MNT: Refactor projection handling in Formatters

Move the source and target projection calculation into the set_axis() call instead of the __call__ method.
SciTools · Nov 10, 2023 · a6c3419 · a6c3419
1 parent d4c0ef0
commit a6c3419
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Showing 2 changed files with 35 additions and 31 deletions.
diff --git a/lib/cartopy/mpl/ticker.py b/lib/cartopy/mpl/ticker.py
@@ -19,9 +19,6 @@ class _PlateCarreeFormatter(Formatter):
     rectangular projection (e.g. Plate Carree, Mercator).
 
     """
-
-    _target_projection = ccrs.PlateCarree()
-
     def __init__(self, direction_label=True, degree_symbol='°',
                  number_format='g', transform_precision=1e-8, dms=False,
                  minute_symbol='′', second_symbol='″',
@@ -52,24 +49,14 @@ def __init__(self, direction_label=True, degree_symbol='°',
             cardinal_labels = {}
         self._cardinal_labels = cardinal_labels
         self._decimal_point = decimal_point
+        self._source_projection = None
+        self._target_projection = None
 
     def __call__(self, value, pos=None):
-        if self.axis is not None and isinstance(self.axis.axes, GeoAxes):
-
-            # We want to produce labels for values in the familiar Plate Carree
-            # projection, so convert the tick values from their own projection
-            # before formatting them.
-            source = self.axis.axes.projection
-            if not isinstance(source, (ccrs._RectangularProjection,
-                                       ccrs.Mercator)):
-                raise TypeError("This formatter cannot be used with "
-                                "non-rectangular projections.")
-            if source.globe != self._target_projection.globe:
-                # The transforms need to use the same globe
-                self._target_projection = ccrs.PlateCarree(globe=source.globe)
+        if self._source_projection is not None:
             projected_value = self._apply_transform(value,
                                                     self._target_projection,
-                                                    source)
+                                                    self._source_projection)
 
             # Round the transformed value using a given precision for display
             # purposes. Transforms can introduce minor rounding errors that
@@ -140,6 +127,24 @@ def _get_dms(self, x):
         secs = np.round((y - mins) * 60, self._precision - 3)
         return x, degs, mins, secs
 
+    def set_axis(self, axis):
+        super().set_axis(axis)
+
+        # Set the source and target projections for the formatter
+        # setting them to None if we aren't interacting with a GeoAxes
+        if self.axis is None or not isinstance(self.axis.axes, GeoAxes):
+            self._source_projection = None
+            self._target_projection = None
+            return
+
+        self._source_projection = self.axis.axes.projection
+        if not isinstance(self._source_projection, (ccrs._RectangularProjection,
+                                                    ccrs.Mercator)):
+            raise TypeError("This formatter cannot be used with "
+                            "non-rectangular projections.")
+        # The transforms need to use the same globe
+        self._target_projection = ccrs.PlateCarree(globe=self._source_projection.globe)
+
     def set_locs(self, locs):
         Formatter.set_locs(self, locs)
         if not self._auto_hide:

diff --git a/lib/cartopy/tests/mpl/test_ticker.py b/lib/cartopy/tests/mpl/test_ticker.py
@@ -23,16 +23,15 @@
 @pytest.mark.parametrize('cls', [LatitudeFormatter, LongitudeFormatter])
 def test_formatter_bad_projection(cls):
     formatter = cls()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=ccrs.Orthographic()))
     match = r'This formatter cannot be used with non-rectangular projections\.'
     with pytest.raises(TypeError, match=match):
-        formatter(0)
+        formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=ccrs.Orthographic())))
 
