From 58195096ba1d4ecaec8c294928c09c42fe652a0f Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Tue, 16 Sep 2025 18:11:55 +0200
Subject: [PATCH 01/27] initial version of a convention converter

---
 xdggs/accessor.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index d0656c35..6db69eea 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -1,6 +1,7 @@
 import numpy.typing as npt
 import xarray as xr
 
+from xdggs import conventions
 from xdggs.grid import DGGSInfo
 from xdggs.index import DGGSIndex
 from xdggs.plotting import explore
@@ -234,3 +235,31 @@ def explore(self, *, cmap="viridis", center=None, alpha=None, coords=None):
             alpha=alpha,
             coords=coords,
         )
+
+    def as_convention(self, *, convention: str):
+        """Convert the dataset to a specific convention
+
+        Parameters
+        ----------
+        convention : str
+            The name of the convention. Supported are:
+            - "easygems": ``grid_mapping`` coordinate and ``cell`` dimension and ``cell`` coordinate with a `pandas` index.
+            - "cf": ``grid_mapping`` coordinate with ``cell_index`` coordinate and ``cell`` dimension.
+            - "xdggs": ``cell_ids`` coordinate with grid metadata and a ``cells`` coordinate.
+
+        Returns
+        -------
+        obj : xr.DataArray or xr.Dataset
+            The object converted to the given dimension.
+        """
+        converters = {
+            "easygems": conventions.easygems,
+            "cf": conventions.cf,
+            "xdggs": conventions.xdggs,
+        }
+
+        converter = converters.get(convention)
+        if converter is None:
+            raise ValueError(f"unknown convention: {convention}")
+
+        return converter(self._obj)

From f3a51ab8f8ea8ef289457473c38d2f23cdedce80 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Tue, 16 Sep 2025 18:12:07 +0200
Subject: [PATCH 02/27] implement the `easygems` convention

---
 xdggs/conventions.py | 51 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 xdggs/conventions.py

diff --git a/xdggs/conventions.py b/xdggs/conventions.py
new file mode 100644
index 00000000..f920ec26
--- /dev/null
+++ b/xdggs/conventions.py
@@ -0,0 +1,51 @@
+import xarray as xr
+
+
+def call_on_dataset(func, obj, name, *args, kwargs=None):
+    if kwargs is None:
+        kwargs = {}
+
+    if isinstance(obj, xr.DataArray):
+        ds = obj._to_temp_dataset()
+    else:
+        ds = obj
+
+    result = func(ds, *args, **kwargs)
+
+    if isinstance(obj, xr.DataArray):
+        return xr.DataArray._from_temp_dataset(result, name=obj.name)
+    else:
+        return result
+
+
+def easygems(obj):
+    orders = {"nested": "nest", "ring": "ring"}
+
+    def _convert(ds):
+        grid_info = ds.dggs.grid_info
+        dim = ds.dggs.index._dim
+        coord = ds.dggs._name
+
+        order = orders.get(grid_info.indexing_scheme)
+        if order is None:
+            raise ValueError(f"easygems: unsupported indexing scheme: {order}")
+
+        crs = xr.Variable(
+            (),
+            0,
+            {
+                "grid_mapping_name": "healpix",
+                "healpix_nside": grid_info.nside,
+                "healpix_order": order,
+            },
+        )
+
+        return (
+            ds.assign_coords(crs=crs)
+            .drop_indexes(coord)
+            .rename_dims({dim: "cell"})
+            .rename_vars({coord: "cell"})
+            .set_xindex("cell")
+        )
+
+    return call_on_dataset(_convert, obj)

From d7636d3d67fa05e4f1b5ef3dfd8d9e5ead7152a5 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 17 Sep 2025 12:05:30 +0200
Subject: [PATCH 03/27] implement a generalized cf convention

---
 xdggs/conventions.py | 57 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 47 insertions(+), 10 deletions(-)

diff --git a/xdggs/conventions.py b/xdggs/conventions.py
index f920ec26..b513bbd1 100644
--- a/xdggs/conventions.py
+++ b/xdggs/conventions.py
@@ -1,7 +1,18 @@
+import numpy as np
 import xarray as xr
 
+from xdggs.utils import GRID_REGISTRY
 
-def call_on_dataset(func, obj, name, *args, kwargs=None):
+
+def infer_grid_name(index):
+    for name, cls in GRID_REGISTRY.items():
+        if cls is type(index):
+            return name
+
+    raise ValueError("unknown index")
+
+
+def call_on_dataset(func, obj, *args, kwargs=None):
     if kwargs is None:
         kwargs = {}
 
@@ -30,15 +41,12 @@ def _convert(ds):
         if order is None:
             raise ValueError(f"easygems: unsupported indexing scheme: {order}")
 
-        crs = xr.Variable(
-            (),
-            0,
-            {
-                "grid_mapping_name": "healpix",
-                "healpix_nside": grid_info.nside,
-                "healpix_order": order,
-            },
-        )
+        metadata = {
+            "grid_mapping_name": "healpix",
+            "healpix_nside": grid_info.nside,
+            "healpix_order": order,
+        }
+        crs = xr.Variable((), np.int8(0), metadata)
 
         return (
             ds.assign_coords(crs=crs)
@@ -49,3 +57,32 @@ def _convert(ds):
         )
 
     return call_on_dataset(_convert, obj)
+
+
+def cf(obj):
+    def _convert(ds):
+        grid_info = ds.dggs.grid_info
+        dim = ds.dggs.index._dim
+        coord = ds.dggs._name
+
+        grid_name = infer_grid_name(ds.dggs.index)
+        metadata = grid_info.to_dict() | {"grid_mapping_name": grid_name}
+        metadata["refinement_level"] = metadata.pop("level")
+
+        crs = xr.Variable((), np.int8(0), metadata)
+
+        additional_var_attrs = {"coordinates": coord, "grid_mapping": "crs"}
+        coord_attrs = {"standard_name": "healpix_index", "units": "1"}
+
+        new = ds.copy(deep=False)
+        for key, var in new.variables.items():
+            if key == coord or dim not in var.dims:
+                continue
+
+            var.attrs |= additional_var_attrs
+
+        new[coord].attrs |= coord_attrs
+
+        return new.assign_coords({"crs": crs})
+
+    return call_on_dataset(_convert, obj)

From 433e75986deccb503eeedfe6b1ba44ac5148275d Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 17 Sep 2025 12:08:09 +0200
Subject: [PATCH 04/27] implement a converter to the `xdggs` convention

---
 xdggs/conventions.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xdggs/conventions.py b/xdggs/conventions.py
index b513bbd1..01e59481 100644
--- a/xdggs/conventions.py
+++ b/xdggs/conventions.py
@@ -86,3 +86,15 @@ def _convert(ds):
         return new.assign_coords({"crs": crs})
 
     return call_on_dataset(_convert, obj)
+
+
+def xdggs(obj):
+    def _convert(ds):
+        coord = ds.dggs._name
+
+        grid_name = infer_grid_name(ds.dggs.index)
+        metadata = {"grid_name": grid_name} | ds.dggs.grid_info.to_dict()
+
+        return ds.assign_coords({coord: lambda ds: ds[coord].assign_attrs(metadata)})
+
+    return call_on_dataset(_convert, obj)

From 7234042491658aefab2287e4f8582f069229328a Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 17 Sep 2025 12:08:27 +0200
Subject: [PATCH 05/27] don't require `convention` as a public kwarg

---
 xdggs/accessor.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index 6db69eea..a6170c7e 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -236,7 +236,7 @@ def explore(self, *, cmap="viridis", center=None, alpha=None, coords=None):
             coords=coords,
         )
 
-    def as_convention(self, *, convention: str):
+    def as_convention(self, convention: str):
         """Convert the dataset to a specific convention
 
         Parameters

From 55b05668251b35cb7db163cb995d99f86316994e Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 14:47:49 +0200
Subject: [PATCH 06/27] refactor the conventions module

---
 xdggs/conventions/__init__.py                 | 23 ++++++++++++
 xdggs/conventions/registry.py                 | 36 ++++++++++++++++++
 .../writers.py}                               | 37 ++++++-------------
 xdggs/utils.py                                | 19 ++++++++++
 4 files changed, 90 insertions(+), 25 deletions(-)
 create mode 100644 xdggs/conventions/__init__.py
 create mode 100644 xdggs/conventions/registry.py
 rename xdggs/{conventions.py => conventions/writers.py} (84%)

diff --git a/xdggs/conventions/__init__.py b/xdggs/conventions/__init__.py
new file mode 100644
index 00000000..f624f47e
--- /dev/null
+++ b/xdggs/conventions/__init__.py
@@ -0,0 +1,23 @@
+from xdggs.conventions.registry import decoders as _decoders
+from xdggs.conventions.registry import encoders as _encoders  # noqa: F401
+from xdggs.conventions.registry import (
+    register_decoder,
+    register_encoder,
+)
+
+
+class DecoderError(Exception):
+    pass
+
+
+def detect_convention_decoder(obj, grid_info, name):
+    for name, decoder in _decoders.items():
+        try:
+            return decoder(obj, grid_info=grid_info, name=name)
+        except DecoderError:
+            pass
+
+    raise ValueError("cannot detect a matching convention")
+
+
+__all__ = ["register_decoder", "register_encoder"]
diff --git a/xdggs/conventions/registry.py b/xdggs/conventions/registry.py
new file mode 100644
index 00000000..c28913f6
--- /dev/null
+++ b/xdggs/conventions/registry.py
@@ -0,0 +1,36 @@
+import warnings
+
+decoders = {}
+encoders = {}
+
+
+class DecoderWarning(UserWarning):
+    pass
+
+
+def register_decoder(name):
+    def register(func):
+        if name in decoders:
+            warnings.warn(
+                DecoderWarning(f"Overwriting existing convention decoder {name!r}.")
+            )
+
+        decoders[name] = func
+
+        return func
+
+    return register
+
+
+def register_encoder(name):
+    def register(func):
+        if name in decoders:
+            warnings.warn(
+                DecoderWarning(f"Overwriting existing convention encoder {name!r}.")
+            )
+
+        encoders[name] = func
+
+        return func
+
+    return register
diff --git a/xdggs/conventions.py b/xdggs/conventions/writers.py
similarity index 84%
rename from xdggs/conventions.py
rename to xdggs/conventions/writers.py
index 01e59481..507b728f 100644
--- a/xdggs/conventions.py
+++ b/xdggs/conventions/writers.py
@@ -1,7 +1,8 @@
 import numpy as np
 import xarray as xr
 
