The HEALPix Primer
HEALPix is a Hierarchical, Equal Area, and iso-Latitude Pixelation 
of the sphere  designed to support efficiently
(1) local operations on the pixel set,
(2) a hierarchical tree structure for  multi-resolution applications, and
(3) the global Fast Spherical Harmonic transform.
HEALPix based mathematical software meets the challenges presented by
high resolution and large volume data sets, such as
the WMAP and Planck CMB mission products.
Krzysztof M. Górski, Benjamin D. Wandelt, Eric Hivon, Frode K. Hansen,
and Anthony J. Banday
Revision: Version 3.83; November 13, 2024
https://healpix.sourceforge.io
http://healpix.sf.net
Version 3.83, 2024-11-13