fast SWHT

[griffinfoster]

There is a collection of previous work on performing fast spherical harmonic transforms (SHT), can this be adapted to the SWHT? The SHT operates on the surface of a unit sphere, but the SWHT operates with radial information also, so maybe it is not possible. Worth a moment of thought.

[griffinfoster]

The visibilities can be gridded onto a volume, similar to FFT gridding. This can include a weighting function also. This will be necessary for the deep KAIRA integration data sets.