support MTG data

[brancomat]

https://user.eumetsat.int/resources/user-guides/mtg-test-data

[spanezz]

I had a first glance. What I found:

• data are disseminated in NetCDF format, a special case of HDF5, and the special compression algorithm is free software and already distributed as an HDF5 filter plugin: https://github.com/silx-kit/hdf5plugin
• once the filter plugin is installed, any NetCDF/HDF5 library in C++ or Python will be able to open and read the files
• the structure of the data inside the files seems to be well described

However, due to the different set of instruments in MTG compared to MSG the data is very different both in what is measured and how it is used: I've seen mentions of things like vertical soundings and lightning detection, for example.

It looks like python should be able to load MTG data without any involvement from meteosatlib at all.

It may be that accessing data directly will need some common postprocessing that is best shared into a library, and in that case meteosatlib could be well placed to be that library. I would sat that it will however not be defined by the data format itself, but by the way the data will be used, and that is outside my personal field of expertise

[spanezz]

Also, satpy is already able to read MTG files, and we might want to evaluate if there are things that meteosatlib does that satpy doesn't, and if not, considering discontinuing meteosatlib and migrating to satpy: https://satpy.readthedocs.io/en/stable/#id1