ENH: Add cartesian projection (#168)

* Added cartesian projection

* Added comment

* Changed idealized treatment to skip CRS creation

* Added ideal.nc test file

* Added test for grid of idealized WRF data

* Removed ideal from being tested for grid_mapping existance

tests/test_grid.py

@@ -86,3 +86,15 @@ def test_grid_construction_against_own_latlon(test_grid, cf_grid_mapping_name):
                 decimal=2,
                 err_msg=f"Computed {varname + '_M'} does not match with raw output",
             )
+
+
+@pytest.mark.parametrize(
+    'test_grid',
+    [
+        'ideal',
+    ],
+    indirect=True,
+)
+def test_ideal_grid(test_grid):
+    grid_params = _wrf_grid_from_dataset(test_grid)
+    assert grid_params['crs'] is None

tests/test_postprocess.py

@@ -61,7 +61,7 @@ def test_include_projection_coordinates(sample_dataset):
 
 
 @pytest.mark.parametrize(
-    'sample_dataset', set(xwrf.tutorial.sample_datasets.keys()) - {'tiny'}, indirect=True
+    'sample_dataset', set(xwrf.tutorial.sample_datasets.keys()) - {'tiny', 'ideal'}, indirect=True
 )
 def test_grid_mapping_is_in_all_vars(sample_dataset):
     dataset = xwrf.postprocess._include_projection_coordinates(sample_dataset)

xwrf/grid.py

@@ -38,7 +38,10 @@ def _wrf_grid_from_dataset(ds: xr.Dataset) -> Mapping[Hashable, pyproj.CRS | np.
         'center_lon': cen_lon,
     }
 
-    if proj_id == 1:
+    if proj_id == 0:
+        # Idealized Run, Cartesian grid
+        pass
+    elif proj_id == 1:
         # Lambert
         pargs['proj'] = 'lcc'
         del pargs['center_lon']
@@ -57,14 +60,20 @@ def _wrf_grid_from_dataset(ds: xr.Dataset) -> Mapping[Hashable, pyproj.CRS | np.
     else:
         raise NotImplementedError(f'WRF proj not implemented yet: {proj_id}')
 
-    # Construct the pyproj CRS (letting errors fail through)
-    crs = pyproj.CRS(pargs)
+    if proj_id == 0:
+        # As this is an idealized run, there is no physical CRS
+        crs = None
+        e, n = cen_lon, cen_lat
+    else:
+        # Construct the pyproj CRS (letting errors fail through)
+        crs = pyproj.CRS(pargs)
+
+        # Get grid specifications
+        trf = pyproj.Transformer.from_crs(wgs84, crs, always_xy=True)
+        e, n = trf.transform(cen_lon, cen_lat)
 
-    # Get grid specifications
-    trf = pyproj.Transformer.from_crs(wgs84, crs, always_xy=True)
     nx = ds.sizes['west_east']
     ny = ds.sizes['south_north']
-    e, n = trf.transform(cen_lon, cen_lat)
     x0 = -(nx - 1) / 2.0 * dx + e  # DL corner
     y0 = -(ny - 1) / 2.0 * dy + n  # DL corner
 

xwrf/postprocess.py

@@ -105,11 +105,12 @@ def _include_projection_coordinates(ds: xr.Dataset) -> xr.Dataset:
     for dim in horizontal_dims:
         ds[dim] = (dim, grid_components[dim], config.get(f'cf_attribute_map.{dim}'))
 
-    # Include CRS
-    ds['wrf_projection'] = (tuple(), grid_components['crs'], grid_components['crs'].to_cf())
-    for varname in ds.data_vars:
-        if any(dim in ds[varname].dims for dim in horizontal_dims):
-            ds[varname].attrs['grid_mapping'] = 'wrf_projection'
+    # Include CRS if we don't have idealized coords
+    if grid_components['crs'] is not None:
+        ds['wrf_projection'] = (tuple(), grid_components['crs'], grid_components['crs'].to_cf())
+        for varname in ds.data_vars:
+            if any(dim in ds[varname].dims for dim in horizontal_dims):
+                ds[varname].attrs['grid_mapping'] = 'wrf_projection'
 
     return ds
 

xwrf/tutorial.py

@@ -38,6 +38,7 @@ def _construct_cache_dir(path):
     'tiny': 'data/tiny.nc',
     'met_em_sample': 'data/met_em.d01.2005-08-28_12:00:00.nc',
     'wrfout': 'data/wrfout_d01_2099-10-01_00:00:00.nc',
+    'ideal': 'data/ideal.nc',
 }
 
 
@@ -65,6 +66,7 @@ def open_dataset(
     * ``"mercator"``
     * ``"met_em_sample"``
     * ``"wrfout"``
+    * ``"ideal"``
 
     Parameters
     ----------