t.rast.import.netcdf: handle empty CRS and no subdataset

.github/workflows/apt.txt

@@ -12,9 +12,12 @@ libopenblas-dev
 libpng-dev
 libproj-dev
 libreadline-dev
+libudunits2-dev
+libudunits2-data
 libzstd-dev
 proj-bin
 pdal
 sqlite3
 subversion
+udunits-bin
 zlib1g-dev

.github/workflows/ci.yml

@@ -102,6 +102,8 @@ jobs:
         run: |
           GDAL_VERSION="$(gdal-config --version)"
           export GDAL_VERSION
+          UDUNITS2_XML_PATH=/usr/share/xml/udunits/udunits2.xml
+          export UDUNITS2_XML_PATH
           pip install -r grass-addons/.github/workflows/extra_requirements.txt
 
       - name: Set up R

.github/workflows/extra_requirements.txt

@@ -4,5 +4,5 @@ pandas
 scikit-learn
 GDAL==${GDAL_VERSION}
 pygbif
-cf_units
+cf_units @ git+https://github.com/SciTools/cf-units@f57a7f1fdba4e9424e4dbbc01b614e521a88086c
 thredds_crawler

src/temporal/t.rast.import.netcdf/t.rast.import.netcdf.html

@@ -15,10 +15,18 @@ <h2>DESCRIPTION</h2>
 can be imported via <em>r.in.gdal</em> or linked with <em>r.external</em>.
 
 <p>
-<em>t.rast.import.netcdf</em> can use GDALs Virtual Raster format (VRT) if data's
+<em>t.rast.import.netcdf</em> uses GDALs Virtual Raster format (VRT) if data's
 Coordinate Reference system differs from the one of the current location where they
 are supposed to be imported.
 
+<p>
+Reprojection on import is done using GDAL warp if necessary. In that case,
+users should be aware of the extent and resolution of the data to import
+and the current computational region. Import is limited to and aligned with
+the current computational region, if the <b>r-flag</b> is set. Otherwise,
+extent and resolution in the target CRS is guessed by GDAL. Import of global
+data to coordinate systems that do not support that extent will thus fail.
+
 <p>
 Starting with GRASS GIS version 8.0, different variables or subdatasets in a
 NetCDF file can be imported as "semantic_label" into one STRDS. To achieve this,