Data Sources
============

``flexprep`` supports multiple input data sources for obtaining ECMWF IFS data.
Each source provides the same type of dataset suitable for the preprocessing step.


Available Sources
-----------------

.. list-table::
   :header-rows: 1
   :widths: 10 25 45 30

   * - Source
     - Module
     - Description
     - Access Requirements
   * - **Local**
     - ``flexprep.sources.local``
     - Reads existing GRIB files from a local directory. Ideal for offline use or testing.
     - No restrictions.
   * - **MARS**
     - ``flexprep.sources.mars``
     - Downloads IFS HRES data directly from the ECMWF **MARS** archive.
     - Requires ECMWF membership and valid MARS access rights.
       See `ECMWF: Access to MARS <https://www.ecmwf.int/en/forecasts/accessing-forecasts/order-historical-datasets>`_.
   * - **Polytope**
     - ``flexprep.sources.polytope``
     - Retrieves IFS data using *earthkit-data*’s Polytope source. Core model-level
       variables (winds, temperature, ``etadot``) are fetched from the
       ``swiss-meteo`` collection, while all other model-level, surface, and
       constant fields are retrieved from the ECMWF ``ecmwf-mars`` collection.
     - Access is restricted to ECMWF member states. Access to the
       ``swiss-meteo`` collection must be authorized by ECMWF. To request access,
       contact ``nina.burgdorfer@meteoswiss.ch``.


.. note::

   **Developer note:** Figure out how to use Polytope *feature extraction* with
   the Polytope source data.

   Documentation:
   https://polytope.readthedocs.io/en/latest/