 
 def test_LatitudeFormatter():
     formatter = LatitudeFormatter()
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-90, -60, -30, 0, 30, 60, 90]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['90°S', '60°S', '30°S', '0°', '30°N', '60°N', '90°N']
@@ -42,7 +41,7 @@ def test_LatitudeFormatter():
 def test_LatitudeFormatter_direction_label():
     formatter = LatitudeFormatter(direction_label=False)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-90, -60, -30, 0, 30, 60, 90]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['-90°', '-60°', '-30°', '0°', '30°', '60°', '90°']
@@ -52,7 +51,7 @@ def test_LatitudeFormatter_direction_label():
 def test_LatitudeFormatter_degree_symbol():
     formatter = LatitudeFormatter(degree_symbol='')
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-90, -60, -30, 0, 30, 60, 90]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['90S', '60S', '30S', '0', '30N', '60N', '90N']
@@ -62,7 +61,7 @@ def test_LatitudeFormatter_degree_symbol():
 def test_LatitudeFormatter_number_format():
     formatter = LatitudeFormatter(number_format='.2f', dms=False)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-90, -60, -30, 0, 30, 60, 90]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['90.00°S', '60.00°S', '30.00°S', '0.00°',
@@ -73,7 +72,7 @@ def test_LatitudeFormatter_number_format():
 def test_LatitudeFormatter_mercator():
     formatter = LatitudeFormatter()
     p = ccrs.Mercator()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-15496570.739707904, -8362698.548496634,
                   -3482189.085407435, 0.0, 3482189.085407435,
                   8362698.548496634, 15496570.739707898]
@@ -85,7 +84,7 @@ def test_LatitudeFormatter_mercator():
 def test_LatitudeFormatter_small_numbers():
     formatter = LatitudeFormatter(number_format='.7f', dms=False)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [40.1275150, 40.1275152, 40.1275154]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['40.1275150°N', '40.1275152°N', '40.1275154°N']
@@ -97,7 +96,7 @@ def test_LongitudeFormatter_direction_label():
                                    dateline_direction_label=True,
                                    zero_direction_label=True)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-180, -120, -60, 0, 60, 120, 180]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['-180°', '-120°', '-60°', '0°', '60°', '120°', '180°']
@@ -116,7 +115,7 @@ def test_LongitudeFormatter_central_longitude(central_longitude, kwargs,
                                               expected):
     formatter = LongitudeFormatter(**kwargs)
     p = ccrs.PlateCarree(central_longitude=central_longitude)
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-180, -120, -60, 0, 60, 120, 180]
     result = [formatter(tick) for tick in test_ticks]
     assert result == expected
@@ -126,7 +125,7 @@ def test_LongitudeFormatter_degree_symbol():
     formatter = LongitudeFormatter(degree_symbol='',
                                    dateline_direction_label=True)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-180, -120, -60, 0, 60, 120, 180]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['180W', '120W', '60W', '0', '60E', '120E', '180E']
@@ -137,7 +136,7 @@ def test_LongitudeFormatter_number_format():
     formatter = LongitudeFormatter(number_format='.2f', dms=False,
                                    dateline_direction_label=True)
     p = ccrs.PlateCarree()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-180, -120, -60, 0, 60, 120, 180]
     result = [formatter(tick) for tick in test_ticks]
     expected = ['180.00°W', '120.00°W', '60.00°W', '0.00°',
@@ -148,7 +147,7 @@ def test_LongitudeFormatter_number_format():
 def test_LongitudeFormatter_mercator():
     formatter = LongitudeFormatter(dateline_direction_label=True)
     p = ccrs.Mercator()
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-20037508.342783064, -13358338.895188706,
                   -6679169.447594353, 0.0, 6679169.447594353,
                   13358338.895188706, 20037508.342783064]
@@ -166,7 +165,7 @@ def test_LongitudeFormatter_small_numbers(central_longitude,
     formatter = LongitudeFormatter(number_format='.7f', dms=False,
                                    zero_direction_label=zero_direction_label)
     p = ccrs.PlateCarree(central_longitude=central_longitude)
-    formatter.axis = Mock(axes=Mock(GeoAxes, projection=p))
+    formatter.set_axis(Mock(axes=Mock(GeoAxes, projection=p)))
     test_ticks = [-17.1142343, -17.1142340, -17.1142337]
     result = [formatter(tick) for tick in test_ticks]
     assert result == expected