From a02cc4d2a645c26f90ad88a441e6488eea11bb85 Mon Sep 17 00:00:00 2001
From: Do Ngoc Khanh <14163153+epn09@users.noreply.github.com>
Date: Tue, 3 Feb 2026 15:24:07 +0900
Subject: [PATCH] Expose +gamma for Oblique Mercator

---
 lib/cartopy/crs.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/cartopy/crs.py b/lib/cartopy/crs.py
index 8a6dd4ccf..bb72e1557 100644
--- a/lib/cartopy/crs.py
+++ b/lib/cartopy/crs.py
@@ -3160,7 +3160,7 @@ class ObliqueMercator(Projection):
 
     def __init__(self, central_longitude=0.0, central_latitude=0.0,
                  false_easting=0.0, false_northing=0.0,
-                 scale_factor=1.0, azimuth=0.0, globe=None):
+                 scale_factor=1.0, azimuth=0.0, gamma=None, globe=None):
         """
         Parameters
         ----------
@@ -3178,6 +3178,9 @@ def __init__(self, central_longitude=0.0, central_latitude=0.0,
         azimuth: optional
             Azimuth of centerline clockwise from north at the center point of
             the centre line. Defaults to 0.
+        gamma: optional
+            Azimuth of centerline clockwise from north of the rectified bearing
+            of centre line. If omitted, `alpha` determines the values of `gamma`.
         globe: optional
             An instance of :class:`cartopy.crs.Globe`. If omitted, a default
             globe is created.
@@ -3198,6 +3201,9 @@ def __init__(self, central_longitude=0.0, central_latitude=0.0,
                         ('x_0', false_easting), ('y_0', false_northing),
                         ('alpha', azimuth), ('units', 'm')]
 
+        if gamma is not None:
+            proj4_params.append(('gamma', gamma))
+
         super().__init__(proj4_params, globe=globe)
 
         # Couple limits to those of Mercator - delivers acceptable plots, and