Identification and extraction of subcubes based on world axis types

[Cadair]

Various analysis routines or functions are going to be specific to cubes that contain certain world axes types, i.e. a cube with one or two celestial axes.

For example @wtbarnes and I are discussing a function which extracts pixels at certain coordinates along any celestial axes. This function could be written to work with any cube which has one or more celestial axes as long as it's possible to identify which array axes correspond to the celestial axes. (Which is possible now with the correlation matrix / world axis physical types but not exactly pretty).

In addition to this, I think it would be cool to provide a WCS.sub like function which could use the logic to identify axes of certain types to return sub cubes.

[DanRyanIrish]

As an example, say we have a spectral, space, space cube. Would this feature slice the cube at an arbitrary point along the spectral axis and then drop the spectral value that slicing puts into global coords?

[Cadair]

That's kinda what I was thinking yes. I think the identification logic will probably be more useful than then subcube function, but still potentially useful.

[Cadair]

Alternatively the sub function could return N cubes of only the given axes, so instead of a time series you have N celestial-only cubes.

[DanRyanIrish]

The second option is an elaboration on explode_along_axis.