Now throws a warning if latlon is set to True, but there is no coordinate metadata for vertcross and interpline. Fixes #38.

src/wrf/interp.py

@@ -199,6 +199,15 @@ def vertcross(field3d, vert, levels=None, missing=default_fill(np.float64),
             horizontal line and include this information in the metadata 
             (if enabled). This can be helpful for plotting.  Default is False.
             
+            Note:
+            
+                Currently, *field3d* must be of type :class:`xarray.DataArray` 
+                and contain coordinate information in order to generate the 
+                latitude and longitude coordinates along the line if 
+                *latlon* is set to True. Otherwise, a warning will be issued,
+                and the latitude and longitude information will not be 
+                present.
+             
         cache (:obj:`dict`, optional): A dictionary of (varname, ndarray) 
             that can be used to supply pre-extracted NetCDF variables to the 
             computational routines.  It is primarily used for internal 
@@ -365,6 +374,15 @@ def interpline(field2d, pivot_point=None,
             horizontal line and include this information in the metadata 
             (if enabled).  This can be helpful for plotting.  Default is False.
             
+            Note:
+            
+                Currently, *field2d* must be of type :class:`xarray.DataArray` 
+                and contain coordinate information in order to generate the 
+                latitude and longitude coordinates along the line if 
+                *latlon* is set to True. Otherwise, a warning will be issued,
+                and the latitude and longitude information will not be 
+                present.
+            
         cache (:obj:`dict`, optional): A dictionary of (varname, ndarray) 
             that can be used to supply pre-extracted NetCDF variables to the 
             computational routines.  It is primarily used for internal 

src/wrf/metadecorators.py

@@ -1,5 +1,6 @@
 from __future__ import (absolute_import, division, print_function, 
                         unicode_literals)
+import warnings
 import wrapt 
 from collections import OrderedDict
 
@@ -1022,6 +1023,8 @@ def _set_cross_meta(wrapped, instance, args, kwargs):
                     outcoords["xy_loc"] = (loc_dimnames, latlon_loc)
                     
             else:
+                warnings.warn("'latlon' is set to True, but 'field3d' "
+                "             contains no coordinate information")
                 outcoords["xy_loc"] = ("cross_line_idx", np.asarray(tuple(
                                                 CoordPair(xy[i,0], xy[i,1]) 
                                           for i in py3range(xy.shape[-2]))))
@@ -1034,6 +1037,10 @@ def _set_cross_meta(wrapped, instance, args, kwargs):
         outcoords["vertical"] = z_var2d[:]
         
     else:
+        if inc_latlon:
+            warnings.warn("'latlon' is set to True, but 'field3d' is "
+                          "not of type xarray.DataArray and contains no "
+                          "coordinate information")
         outname = "field3d_cross"
         outattrs = OrderedDict()
     
@@ -1229,6 +1236,8 @@ def _set_line_meta(wrapped, instance, args, kwargs):
                     outcoords["xy_loc"] = (loc_dimnames, latlon_loc)
                     
             else:
+                warnings.warn("'latlon' is set to True, but 'field2d' "
+                              "contains no coordinate information")
                 outcoords["xy_loc"] = ("line_idx", np.asarray(tuple(
                                                 CoordPair(xy[i,0], xy[i,1]) 
                                           for i in py3range(xy.shape[-2]))))
@@ -1239,6 +1248,10 @@ def _set_line_meta(wrapped, instance, args, kwargs):
                                           for i in py3range(xy.shape[-2]))))
         
     else:
+        if inc_latlon:
+            warnings.warn("'latlon' is set to True, but 'field2d' is "
+                          "not of type xarray.DataArray and contains no "
+                          "coordinate information")
         outname = "field2d_line"
         outattrs = OrderedDict()