Merge pull request #1978 from rhattersley/clip-latitude

Clip guessed latitude bounds to [-90, 90].

lib/iris/__init__.py

@@ -135,7 +135,8 @@ class Future(threading.local):
     """Run-time configuration controller."""
 
     def __init__(self, cell_datetime_objects=False, netcdf_promote=False,
-                 strict_grib_load=False, netcdf_no_unlimited=False):
+                 strict_grib_load=False, netcdf_no_unlimited=False,
+                 clip_latitudes=False):
         """
         A container for run-time options controls.
 
@@ -178,17 +179,24 @@ def __init__(self, cell_datetime_objects=False, netcdf_promote=False,
         unlimited.  The current default is that the leading dimension is
         unlimited unless otherwise specified.
 
+        The option `clip_latitudes` controls whether the
+        :meth:`iris.coords.Coord.guess_bounds()` method limits the
+        guessed bounds to [-90, 90] for latitudes.
+
         """
         self.__dict__['cell_datetime_objects'] = cell_datetime_objects
         self.__dict__['netcdf_promote'] = netcdf_promote
         self.__dict__['strict_grib_load'] = strict_grib_load
         self.__dict__['netcdf_no_unlimited'] = netcdf_no_unlimited
+        self.__dict__['clip_latitudes'] = clip_latitudes
 
     def __repr__(self):
         msg = ('Future(cell_datetime_objects={}, netcdf_promote={}, '
-               'strict_grib_load={}, netcdf_no_unlimited={})')
+               'strict_grib_load={}, netcdf_no_unlimited={}, '
+               'clip_latitudes={})')
         return msg.format(self.cell_datetime_objects, self.netcdf_promote,
-                          self.strict_grib_load, self.netcdf_no_unlimited)
+                          self.strict_grib_load, self.netcdf_no_unlimited,
+                          self.clip_latitudes)
 
     def __setattr__(self, name, value):
         if name not in self.__dict__:

lib/iris/coords.py

@@ -1011,8 +1011,9 @@ def _guess_bounds(self, bound_position=0.5):
 
         Kwargs:
 
-        * bound_position - The desired position of the bounds relative to the
-                           position of the points.
+        * bound_position:
+            The desired position of the bounds relative to the position
+            of the points.
 
         Returns:
             A numpy array of shape (len(self.points), 2).
@@ -1021,6 +1022,15 @@ def _guess_bounds(self, bound_position=0.5):
 
             This method only works for coordinates with ``coord.ndim == 1``.
 
+        .. note::
+
+            If `iris.FUTURE.clip_latitudes` is True, then this method
+            will clip the coordinate bounds to the range [-90, 90] when:
+
+            - it is a `latitude` or `grid_latitude` coordinate,
+            - the units are degrees,
+            - all the points are in the range [-90, 90].
+
         """
         # XXX Consider moving into DimCoord
         # ensure we have monotonic points
@@ -1056,6 +1066,13 @@ def _guess_bounds(self, bound_position=0.5):
 
         bounds = np.array([min_bounds, max_bounds]).transpose()
 
+        if (iris.FUTURE.clip_latitudes and
+                self.name() in ('latitude', 'grid_latitude') and
+                self.units == 'degree'):
+            points = self.points
+            if (points >= -90).all() and (points <= 90).all():
+                np.clip(bounds, -90, 90, out=bounds)
+
         return bounds
 
     def guess_bounds(self, bound_position=0.5):
@@ -1073,8 +1090,9 @@ def guess_bounds(self, bound_position=0.5):
 
         Kwargs:
 
-        * bound_position - The desired position of the bounds relative to the
-                           position of the points.
+        * bound_position:
+            The desired position of the bounds relative to the position
+            of the points.
 
         .. note::
 
@@ -1087,6 +1105,15 @@ def guess_bounds(self, bound_position=0.5):
             produce unexpected results :  In such cases you should assign
             suitable values directly to the bounds property, instead.
 
