuth: bool, default=True
+            if True, the third return value will be the back azimuth,
+            Otherwise, it will be the forward azimuth.
 
         Returns
         -------
@@ -284,14 +295,16 @@ def fwd(  # pylint: disable=invalid-name
         scalar or array:
             Latitude(s) of terminus point(s)
         scalar or array:
-            Back azimuth(s)
+            Back azimuth(s) or Forward azimuth(s)
         """
         # process inputs, making copies that support buffer API.
         inx, x_data_type = _copytobuffer(lons)
         iny, y_data_type = _copytobuffer(lats)
         inz, z_data_type = _copytobuffer(az)
         ind = _copytobuffer(dist)[0]
-        self._fwd(inx, iny, inz, ind, radians=radians)
+        self._fwd(
+            inx, iny, inz, ind, radians=radians, return_back_azimuth=return_back_azimuth
+        )
         # if inputs were lists, tuples or floats, convert back.
         outx = _convertback(x_data_type, inx)
         outy = _convertback(y_data_type, iny)

test/test_proj.py

@@ -13,6 +13,7 @@
 import pyproj
 from pyproj import Geod, Proj, pj_ellps, pj_list, transform
 from pyproj.exceptions import CRSError, ProjError
+from pyproj.utils import reverse_azimuth
 from test.conftest import proj_network_env
 
 
@@ -300,14 +301,22 @@ def test_fwd_radians(self):
         )
 
         # Calculate Portland's lon/lat from bearing and distance in radians
-        endlon_r, endlat_r, backaz_r = self.g.fwd(
-            self.boston_r[0], self.boston_r[1], math.radians(az12_d), dist, radians=True
-        )
-
-        # Check they are equal
-        self.assertAlmostEqual(endlon_d, math.degrees(endlon_r))
-        self.assertAlmostEqual(endlat_d, math.degrees(endlat_r))
-        self.assertAlmostEqual(backaz_d, math.degrees(backaz_r))
+        for return_back_azimuth in [False, True]:
+            endlon_r, endlat_r, backaz_r = self.g.fwd(
+                self.boston_r[0],
+                self.boston_r[1],
+                math.radians(az12_d),
+                dist,
+                radians=True,
+                return_back_azimuth=return_back_azimuth,
+            )
+            if not return_back_azimuth:
+                backaz_r = reverse_azimuth(backaz_r)
+
+            # Check they are equal
+            self.assertAlmostEqual(endlon_d, math.degrees(endlon_r))
+            self.assertAlmostEqual(endlat_d, math.degrees(endlat_r))
+            self.assertAlmostEqual(backaz_d, math.degrees(backaz_r))
 
         # Check to make sure we're back in Portland
         self.assertAlmostEqual(endlon_d, self.portland_d[0])