Add Spectrum and CountSpectrum objects

[samaloney]

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Heavily based off of the Spectrum object in specutils but also significantly stripped down. I think since the API is a subset it would easy enough to adopt the full API from specutils in the future if we decide to go that way. Since we know we will have a X-ray count spectra added a specific class for this as will have different properties.

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Files	Patch %	Lines
sunkit_spex/spectrum/spectrum.py	26.43%	64 Missing :warning:

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[samaloney]

Rendered docs: https://sunkit-spex--142.org.readthedocs.build/en/142/reference/index.html#module-sunkit_spex.spectrum.spectrum

[samaloney]

I think the work we are doing in stixpy (TCDSolar/stixpy/pull/109) might be relevant here too @DanRyanIrish

[DanRyanIrish]

I should point out a likely future direction of NDCube is to add an attribute contained an NDCoords class, which provides in easier API for accessing coordinate info. A possible implementation can be seen in ndcube#710.

In order to make the Tabular WCS infrastructure work properly with edges, we would also need to finish ndcube#713.

Once, these features are available, the only advantage I see for a Spectrum class in sunkit-spex would be a simpler instantiation API which doesn't require a WCS to be constructed manually beforehand. Everything else we needed would be on NDCube.

Lowering the instantiation barrier for users is important. Alternatively to a Spectrum class, this could be done by providing a function, build_spectral_cube(), which takes a data quantity, spectral axis quantity, and other optional NDCube inputs, and outputs an NDCube with the correct format. Dummy world axes with pixel units could be assigned if the data array was multi-dimensional.

If we agree this is the way forward, then working on the above two ndcube PRs becomes the bulk of the work needed for a de-facto Spectrum data object.

[samaloney]

I should point out a likely future direction of NDCube is to add an attribute contained an NDCoords class, which provides in easier API for accessing coordinate info. A possible implementation can be seen in ndcube#710.

In order to make the Tabular WCS infrastructure work properly with edges, we would also need to finish ndcube#713.

Once, these features are available, the only advantage I see for a Spectrum class in sunkit-spex would be a simpler instantiation API which doesn't require a WCS to be constructed manually beforehand. Everything else we needed would be on NDCube.

Lowering the instantiation barrier for users is important. Alternatively to a Spectrum class, this could be done by providing a function, build_spectral_cube(), which takes a data quantity, spectral axis quantity, and other optional NDCube inputs, and outputs an NDCube with the correct format. Dummy world axes with pixel units could be assigned if the data array was multi-dimensional.

If we agree this is the way forward, then working on the above two ndcube PRs becomes the bulk of the work needed for a de-facto Spectrum data object.

What is the best way to get these changes, extern the whole of NDCube and add the changes from these PRs 😆

[samaloney]

So I think we should maybe just merge this so we a very basic spectrum object