-from xdggs.utils import GRID_REGISTRY
+from xdggs.registry import register_encoder
+from xdggs.utils import GRID_REGISTRY, call_on_dataset
 
 
 def infer_grid_name(index):
@@ -12,23 +13,20 @@ def infer_grid_name(index):
     raise ValueError("unknown index")
 
 
-def call_on_dataset(func, obj, *args, kwargs=None):
-    if kwargs is None:
-        kwargs = {}
+@register_encoder("xdggs")
+def xdggs(obj):
+    def _convert(ds):
+        coord = ds.dggs._name
 
-    if isinstance(obj, xr.DataArray):
-        ds = obj._to_temp_dataset()
-    else:
-        ds = obj
+        grid_name = infer_grid_name(ds.dggs.index)
+        metadata = {"grid_name": grid_name} | ds.dggs.grid_info.to_dict()
 
-    result = func(ds, *args, **kwargs)
+        return ds.assign_coords({coord: lambda ds: ds[coord].assign_attrs(metadata)})
 
-    if isinstance(obj, xr.DataArray):
-        return xr.DataArray._from_temp_dataset(result, name=obj.name)
-    else:
-        return result
+    return call_on_dataset(_convert, obj)
 
 
+@register_encoder("easygems")
 def easygems(obj):
     orders = {"nested": "nest", "ring": "ring"}
 
@@ -59,6 +57,7 @@ def _convert(ds):
     return call_on_dataset(_convert, obj)
 
 
+@register_encoder("cf")
 def cf(obj):
     def _convert(ds):
         grid_info = ds.dggs.grid_info
@@ -86,15 +85,3 @@ def _convert(ds):
         return new.assign_coords({"crs": crs})
 
     return call_on_dataset(_convert, obj)
-
-
-def xdggs(obj):
-    def _convert(ds):
-        coord = ds.dggs._name
-
-        grid_name = infer_grid_name(ds.dggs.index)
-        metadata = {"grid_name": grid_name} | ds.dggs.grid_info.to_dict()
-
-        return ds.assign_coords({coord: lambda ds: ds[coord].assign_attrs(metadata)})
-
-    return call_on_dataset(_convert, obj)
diff --git a/xdggs/utils.py b/xdggs/utils.py
index aec20428..d24ff5aa 100644
--- a/xdggs/utils.py
+++ b/xdggs/utils.py
@@ -1,3 +1,5 @@
+import xarray as xr
+
 GRID_REGISTRY = {}
 
 
@@ -17,3 +19,20 @@ def _extract_cell_id_variable(variables):
     dim = next(iter(var.dims))
 
     return name, var, dim
+
+
+def call_on_dataset(func, obj, *args, kwargs=None):
+    if kwargs is None:
+        kwargs = {}
+
+    if isinstance(obj, xr.DataArray):
+        ds = obj._to_temp_dataset()
+    else:
+        ds = obj
+
+    result = func(ds, *args, **kwargs)
+
+    if isinstance(obj, xr.DataArray):
+        return xr.DataArray._from_temp_dataset(result, name=obj.name)
+    else:
+        return result

From e9474b91ca0b74de524dc92ce6ada094db988fdd Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 16:05:02 +0200
Subject: [PATCH 07/27] refactor the decoding machinery

---
 xdggs/accessor.py                             | 26 ++++++++++-----
 xdggs/conventions/__init__.py                 |  6 ++--
 xdggs/conventions/decoders.py                 | 33 +++++++++++++++++++
 xdggs/conventions/{writers.py => encoders.py} |  2 +-
 4 files changed, 55 insertions(+), 12 deletions(-)
 create mode 100644 xdggs/conventions/decoders.py
 rename xdggs/conventions/{writers.py => encoders.py} (97%)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index a6170c7e..651380ae 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -30,7 +30,9 @@ def __init__(self, obj: xr.Dataset | xr.DataArray):
         self._name = name
         self._index = index
 
-    def decode(self, grid_info=None, *, name="cell_ids") -> xr.Dataset | xr.DataArray:
+    def decode(
+        self, grid_info=None, *, name="cell_ids", convention=None
+    ) -> xr.Dataset | xr.DataArray:
         """decode the DGGS cell ids
 
         Parameters
@@ -46,13 +48,21 @@ def decode(self, grid_info=None, *, name="cell_ids") -> xr.Dataset | xr.DataArra
         obj : xarray.DataArray or xarray.Dataset
             The object with a DGGS index on the cell id coordinate.
         """
-        var = self._obj[name]
-        if isinstance(grid_info, DGGSInfo):
-            grid_info = grid_info.to_dict()
-        if isinstance(grid_info, dict):
-            var.attrs = grid_info
-
-        return self._obj.drop_indexes(name, errors="ignore").set_xindex(name, DGGSIndex)
+        if convention is None:
+            decoder = conventions.detect_decoder
+        elif callable(convention):
+            decoder = convention
+        else:
+            decoder = conventions.decoders.get(convention)
+            if decoder is None:
+                valid_names = conventions.decoders.keys()
+                raise ValueError(
+                    f"unknown convention: {convention}."
+                    f" Choose a known convention: {', '.join(valid_names)}"
+                )
+
+        coords = decoder(self._obj, grid_info=grid_info, name=name)
+        return self._obj.assign_coords(coords)
 
     @property
     def index(self) -> DGGSIndex:
diff --git a/xdggs/conventions/__init__.py b/xdggs/conventions/__init__.py
index f624f47e..4674b43c 100644
--- a/xdggs/conventions/__init__.py
+++ b/xdggs/conventions/__init__.py
@@ -1,5 +1,5 @@
+from xdggs.conventions import decoders, encoders  # noqa: F401
 from xdggs.conventions.registry import decoders as _decoders
-from xdggs.conventions.registry import encoders as _encoders  # noqa: F401
 from xdggs.conventions.registry import (
     register_decoder,
     register_encoder,
@@ -10,8 +10,8 @@ class DecoderError(Exception):
     pass
 
 
-def detect_convention_decoder(obj, grid_info, name):
-    for name, decoder in _decoders.items():
+def detect_decoder(obj, grid_info, name):
+    for decoder_name, decoder in _decoders.items():
         try:
             return decoder(obj, grid_info=grid_info, name=name)
         except DecoderError:
diff --git a/xdggs/conventions/decoders.py b/xdggs/conventions/decoders.py
new file mode 100644
index 00000000..e9cd2918
--- /dev/null
+++ b/xdggs/conventions/decoders.py
@@ -0,0 +1,33 @@
+import xarray as xr
+
+from xdggs.conventions.registry import register_decoder
+from xdggs.grid import DGGSInfo
+from xdggs.utils import GRID_REGISTRY
+
+
+@register_decoder("xdggs")
+def xdggs(obj, grid_info, name):
+    try:
+        var = obj[name]
+    except IndexError:
+        raise ValueError("Cannot find the cell ids coordinate")
+
+    if len(var.dims) != 1:
+        # TODO: allow 0D
+        raise ValueError("cell id coordinate must be 1D")
+    [dim] = var.dims
+
+    if grid_info is None:
+        grid_info = var.attrs
+    elif isinstance(grid_info, DGGSInfo):
+        # TODO: avoid serializing / deserializing cycle
+        grid_info = grid_info.to_dict()
+
+    grid_name = grid_info["grid_name"]
+    if grid_name not in GRID_REGISTRY:
+        raise ValueError(f"unknown grid name: {grid_name}")
+    index_cls = GRID_REGISTRY[grid_name]
+
+    index = index_cls.from_variables({name: var}, options=grid_info)
+
+    return xr.Coordinates({name: var.variable}, indexes={name: index})
diff --git a/xdggs/conventions/writers.py b/xdggs/conventions/encoders.py
similarity index 97%
rename from xdggs/conventions/writers.py
rename to xdggs/conventions/encoders.py
index 507b728f..06203dc9 100644
--- a/xdggs/conventions/writers.py
+++ b/xdggs/conventions/encoders.py
@@ -1,7 +1,7 @@
 import numpy as np
 import xarray as xr
 
-from xdggs.registry import register_encoder
+from xdggs.conventions.registry import register_encoder
 from xdggs.utils import GRID_REGISTRY, call_on_dataset
 
 

From 8e33eb5ef40ef7d02ca5ae4d9e6bc0f414267100 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 16:05:53 +0200
Subject: [PATCH 08/27] typo

---
 xdggs/conventions/registry.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xdggs/conventions/registry.py b/xdggs/conventions/registry.py
index c28913f6..391ca01b 100644
--- a/xdggs/conventions/registry.py
+++ b/xdggs/conventions/registry.py
@@ -24,7 +24,7 @@ def register(func):
 
 def register_encoder(name):
     def register(func):
-        if name in decoders:
+        if name in encoders:
             warnings.warn(
                 DecoderWarning(f"Overwriting existing convention encoder {name!r}.")
             )

From 27e3a19153077d368ff9782c162447ee5732d5d3 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 18:59:01 +0200
Subject: [PATCH 09/27] use the registry objects in the accessor

