mosaicing at low declination

[twshimwell]

Presently at low dec we use an elliptical beam which is a bit of a pain when mosaicing because of projection effects meaning its slightly rotated between all the pointings we are mosaicing.

Could either:

• switch to a circular beam for the low declination obs for simplicity
• during the mosaicing calculate the smallest ellipse the encompasses all the individual restoring beams (once projected onto a common projection).