Convert obs units

src/metpy/plots/declarative.py

@@ -1305,12 +1305,14 @@ class PlotObs(HasTraits):
       * time
       * fields
       * locations (optional)
-      * time_range (optional)
+      * time_window (optional)
       * formats (optional)
       * colors (optional)
+      * plot_units (optional)
       * vector_field (optional)
       * vector_field_color (optional)
       * vector_field_length (optional)
+      * vector_plot_units (optional)
       * reduce_points (optional)
     """
 
@@ -1393,6 +1395,20 @@ class PlotObs(HasTraits):
     reduce_points = Float(default_value=0)
     reduce_points.__doc__ = """Float to reduce number of points plotted. (optional)"""
 
+    plot_units = List(default_value=[None], allow_none=True)
+    plot_units.__doc__ = """A list of the desired units to plot the fields in.
+
+    Setting this attribute will convert the units of the field variable to the given units for
+    plotting using the MetPy Units module, provided that units are attached to the DataFrame.
+    """
+
+    vector_plot_units = Unicode(default_value=None, allow_none=True)
+    vector_plot_units.__doc__ = """The desired units to plot the vector field in.
+
+    Setting this attribute will convert the units of the field variable to the given units for
+    plotting using the MetPy Units module, provided that units are attached to the DataFrame.
+    """
+
     def clear(self):
         """Clear the plot.
 
@@ -1519,34 +1535,57 @@ def _build(self):
                                   transform=ccrs.PlateCarree(), fontsize=10)
 
         for i, ob_type in enumerate(self.fields):
+            field_kwargs = {}
             if len(self.locations) > 1:
                 location = self.locations[i]
             else:
                 location = self.locations[0]
             if len(self.colors) > 1:
-                color = self.colors[i]
+                field_kwargs['color'] = self.colors[i]
             else:
-                color = self.colors[0]
+                field_kwargs['color'] = self.colors[0]
             if len(self.formats) > 1:
-                formats = self.formats[i]
+                field_kwargs['formatter'] = self.formats[i]
+            else:
+                field_kwargs['formatter'] = self.formats[0]
+            if len(self.plot_units) > 1:
+                field_kwargs['plot_units'] = self.plot_units[i]
             else:
-                formats = self.formats[0]
-            if formats is not None:
-                mapper = getattr(wx_symbols, str(formats), None)
+                field_kwargs['plot_units'] = self.plot_units[0]
+            if hasattr(self.data, 'units') and (field_kwargs['plot_units'] is not None):
+                parameter = data[ob_type][subset].values * units(self.data.units[ob_type])
+            else:
+                parameter = data[ob_type][subset]
+            if field_kwargs['formatter'] is not None:
+                mapper = getattr(wx_symbols, str(field_kwargs['formatter']), None)
                 if mapper is not None:
-                    self.handle.plot_symbol(location, data[ob_type][subset],
-                                            mapper, color=color)
+                    field_kwargs.pop('formatter')
+                    self.handle.plot_symbol(location, parameter,
+                                            mapper, **field_kwargs)
                 else:
-                    if formats == 'text':
-                        self.handle.plot_text(location, data[ob_type][subset], color=color)
+                    if self.formats[i] == 'text':
+                        self.handle.plot_text(location, data[ob_type][subset],
+                                              color=field_kwargs['color'])
                     else:
                         self.handle.plot_parameter(location, data[ob_type][subset],
-                                                   color=color, formatter=self.formats[i])
+                                                   **field_kwargs)
             else:
-                self.handle.plot_parameter(location, data[ob_type][subset], color=color)
+                field_kwargs.pop('formatter')
+                self.handle.plot_parameter(location, parameter, **field_kwargs)
+
         if self.vector_field[0] is not None:
-            kwargs = {'color': self.vector_field_color}
+            vector_kwargs = {}
+            vector_kwargs['color'] = self.vector_field_color
+            vector_kwargs['plot_units'] = self.vector_plot_units
+            if hasattr(self.data, 'units') and (vector_kwargs['plot_units'] is not None):
+                u = (data[self.vector_field[0]][subset].values
+                     * units(self.data.units[self.vector_field[0]]))
+                v = (data[self.vector_field[1]][subset].values
+                     * units(self.data.units[self.vector_field[1]]))
+            else:
+                vector_kwargs.pop('plot_units')
+                u = data[self.vector_field[0]][subset]
+                v = data[self.vector_field[1]][subset]
             if self.vector_field_length is not None:
-                kwargs['length'] = self.vector_field_length
-            self.handle.plot_barb(data[self.vector_field[0]][subset],
-                                  data[self.vector_field[1]][subset], **kwargs)
+                vector_kwargs['length'] = self.vector_field_length
+            self.handle.plot_barb(u, v, **vector_kwargs)

src/metpy/plots/station_plot.py

@@ -185,6 +185,8 @@ def plot_parameter(self, location, parameter, formatter='.0f', **kwargs):
             How to format the data as a string for plotting. If a string, it should be
             compatible with the :func:`format` builtin. If a callable, this should take a
             value and return a string. Defaults to '0.f'.
+        plot_units: `pint.unit`
+            Units to plot in (performing conversion if necessary). Defaults to given units.
         kwargs
             Additional keyword arguments to use for matplotlib's plotting functions.
 
