Support semantic_labels for STRDS

[ninsbl]

Space Time Raster Datasets can have semantic labels that can be understood similarly to variables in ZARR or NetCDF.

It would be great if xarray-grass would support those and split STRDS with multiple semantic labels into multiple variables.

semantic_labels (number and list of semantic_labels) are part of the t.info return.

[lrntct]

Hi Stefan,

If I understand well, you're proposing to split one STRDS into X+1 number of variables, each sharing the same x,y,time dimensions, with X being the number of semantic_labels present in the STRDS, +1 for those maps without any label.
If a map has multiple labels, the map would be duplicated across each corresponding variables in the datacube.
Each variable name could be f"{strds_name}_{semantic_label}", plus attributes entry for source_strds, and semantic_label, or maybe an additional coordinate for source strds, but that might make the datamodel unecessarily messy.

That would cover only the grass->xarray transition, not xarray->grass one.

Does this fits how you envision this to work? Because I don't think I've ever used semantic_labels, so I'm not familiar with the actual use cases.

[ninsbl]

semantic_labels were introduced originally as bands, and the background has been to better handle satellite imagery. So, that is a - if not the most - common use-case for semantic_labels. They exist only in STRDS and only in version >= 3 of the TGIS database (meaning databases.

Sentinel-2 import addons for example create semantic_labels like S2_1 for band 1, S2_2 for band 2 and so on, where one scene can have e.g. 13 different "bands" (=semantic_labels). Each band is represented by a different GRASS raster map with a unique name, but all raster maps from one scene share the same start_time.

So, as an example: if you have 3 sensinel-2 scenes (say from 2026-06-01 11:00:00, 2026-07-01 11:00:00 and 2026-08-01 11:00:00) with just the RGB bands (S2_4, S2_3 and S2_2) in a STRDS, whe strds info would show 9 maps and tree semantic labels, and start_time=2026-06-01 11:00:00, end_time=2026-08-01 11:00:00. The list of semantic_labels would be S2_2, S2_3, S2_4. However, notice that the time interval does not have to be regular. And I don`t think there is any enforcment of "complete" images in STRDS (meanign that all semantic_labels are present for all time steps...

[ninsbl]

I may be able to come up with a PR in a little while...