---
 xdggs/accessor.py             | 12 +++---------
 xdggs/conventions/__init__.py |  1 +
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index 651380ae..5d577e70 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -53,9 +53,9 @@ def decode(
         elif callable(convention):
             decoder = convention
         else:
-            decoder = conventions.decoders.get(convention)
+            decoder = conventions._decoders.get(convention)
             if decoder is None:
-                valid_names = conventions.decoders.keys()
+                valid_names = conventions._decoders.keys()
                 raise ValueError(
                     f"unknown convention: {convention}."
                     f" Choose a known convention: {', '.join(valid_names)}"
@@ -262,13 +262,7 @@ def as_convention(self, convention: str):
         obj : xr.DataArray or xr.Dataset
             The object converted to the given dimension.
         """
-        converters = {
-            "easygems": conventions.easygems,
-            "cf": conventions.cf,
-            "xdggs": conventions.xdggs,
-        }
-
-        converter = converters.get(convention)
+        converter = conventions._encoders.get(convention)
         if converter is None:
             raise ValueError(f"unknown convention: {convention}")
 
diff --git a/xdggs/conventions/__init__.py b/xdggs/conventions/__init__.py
index 4674b43c..8ad165df 100644
--- a/xdggs/conventions/__init__.py
+++ b/xdggs/conventions/__init__.py
@@ -1,5 +1,6 @@
 from xdggs.conventions import decoders, encoders  # noqa: F401
 from xdggs.conventions.registry import decoders as _decoders
+from xdggs.conventions.registry import encoders as _encoders  # noqa: F401
 from xdggs.conventions.registry import (
     register_decoder,
     register_encoder,

From 4635a027a884d233548871092a179024a75c5c30 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 18:59:35 +0200
Subject: [PATCH 10/27] remove the `grid_name` attr from the metadata

---
 xdggs/conventions/encoders.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xdggs/conventions/encoders.py b/xdggs/conventions/encoders.py
index 06203dc9..dfab0738 100644
--- a/xdggs/conventions/encoders.py
+++ b/xdggs/conventions/encoders.py
@@ -67,6 +67,7 @@ def _convert(ds):
         grid_name = infer_grid_name(ds.dggs.index)
         metadata = grid_info.to_dict() | {"grid_mapping_name": grid_name}
         metadata["refinement_level"] = metadata.pop("level")
+        metadata.pop("grid_name", None)
 
         crs = xr.Variable((), np.int8(0), metadata)
 

From cbe7698287c82999248cab8047cdec78a011698f Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 20:34:45 +0200
Subject: [PATCH 11/27] implement the cf convention decoder

---
 xdggs/conventions/decoders.py | 43 ++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/xdggs/conventions/decoders.py b/xdggs/conventions/decoders.py
index e9cd2918..b05f2456 100644
--- a/xdggs/conventions/decoders.py
+++ b/xdggs/conventions/decoders.py
@@ -2,7 +2,7 @@
 
 from xdggs.conventions.registry import register_decoder
 from xdggs.grid import DGGSInfo
-from xdggs.utils import GRID_REGISTRY
+from xdggs.utils import GRID_REGISTRY, call_on_dataset
 
 
 @register_decoder("xdggs")
@@ -31,3 +31,44 @@ def xdggs(obj, grid_info, name):
     index = index_cls.from_variables({name: var}, options=grid_info)
 
     return xr.Coordinates({name: var.variable}, indexes={name: index})
+
+
+@register_decoder("cf")
+def cf(obj, grid_info, name):
+    vars_ = call_on_dataset(
+        lambda ds: ds.variables,
+        obj,
+    )
+    grid_mapping_vars = {
+        name: var for name, var in vars_.items() if "grid_mapping_name" in var.attrs
+    }
+    if len(grid_mapping_vars) != 1:
+        raise ValueError("needs exactly one grid mapping variable for now")
+    crs = next(iter(grid_mapping_vars.values()))
+
+    if name is None:
+        coords = list(
+            dict.fromkeys(
+                var.attrs["coordinates"]
+                for name, var in vars_.items()
+                if "coordinates" in var.attrs
+            )
+        )
+        name = coords[0]
+    var = vars_[name].copy(deep=False)
+    var.attrs.pop("standard_name", None)
+    var.attrs.pop("units", None)
+
+    translations = {"refinement_level": "level"}
+    grid_info = {
+        translations.get(name, name): value for name, value in crs.attrs.items()
+    }
+
+    grid_name = grid_info.pop("grid_mapping_name")
+    if grid_name not in GRID_REGISTRY:
+        raise ValueError(f"unknown grid name: {grid_name}")
+    index_cls = GRID_REGISTRY[grid_name]
+
+    index = index_cls.from_variables({name: var}, options=grid_info)
+
+    return xr.Coordinates({name: var}, indexes={name: index})

From 012da3154b527a4ec9df23d415bfb8fec77659ce Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 20:34:58 +0200
Subject: [PATCH 12/27] default to `name=None` and override it in the xdggs
 convention

---
 xdggs/accessor.py             | 2 +-
 xdggs/conventions/decoders.py | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index 5d577e70..7c7e2049 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -31,7 +31,7 @@ def __init__(self, obj: xr.Dataset | xr.DataArray):
         self._index = index
 
     def decode(
-        self, grid_info=None, *, name="cell_ids", convention=None
+        self, grid_info=None, *, name=None, convention=None
     ) -> xr.Dataset | xr.DataArray:
         """decode the DGGS cell ids
 
diff --git a/xdggs/conventions/decoders.py b/xdggs/conventions/decoders.py
index b05f2456..0be0bdd9 100644
--- a/xdggs/conventions/decoders.py
+++ b/xdggs/conventions/decoders.py
@@ -7,6 +7,9 @@
 
 @register_decoder("xdggs")
 def xdggs(obj, grid_info, name):
+    if name is None:
+        name = "cell_ids"
+
     try:
         var = obj[name]
     except IndexError:

From ac4ebe53f532f2632996d38bd93eaf298f126674 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 20:36:03 +0200
Subject: [PATCH 13/27] don't try to guess the convention

---
 xdggs/accessor.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index 7c7e2049..24450468 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -31,7 +31,7 @@ def __init__(self, obj: xr.Dataset | xr.DataArray):
         self._index = index
 
     def decode(
-        self, grid_info=None, *, name=None, convention=None
+        self, grid_info=None, *, name=None, convention="xdggs"
     ) -> xr.Dataset | xr.DataArray:
         """decode the DGGS cell ids
 
@@ -48,9 +48,7 @@ def decode(
         obj : xarray.DataArray or xarray.Dataset
             The object with a DGGS index on the cell id coordinate.
         """
-        if convention is None:
-            decoder = conventions.detect_decoder
-        elif callable(convention):
+        if callable(convention):
             decoder = convention
         else:
             decoder = conventions._decoders.get(convention)

From 45c7927dbf22390066c0ec52d698e414eed41af9 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Wed, 8 Oct 2025 23:00:19 +0200
Subject: [PATCH 14/27] extend the docstring of `decode`

---
 xdggs/accessor.py | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/xdggs/accessor.py b/xdggs/accessor.py
index 24450468..e6f1d8d0 100644
--- a/xdggs/accessor.py
+++ b/xdggs/accessor.py
@@ -40,8 +40,22 @@ def decode(
         grid_info : dict or DGGSInfo, optional
             Override the grid parameters on the dataset. Useful to set attributes on
             the dataset.
-        name : str, default: "cell_ids"
-            The name of the coordinate containing the cell ids.
+        name : str, optional
+            The name of the coordinate containing the cell ids. The default name
+            depends on the convention.
+        convention : str, default: "xdggs"
+            The name of the metadata convention. Built-in conventions are:
+
+            - "xdggs": the existing xdggs convention. ``name`` points to the
+              coordinate containing cell ids, and which has all the grid
+              metadata. The ``name`` parameter defaults to ``"cell_ids"``.
+            - "cf": the upcoming CF convention standardization. While the
+              convention extension is specialized on ``healpix`` for now, the
+              decoder can work with other DGGS as well. For this, all metadata
+              lives on a variable with a ``grid_mapping_name`` attribute, and
+              the cell ids coordinate is indicated by the ``coordinates``
+              attribute on data variables / other coordinates (this can be
+              overridden by the ``name`` parameter).
 
         Returns
         -------

From 5dc6272f4cfbc0f363bf2f2dcbb1f58cab81ed9e Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 11:46:32 +0200
Subject: [PATCH 15/27] tests for the xdggs convention decoder

---
 xdggs/tests/conventions/test_decoders.py | 107 +++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 xdggs/tests/conventions/test_decoders.py