@@ -194,6 +196,9 @@ def plot_parameter(self, location, parameter, formatter='.0f', **kwargs):
         plot_barb, plot_symbol, plot_text
 
         """
+        # If plot_units specified, convert the data to those units
+        plotting_units = kwargs.pop('plot_units', None)
+        parameter = self._scalar_plotting_units(parameter, plotting_units)
         if hasattr(parameter, 'units'):
             parameter = parameter.magnitude
         text = self._to_string_list(parameter, formatter)
@@ -266,7 +271,7 @@ def plot_barb(self, u, v, **kwargs):
 
         # If plot_units specified, convert the data to those units
         plotting_units = kwargs.pop('plot_units', None)
-        u, v = self._plotting_units(u, v, plotting_units)
+        u, v = self._vector_plotting_units(u, v, plotting_units)
 
         # Empirically determined
         pivot = 0.51 * np.sqrt(self.fontsize)
@@ -309,7 +314,7 @@ def plot_arrow(self, u, v, **kwargs):
 
         # If plot_units specified, convert the data to those units
         plotting_units = kwargs.pop('plot_units', None)
-        u, v = self._plotting_units(u, v, plotting_units)
+        u, v = self._vector_plotting_units(u, v, plotting_units)
 
         defaults = {'pivot': 'tail', 'scale': 20, 'scale_units': 'inches', 'width': 0.002}
         defaults.update(kwargs)
@@ -321,7 +326,7 @@ def plot_arrow(self, u, v, **kwargs):
         self.arrows = self.ax.quiver(self.x, self.y, u, v, **defaults)
 
     @staticmethod
-    def _plotting_units(u, v, plotting_units):
+    def _vector_plotting_units(u, v, plotting_units):
         """Handle conversion to plotting units for barbs and arrows."""
         if plotting_units:
             if hasattr(u, 'units') and hasattr(v, 'units'):
@@ -336,6 +341,17 @@ def _plotting_units(u, v, plotting_units):
         v = np.array(v)
         return u, v
 
+    @staticmethod
+    def _scalar_plotting_units(scalar_value, plotting_units):
+        """Handle conversion to plotting units for barbs and arrows."""
+        if plotting_units:
+            if hasattr(scalar_value, 'units'):
+                scalar_value = scalar_value.to(plotting_units)
+            else:
+                raise ValueError('To convert to plotting units, units must be attached to '
+                                 'scalar value being converted.')
+        return scalar_value
+
     def _make_kwargs(self, kwargs):
         """Assemble kwargs as necessary.
 

tests/plots/test_declarative.py

@@ -18,6 +18,7 @@
 
 from metpy.cbook import get_test_data
 from metpy.io import GiniFile
+from metpy.io.metar import parse_metar_file
 from metpy.plots import (BarbPlot, ContourPlot, FilledContourPlot, ImagePlot, MapPanel,
                          PanelContainer, PlotObs)
 # Fixtures to make sure we have the right backend
@@ -736,6 +737,48 @@ def test_declarative_upa_obs():
     return pc.figure
 
 
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.08)
+def test_declarative_upa_obs_convert_barb_units():
+    """Test making a full upperair observation plot."""
+    data = pd.read_csv(get_test_data('UPA_obs.csv', as_file_obj=False))
+    data.units = ''
+    data.units = {'pressure': 'hPa', 'height': 'meters', 'temperature': 'degC',
+                  'dewpoint': 'degC', 'direction': 'degrees', 'speed': 'knots',
+                  'station': None, 'time': None, 'u_wind': 'knots', 'v_wind': 'knots',
+                  'latitude': 'degrees', 'longitude': 'degrees'}
+
+    obs = PlotObs()
+    obs.data = data
+    obs.time = datetime(1993, 3, 14, 0)
+    obs.level = 500 * units.hPa
+    obs.fields = ['temperature', 'dewpoint', 'height']
+    obs.locations = ['NW', 'SW', 'NE']
+    obs.formats = [None, None, lambda v: format(v, '.0f')[:3]]
+    obs.vector_field = ('u_wind', 'v_wind')
+    obs.vector_field_length = 7
+    obs.vector_plot_units = 'm/s'
+    obs.reduce_points = 0
+
+    # Panel for plot with Map features
+    panel = MapPanel()
+    panel.layout = (1, 1, 1)
+    panel.area = (-124, -72, 20, 53)
+    panel.projection = 'lcc'
+    panel.layers = ['coastline', 'borders', 'states', 'land']
+    panel.plots = [obs]
+
+    # Bringing it all together
+    pc = PanelContainer()
+    pc.size = (15, 10)
+    pc.panels = [panel]
+
+    pc.draw()
+
+    obs.level = 300 * units.hPa
+
+    return pc.figure
+
+
 def test_attribute_error_time():
     """Make sure we get a useful error when the time variable is not found."""
     data = pd.read_csv(get_test_data('SFC_obs.csv', as_file_obj=False),
@@ -798,6 +841,76 @@ def test_attribute_error_station():
         pc.draw()
 
