Updated example_concentration, and made estimation of pixel size x,y/lon,lat more precise

Author: knutfrode

examples/example_concentration.py

@@ -35,6 +35,13 @@
 ds_c.isel(time=12).number_area_concentration.plot()
 plt.show()
 
+#%%
+# Plot the number concentration (number/area) for surface oil only (elements where z=0)
+ds_surface = ds.where(ds.z==0).traj.concentration(grid)
+ds_surface.isel(time=12).number_area_concentration.plot()
+plt.title('Concentration of elements at surface')
+plt.show()
+
 #%% 
 # We see that the cell area decreases slightly away from equator.
 # This is accounted for when calculating area/volume concentration.

trajan/traj.py

@@ -1248,7 +1248,7 @@ def make_grid(self, dx, dy=None, z=None,
 
         if self.crs.is_geographic:
             # dx is given in meters, but must be converted to degrees
-            dy = dy / 111000
+            dy = dy / 111500
             dx = dy / np.cos(np.radians((ymin + ymax)/2)).values
             xdimname = 'lon'
             ydimname = 'lat'