Use GAMMAPY_DATA in Gammapy codebase

[Bultako]

This PR replaces $GAMMAPY_EXTRA by $GAMMAPY_DATA hardcoded in the codebase of Gammapy, which prevents reproducibility of tutorials and catalog access for users not having env vars like $GAMMAPY_EXTRA or $GAMMA_CAT.

We can see $GAMMAPY_DATA has a data-repo stuck to Gammapy that is defined in http://gammapy.org/download/data/gammapy-data-index.json The codebase of Gammapy needs $GAMMAPY_DATA, only a few exceptional cases (mostly related with gammacat) may still be fixed.

• gammapy download datasets downloads the whole $GAMMAPY_DATA repo.
• gammapy download notebooks downloads does not download the repo.
• gammapy download tutorials downloads a big fraction of this repo, almost all the datasets of $GAMMAPY_DATA are used in the tutorials.

I have left $GAMMAPY_EXTRA in the test_*.py scripts, this env var is used by developers to access datasets that will not be provided to users.

I'm afraid developers should have $GAMMAPY_EXTRA and $GAMMAPY_DATA pointing to the same path ? export GAMMAPY_DATA=$GAMMAPY_EXTRA/datasets

Local regression test pass, and three notebooks remain broken for those not having $GAMMAPY_FERMI_LAT_DATA or $GAMMA_CATdeclared:

• fermilat needs $GAMMAPY_FERMI_LAT_DATA
• sed_fitting_gammacat_fermi needs $GAMMA_CAT
• spectrum_pipe needs $GAMMA_CAT

[cdeil]

I'm afraid developers should have $GAMMAPY_EXTRA and $GAMMAPY_DATA pointing to the same path ?

I don't have it pointing to the same path. I just have them separately.

Since not all files from GAMMAPY_DATA come from gammapy-extra (maybe that's still the case, but it won't remain like this), I think the proper dev setup is to just have them separately.

We can consider completely raplacing the use of GAMMAPY_EXTRA by GAMMAPY_DATA, also for test files, but that might not be a great solution (exposing test datasets to users a bit), and anyways isn't high priority.

I think for devs it's acceptable to have an extra 5 min of setup and to clone and set up GAMMAPY_EXTRA as well. Of course, we need to improve the Gammapy developer docs and explain the steps / setup clearly, but then I think it'll be OK.

[cdeil]

@Bultako - Thanks!

Let me know if I should do anything (e.g. edit notebooks).

For gamma-cat, it's particularly complicated because it's a "live catalog", the version at https://gamma-cat.readthedocs.io/output/gammacat.fits.gz can change any day if a new source is discovered and if someone has time to make a data entry there.

But for testing and tutorials, we probably want a fixed, pre-downloaded version.

That makes it especially complicated.

But let's leave that discussion for another day, and for now everywhere just use the fixed version in gammapy-extra.

[Bultako]

Ok, thanks.
It's fine for me, I still have some clean up to finish and then I slow down a bit in the next week.. :)