 
+@pytest.mark.mpl_image_compare(remove_text=True,
+                               tolerance={'2.1': 0.407}.get(MPL_VERSION, 0.022))
+def test_declarative_sfc_obs_change_units():
+    """Test making a surface observation plot."""
+    data = parse_metar_file(get_test_data('metar_20190701_1200.txt', as_file_obj=False),
+                            year=2019, month=7)
+
+    obs = PlotObs()
+    obs.data = data
+    obs.time = datetime(2019, 7, 1, 12)
+    obs.time_window = timedelta(minutes=15)
+    obs.level = None
+    obs.fields = ['air_temperature']
+    obs.color = ['black']
+    obs.plot_units = ['degF']
+
+    # Panel for plot with Map features
+    panel = MapPanel()
+    panel.layout = (1, 1, 1)
+    panel.projection = ccrs.PlateCarree()
+    panel.area = 'in'
+    panel.layers = ['states']
+    panel.plots = [obs]
+
+    # Bringing it all together
+    pc = PanelContainer()
+    pc.size = (10, 10)
+    pc.panels = [panel]
+
+    pc.draw()
+
+    return pc.figure
+
+
+@pytest.mark.mpl_image_compare(remove_text=True,
+                               tolerance={'2.1': 0.09}.get(MPL_VERSION, 0.022))
+def test_declarative_multiple_sfc_obs_change_units():
+    """Test making a surface observation plot."""
+    data = parse_metar_file(get_test_data('metar_20190701_1200.txt', as_file_obj=False),
+                            year=2019, month=7)
+
+    obs = PlotObs()
+    obs.data = data
+    obs.time = datetime(2019, 7, 1, 12)
+    obs.time_window = timedelta(minutes=15)
+    obs.level = None
+    obs.fields = ['air_temperature', 'dew_point_temperature', 'air_pressure_at_sea_level']
+    obs.locations = ['NW', 'W', 'NE']
+    obs.colors = ['red', 'green', 'black']
+    obs.reduce_points = 0.75
+    obs.plot_units = ['degF', 'degF', None]
+
+    # Panel for plot with Map features
+    panel = MapPanel()
+    panel.layout = (1, 1, 1)
+    panel.projection = ccrs.PlateCarree()
+    panel.area = 'in'
+    panel.layers = ['states']
+    panel.plots = [obs]
+
+    # Bringing it all together
+    pc = PanelContainer()
+    pc.size = (12, 12)
+    pc.panels = [panel]
+
+    pc.draw()
+
+    return pc.figure
+
+
 def test_save():
     """Test that our saving function works."""
     pc = PanelContainer()

tests/plots/test_station_plot.py

@@ -434,3 +434,38 @@ def test_symbol_pandas_timeseries():
     ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%-d'))
 
     return fig
+
+
+@pytest.mark.mpl_image_compare(tolerance=2.444, savefig_kwargs={'dpi': 300}, remove_text=True)
+def test_stationplot_unit_conversion():
+    """Test the StationPlot API."""
+    fig = plt.figure(figsize=(9, 9))
+
+    # testing data
+    x = np.array([1, 5])
+    y = np.array([2, 4])
+
+    # Make the plot
+    sp = StationPlot(fig.add_subplot(1, 1, 1), x, y, fontsize=16)
+    sp.plot_barb([20, 0], [0, -50])
+    sp.plot_text('E', ['KOKC', 'ICT'], color='blue')
+    sp.plot_parameter('NW', [10.5, 15] * units.degC, plot_units='degF', color='red')
+    sp.plot_symbol('S', [5, 7], high_clouds, color='green')
+
+    sp.ax.set_xlim(0, 6)
+    sp.ax.set_ylim(0, 6)
+
+    return fig
+
+
+def test_scalar_unit_conversion_exception():
+    """Test that errors are raise if unit conversion is requested on un-united data."""
+    T = 50
+    x_pos = np.array([0])
+    y_pos = np.array([0])
+
+    fig = plt.figure()
+    ax = fig.add_subplot(1, 1, 1)
+    stnplot = StationPlot(ax, x_pos, y_pos)
+    with pytest.raises(ValueError):
+        stnplot.plot_parameter('C', T, plot_units='degC')