BUG: ugriddatasetaccessor.to_geodataframe

[hboisgon]

I tried using the to_geodataframe method for UgridDataset but found two issues:

• sometimes, the Dataset can contain no variables yet (eg uds = Ugrid2d.to_datatset()) and this is not allowed
• the crs is not passed to the geodataframe and is lost in the conversion.

The lines in question:

xugrid/xugrid/core/dataset_accessor.py

Lines 394 to 403 in b6c4fb5

	variables = [var for var in ds.data_vars if dim in ds[var].dims]
	# TODO deal with time-dependent data, etc.
	# Basically requires checking which variables are static, which aren't.
	# For non-static, requires repeating all geometries.
	# Call reset_index on multi-index to generate them as regular columns.
	gdfs.append(
	gpd.GeoDataFrame(
	data=ds[variables].to_dataframe(dim_order=dim_order),
	geometry=grid.to_shapely(dim),
	)

An idea of implementation:

gdf = gpd.GeoDataFrame(
    index=grid.to_dataset()[dim].values.astype(str),
    data=ds[variables].to_dataframe(dim_order=dim_order) if len(variables)>0 else None,
    geometry=grid.to_shapely(dim),
    crs = grid.crs,
)

[Huite]

Hi @hboisgon,

The CRS thing has an issue for itself with #138. Allowing to create a GeoDataFrame with only geometry seems reasonable.