+        .. note::
+
+            If `iris.FUTURE.clip_latitudes` is True, then this method
+            will clip the coordinate bounds to the range [-90, 90] when:
+
+            - it is a `latitude` or `grid_latitude` coordinate,
+            - the units are degrees,
+            - all the points are in the range [-90, 90].
+
         """
         self.bounds = self._guess_bounds(bound_position)
 

lib/iris/tests/unit/coords/test_Coord.py

@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2013 - 2015, Met Office
+# (C) British Crown Copyright 2013 - 2016, Met Office
 #
 # This file is part of Iris.
 #
@@ -27,6 +27,7 @@
 
 import numpy as np
 
+import iris
 from iris.coords import DimCoord, AuxCoord, Coord
 from iris.tests import mock
 
@@ -158,6 +159,80 @@ def test_circular_decreasing_alt_range(self):
         self.assertArrayEqual(target, self.coord.bounds)
 
 
+class Test_guess_bounds__default_latitude_clipping(tests.IrisTest):
+    def test_all_inside(self):
+        lat = DimCoord([-10, 0, 20], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-15, -5], [-5, 10], [10, 30]])
+
+    def test_points_inside_bounds_outside(self):
+        lat = DimCoord([-80, 0, 70], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-120, -40], [-40, 35], [35, 105]])
+
+    def test_points_to_edges_bounds_outside(self):
+        lat = DimCoord([-90, 0, 90], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-135, -45], [-45, 45], [45, 135]])
+
+    def test_points_outside(self):
+        lat = DimCoord([-100, 0, 120], units='degree',
+                       standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-150, -50], [-50, 60], [60, 180]])
+
+
+class Test_guess_bounds__enabled_latitude_clipping(tests.IrisTest):
+    def setUp(self):
+        iris.FUTURE.clip_latitudes = True
+
+    def tearDown(self):
+        iris.FUTURE.clip_latitudes = False
+
+    def test_all_inside(self):
+        lat = DimCoord([-10, 0, 20], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-15, -5], [-5, 10], [10, 30]])
+
+    def test_points_inside_bounds_outside(self):
+        lat = DimCoord([-80, 0, 70], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-90, -40], [-40, 35], [35, 90]])
+
+    def test_points_inside_bounds_outside_grid_latitude(self):
+        lat = DimCoord([-80, 0, 70], units='degree',
+                       standard_name='grid_latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-90, -40], [-40, 35], [35, 90]])
+
+    def test_points_to_edges_bounds_outside(self):
+        lat = DimCoord([-90, 0, 90], units='degree', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-90, -45], [-45, 45], [45, 90]])
+
+    def test_points_outside(self):
+        lat = DimCoord([-100, 0, 120], units='degree',
+                       standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-150, -50], [-50, 60], [60, 180]])
+
+    def test_points_inside_bounds_outside_wrong_unit(self):
+        lat = DimCoord([-80, 0, 70], units='feet', standard_name='latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-120, -40], [-40, 35], [35, 105]])
+
+    def test_points_inside_bounds_outside_wrong_name(self):
+        lat = DimCoord([-80, 0, 70], units='degree', standard_name='longitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-120, -40], [-40, 35], [35, 105]])
+
+    def test_points_inside_bounds_outside_wrong_name_2(self):
+        lat = DimCoord([-80, 0, 70], units='degree',
+                       long_name='other_latitude')
+        lat.guess_bounds()
+        self.assertArrayEqual(lat.bounds, [[-120, -40], [-40, 35], [35, 105]])
+
+
 class Test_cell(tests.IrisTest):
     def _mock_coord(self):
         coord = mock.Mock(spec=Coord, ndim=1,

lib/iris/tests/unit/test_Future.py

@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2013 - 2015, Met Office
+# (C) British Crown Copyright 2013 - 2016, Met Office
 #
 # This file is part of Iris.
 #
@@ -45,6 +45,12 @@ def test_valid_strict_grib_load(self):
         future.strict_grib_load = new_value
         self.assertEqual(future.strict_grib_load, new_value)
 
+    def test_valid_clip_latitudes(self):
+        future = Future()
+        new_value = not future.clip_latitudes
+        future.clip_latitudes = new_value
+        self.assertEqual(future.clip_latitudes, new_value)
+
     def test_invalid_attribute(self):
         future = Future()
         with self.assertRaises(AttributeError):