Merge pull request Unidata#1267 from kgoebber/update_declarative_options

adds functionality to obs declarative

src/metpy/plots/declarative.py

@@ -1284,6 +1284,7 @@ class PlotObs(HasTraits):
       * colors (optional)
       * vector_field (optional)
       * vector_field_color (optional)
+      * vector_field_length (optional)
       * reduce_points (optional)
     """
 
@@ -1356,6 +1357,11 @@ class PlotObs(HasTraits):
     vector_field_color = Unicode('black', allow_none=True)
     vector_field_color.__doc__ = """String color name to plot the vector. (optional)"""
 
+    vector_field_length = Int(default_value=None, allow_none=True)
+    vector_field_length.__doc__ = """Integer value to set the length of the plotted vector.
+    (optional)
+    """
+
     reduce_points = Float(default_value=0)
     reduce_points.__doc__ = """Float to reduce number of points plotted. (optional)"""
 
@@ -1493,8 +1499,12 @@ def _build(self):
                 color = self.colors[i]
             else:
                 color = self.colors[0]
-            if self.formats[i] is not None:
-                mapper = getattr(wx_symbols, str(self.formats[i]), None)
+            if len(self.formats) > 1:
+                formats = self.formats[i]
+            else:
+                formats = self.formats[0]
+            if formats is not None:
+                mapper = getattr(wx_symbols, str(formats), None)
                 if mapper is not None:
                     self.handle.plot_symbol(location, data[ob_type][subset],
                                             mapper, color=color)
@@ -1504,5 +1514,7 @@ def _build(self):
             else:
                 self.handle.plot_parameter(location, data[ob_type][subset], color=color)
         if self.vector_field[0] is not None:
+            kwargs = ({'length': self.vector_field_length}
+                      if self.vector_field_length is not None else {})
             self.handle.plot_barb(data[self.vector_field[0]][subset],
-                                  data[self.vector_field[1]][subset])
+                                  data[self.vector_field[1]][subset], **kwargs)

tests/plots/test_declarative.py

@@ -536,6 +536,7 @@ def test_declarative_upa_obs():
     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.reduce_points = 0
 
     # Panel for plot with Map features