Shade area on SkewT

.travis.yml

@@ -41,6 +41,7 @@ matrix:
     - python: 2.7
       env:
         - VERSIONS="numpy==1.9.1 matplotlib==1.4.0 scipy==0.14.0 pint==0.7"
+        - TASK="coverage"
         - TEST_OUTPUT_CONTROL=""
     - python: 3.4
       env:

metpy/plots/_mpl.py

@@ -368,3 +368,29 @@ def get_usetex(self):
 
     # Monkey-patch scattertext onto Axes
     Axes.scattertext = scattertext
+
+
+# See if we need to add in the Tableau colors which were added in Matplotlib 2.0
+import matplotlib.colors  # noqa: E402
+if not hasattr(matplotlib.colors, 'TABLEAU_COLORS'):
+    from collections import OrderedDict
+
+    # These colors are from Tableau
+    TABLEAU_COLORS = (
+        ('blue', '#1f77b4'),
+        ('orange', '#ff7f0e'),
+        ('green', '#2ca02c'),
+        ('red', '#d62728'),
+        ('purple', '#9467bd'),
+        ('brown', '#8c564b'),
+        ('pink', '#e377c2'),
+        ('gray', '#7f7f7f'),
+        ('olive', '#bcbd22'),
+        ('cyan', '#17becf'),
+    )
+
+    # Normalize name to "tab:<name>" to avoid name collisions.
+    matplotlib.colors.TABLEAU_COLORS = OrderedDict(
+        ('tab:' + name, value) for name, value in TABLEAU_COLORS)
+
+    matplotlib.colors.cnames.update(matplotlib.colors.TABLEAU_COLORS)

metpy/plots/skewt.py

@@ -524,6 +524,114 @@ def plot_mixing_lines(self, w=None, p=None, **kwargs):
         kwargs.setdefault('alpha', 0.8)
         return self.ax.add_collection(LineCollection(linedata, **kwargs))
 
+    def shade_area(self, y, x1, x2=0, which='both', **kwargs):
+        r"""Shade area between two curves.
+
+        Shades areas between curves. Area can be where one is greater or less than the other
+        or all areas shaded.
+
+        Parameters
+        ----------
+        y : array_like
+            1-dimensional array of numeric y-values
+        x1 : array_like
+            1-dimensional array of numeric x-values
+        x2 : array_like
+            1-dimensional array of numeric x-values
+        which : string
+            Specifies if `positive`, `negative`, or `both` areas are being shaded.
+            Will be overridden by where.
+        kwargs
+            Other keyword arguments to pass to :class:`matplotlib.collections.PolyCollection`
+
+        Returns
+        -------
+        :class:`matplotlib.collections.PolyCollection`
+
+        See Also
+        --------
+        :class:`matplotlib.collections.PolyCollection`
+        :func:`matplotlib.axes.Axes.fill_betweenx`
+        """
+        fill_properties = {'positive':
+                           {'facecolor': 'tab:red', 'alpha': 0.4, 'where': x1 > x2},
+                           'negative':
+                           {'facecolor': 'tab:blue', 'alpha': 0.4, 'where': x1 < x2},
+                           'both':
+                           {'facecolor': 'tab:green', 'alpha': 0.4, 'where': None}}
+
+        try:
+            fill_args = fill_properties[which]
+            fill_args.update(kwargs)
+        except KeyError:
+            raise ValueError('Unknown option for which: {0}'.format(str(which)))
+
+        arrs = y, x1, x2
+
+        if fill_args['where'] is not None:
+            arrs = arrs + (fill_args['where'],)
+            fill_args.pop('where', None)
+
+        arrs = delete_masked_points(*arrs)
+
+        return self.ax.fill_betweenx(*arrs, **fill_args)
+
+    def shade_cape(self, p, t, t_parcel, **kwargs):
+        r"""Shade areas of CAPE.
+
+        Shades areas where the parcel is warmer than the environment (areas of positive
+        buoyancy.
+
+        Parameters
+        ----------
+        p : array_like
+            Pressure values
+        t : array_like
+            Temperature values
+        t_parcel : array_like
+            Parcel path temperature values
+        kwargs
+            Other keyword arguments to pass to :class:`matplotlib.collections.PolyCollection`
+
+        Returns
+        -------
+        :class:`matplotlib.collections.PolyCollection`
+
+        See Also
+        --------
+        :class:`matplotlib.collections.PolyCollection`
+        :func:`matplotlib.axes.Axes.fill_betweenx`
+        """
+        return self.shade_area(p, t_parcel, t, which='positive', **kwargs)
+
+    def shade_cin(self, p, t, t_parcel, **kwargs):
+        r"""Shade areas of CIN.
+
+        Shades areas where the parcel is cooler than the environment (areas of negative
+        buoyancy.
+
+        Parameters
+        ----------
+        p : array_like
+            Pressure values
+        t : array_like
+            Temperature values
+        t_parcel : array_like
+            Parcel path temperature values
+        kwargs
+            Other keyword arguments to pass to :class:`matplotlib.collections.PolyCollection`
+
+        Returns
+        -------
+        :class:`matplotlib.collections.PolyCollection`
+
+        See Also
+        --------
+        :class:`matplotlib.collections.PolyCollection`
+        :func:`matplotlib.axes.Axes.fill_betweenx`
+        """
+        return self.shade_area(p, t_parcel, t, which='negative', **kwargs)
+
 