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
new file mode 100644
index 00000000..230d0690
--- /dev/null
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -0,0 +1,107 @@
+import numpy as np
+import pytest
+import xarray as xr
+
+import xdggs
+from xdggs.conventions import decoders
+
+
+def clear_attrs(var):
+    new_var = var.copy(deep=False)
+    new_var.attrs.clear()
+
+    return new_var
+
+
+def generate_h3_cells(level):
+    from h3ronpy import change_resolution
+
+    base_cells = [
+        576495936675512319,
+        576531121047601151,
+        576566305419689983,
+        576601489791778815,
+        576636674163867647,
+        576671858535956479,
+        576707042908045311,
+        576742227280134143,
+        576777411652222975,
+        576812596024311807,
+    ]
+
+    return change_resolution(base_cells, level)
+
+
+def create_coordinate(grid_name, dim, level, **options):
+    generators = {
+        "healpix": lambda level: np.arange(12 * 4**level),
+        "h3": generate_h3_cells,
+    }
+
+    cell_ids = generators[grid_name](level)
+    grid_info = {"grid_name": grid_name, "refinement_level": level, **options}
+    return xr.Variable(dim, cell_ids, grid_info)
+
+
+def create_index(name, coord, grid_info):
+    translations = {"refinement_level": "level"}
+
+    if grid_info is None:
+        grid_info = {
+            translations.get(name, name): value for name, value in coord.attrs.items()
+        }
+
+    var = coord.copy(deep=False)
+    var.attrs = grid_info
+
+    return xdggs.HealpixIndex.from_variables({name: var}, options={})
+
+
+@pytest.mark.parametrize("obj_type", ["DataArray", "Dataset"])
+@pytest.mark.parametrize(
+    ["coord_name", "coord", "grid_info", "name"],
+    (
+        pytest.param(
+            "cell_ids",
+            create_coordinate("healpix", "cells", 0, indexing_scheme="ring"),
+            None,
+            None,
+            id="healpix-all_defaults",
+        ),
+        pytest.param(
+            "cell_ids",
+            create_coordinate("h3", "cells", 0),
+            None,
+            None,
+            id="h3-all_defaults",
+        ),
+        pytest.param(
+            "zone_ids",
+            create_coordinate("healpix", "zones", 0, indexing_scheme="nested"),
+            None,
+            "zone_ids",
+            id="healpix-override_name",
+        ),
+        pytest.param(
+            "cell_ids",
+            clear_attrs(create_coordinate("h3", "cells", 2)),
+            {"grid_name": "h3", "level": 2},
+            None,
+            id="h3-override_grid_info",
+        ),
+    ),
+)
+def test_xdggs(obj_type, coord_name, coord, grid_info, name):
+    if obj_type == "Dataset":
+        obj = xr.Dataset(coords={coord_name: coord})
+    else:
+        obj = xr.DataArray(
+            np.zeros_like(coord.data), coords={coord_name: coord}, dims=coord.dims
+        )
+
+    expected = xr.Coordinates(
+        {coord_name: coord},
+        indexes={coord_name: create_index(coord_name, coord, grid_info)},
+    )
+    actual = decoders.xdggs(obj, grid_info, name)
+    xr.testing.assert_identical(actual.to_dataset(), expected.to_dataset())

From 145dbed0cf90f466a8b9deb64744cbfb1de6ad27 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 11:46:59 +0200
Subject: [PATCH 16/27] add `h3-py` to the dev deps

---
 pixi.lock      | 208 ++++++++++++++++++++++++++++++++++++-------------
 pyproject.toml |   1 +
 2 files changed, 154 insertions(+), 55 deletions(-)

