Some CMIP6 support

both for autoguessing and long_name == cell index along (first|second) dimension

cf_xarray/criteria.py

@@ -5,6 +5,7 @@
 """
 
 
+import copy
 import re
 from typing import MutableMapping, Tuple
 
@@ -74,19 +75,20 @@
 }
 
 # "long_name" and "standard_name" criteria are the same. For convenience.
-coordinate_criteria["long_name"] = coordinate_criteria["standard_name"]
+coordinate_criteria["long_name"] = copy.deepcopy(coordinate_criteria["standard_name"])
+coordinate_criteria["long_name"]["X"] += ("cell index along first dimension",)
+coordinate_criteria["long_name"]["Y"] += ("cell index along second dimension",)
 
 #: regular expressions for guess_coord_axis
 regex = {
     "time": re.compile("\\bt\\b|(time|min|hour|day|week|month|year)[0-9]*"),
-    "vertical": re.compile(
-        "(z|nav_lev|gdep|lv_|bottom_top|sigma|h(ei)?ght|altitude|depth|"
+    "Z": re.compile(
+        "(z|nav_lev|gdep|lv_|[o]*lev|bottom_top|sigma|h(ei)?ght|altitude|depth|"
         "isobaric|pres|isotherm)[a-z_]*[0-9]*"
     ),
-    "Y": re.compile("y"),
+    "Y": re.compile("y|j|nlat|nj"),
     "latitude": re.compile("y?(nav_lat|lat|gphi)[a-z0-9]*"),
-    "X": re.compile("x"),
+    "X": re.compile("x|i|nlon|ni"),
     "longitude": re.compile("x?(nav_lon|lon|glam)[a-z0-9]*"),
 }
-regex["Z"] = regex["vertical"]
 regex["T"] = regex["time"]

cf_xarray/tests/test_accessor.py

@@ -780,9 +780,9 @@ def _make_names(prefixes):
         "nav_lev",
     ]
 )
-_X_NAMES = _make_names(["x"])
-_Y_NAMES = _make_names(["y"])
-_Z_NAMES = _VERTICAL_NAMES
+_X_NAMES = _make_names(["x", "nlon", "i", "ni"])
+_Y_NAMES = _make_names(["y", "nlat", "j", "nj"])
+_Z_NAMES = _VERTICAL_NAMES + ["olevel", "level", "zlevel"]
 _LATITUDE_NAMES = _make_names(["lat", "latitude", "gphi", "nav_lat"])
 _LONGITUDE_NAMES = _make_names(["lon", "longitude", "glam", "nav_lon"])
 
@@ -1193,3 +1193,24 @@ def test_differentiate_positive_upward(obj):
     obj.z.attrs["positive"] = "zzz"
     with pytest.raises(ValueError):
         obj.cf.differentiate("z", positive_upward=True)
+
+
+def test_cmip6_attrs():
+    da = xr.DataArray(
+        np.ones((10, 10)),
+        dims=("nlon", "nlat"),
+        coords={
+            "nlon": (
+                "nlon",
+                np.arange(10),
+                {"long_name": "cell index along first dimension"},
+            ),
+            "nlat": (
+                "nlat",
+                np.arange(10),
+                {"long_name": "cell index along second dimension"},
+            ),
+        },
+    )
+    assert da.cf.axes["X"] == ["nlon"]
+    assert da.cf.axes["Y"] == ["nlat"]