Improve time handling

.github/workflows/tests.yml

@@ -17,8 +17,8 @@ jobs:
     steps:
     - name: Install dependencies
       run: |
-        apt update
-        apt install -y ca-certificates
+        apt-get update
+        apt-get install -y ca-certificates
 
     - uses: actions/checkout@v5
 

README.md

@@ -21,23 +21,27 @@ You need to install GRASS independently.
 >>> import xarray as xr
 >>> test_ds = xr.open_dataset("/home/lc/grassdata/nc_spm_08_grass7/PERMANENT/", raster=["boundary_county_500m", "elevation"])
 >>> test_ds
-<xarray.Dataset> Size: 244kB
-Dimensions:               (y: 150, x: 135)
+<xarray.Dataset> Size: 253kB
+Dimensions:               (y: 150, x: 140)
 Coordinates:
   * y                     (y) float32 600B 2.2e+05 2.2e+05 ... 2.207e+05
-  * x                     (x) float32 540B 6.383e+05 6.383e+05 ... 6.39e+05
+  * x                     (x) float32 560B 6.383e+05 6.383e+05 ... 6.39e+05
 Data variables:
-    boundary_county_500m  (y, x) float64 162kB ...
-    elevation             (y, x) float32 81kB ...
+    boundary_county_500m  (y, x) float64 168kB ...
+    elevation             (y, x) float32 84kB ...
 Attributes:
-    crs_wkt:   PROJCRS["NAD83(HARN) / North Carolina",BASEGEOGCRS["NAD83(HARN...
+    crs_wkt:      PROJCRS["NAD83(HARN) / North Carolina",BASEGEOGCRS["NAD83(H...
+    Conventions:  CF-1.13-draft
+    history:      2025-10-31 18:22:16.644873+00:00: Created with xarray-grass...
+    source:       GRASS database. project: <nc_spm_08_grass7>, mapset:<PERMAN...
+
 ```
 
 You can choose which maps you want to load with the `raster`, `raster_3d`, `strds` and `str3ds` parameters to `open_dataset`.
 Those accept either a single string or an iterable.
 If none of those are specified, the whole mapset will be loaded, ignoring single maps that are already registered in either a `strds` or `str3ds`;
 those maps will be loaded into the Xarray Dataset for being part of the GRASS Space Time Dataset.
-As of version 0.2.0, any time-stamp associated to a single map not registered in a stds is ignored.
+Any time-stamp associated to a single map not registered in a stds is ignored.
 
 The extent and resolution of the resulting `Dataset` is defined by the region setting of GRASS, set with the `g.region` GRASS tool.
 Note that in GRASS the 3D resolution is independent from the 2D resolution.
@@ -46,8 +50,12 @@ The coordinates in the Xarray `Dataset` correspond to the center of the GRASS ce
 
 If run from outside a GRASS session, `xarray-grass` will automatically create a session in the requested project and mapset.
 If run from within GRASS, only maps from accessible mapsets could be loaded.
-In GRASS, you can list the accessible mapsets with `g.mapsets`.
+You can list the accessible mapsets with `g.mapsets` from GRASS.
+
+In GRASS, the time dimension of various STDSs is not homogeneous, as it is for the spatial coordinates.
+To reflect this, xarray-grass will create one time dimension for each STDS loaded.
 
+From within a grass session, it is possible to access various mapsets.
 
 ## CF conventions attributes mapping
 
@@ -64,11 +72,65 @@ The attributes of the coordinates are in line with CF Conventions.
 
 ### Dataset attributes
 
-The only attributes set at the dataset level are `crs_wkt` and `Conventions`.
+The attributes set at the dataset level are:
+  - `crs_wkt` from the g.proj command
+  - `Conventions`, the CF Convention version
+  - `history`, the time of creation and version of xarray-grass
+  - `source`, the name of the current grass project and mapset
 
 ## Writing an Xarray Dataset or DataArray to GRASS
 
-TODO.
+
+```python
+import xarray as xr
+from xarray_grass import to_grass
+
+mapset = "/home/lc/grassdata/nc_spm_08_grass7/PERMANENT/"  # Or pathlib.Path
+
+test_ds = xr.open_dataset(
+    mapset,
+    raster=["boundary_county_500m", "elevation"],
+    strds="LST_Day_monthly@modis_lst",
+)
+
+print(test_ds)
+
+# Let's write the modis time series back into the PERMANENT mapset
+
+da_modis = test_ds["LST_Day_monthly"]
+# xarray-grass needs the CRS information to write to GRASS
+da_modis.attrs["crs_wkt"] = test_ds.attrs["crs_wkt"]
+
+to_grass(
+    dataset=da_modis,
+    mapset=mapset,
+    dims={
+        "LST_Day_monthly": {"start_time": "start_time_LST_Day_monthly"},
+    },
+    overwrite=False
+)
+```
+
+The above `print` statement should return this:
+
+```
+<xarray.Dataset> Size: 3MB
+Dimensions:                     (y: 165, x: 179, start_time_LST_Day_monthly: 24)
+Coordinates:
+  * y                           (y) float32 660B 2.196e+05 ... 2.212e+05
+  * x                           (x) float32 716B 6.377e+05 ... 6.395e+05
+  * start_time_LST_Day_monthly  (start_time_LST_Day_monthly) datetime64[ns] 192B ...
+    end_time_LST_Day_monthly    (start_time_LST_Day_monthly) datetime64[ns] 192B ...
+Data variables:
+    boundary_county_500m        (y, x) float64 236kB ...
+    elevation                   (y, x) float32 118kB ...
+    LST_Day_monthly             (start_time_LST_Day_monthly, y, x) int32 3MB ...
+Attributes:
+    crs_wkt:      PROJCRS["NAD83(HARN) / North Carolina",BASEGEOGCRS["NAD83(H...
+    Conventions:  CF-1.13-draft
+    history:      2025-11-01 02:10:24.652838+00:00: Created with xarray-grass...
+    source:       GRASS database. project: <nc_spm_08_grass7_test>, mapset:<P...
+```
 
 ## Roadmap
 
@@ -86,7 +148,7 @@ TODO.
   - [x] Write to STRDS
   - [x] Write to 3D raster
   - [x] Write to STR3DS
-  - [ ] Honour the `dims` argument: transpose if dimensions are not in the expected order
+  - [ ] Transpose if dimensions are not in the expected order
   - [ ] Support time units for relative time
   - [ ] Support `end_time`
   - [ ] Accept writing into a specific mapset (GRASS 8.5)