 @exporter.export
 class Hodograph(object):

metpy/plots/tests/test_skewt.py

@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 """Tests for the `skewt` module."""
 
+import matplotlib
 from matplotlib.gridspec import GridSpec
 import matplotlib.pyplot as plt
 import numpy as np
@@ -13,6 +14,8 @@
 from metpy.testing import patch_round, set_agg_backend  # noqa: F401
 from metpy.units import units
 
+MPL_VERSION = matplotlib.__version__[:3]
+
 
 @pytest.mark.mpl_image_compare(tolerance=0.021, remove_text=True)
 def test_skewt_api():
@@ -60,6 +63,60 @@ def test_skewt_with_grid_enabled():
         SkewT()
 
 
+@pytest.fixture()
+def test_profile():
+    """Return data for a test profile."""
+    return np.linspace(1000, 100, 10), np.linspace(20, -20, 10), np.linspace(25, -30, 10)
+
+
+@pytest.mark.mpl_image_compare(tolerance={'1.4': 1.71}.get(MPL_VERSION, 0.), remove_text=True)
+def test_skewt_shade_cape_cin(test_profile):
+    """Test shading CAPE and CIN on a SkewT plot."""
+    p, t, tp = test_profile
+    fig = plt.figure(figsize=(9, 9))
+    skew = SkewT(fig)
+    skew.plot(p, t, 'r')
+    skew.plot(p, tp, 'k')
+    skew.shade_cape(p, t, tp)
+    skew.shade_cin(p, t, tp)
+    return fig
+
+
+@pytest.mark.mpl_image_compare(tolerance={'1.4': 1.70}.get(MPL_VERSION, 0.), remove_text=True)
+def test_skewt_shade_area(test_profile):
+    """Test shading areas on a SkewT plot."""
+    p, t, tp = test_profile
+    fig = plt.figure(figsize=(9, 9))
+    skew = SkewT(fig)
+    skew.plot(p, t, 'r')
+    skew.plot(p, tp, 'k')
+    skew.shade_area(p, t, tp)
+    return fig
+
+
+def test_skewt_shade_area_invalid(test_profile):
+    """Test shading areas on a SkewT plot."""
+    p, t, tp = test_profile
+    fig = plt.figure(figsize=(9, 9))
+    skew = SkewT(fig)
+    skew.plot(p, t, 'r')
+    skew.plot(p, tp, 'k')
+    with pytest.raises(ValueError):
+        skew.shade_area(p, t, tp, which='positve')
+
+
+@pytest.mark.mpl_image_compare(tolerance={'1.4': 1.75}.get(MPL_VERSION, 0.), remove_text=True)
+def test_skewt_shade_area_kwargs(test_profile):
+    """Test shading areas on a SkewT plot with kwargs."""
+    p, t, tp = test_profile
+    fig = plt.figure(figsize=(9, 9))
+    skew = SkewT(fig)
+    skew.plot(p, t, 'r')
+    skew.plot(p, tp, 'k')
+    skew.shade_area(p, t, tp, facecolor='m')
+    return fig
+
+
 @pytest.mark.mpl_image_compare(tolerance=0, remove_text=True)
 def test_hodograph_api():
     """Basic test of Hodograph API."""