diff --git a/pixi.lock b/pixi.lock
index d8b5a274..7479bfac 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -2388,6 +2388,8 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/linux-64/glog-0.7.1-hbabe93e_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/linux-64/h3-4.3.0-h3e4d06c_1.conda
+        - conda: https://conda.anaconda.org/conda-forge/linux-64/h3-py-4.3.0-py313h5d5ffb9_2.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/h3ronpy-0.22.0-py313h920b4c0_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h5netcdf-1.6.4-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/h5py-3.14.0-nompi_py313h253c126_101.conda
@@ -2684,6 +2686,8 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/glog-0.7.1-heb240a5_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h3-4.3.0-hc039f4b_1.conda
+        - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h3-py-4.3.0-py313hab38a8b_2.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h3ronpy-0.22.0-py313hdde674f_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h5netcdf-1.6.4-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h5py-3.14.0-nompi_py313ha10fd41_101.conda
@@ -2967,6 +2971,8 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/geos-3.13.1-h9ea8674_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/win-64/h3-4.3.0-h2854ae6_1.conda
+        - conda: https://conda.anaconda.org/conda-forge/win-64/h3-py-4.3.0-py313h927ade5_2.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/h3ronpy-0.22.0-py313hf3b5b86_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/h5netcdf-1.6.4-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/h5py-3.14.0-nompi_py313hf7f959b_101.conda
@@ -4039,16 +4045,16 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/linux-64/zlib-1.3.1-hb9d3cd8_2.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/zstandard-0.25.0-py313h54dd161_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/zstd-1.5.7-hb8e6e7a_2.conda
-        - pypi: git+https://github.com/astropy/astropy.git#0519229eb0f0a1ff3fdbe4c5a0565c33b101bd9f
-        - pypi: https://files.pythonhosted.org/packages/03/8c/a556b71e4603d6156814da968b7cefa9bd882e59dc691168584418f4de77/astropy_iers_data-0.2025.9.15.0.37.0-py3-none-any.whl
-        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#54d3467b28a87cdfdb696aacbd225ae1db81def1
+        - pypi: git+https://github.com/astropy/astropy.git#0bc65a152cbc43f8e9f16ac7671f6b8e22fa755b
+        - pypi: https://files.pythonhosted.org/packages/c5/38/be921eaf8fc67333fd2c2657ea965103ccc4050c29a66d5fd5f3db881c0f/astropy_iers_data-0.2025.10.6.0.35.25-py3-none-any.whl
+        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#1d34a649bfa7270562a5def7322abfdd0f6c9e4e
         - pypi: git+https://github.com/keewis/h3ronpy.git?subdirectory=h3ronpy&rev=version#98fa563245092e2578cc6f1f0d860a9f511475f1
-        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#7ad4a7652363b5f9b97e143434de4680f5dfd93f
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl
+        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#2c79f767ec4b9fe9634574c0f7f5857fa12230c6
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl
         - pypi: https://files.pythonhosted.org/packages/e5/e0/050018d855d26d3c0b4a7d1b2ed692be758ce276d8289e2a2b44ba1014a5/pyerfa-2.0.1.5-cp39-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
         - pypi: https://files.pythonhosted.org/packages/04/24/b7721e4845c2f162d26f50521b825fb061bc0a5afcf9a386840f23ea19fa/PyYAML-6.0.2-cp313-cp313-manylinux_2_17_x86_64.manylinux2014_x86_64.whl
         - pypi: https://files.pythonhosted.org/packages/5c/23/c7abc0ca0a1526a0774eca151daeb8de62ec457e77262b66b359c3c7679e/tzdata-2025.2-py2.py3-none-any.whl
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev19+g4394792ab/xarray-2025.9.1.dev19+g4394792ab-py3-none-any.whl
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev47+gc703ce4ef/xarray-2025.9.1.dev47+gc703ce4ef-py3-none-any.whl
         - pypi: ./
       osx-arm64:
         - conda: https://conda.anaconda.org/conda-forge/noarch/anywidget-0.9.18-pyhd8ed1ab_0.conda
@@ -4248,16 +4254,16 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/zlib-1.3.1-h8359307_2.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/zstandard-0.25.0-py313h9734d34_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/zstd-1.5.7-h6491c7d_2.conda
-        - pypi: git+https://github.com/astropy/astropy.git#0519229eb0f0a1ff3fdbe4c5a0565c33b101bd9f
-        - pypi: https://files.pythonhosted.org/packages/03/8c/a556b71e4603d6156814da968b7cefa9bd882e59dc691168584418f4de77/astropy_iers_data-0.2025.9.15.0.37.0-py3-none-any.whl
-        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#54d3467b28a87cdfdb696aacbd225ae1db81def1
+        - pypi: git+https://github.com/astropy/astropy.git#0bc65a152cbc43f8e9f16ac7671f6b8e22fa755b
+        - pypi: https://files.pythonhosted.org/packages/c5/38/be921eaf8fc67333fd2c2657ea965103ccc4050c29a66d5fd5f3db881c0f/astropy_iers_data-0.2025.10.6.0.35.25-py3-none-any.whl
+        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#1d34a649bfa7270562a5def7322abfdd0f6c9e4e
         - pypi: git+https://github.com/keewis/h3ronpy.git?subdirectory=h3ronpy&rev=version#98fa563245092e2578cc6f1f0d860a9f511475f1
-        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#7ad4a7652363b5f9b97e143434de4680f5dfd93f
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-macosx_11_0_arm64.whl
+        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#2c79f767ec4b9fe9634574c0f7f5857fa12230c6
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-macosx_11_0_arm64.whl
         - pypi: https://files.pythonhosted.org/packages/11/4a/31a363370478b63c6289a34743f2ba2d3ae1bd8223e004d18ab28fb92385/pyerfa-2.0.1.5-cp39-abi3-macosx_11_0_arm64.whl
         - pypi: https://files.pythonhosted.org/packages/45/9f/3b1c20a0b7a3200524eb0076cc027a970d320bd3a6592873c85c92a08731/PyYAML-6.0.2-cp313-cp313-macosx_11_0_arm64.whl
         - pypi: https://files.pythonhosted.org/packages/5c/23/c7abc0ca0a1526a0774eca151daeb8de62ec457e77262b66b359c3c7679e/tzdata-2025.2-py2.py3-none-any.whl
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev19+g4394792ab/xarray-2025.9.1.dev19+g4394792ab-py3-none-any.whl
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev47+gc703ce4ef/xarray-2025.9.1.dev47+gc703ce4ef-py3-none-any.whl
         - pypi: ./
       win-64:
         - conda: https://conda.anaconda.org/conda-forge/win-64/_openmp_mutex-4.5-2_gnu.conda
@@ -4449,16 +4455,16 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/zlib-1.3.1-h2466b09_2.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/zstandard-0.25.0-py313h5fd188c_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/zstd-1.5.7-hbeecb71_2.conda
-        - pypi: git+https://github.com/astropy/astropy.git#0519229eb0f0a1ff3fdbe4c5a0565c33b101bd9f
-        - pypi: https://files.pythonhosted.org/packages/03/8c/a556b71e4603d6156814da968b7cefa9bd882e59dc691168584418f4de77/astropy_iers_data-0.2025.9.15.0.37.0-py3-none-any.whl
-        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#54d3467b28a87cdfdb696aacbd225ae1db81def1
+        - pypi: git+https://github.com/astropy/astropy.git#0bc65a152cbc43f8e9f16ac7671f6b8e22fa755b
+        - pypi: https://files.pythonhosted.org/packages/c5/38/be921eaf8fc67333fd2c2657ea965103ccc4050c29a66d5fd5f3db881c0f/astropy_iers_data-0.2025.10.6.0.35.25-py3-none-any.whl
+        - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#1d34a649bfa7270562a5def7322abfdd0f6c9e4e
         - pypi: git+https://github.com/keewis/h3ronpy.git?subdirectory=h3ronpy&rev=version#98fa563245092e2578cc6f1f0d860a9f511475f1
-        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#7ad4a7652363b5f9b97e143434de4680f5dfd93f
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-win_amd64.whl
+        - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#2c79f767ec4b9fe9634574c0f7f5857fa12230c6
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-win_amd64.whl
         - pypi: https://files.pythonhosted.org/packages/b4/11/97233cf23ad5411ac6f13b1d6ee3888f90ace4f974d9bf9db887aa428912/pyerfa-2.0.1.5-cp39-abi3-win_amd64.whl
         - pypi: https://files.pythonhosted.org/packages/fa/de/02b54f42487e3d3c6efb3f89428677074ca7bf43aae402517bc7cca949f3/PyYAML-6.0.2-cp313-cp313-win_amd64.whl
         - pypi: https://files.pythonhosted.org/packages/5c/23/c7abc0ca0a1526a0774eca151daeb8de62ec457e77262b66b359c3c7679e/tzdata-2025.2-py2.py3-none-any.whl
-        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev19+g4394792ab/xarray-2025.9.1.dev19+g4394792ab-py3-none-any.whl
+        - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev47+gc703ce4ef/xarray-2025.9.1.dev47+gc703ce4ef-py3-none-any.whl
         - pypi: ./
 packages:
   - conda: https://conda.anaconda.org/conda-forge/linux-64/_libgcc_mutex-0.1-conda_forge.tar.bz2
@@ -5099,35 +5105,35 @@ packages:
       - pkg:pypi/arrow?source=hash-mapping
     size: 99951
     timestamp: 1733584345583
-  - pypi: git+https://github.com/astropy/astropy.git#0519229eb0f0a1ff3fdbe4c5a0565c33b101bd9f
+  - pypi: git+https://github.com/astropy/astropy.git#0bc65a152cbc43f8e9f16ac7671f6b8e22fa755b
     name: astropy
-    version: 7.2.dev538+g0519229eb
+    version: 7.2.dev635+g0bc65a152
     requires_dist:
       - numpy>=1.24
       - pyerfa>=2.0.1.1
-      - astropy-iers-data>=0.2025.9.1.0.42.11
+      - astropy-iers-data>=0.2025.9.29.0.35.48
       - pyyaml>=6.0.0
       - packaging>=22.0.0
       - scipy>=1.9.2 ; extra == 'recommended'
       - matplotlib>=3.8.0 ; extra == 'recommended'
+      - narwhals>=1.42.0 ; extra == 'recommended'
       - ipython>=8.0.0 ; extra == 'ipython'
       - astropy[ipython] ; extra == 'jupyter'
       - ipywidgets>=7.7.3 ; extra == 'jupyter'
       - ipykernel>=6.16.0 ; extra == 'jupyter'
       - ipydatagrid>=1.1.13 ; extra == 'jupyter'
       - jupyter-core>=4.11.2 ; extra == 'jupyter'
-      - pandas>=1.5.0 ; extra == 'jupyter'
+      - pandas>=2.0.0 ; extra == 'jupyter'
       - astropy[recommended] ; extra == 'all'
       - astropy[ipython] ; extra == 'all'
       - astropy[jupyter] ; extra == 'all'
       - certifi>=2022.6.15.1 ; extra == 'all'
-      - dask[array]>=2022.5.1 ; extra == 'all'
+      - dask[dataframe]>=2024.8.0 ; extra == 'all'
       - h5py>=3.9.0 ; extra == 'all'
-      - pyarrow>=10.0.1 ; extra == 'all'
+      - pyarrow>=14.0.2 ; extra == 'all'
       - beautifulsoup4>=4.9.3 ; extra == 'all'
       - html5lib>=1.1 ; extra == 'all'
       - bleach>=3.2.1 ; extra == 'all'
-      - pandas>=2.0 ; extra == 'all'
       - sortedcontainers>=1.5.7 ; extra == 'all'
       - pytz>=2016.10 ; extra == 'all'
       - jplephem>=2.15 ; extra == 'all'
@@ -5153,7 +5159,8 @@ packages:
       - sgp4>=2.3 ; extra == 'test-all'
       - array-api-strict>=1.0 ; extra == 'test-all'
       - array-api-strict<2.4 ; python_full_version < '3.12' and extra == 'test-all'
-      - pandas-stubs>=2.0 ; extra == 'typing'
