Allow using custom energy dependent cuts (e.g. based on sensitivity optimization) for IRFs and DL3

[gabemery]

Currently, IRF and DL3 creation tools only allow for global or energy-dependent gammaness, theta or alpha cuts calculated based on MC gamma-ray efficiency.

These changes introduce the option to provide custom previously calculated energy-dependent cuts on gammaness, theta or alpha during the IRFs creation. And provides associated metadata in the IRFs and DL3 files.

Why is it needed : Allows to provide energy dependent cuts based on criteria different from gamma efficiency. Such as best sensitivity.

Tool usage change with the new implementation :
Removed flags --energy-dependent-gh, --energy-dependent-theta and --energy-dependent-alpha and replaced them by a --cut_strategy-{gh, theta, alpha} which receives the technique used as a string input.

The implementation is near complete and can be reviewed, but some points need discussion/further work.
To do before merging :

• (optionnal) Decide how to store the energy dependent cuts : Should the input be stored in the metadata? Before or after re-binning? Other strategy?
• Implement tests

[morcuended]

Hi @gabemery, thanks for the implementation, I think it makes sense to support this. Maybe have a look at how it was recently done in ctapipe, so here we use similar naming and so on (cta-observatory/ctapipe#2473).

Specifically, they implement:
Two components for calculating G/H and optionally theta cuts are added:
PercentileCuts keeps a certain percentage of gamma events in each bin and (what we had already)
PointSourceSensitivityOptimizer optimizes G/H cuts for maximum point source sensitivity and
optionally calculates percentile theta cuts.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.99%. Comparing base (76540cc) to head (87056e5).

Additional details and impacted files

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+ Coverage   72.86%   72.99%   +0.12%     
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  Files         137      137              
  Lines       14515    14583      +68     
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+ Hits        10577    10645      +68     
  Misses       3938     3938              

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[gabemery]

@morcuended Thanks for bringing the ctapipe version to my attention. I will have a look and see what can be implemented without re-writing the full tool.

[gabemery]

After having a look, there is nothing to directly implement from the ctapipe irf production into this PR since the pipelines are very different.
It could be interesting to fully transition to the ctapipe tools later. But I would say this is out of the scope of this feature addition.

[moralejo]

@morcuended can you approve? I had a quick look and it seems ok to me, but probably you know this better.

[morcuended]

Let me have a look first