CDO

Hello Niklas,

With selgrid,2 it works for me without any problems and that is also the only solution, because the other grids in the input file have no coordinates:

cdo gennn,target_grid_icon_d2_002.txt -selgrid,2 ../icon_grid_0047_R19B07_L.nc weights_icon_d2_002.nc

Cheers,
Uwe

Hello Uwe, thanks for answering! The bug is still there, but your reply helped me to localize it more precisely. I apologize for being wrong at the respective point.
What I forgot to mention is that in the first attempt I didn't execute the command at its own but included in a bash script (inspired from https://www.dwd.de/DE/leistungen/opendata/help/modelle/Opendata_cdo_DE.pdf?__blob=publicationFile&v=4, page 3/4). I tried out your command on its own and indeed it does work. And I realized it also did in the bash script (it also does now after inserting "-selgrid,2"). So I was wrong thinking that it would fail at this step (line 10 in the script in the linked pdf).
The error message itself is referred to the actual remapping process which is line 16 in the script of the pdf. If you or someone else wants to check what I did you can take a grib2 file from opendata.dwd.de as example, in my case I tried with files from https://opendata.dwd.de/weather/nwp/icon-d2-eps/grib/00/u_10m/ and https://opendata.dwd.de/weather/nwp/icon-d2/grib/00/u_10m/ (to see if there is a difference between icon-d2-eps_germany[...] and icon-d2_germany[...] files, but in my case there isn't, the bug is the same in both cases). So, assuming all respective files are in the same folder (for simplicity), including the output file (test.grib2 in this case), the command would be e.g.:

cdo -f grb2 remap,target_grid_icon_d2_002.txt,weights_icon_d2_002.nc icon-d2-eps_germany_icosahedral_single-level_2023021700_000_2d_u_10m.grib2 test.grib2

And this just gives me the error message (as mentioned in my first post, but shown more in detail here):

cdo remap (Warning): Reference to horizontal grid not available!

cdo remap (Abort): Reference to source grid not found!

And this is the actual point where I'm stuck. Using cdo sinfov icon-d2-eps_germany_icosahedral_single-level_2023021700_000_2d_u_10m.grib2 I get (as part of larger file information):

[...]

Grid coordinates :
1 : unstructured : points=542040

[...]

At least this shows me that the grid size matches in all respective files and should not be the reason for the error. All I can say to my understanding is that missing "References" are the main point of the bug. But at the moment I have no further idea how to fix it... So I hope based onto this more detailed information you and/or someone else will be able to help at this point.

Thank you so far and best regards!

I tried it with the following data and it works fine on different machines from CDO version 2.0.0:

cdo -f grb2 remap,target_grid_icon_d2_002.txt,weights_icon_d2_002.nc icon-d2-eps_germany_icosahedral_single-level_2023022100_000_2d_u_10m.grib2 test.grib2

Hi Uwe! Good question, indeed I could/should have given this information in advance. During my last tries I had been working with version 2.1.1, the most current one I was able to find then. Based onto what you wrote I replaced this version with the 2.0.0 one and gave it another try, but unfortunately this doesn't fix the error either...

I don't know if it's relevant but here I list you the installed versions of the other mandatory packages in the "background":

eccodes-2.28.0
hdf5-1.12.2
netcdf-4.9.1
zlib-1.2.13

...and some additional ones (optional and/or not included in the outdated tutorial I linked above):

curl-7.88.1
jasper-4.0.0
libaec-1.0.6 (Adaptive Entropy Coding)

Do you think it could be useful to replace one or several packages with other versions? Maybe my way of thinking "the more up to date the better" is not necessarily always true... ;-)

I suspect replacing libraries will not help.
Maybe the cdo verbose output will help (cdo -v remap...). For me, the relevant part looks like this:

cdo -f grb2 -v remap,target_grid_icon_d2_002.txt,weights_icon_d2_002.nc icon-d2-eps_germany_icosahedral_single-level_2023022100_000_2d_u_10m.grib2 test.grib2

cdo    remap: Set max_remaps to 2
cdo    remap: Reading remap weights: SCRIP remapping with CDO
cdo    remap: From file: weights_icon_d2_002.nc
cdo    remap: mapType = Nearest neighbor
cdo    remap: normalize_opt = none
cdo    remap: Remapping between: unstructured and lonlat
cdo    remap: Using remap 0

Hello Uwe, sorry for replying late!

I tried your "verbose" suggestion which did work as far as I remember, though it didn't really contribute to fix the issue. But it's solved meanwhile otherwise: When changing back from cdo version 2.0.0 back to 2.1.1 I had to download the package again - nothing special, but for whatever reason after this download and setting up the 2.1.1 version again as usual it's working now. My only explanation for this is that something must have went wrong during the former downloads which caused cdo to fail... I have no idea what but as long as it works, I will not speculate about further details and hope it stays this way now. ;)
Thank you for your support though, I learned some further backgrounds about all this and maybe in case of other bugs I can come back to it and maybe find solutions on my own before asking again here. ;-)

Best regards!