+      - pandas-stubs>=2.0.0 ; extra == 'typing'
+      - narwhals>=1.42.0 ; extra == 'typing'
       - astropy[recommended] ; extra == 'docs'
       - sphinx>=8.2.0 ; extra == 'docs'
       - sphinx-astropy[confv2]>=1.9.1 ; extra == 'docs'
@@ -5372,10 +5379,10 @@ packages:
       - pkg:pypi/astropy?source=hash-mapping
     size: 9464202
     timestamp: 1757120315355
-  - pypi: https://files.pythonhosted.org/packages/03/8c/a556b71e4603d6156814da968b7cefa9bd882e59dc691168584418f4de77/astropy_iers_data-0.2025.9.15.0.37.0-py3-none-any.whl
+  - pypi: https://files.pythonhosted.org/packages/c5/38/be921eaf8fc67333fd2c2657ea965103ccc4050c29a66d5fd5f3db881c0f/astropy_iers_data-0.2025.10.6.0.35.25-py3-none-any.whl
     name: astropy-iers-data
-    version: 0.2025.9.15.0.37.0
-    sha256: 4ea19813150f2d6dfb0257c5e96d14ae9eac6e5a80af27ec79e3aaef8aadfa93
+    version: 0.2025.10.6.0.35.25
+    sha256: b6f572ee3ae4e02e4ae377229b533ed89d6f8eb027ae31e380cbc8096735ba49
     requires_dist:
       - pytest ; extra == 'docs'
       - hypothesis ; extra == 'test'
@@ -6671,7 +6678,7 @@ packages:
       - pkg:pypi/cached-property?source=hash-mapping
     size: 11065
     timestamp: 1615209567874
-  - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#54d3467b28a87cdfdb696aacbd225ae1db81def1
+  - pypi: git+https://github.com/cds-astro/cds-healpix-python.git#1d34a649bfa7270562a5def7322abfdd0f6c9e4e
     name: cdshealpix
     version: 0.7.1
     requires_dist:
@@ -8125,6 +8132,98 @@ packages:
       - pkg:pypi/h2?source=compressed-mapping
     size: 95967
     timestamp: 1756364871835
+  - conda: https://conda.anaconda.org/conda-forge/linux-64/h3-4.3.0-h3e4d06c_1.conda
+    sha256: b9f46e0f9a24c321b065bc0d2563604a1b0fb7e02a06105e264411f74010a54e
+    md5: 7a9b1ee49ab4ac8ee2a0bda9e9f666d5
+    depends:
+      - libstdcxx >=13
+      - libgcc >=13
+      - __glibc >=2.17,<3.0.a0
+    license: Apache-2.0
+    license_family: APACHE
+    purls: []
+    size: 132463
+    timestamp: 1751353376725
+  - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h3-4.3.0-hc039f4b_1.conda
+    sha256: 088306a565263030bb5c281a6c39a75a98c3db3a846ecbe2697a17d9119d688f
+    md5: cf54e9f5b7d0abd3060b10b2123be427
+    depends:
+      - libcxx >=18
+      - __osx >=11.0
+    license: Apache-2.0
+    license_family: APACHE
+    purls: []
+    size: 129453
+    timestamp: 1751353401084
+  - conda: https://conda.anaconda.org/conda-forge/win-64/h3-4.3.0-h2854ae6_1.conda
+    sha256: 3f1d375d6dcd95cb9cf34cc7aa638c63f7fbcc23362c1aa80e7a0a1c578dff45
+    md5: 3fd116e60190e3940f3dcae5a21a9fd0
+    depends:
+      - vc >=14.3,<15
+      - vc14_runtime >=14.44.35208
+      - ucrt >=10.0.20348.0
+      - vc >=14.3,<15
+      - vc14_runtime >=14.44.35208
+      - ucrt >=10.0.20348.0
+    license: Apache-2.0
+    license_family: APACHE
+    purls: []
+    size: 125555
+    timestamp: 1751353416300
+  - conda: https://conda.anaconda.org/conda-forge/linux-64/h3-py-4.3.0-py313h5d5ffb9_2.conda
+    sha256: 872fc4bea50c561302cfdf2186199818744dec1111c451d432d6765a8f599c68
+    md5: e82220be2170a7c6cabec5d84a980ed3
+    depends:
+      - python
+      - numpy
+      - h3 ==4.3.0
+      - __glibc >=2.17,<3.0.a0
+      - libstdcxx >=14
+      - libgcc >=14
+      - python_abi 3.13.* *_cp313
+    license: Apache-2.0
+    license_family: APACHE
+    purls:
+      - pkg:pypi/h3?source=hash-mapping
+    size: 369574
+    timestamp: 1756762902201
+  - conda: https://conda.anaconda.org/conda-forge/osx-arm64/h3-py-4.3.0-py313hab38a8b_2.conda
+    sha256: 43bc37ba2a97d62a8793a6489894b5d0f6b3424aed8775a99d09824459241867
+    md5: 9df00ebbf3438029049698ff234b5c13
+    depends:
+      - python
+      - numpy
+      - h3 ==4.3.0
+      - libcxx >=19
+      - __osx >=11.0
+      - python 3.13.* *_cp313
+      - python_abi 3.13.* *_cp313
+    license: Apache-2.0
+    license_family: APACHE
+    purls:
+      - pkg:pypi/h3?source=hash-mapping
+    size: 292854
+    timestamp: 1756762925790
+  - conda: https://conda.anaconda.org/conda-forge/win-64/h3-py-4.3.0-py313h927ade5_2.conda
+    sha256: 99ce3204be895392d16d634bfc82c7b7a7256c61f5e33a10c44b1d641f63ce48
+    md5: f840d9c02f75adaed96f89ac922916d1
+    depends:
+      - python
+      - numpy
+      - h3 ==4.3.0
+      - vc >=14.3,<15
+      - vc14_runtime >=14.44.35208
+      - ucrt >=10.0.20348.0
+      - vc >=14.3,<15
+      - vc14_runtime >=14.44.35208
+      - ucrt >=10.0.20348.0
+      - python_abi 3.13.* *_cp313
+    license: Apache-2.0
+    license_family: APACHE
+    purls:
+      - pkg:pypi/h3?source=hash-mapping
+    size: 303912
+    timestamp: 1756762936753
   - pypi: git+https://github.com/keewis/h3ronpy.git?subdirectory=h3ronpy&rev=version#98fa563245092e2578cc6f1f0d860a9f511475f1
     name: h3ronpy
     version: 0.22.0
@@ -8590,7 +8689,7 @@ packages:
     purls: []
     size: 2031491
     timestamp: 1753357255237
-  - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#7ad4a7652363b5f9b97e143434de4680f5dfd93f
+  - pypi: git+https://github.com/eopf-dggs/healpix-geo.git#2c79f767ec4b9fe9634574c0f7f5857fa12230c6
     name: healpix-geo
     version: 0.0.7
     requires_dist:
@@ -13294,16 +13393,16 @@ packages:
       - pkg:pypi/packaging?source=hash-mapping
     size: 62477
     timestamp: 1745345660407
-  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-macosx_11_0_arm64.whl
+  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-macosx_11_0_arm64.whl
     name: pandas
-    version: 3.0.0.dev0+2396.gcc40732889
+    version: 3.0.0.dev0+2520.g10102e611d
     requires_dist:
       - numpy>=1.26.0
       - python-dateutil>=2.8.2
       - tzdata>=2023.3
       - hypothesis>=6.116.0 ; extra == 'test'
-      - pytest>=7.3.2 ; extra == 'test'
-      - pytest-xdist>=3.4.0 ; extra == 'test'
+      - pytest>=8.3.4 ; extra == 'test'
+      - pytest-xdist>=3.6.1 ; extra == 'test'
       - pyarrow>=13.0.0 ; extra == 'pyarrow'
       - bottleneck>=1.4.2 ; extra == 'performance'
       - numba>=0.60.0 ; extra == 'performance'
@@ -13365,8 +13464,8 @@ packages:
       - pymysql>=1.1.1 ; extra == 'all'
       - pyqt5>=5.15.9 ; extra == 'all'
       - pyreadstat>=1.2.8 ; extra == 'all'
-      - pytest>=7.3.2 ; extra == 'all'
-      - pytest-xdist>=3.4.0 ; extra == 'all'
+      - pytest>=8.3.4 ; extra == 'all'
+      - pytest-xdist>=3.6.1 ; extra == 'all'
       - python-calamine>=0.3.0 ; extra == 'all'
       - pytz>=2024.2 ; extra == 'all'
       - pyxlsb>=1.0.10 ; extra == 'all'
@@ -13381,16 +13480,16 @@ packages:
       - xlsxwriter>=3.2.0 ; extra == 'all'
       - zstandard>=0.23.0 ; extra == 'all'
     requires_python: ">=3.11"
-  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl
+  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl
     name: pandas
-    version: 3.0.0.dev0+2396.gcc40732889
+    version: 3.0.0.dev0+2520.g10102e611d
     requires_dist:
       - numpy>=1.26.0
       - python-dateutil>=2.8.2
       - tzdata>=2023.3
       - hypothesis>=6.116.0 ; extra == 'test'
-      - pytest>=7.3.2 ; extra == 'test'
-      - pytest-xdist>=3.4.0 ; extra == 'test'
+      - pytest>=8.3.4 ; extra == 'test'
+      - pytest-xdist>=3.6.1 ; extra == 'test'
       - pyarrow>=13.0.0 ; extra == 'pyarrow'
       - bottleneck>=1.4.2 ; extra == 'performance'
       - numba>=0.60.0 ; extra == 'performance'
@@ -13452,8 +13551,8 @@ packages:
       - pymysql>=1.1.1 ; extra == 'all'
       - pyqt5>=5.15.9 ; extra == 'all'
       - pyreadstat>=1.2.8 ; extra == 'all'
-      - pytest>=7.3.2 ; extra == 'all'
-      - pytest-xdist>=3.4.0 ; extra == 'all'
+      - pytest>=8.3.4 ; extra == 'all'
+      - pytest-xdist>=3.6.1 ; extra == 'all'
       - python-calamine>=0.3.0 ; extra == 'all'
       - pytz>=2024.2 ; extra == 'all'
       - pyxlsb>=1.0.10 ; extra == 'all'
@@ -13468,16 +13567,16 @@ packages:
       - xlsxwriter>=3.2.0 ; extra == 'all'
       - zstandard>=0.23.0 ; extra == 'all'
     requires_python: ">=3.11"
-  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2396.gcc40732889/pandas-3.0.0.dev0+2396.gcc40732889-cp313-cp313-win_amd64.whl
+  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/pandas/3.0.0.dev0+2520.g10102e611d/pandas-3.0.0.dev0+2520.g10102e611d-cp313-cp313-win_amd64.whl
     name: pandas
-    version: 3.0.0.dev0+2396.gcc40732889
+    version: 3.0.0.dev0+2520.g10102e611d
     requires_dist:
       - numpy>=1.26.0
       - python-dateutil>=2.8.2
       - tzdata>=2023.3
       - hypothesis>=6.116.0 ; extra == 'test'
-      - pytest>=7.3.2 ; extra == 'test'
-      - pytest-xdist>=3.4.0 ; extra == 'test'
+      - pytest>=8.3.4 ; extra == 'test'
+      - pytest-xdist>=3.6.1 ; extra == 'test'
       - pyarrow>=13.0.0 ; extra == 'pyarrow'
       - bottleneck>=1.4.2 ; extra == 'performance'
       - numba>=0.60.0 ; extra == 'performance'
@@ -13539,8 +13638,8 @@ packages:
       - pymysql>=1.1.1 ; extra == 'all'
       - pyqt5>=5.15.9 ; extra == 'all'
       - pyreadstat>=1.2.8 ; extra == 'all'
-      - pytest>=7.3.2 ; extra == 'all'
-      - pytest-xdist>=3.4.0 ; extra == 'all'
+      - pytest>=8.3.4 ; extra == 'all'
+      - pytest-xdist>=3.6.1 ; extra == 'all'
       - python-calamine>=0.3.0 ; extra == 'all'
       - pytz>=2024.2 ; extra == 'all'
       - pyxlsb>=1.0.10 ; extra == 'all'
@@ -17562,9 +17661,9 @@ packages:
       - pkg:pypi/wrapt?source=hash-mapping
     size: 63385
     timestamp: 1756851987645
-  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev19+g4394792ab/xarray-2025.9.1.dev19+g4394792ab-py3-none-any.whl
+  - pypi: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/xarray/2025.9.1.dev47+gc703ce4ef/xarray-2025.9.1.dev47+gc703ce4ef-py3-none-any.whl
     name: xarray
-    version: 2025.9.1.dev19+g4394792ab
+    version: 2025.9.1.dev47+gc703ce4ef
     requires_dist:
       - numpy>=1.26
       - packaging>=24.1
@@ -17572,10 +17671,9 @@ packages:
       - scipy>=1.13 ; extra == 'accel'
       - bottleneck ; extra == 'accel'
       - numbagg>=0.8 ; extra == 'accel'
-      - numba>=0.59 ; extra == 'accel'
+      - numba>=0.62 ; extra == 'accel'
       - flox>=0.9 ; extra == 'accel'
       - opt-einsum ; extra == 'accel'
-      - numpy<2.3 ; extra == 'accel'
       - xarray[accel,etc,io,parallel,viz] ; extra == 'complete'
       - netcdf4>=1.6.0 ; extra == 'io'
       - h5netcdf ; extra == 'io'
@@ -17646,8 +17744,8 @@ packages:
     timestamp: 1756981236899
   - pypi: ./
     name: xdggs
-    version: 0.2.3.dev0+g6e574369a.d20250915
-    sha256: 25ee4943bca97abde42e762b8dc1ff5ab22160b173c644dd9dcdbc85eaede470
+    version: 0.2.3.dev15+g45c7927db.d20251009
+    sha256: 3468e2264737d22c8b940aebdb85ce9d909ba407e3c6870f3f1fd323539294db
     requires_dist:
       - arro3-core>=0.4.0
       - cdshealpix
diff --git a/pyproject.toml b/pyproject.toml
index a8f7c32a..525ff2e7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -213,6 +213,7 @@ jupyterlab = "*"
 jupyter-resource-usage = "*"
 jupyterlab_code_formatter = "*"
 python-build = ">=1.3.0,<2"
+h3-py = ">=4.3.0,<5"
 
