Add Gamera spectral model example

[gschwefer]

Hello everyone,

this PR contains an example of how to use the Gamera source modelling tool to fit spectra in gammapy.

There are essentially two ways, one is to subclass SpectralModel with a GameraSpectralModel, the other to use a TemplateNDSpectralModel

One Problem with this is that gamera is not pip installable, therefore the notebook can't just be run after installing the environment from the env.yml, it requires the extra installation of gamera. A link to the installation info i in the notebook, but of course this is not ideal. Do you have any other suggestions for how to deal with this?

Also, are there any figures you would like to see added to this notebook?

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[registerrier]

Thanks @gschwefer . This is interesting but I think we have a practical issue here.

For this recipe to run, gamera must be installed via the conda environment here.This would require a much more complex scheme where the Action will git clone and make gamera before running the notebook...

[adonath]

@registerrier and @gschwefer I agree making pip install work with Gamera would be very helpful (see libgamera/GAMERA#6)

[maxnoe]

@adonath @registerrier We are trying to make that happen.

It should already work with:

pip install git+https://github.com/maxnoe/GAMERA@scikit-build

[registerrier]

@adonath @registerrier We are trying to make that happen.

It should already work with:

pip install git+https://github.com/maxnoe/GAMERA@scikit-build

This is really cool @maxnoe !

I have first run mamba install gsl swig in a gammapy conda environment.
Then when calling pip install git+https://github.com/maxnoe/GAMERA@scikit-build, I have an error with:

 CMake Error at /private/var/folders/p2/l2vqhn_17zbghwxxwwdnvk0m0000gn/T/pip-build-env-nc41s2nw/normal/lib/python3.10/site-packages/cmake/data/share/cmake-3.29/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
        Could NOT find GSL (missing: GSL_INCLUDE_DIR GSL_LIBRARY) (found version
        "2.7.1")

I tried to set the env variable but it did not work. Any idea?

[maxnoe]

For compiling things in the conda env, also install the compilers package and make sure to deactivate / reactivate the env.

That makes sure everything is setup correctly for libraries to be found.

Side note: swig is not needed in the conda env, it's only a build time dependency and is installed in the build env automatically.

[registerrier]

For compiling things in the conda env, also install the compilers package and make sure to deactivate / reactivate the env.

That makes sure everything is setup correctly for libraries to be found.

Side note: swig is not needed in the conda env, it's only a build time dependency and is installed in the build env automatically.

Thanks. It worked!