46 implement actris ebas reader

[jgriesfeller]

1st iteration of an ACTRIS-EBAS reader (1st because neither the API nor the netcdf file's format is stable yet).

Done due to the need to test and use what NILU does to find errors on their side

closes #46

[magnusuMET]

The implementation is rather complicated to understand since it downloads data on use instead of acting on pre-downloaded files. I wish the download part could be separated from making the data accessible for pyaerocom

[magnusuMET]

This function is eager and does all the reading of all variables at once, where as I think we would like to have the reading done when calling data(var_to_read), for minimising the amount of data kept per iteration. Just a note as refactoring at this point might be a lot of work.

[jgriesfeller]

The problem is that in pyaerocom there's a check against supported variables.

https://github.com/metno/pyaerocom/blob/43f6fce139d1b09facc9ed01cb96d14e287b192f/pyaerocom/io/pyaro/read_pyaro.py#L48-L52

For that info to get, pyro has to know the variable names AFTER the variable name changing reader and is calling data(var_to_read) for that. And that is the reason the data is read early on (if I understood the code correctly).
In any case, this reader needs an variable name filter anyway.

[jgriesfeller]

The nature of this reader is to work online. The data can change at any time and it would too computational heavy to download all data from Nilu (for Nilu). Therefore the online reading is intended and part of the contract with ACTRIS.

[magnusuMET]

Approving to include this reader as a prototype for the release of this month