add some comments

Author: Jeff Whitaker

examples/test_rotpole.py

@@ -23,6 +23,16 @@
 plt.title('rotated pole data in polar stere map')
 
 plt.figure()
+# o_lon_p, o_lat_p: true lat/lon of pole in rotated coordinate system
+# mapping to CF metadata convention:
+# grid_north_pole_longitude = normalize180(180 + lon_0), where normalize180
+#  is a function that maps to interval [-180,180], i.e. 
+#    def normalize180(angle):
+#        if angle >  180: angle = angle+360
+#        if angle < -180: angle = angle+360
+#        return angle
+# grid_north_pole_latitude = o_lat_p
+# north_pole_grid_longitude = o_lon_p (optional, assumed zero if not present)
 m = Basemap(projection='rotpole',lon_0=rotpole.grid_north_pole_longitude-180.,\
             o_lon_p=rotpole.north_pole_grid_longitude,\
             o_lat_p=rotpole.grid_north_pole_latitude,\
@@ -42,6 +52,8 @@
             o_lat_p=rotpole.grid_north_pole_latitude,\
             llcrnry = rlats[0,0], urcrnry = rlats[-1,-1],\
             llcrnrx = rlons[0,0], urcrnrx = rlons[-1,-1],resolution='c')
+print m.llcrnrx,m.llcrnry
+print m.urcrnrx,m.urcrnry
 x,y = m(lons,lats)
 m.drawcoastlines()
 m.contourf(x,y,data,20)