 [tool.pixi.environments]
 nightly = { features = ["tests", "nightly"], no-default-feature = true }

From 156b1e5fef67b16c72b912286b566a08cc56bd7e Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 11:48:58 +0200
Subject: [PATCH 17/27] override the variable metadata

---
 xdggs/conventions/decoders.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xdggs/conventions/decoders.py b/xdggs/conventions/decoders.py
index 0be0bdd9..7732188f 100644
--- a/xdggs/conventions/decoders.py
+++ b/xdggs/conventions/decoders.py
@@ -31,7 +31,9 @@ def xdggs(obj, grid_info, name):
         raise ValueError(f"unknown grid name: {grid_name}")
     index_cls = GRID_REGISTRY[grid_name]
 
-    index = index_cls.from_variables({name: var}, options=grid_info)
+    var_ = var.copy(deep=True)
+    var_.attrs = grid_info
+    index = index_cls.from_variables({name: var_}, options={})
 
     return xr.Coordinates({name: var.variable}, indexes={name: index})
 

From c9b190ba54786b19516486eef1f0669bbb0b70d6 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 11:49:13 +0200
Subject: [PATCH 18/27] use the correct metadata for the convention

---
 xdggs/tests/conventions/test_decoders.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index 230d0690..6a7e86c7 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -39,7 +39,7 @@ def create_coordinate(grid_name, dim, level, **options):
     }
 
     cell_ids = generators[grid_name](level)
-    grid_info = {"grid_name": grid_name, "refinement_level": level, **options}
+    grid_info = {"grid_name": grid_name, "level": level, **options}
     return xr.Variable(dim, cell_ids, grid_info)
 
 

From 7317f6eda6628d7e6704c1658f1f7cc54e39e28b Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 14:22:17 +0200
Subject: [PATCH 19/27] add jupyterlab-myst

---
 pixi.lock      | 21 +++++++++++++++++++--
 pyproject.toml |  1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/pixi.lock b/pixi.lock
index d8c3228b..fe93b294 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -2664,6 +2664,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server-2.17.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server_terminals-0.5.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-4.4.9-pyhd8ed1ab_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-myst-2.4.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_code_formatter-3.0.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_pygments-0.3.0-pyhd8ed1ab_2.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_server-2.27.3-pyhd8ed1ab_1.conda
@@ -3010,6 +3011,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server-2.17.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server_terminals-0.5.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-4.4.9-pyhd8ed1ab_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-myst-2.4.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_code_formatter-3.0.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_pygments-0.3.0-pyhd8ed1ab_2.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_server-2.27.3-pyhd8ed1ab_1.conda
@@ -3340,6 +3342,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server-2.17.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyter_server_terminals-0.5.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-4.4.9-pyhd8ed1ab_0.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-myst-2.4.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_code_formatter-3.0.2-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_pygments-0.3.0-pyhd8ed1ab_2.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_server-2.27.3-pyhd8ed1ab_1.conda
@@ -10430,6 +10433,20 @@ packages:
       - pkg:pypi/jupyterlab?source=compressed-mapping
     size: 8454849
     timestamp: 1758914033168
+  - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab-myst-2.4.2-pyhd8ed1ab_1.conda
+    sha256: 9ac0455d6ed74d317e7394dc89158d44d99089f35a144eee8964015903699475
+    md5: 1a76cdfb2080ae8007cd58b79707fb6b
+    depends:
+      - jupyter_server >=2.0.1,<3
+      - python >=3.9
+    constrains:
+      - jupyterlab >=4,<5
+    license: BSD-3-Clause
+    license_family: BSD
+    purls:
+      - pkg:pypi/jupyterlab-myst?source=hash-mapping
+    size: 2125353
+    timestamp: 1736260161474
   - conda: https://conda.anaconda.org/conda-forge/noarch/jupyterlab_code_formatter-3.0.2-pyhd8ed1ab_1.conda
     sha256: 43f2eab266e856785b4554681eb03561872a37aaee2688f4f8a389ed66d04ce3
     md5: f41368c2e6ca4338e6d8a05eaeda35cf
@@ -20032,8 +20049,8 @@ packages:
     timestamp: 1759875189286
   - pypi: ./
     name: xdggs
-    version: 0.2.3.dev19+gc9b190ba5.d20251009
-    sha256: 39223f51784c0474137d916a8b202c7c2099e035f76ec6eebb501b25ac4dac2b
+    version: 0.3.1.dev22+g6e87ff742.d20251009
+    sha256: daf76a1e03f7ead0a2b2438d4afc6c6a471f9f167d39d8316f40df96c6478dae
     requires_dist:
       - arro3-core>=0.4.0
       - cdshealpix
diff --git a/pyproject.toml b/pyproject.toml
index f97135ce..f265caf9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -218,6 +218,7 @@ python-build = ">=1.3.0,<2"
 h3-py = ">=4.3.0,<5"
 geopandas = ">=1.1.1,<2"
 pyinstrument = ">=5.1.1,<6"
+jupyterlab-myst = ">=2.4.2,<3"
 
 [tool.pixi.environments]
 nightly = { features = ["tests", "nightly"], no-default-feature = true }

From d40bc5677192e5023760bec2d55a4256a70e5ba5 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 15:14:20 +0200
Subject: [PATCH 20/27] pass index options along

---
 xdggs/conventions/decoders.py | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/xdggs/conventions/decoders.py b/xdggs/conventions/decoders.py
index 7732188f..deda4c14 100644
--- a/xdggs/conventions/decoders.py
+++ b/xdggs/conventions/decoders.py
@@ -6,7 +6,7 @@
 
 
 @register_decoder("xdggs")
-def xdggs(obj, grid_info, name):
+def xdggs(obj, grid_info, name, index_options):
     if name is None:
         name = "cell_ids"
 
@@ -33,13 +33,13 @@ def xdggs(obj, grid_info, name):
 
     var_ = var.copy(deep=True)
     var_.attrs = grid_info
-    index = index_cls.from_variables({name: var_}, options={})
+    index = index_cls.from_variables({name: var_}, options=index_options)
 
     return xr.Coordinates({name: var.variable}, indexes={name: index})
 
 
 @register_decoder("cf")
-def cf(obj, grid_info, name):
+def cf(obj, grid_info, name, index_options):
     vars_ = call_on_dataset(
         lambda ds: ds.variables,
         obj,
@@ -60,20 +60,19 @@ def cf(obj, grid_info, name):
             )
         )
         name = coords[0]
-    var = vars_[name].copy(deep=False)
-    var.attrs.pop("standard_name", None)
-    var.attrs.pop("units", None)
 
     translations = {"refinement_level": "level"}
     grid_info = {
         translations.get(name, name): value for name, value in crs.attrs.items()
     }
-
     grid_name = grid_info.pop("grid_mapping_name")
+    var = vars_[name].copy(deep=False)
+    var.attrs = grid_info
+
     if grid_name not in GRID_REGISTRY:
         raise ValueError(f"unknown grid name: {grid_name}")
     index_cls = GRID_REGISTRY[grid_name]
 
-    index = index_cls.from_variables({name: var}, options=grid_info)
+    index = index_cls.from_variables({name: var}, options=index_options)
 
     return xr.Coordinates({name: var}, indexes={name: index})

From c1fbd1638a3115b591d5291dd439c1499d78223c Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 16:11:25 +0200
Subject: [PATCH 21/27] bump lock file

---
 pixi.lock | 47 +++++++++++++++++++++++------------------------
 1 file changed, 23 insertions(+), 24 deletions(-)

diff --git a/pixi.lock b/pixi.lock
index fe93b294..7ea8a030 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -229,7 +229,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tk-8.6.13-noxft_hd72426e_102.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tornado-6.5.2-py311h49ec1c0_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -460,7 +460,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h892fb3f_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tornado-6.5.2-py311h3696347_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -679,7 +679,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/tbb-2021.13.0-h18a62a1_3.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tk-8.6.13-h2c6b04d_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tornado-6.5.2-py311h3485c13_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -937,7 +937,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tk-8.6.13-noxft_hd72426e_102.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tornado-6.5.2-py312h4c3975b_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -1168,7 +1168,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h892fb3f_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tornado-6.5.2-py312h163523d_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -1387,7 +1387,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/tbb-2021.13.0-h18a62a1_3.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tk-8.6.13-h2c6b04d_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tornado-6.5.2-py312he06e257_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -1644,7 +1644,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tk-8.6.13-noxft_hd72426e_102.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tornado-6.5.2-py313h07c4f96_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -1875,7 +1875,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h892fb3f_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tornado-6.5.2-py313hcdf3177_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -2094,7 +2094,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/tbb-2021.13.0-h18a62a1_3.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tk-8.6.13-h2c6b04d_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tornado-6.5.2-py313h5ea7bf4_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -2850,7 +2850,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/threadpoolctl-3.6.0-pyhecae5ae_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tinycss2-1.4.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tk-8.6.13-noxft_hd72426e_102.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tornado-6.5.2-py313h07c4f96_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -3189,7 +3189,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/threadpoolctl-3.6.0-pyhecae5ae_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tinycss2-1.4.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h892fb3f_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tornado-6.5.2-py313hcdf3177_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -3513,7 +3513,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/threadpoolctl-3.6.0-pyhecae5ae_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tinycss2-1.4.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tk-8.6.13-h2c6b04d_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tornado-6.5.2-py313h5ea7bf4_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -4424,7 +4424,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/sysroot_linux-64-2.28-h4ee821c_8.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tk-8.6.13-noxft_hd72426e_102.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/linux-64/tornado-6.5.2-py313h07c4f96_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -4658,7 +4658,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/noarch/stack_data-0.6.3-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tk-8.6.13-h892fb3f_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/osx-arm64/tornado-6.5.2-py313hcdf3177_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -4880,7 +4880,7 @@ environments:
         - conda: https://conda.anaconda.org/conda-forge/win-64/tbb-2021.13.0-h18a62a1_3.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/tblib-3.1.0-pyhd8ed1ab_0.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tk-8.6.13-h2c6b04d_2.conda
-        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
+        - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
         - conda: https://conda.anaconda.org/conda-forge/win-64/tornado-6.5.2-py313h5ea7bf4_1.conda
         - conda: https://conda.anaconda.org/conda-forge/noarch/traitlets-5.14.3-pyhd8ed1ab_1.conda
@@ -19224,18 +19224,17 @@ packages:
     purls: []
     size: 3466348
     timestamp: 1748388121356
-  - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.2.1-pyhe01879c_2.conda
-    sha256: 040a5a05c487647c089ad5e05ad5aff5942830db2a4e656f1e300d73436436f1
-    md5: 30a0a26c8abccf4b7991d590fe17c699
+  - conda: https://conda.anaconda.org/conda-forge/noarch/tomli-2.3.0-pyhcf101f3_0.conda
+    sha256: cb77c660b646c00a48ef942a9e1721ee46e90230c7c570cdeb5a893b5cce9bff
+    md5: d2732eb636c264dc9aa4cbee404b1a53
     depends:
-      - python >=3.9
+      - python >=3.10
       - python
     license: MIT
-    license_family: MIT
     purls:
       - pkg:pypi/tomli?source=compressed-mapping
-    size: 21238
-    timestamp: 1753796677376
+    size: 20973
+    timestamp: 1760014679845
   - conda: https://conda.anaconda.org/conda-forge/noarch/toolz-1.0.0-pyhd8ed1ab_1.conda
     sha256: eda38f423c33c2eaeca49ed946a8d3bf466cc3364970e083a65eb2fd85258d87
     md5: 40d0ed782a8aaa16ef248e68c06c168d
@@ -20049,8 +20048,8 @@ packages:
     timestamp: 1759875189286
   - pypi: ./
     name: xdggs
-    version: 0.3.1.dev22+g6e87ff742.d20251009
-    sha256: daf76a1e03f7ead0a2b2438d4afc6c6a471f9f167d39d8316f40df96c6478dae
+    version: 0.3.1.dev24+gd40bc5677.d20251009
+    sha256: d7ea91d0c2feb8856b041600f45c5cf5a143d51cadaa250154f3d0e1a13d57f8
     requires_dist:
       - arro3-core>=0.4.0
       - cdshealpix

