Support of the ICON grid in the Earthkit ecosystem

[ninaburg]

Summary:

ICON forecast data are defined on an unstructured grid. Currently, Earthkit can only access cell indices — not lat/lon coordinates — when loading ICON data. This makes native use of ICON data not supported across most Earthkit components and forces users to regrid to regular grids as a workaround.

Earthkit is now evolving to provide native support for the ICON grid, and this issue is used as a public communication and tracking space to share progress, releases, current capabilities, and upcoming features with the community.

Goal
Enable native ICON grid support in Earthkit:

1. Native unstructured grid loading with lat/lon coordinates using ds = earthkit.data.from_source("file", icon_filename).to_xarray()
2. Direct use in plots using earthkit.plots.quickplot(ds)
3. Diect use in regridding. Methods: linear interpolation and nearest neighbour. Using earthkit.regrid.regrid(ds[0], grid=[1,1])

Status tracking
16.02.2026

✅ Native ICON grid loading with latitude and longitude coordinates is now supported in the released version of earthkit-data
-> https://github.com/ecmwf/earthkit-data/releases/tag/0.19.0

✅ Direct plotting of ICON native grid data is now supported in the released version of earthkit-plots, including earthkit.plots.quickplot(ds) without requiring prior regridding
-> https://github.com/ecmwf/earthkit-plots/releases/tag/0.6.0

⚠️ Native regridding support via earthkit-regrid is not yet fully released. However, it is already functional when using the dedicated develop branch together with the compatible environment.

A fully working example environment and demonstration notebook is available here:
https://github.com/MeteoSwiss/nwp-fdb-polytope-demo/blob/native_grid-16022026/examples/Polytope/work_with_data_native_grid.ipynb

This enables end-to-end workflows including:

• loading ICON native grid data with coordinates
• visualising native grid data directly
• regridding using earthkit-regrid from the development branch

Full official release of earthkit-regrid native ICON support is still in progress.

11.02.2026

The goals outlined above can now be achieved using an experimental dependency setup (pre-release packages and development branches).

Setup instructions and a working example are available in this notebook:
https://github.com/MeteoSwiss/nwp-fdb-polytope-demo/blob/native_grid/examples/Polytope/work_with_data_native_grid.ipynb

⚠️ This is a developer preview and not part of a stable Earthkit release yet.

[ninaburg]

Hi @sandorkertesz, thanks a lot for the notebook you shared with us yesterday. I was able to test it and have added a link in the issue to share the current experimental status.

[cedschmidt-lab]

Hello,

I'm trying to reproduce your Notebook but I'm stuck at the f.metadata("gridSpec") line returning KeyError: 'gridSpec'.
I think I miss some definition? Do you have some dependences not explicated in the environment such as the Atlas library ?
Where are you with this topic ?

Thanks for your help !

[ninaburg]

Hello,

I'm trying to reproduce your Notebook but I'm stuck at the f.metadata("gridSpec") line returning KeyError: 'gridSpec'. I think I miss some definition? Do you have some dependences not explicated in the environment such as the Atlas library ? Where are you with this topic ?

Thanks for your help !

Hi @cedschmidt-lab,

Thanks for reporting this. We are currently seeing an error at this stage as well, and ECMWF is working on a proper fix on the library side.

In the meantime, there is a workaround described in the notebook: click the sites.ecmwf link to download the grid file, then move it to the expected local location, for example:

/home/cedschmidt/.local/share/eckit/geo/grid/icon/

and rename it to the filename expected in the logs, for example:

bbbd5a09855499243c7a4aa4c8762920-67adabf5c0cff041ebaafa61a3bda267.ek

Also, please make sure the following environment variable is set:

import os
os.environ["ECCODES_ECKIT_GEO"] = "1"

So this may be either the missing local grid file, or the environment variable not being set early enough.

We’ll update the notebook/library once the fix is available.

Cheers

[ninaburg]

With earthkit-data 0.20.0 we're currently encountering this new error when reading data on the unstructured grid:

import earthkit.data as ekd
src = ekd.from_source("file", "horizontal_constants_icon-ch1-eps.grib2")

f = src[0]
coords = f.to_latlon()

is giving:

---------------------------------------------------------------------------
KeyValueNotFoundError                     Traceback (most recent call last)
[/tmp/ipykernel_2261/3492249565.py](https://localhost:8080/#) in <cell line: 0>()
      5 #method 2
      6 f = src[0]
----> 7 coords = f.to_latlon()
      8 lats = coords["lat"]
      9 lons = coords["lon"]

9 frames
[/content/opendata-nwp-demos/.venv/lib/python3.12/site-packages/gribapi/errors.py](https://localhost:8080/#) in raise_grib_error(errid)
    379     Raise the GribInternalError corresponding to ``errid``.
    380     """
--> 381     raise ERROR_MAP[errid](errid)

KeyValueNotFoundError: Key/value not found