Using the tutorial https://matplotlib.org/stable/gallery/misc/custom_projection.html to create custom projections for the new healpy projview code. Requires some editing of the pip installable healpy as of August 30 2021.
Uses the HEALPix convention defined in Section 6 of Calabretta et al. (2007), doi:10.1111/j.1365-2966.2007.12297.x