Example overlay plot (#27)

docs/examples/plot_wind_overlay.py

@@ -0,0 +1,50 @@
+# -*- coding: utf-8 -*-
+"""
+=============
+Plot overlays
+=============
+
+Add contours and wind arrows to a salem plot
+
+"""
+
+import salem
+import numpy as np
+import matplotlib.pyplot as plt
+
+# get the data at the latest time step
+ds = salem.open_wrf_dataset(salem.get_demo_file('wrfout_d01.nc')).isel(time=-1)
+
+# get the wind data at 10000 m a.s.l.
+u = ds.salem.wrf_zlevel('U', 10000.)
+v = ds.salem.wrf_zlevel('V', 10000.)
+ws = ds.salem.wrf_zlevel('WS', 10000.)
+
+# get the axes ready
+f, ax = plt.subplots()
+
+# plot the salem map background, make countries in grey
+smap = ds.salem.get_map(countries=False)
+smap.set_shapefile(countries=True, color='grey')
+smap.plot(ax=ax)
+
+# transform the coordinates to the map reference system and contour the data
+xx, yy = smap.grid.transform(ws.west_east.values, ws.south_north.values,
+                             crs=ws.salem.grid.proj)
+cs = ax.contour(xx, yy, ws, cmap='viridis', levels=np.arange(0, 81, 10),
+                linewidths=2)
+
+# Quiver only every 7th grid point
+u = u[4::7, 4::7]
+v = v[4::7, 4::7]
+
+# transform their coordinates to the map reference system and plot the arrows
+xx, yy = smap.grid.transform(u.west_east.values, u.south_north.values,
+                             crs=u.salem.grid.proj)
+xx, yy = np.meshgrid(xx, yy)
+qu = ax.quiver(xx, yy, u.values, v.values)
+qk = plt.quiverkey(qu, 0.7, 0.95, 50, '50 m s$^{-1}$',
+                   labelpos='E', coordinates='figure')
+
+# done!
+plt.show()

salem/graphics.py

@@ -645,6 +645,7 @@ def set_shapefile(self, shape=None, countries=False, oceans=False,
             kwargs.setdefault('colors', (0.08984375, 0.65625, 0.8515625))
             return self.set_shapefile(shapefiles['rivers'], **kwargs)
         if countries:
+            kwargs.setdefault('zorder', 98)
             return self.set_shapefile(shapefiles['world_borders'], **kwargs)
 
         # Reset?
@@ -786,6 +787,7 @@ def set_lonlat_contours(self, interval=None, xinterval=None,
         # Done
         kwargs.setdefault('colors', 'gray')
         kwargs.setdefault('linestyles', 'dashed')
+        kwargs.setdefault('zorder', 99)
         self.ll_contour_kw = kwargs
 
     def _shading_base(self, slope=None, relief_factor=0.7):