make attrs compatible with netcdf format

src/xarray_grass/grass_interface.py

@@ -314,7 +314,9 @@ def list_grass_objects(self, mapset: str = None) -> dict[list[str]]:
 
     @staticmethod
     def get_raster_info(raster_id: str) -> Info:
-        return gs.parse_command("r.info", map=raster_id, flags="ge")
+        result = gs.parse_command("r.info", map=raster_id, flags="ge")
+        # Strip quotes from string values (r.info returns quoted strings)
+        return {k: v.strip('"') if isinstance(v, str) else v for k, v in result.items()}
 
     @staticmethod
     def get_raster3d_info(raster3d_id):

src/xarray_grass/to_grass.py

@@ -250,7 +250,7 @@ def _write_stds(self, data: xr.DataArray, dims: Mapping):
         # 1. Determine the temporal coordinate and type
         time_coord = data[dims["start_time"]]
         time_dtype = time_coord.dtype
-        time_unit = None  # Initialize for absolute time case
+        time_unit = ""  # Initialize for absolute time case
         if isinstance(time_dtype, np.dtypes.DateTime64DType):
             temporal_type = "absolute"
         elif np.issubdtype(time_dtype, np.integer):

src/xarray_grass/xarray_grass.py

@@ -258,7 +258,8 @@ def _set_cf_coordinates_attributes(
             for time_dim in time_dims:
                 da[time_dim].attrs["axis"] = "T"
                 da[time_dim].attrs["standard_name"] = "time"
-                da[time_dim].attrs["units"] = time_unit
+                if time_unit:  # NetCDF does not accept units for absolute time
+                    da[time_dim].attrs["units"] = time_unit
         da[x_coord].attrs["axis"] = "X"
         da[y_coord].attrs["axis"] = "Y"
         if self.grass_interface.is_latlon():
@@ -277,8 +278,8 @@ def _set_cf_coordinates_attributes(
             else:
                 da[x_coord].attrs["standard_name"] = "projection_x_coordinate"
                 da[y_coord].attrs["standard_name"] = "projection_y_coordinate"
-                da[x_coord].attrs["units"] = spatial_unit
-                da[y_coord].attrs["units"] = spatial_unit
+                da[x_coord].attrs["units"] = str(spatial_unit)
+                da[y_coord].attrs["units"] = str(spatial_unit)
         return da
 
     def _open_grass_raster(self, raster_name: str) -> xr.DataArray:
@@ -304,8 +305,8 @@ def _open_grass_raster(self, raster_name: str) -> xr.DataArray:
         da_with_attrs.attrs["source"] = ",".join(
             [r_infos["source1"], r_infos["source2"]]
         )
-        da_with_attrs.attrs["units"] = r_infos.get("units", "")
-        da_with_attrs.attrs["comment"] = r_infos.get("comments", "")
+        da_with_attrs.attrs["units"] = str(r_infos.get("units", ""))
+        da_with_attrs.attrs["comment"] = str(r_infos.get("comments", ""))
         # CF attributes "institution" and "references"
         # Do not correspond to a direct GRASS value.
         return da_with_attrs
@@ -352,7 +353,7 @@ def _open_grass_strds(self, strds_name: str) -> xr.DataArray:
         ).values()
         strds_infos = self.grass_interface.get_stds_infos(strds_id, stds_type="strds")
         if strds_infos.temporal_type == "absolute":
-            time_unit = None
+            time_unit = ""
         else:
             time_unit = strds_infos.time_unit
         start_time_dim = f"start_time_{strds_name}"
@@ -421,7 +422,7 @@ def _open_grass_str3ds(self, str3ds_name: str) -> xr.DataArray:
         ).values()
         strds_infos = self.grass_interface.get_stds_infos(str3ds_id, stds_type="str3ds")
         if strds_infos.temporal_type == "absolute":
-            time_unit = None
+            time_unit = ""
         else:
             time_unit = strds_infos.time_unit
         start_time_dim = f"start_time_{str3ds_name}"

tests/test_xarray_grass.py

@@ -272,6 +272,7 @@ def test_attributes_separation(self, grass_i, temp_gisdb) -> None:
             raster=ACTUAL_RASTER_MAP,
             raster_3d=ACTUAL_RASTER3D_MAP,
             strds=ACTUAL_STRDS,
+            str3ds=RELATIVE_STR3DS,
         )
 
         # Dataset-level attributes: only these should be present
@@ -338,8 +339,8 @@ def test_attributes_separation(self, grass_i, temp_gisdb) -> None:
             assert test_dataset[time_coord].attrs["standard_name"] == "time"
 
             # For relative time coordinates, units should be present
-            if time_coord.startswith("start_time_") or time_coord.startswith(
-                "end_time_"
+            if time_coord.endswith(RELATIVE_STR3DS) or time_coord.endswith(
+                RELATIVE_STR3DS
             ):
                 # This is a relative time coordinate, should have units
                 assert "units" in test_dataset[time_coord].attrs