From 1906e86f912eb86f3bca94129034a05b71e74415 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 16:12:44 +0200
Subject: [PATCH 22/27] pass index options along

---
 xdggs/tests/conventions/test_decoders.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index 6a7e86c7..1f8847a7 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -103,5 +103,5 @@ def test_xdggs(obj_type, coord_name, coord, grid_info, name):
         {coord_name: coord},
         indexes={coord_name: create_index(coord_name, coord, grid_info)},
     )
-    actual = decoders.xdggs(obj, grid_info, name)
+    actual = decoders.xdggs(obj, grid_info, name, index_options={})
     xr.testing.assert_identical(actual.to_dataset(), expected.to_dataset())

From f29e55d282338baf3e3a52b4e4b6eb28244c4820 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 17:14:03 +0200
Subject: [PATCH 23/27] only try to convert dataset objects

---
 xdggs/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xdggs/utils.py b/xdggs/utils.py
index d24ff5aa..b94dbefc 100644
--- a/xdggs/utils.py
+++ b/xdggs/utils.py
@@ -32,7 +32,7 @@ def call_on_dataset(func, obj, *args, kwargs=None):
 
     result = func(ds, *args, **kwargs)
 
-    if isinstance(obj, xr.DataArray):
+    if isinstance(obj, xr.DataArray) and isinstance(result, xr.Dataset):
         return xr.DataArray._from_temp_dataset(result, name=obj.name)
     else:
         return result

From 401866830f231a0fb7a17093d37d900be46e06e0 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 17:14:59 +0200
Subject: [PATCH 24/27] move the cell id creation into a separate function

---
 xdggs/tests/conventions/test_decoders.py | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index 1f8847a7..6b6c9921 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -32,14 +32,19 @@ def generate_h3_cells(level):
     return change_resolution(base_cells, level)
 
 
-def create_coordinate(grid_name, dim, level, **options):
+def generate_cell_ids(grid_name, level):
     generators = {
         "healpix": lambda level: np.arange(12 * 4**level),
         "h3": generate_h3_cells,
     }
 
-    cell_ids = generators[grid_name](level)
+    return generators[grid_name](level)
+
+
+def create_coordinate(grid_name, dim, level, **options):
+    cell_ids = generate_cell_ids(grid_name, level)
     grid_info = {"grid_name": grid_name, "level": level, **options}
+
     return xr.Variable(dim, cell_ids, grid_info)
 
 

From 60dc4e8c23b9e214766c974f119d822293845ff8 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 17:15:19 +0200
Subject: [PATCH 25/27] refactor the index creation function

---
 xdggs/tests/conventions/test_decoders.py | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index 6b6c9921..18b13bb4 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -48,18 +48,15 @@ def create_coordinate(grid_name, dim, level, **options):
     return xr.Variable(dim, cell_ids, grid_info)
 
 
-def create_index(name, coord, grid_info):
-    translations = {"refinement_level": "level"}
+def create_index(name, coord, options):
+    translations = {"refinement_level": "level", "grid_mapping_name": "grid_name"}
 
-    if grid_info is None:
-        grid_info = {
-            translations.get(name, name): value for name, value in coord.attrs.items()
-        }
+    if not options:
+        options = coord.attrs
 
-    var = coord.copy(deep=False)
-    var.attrs = grid_info
+    grid_info = {translations.get(name, name): value for name, value in options.items()}
 
-    return xdggs.HealpixIndex.from_variables({name: var}, options={})
+    return xdggs.HealpixIndex.from_variables({name: coord}, options=grid_info)
 
 
 @pytest.mark.parametrize("obj_type", ["DataArray", "Dataset"])

From 0acb855ca7e6ee56374bd28f109562dc11dfa098 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 17:16:05 +0200
Subject: [PATCH 26/27] add tests for the cf convention decoder

---
 xdggs/tests/conventions/test_decoders.py | 72 ++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index 18b13bb4..ca47cfb8 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -107,3 +107,75 @@ def test_xdggs(obj_type, coord_name, coord, grid_info, name):
     )
     actual = decoders.xdggs(obj, grid_info, name, index_options={})
     xr.testing.assert_identical(actual.to_dataset(), expected.to_dataset())
+
+
+@pytest.mark.parametrize("obj_type", ["DataArray", "Dataset"])
+@pytest.mark.parametrize(
+    ["coord_name", "dim", "metadata", "grid_info", "name"],
+    (
+        pytest.param(
+            "cell_ids",
+            "cells",
+            {
+                "grid_mapping_name": "healpix",
+                "refinement_level": 1,
+                "indexing_scheme": "nested",
+            },
+            None,
+            None,
+            id="healpix-all_defaults",
+        ),
+        pytest.param(
+            "cell_ids",
+            "cells",
+            {"grid_mapping_name": "h3", "refinement_level": 2},
+            None,
+            None,
+            id="h3-all_defaults",
+        ),
+        pytest.param(
+            "zone_ids",
+            "zones",
+            {
+                "grid_mapping_name": "healpix",
+                "refinement_level": 1,
+                "indexing_scheme": "nested",
+            },
+            None,
+            "zone_ids",
+            id="healpix-override_name",
+        ),
+        pytest.param(
+            "cell_ids",
+            "cells",
+            {"grid_mapping_name": "h3", "refinement_level": 2},
+            {"grid_name": "h3", "level": 2},
+            None,
+            id="h3-override_grid_info",
+        ),
+    ),
+)
+def test_cf(obj_type, coord_name, dim, metadata, grid_info, name):
+    cell_ids = generate_cell_ids("healpix", level=metadata["refinement_level"])
+    coord = xr.Variable(
+        dim,
+        cell_ids,
+        {"standard_name": f"{metadata['grid_mapping_name']}_index", "units": 1},
+    )
+    crs = xr.Variable((), np.array(0, dtype="uint8"), metadata)
+
+    if obj_type == "Dataset":
+        obj = xr.Dataset(coords={coord_name: coord, "crs": crs})
+    else:
+        obj = xr.DataArray(
+            np.zeros_like(coord.data),
+            coords={coord_name: coord, "crs": crs},
+            dims=coord.dims,
+        )
+
+    expected = xr.Coordinates(
+        {coord_name: coord},
+        indexes={coord_name: create_index(coord_name, coord, grid_info=metadata)},
+    )
+    actual = decoders.cf(obj, grid_info, name, index_options={})
+    xr.testing.assert_identical(actual.to_dataset(), expected.to_dataset())

From ebef9606695a48cdf198f830259a5ff8f5be305a Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Thu, 9 Oct 2025 17:25:01 +0200
Subject: [PATCH 27/27] refactor the index creation

---
 xdggs/tests/conventions/test_decoders.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/xdggs/tests/conventions/test_decoders.py b/xdggs/tests/conventions/test_decoders.py
index ca47cfb8..1dcf713a 100644
--- a/xdggs/tests/conventions/test_decoders.py
+++ b/xdggs/tests/conventions/test_decoders.py
@@ -48,15 +48,17 @@ def create_coordinate(grid_name, dim, level, **options):
     return xr.Variable(dim, cell_ids, grid_info)
 
 
-def create_index(name, coord, options):
+def create_index(name, coord, options=None):
     translations = {"refinement_level": "level", "grid_mapping_name": "grid_name"}
 
-    if not options:
-        options = coord.attrs
+    if options is None:
+        options = {}
 
-    grid_info = {translations.get(name, name): value for name, value in options.items()}
+    grid_info = {
+        translations.get(name, name): value for name, value in coord.attrs.items()
+    }
 
-    return xdggs.HealpixIndex.from_variables({name: coord}, options=grid_info)
+    return xdggs.HealpixIndex.from_variables({name: coord}, options=grid_info | options)
 
 
 @pytest.mark.parametrize("obj_type", ["DataArray", "Dataset"])
@@ -175,7 +177,7 @@ def test_cf(obj_type, coord_name, dim, metadata, grid_info, name):
 
     expected = xr.Coordinates(
         {coord_name: coord},
-        indexes={coord_name: create_index(coord_name, coord, grid_info=metadata)},
+        indexes={coord_name: create_index(coord_name, coord, options=metadata)},
     )
     actual = decoders.cf(obj, grid_info, name, index_options={})
     xr.testing.assert_identical(actual.to_dataset(), expected.to_dataset())