Geographic Information Systems Asked by André Della Libera Zanchetta on January 11, 2021
Problem statement:
I need to implement an easy-to-share script compatible with Windows environment that allows me to open a NetCDF, manipulate it, and save it in Grib2 format.
Attempt 1: iris / iris-grib
I initially implemented my code with success using iris
and iris-grib
in a Linux environment. However, iris-grib
depends on cf-units
/udunits2
/grib_api
packages, which have serious compatibility issues with Windows (e.g. [1]), so it would be hard to make the code easy-to-share.
Attempt 2: xarray + cfgrib
Later, I tried to perform something like:
import xarray as xr
import cfgrib
my_ds = xr.open_dataset(INPUT_FILE_PATH)
[...some manipulation on my_ds...]
cfgrib.to_grib(my_ds, OUTPUT_FILE_PATH, grib_keys={'edition': 2})
Which worked great until the cfgrib.to_grib(...)
line. There I got the error:
ValueError: required grib_key ‘gridType’ not passed nor auto-detected.
As my input NetCDF file is in EPSG:4326 projection (WGS-84), I tried to set the grib_keys
arguments as grib_keys={'edition': 2, 'gridType': 'regular_ll'}
.
ValueError: sample not found: ‘regular_ll_sfc_grib2’
Which seems to be an issue with the cfgrib
installation (done using conda) not being able to find its own ancillary internal files.
Attempt 3: cdo
Ok, so I saw that there is a Python package that wrappers cdo. Great! So with some file writings/readings, I can do what I want. Right?
Not really.
The cdo package installed with conda install cdo
is indeed just a wrapper, so that the system is expected to have the own cdo command available and ready to run. As running cdo on Windows requires a cygwin set up, making the code easy-to-share would be somewhat really messy.
So…
What is a good and easy-to-share way to save a grib2 file on Windows 10 out of a NetCDF file?
[1] https://stackoverflow.com/questions/38979819/iris-for-anaconda-fails-to-read-grib
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