Merge pull request #1331 from kgoebber/new_add_scale

Adds a scale attribute for declarative syntax

src/metpy/plots/declarative.py

@@ -790,6 +790,14 @@ class Plots2D(HasTraits):
     plotting using the MetPy Units module.
     """
 
+    scale = Float(default_value=1e0)
+    scale.__doc__ = """Scale the field to be plotted by the value given.
+
+    This attribute will scale the field by multiplying by the scale. For example, to
+    scale vorticity to be whole values for contouring you could set the scale to 1e5, such that
+    the data values will be scaled by 10^5.
+    """
+
     @property
     def _cmap_obj(self):
         """Return the colormap object.
@@ -929,7 +937,7 @@ def griddata(self):
 
             if self.plot_units is not None:
                 data_subset = data_subset.metpy.convert_units(self.plot_units)
-            self._griddata = data_subset
+            self._griddata = data_subset * self.scale
 
         return self._griddata
 

tests/plots/test_declarative.py

@@ -439,6 +439,35 @@ def test_declarative_barb_earth_relative():
     return pc.figure
 
 
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.612)
+def test_declarative_gridded_scale():
+    """Test making a contour plot."""
+    import numpy as np
+    data = xr.open_dataset(get_test_data('NAM_test.nc', as_file_obj=False))
+
+    contour = ContourPlot()
+    contour.data = data
+    contour.field = 'Geopotential_height_isobaric'
+    contour.level = 300 * units.hPa
+    contour.linewidth = 2
+    contour.contours = np.arange(0, 2000, 12).tolist()
+    contour.scale = 1e-1
+    contour.clabels = True
+
+    panel = MapPanel()
+    panel.area = (-124, -72, 20, 53)
+    panel.projection = 'lcc'
+    panel.layers = ['coastline', 'borders', 'usstates']
+    panel.plots = [contour]
+
+    pc = PanelContainer()
+    pc.size = (8, 8)
+    pc.panels = [panel]
+    pc.draw()
+
+    return pc.figure
+
+
 @pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.347)
 def test_declarative_barb_gfs():
     """Test making a contour plot."""