HEALPix

"HEALPix is an acronym for Hierarchical Equal Area isoLatitude Pixelation of a sphere. As suggested in the name, this pixelation produces a subdivision of a spherical surface in which each pixel covers the same surface area as every other pixel.

The original motivation for devising HEALPix was one of necessity. Satellite missions to measure the cosmic microwave background (CMB) anisotropy -- NASA's Wilkinson Microwave Anisotropy Probe (WMAP), and currently operating ESA's mission Planck -- have been producing multi-frequency data sets sufficient for the construction of full-sky maps of the microwave sky at an angular resolution of a few arcminutes. The principal requirements in the development of HEALPix were to create a mathematical structure which supports a suitable discretization of functions on a sphere at sufficiently high resolution, and to facilitate fast and accurate statistical and astrophysical analysis of massive full-sky data sets.

HEALPix satisfies these requirements because it possesses the following three essential properties:

1. The sphere is hierarchically tessellated into curvilinear quadrilaterals. The lowest resolution partition is comprised of 12 base pixels. Resolution of the tessellation increases by division of each pixel into four new ones. The figure below illustrates (clockwise from upper-left to bottom-left) the resolution increase by three steps from the base level (i.e., the sphere is partitioned, respectively, into 12, 48, 192, and 768 pixels).
2. Areas of all pixels at a given resolution are identical.
3. Pixels are distributed on lines of constant latitude. This property is essential for all harmonic analysis applications involving spherical harmonics. Due to the iso-latitude distribution of sampling points the speed of computation of integrals over individual spherical harmonics scales as ~N^1/2 with the total number of pixels, as opposed to the ~N scaling for the non-iso-latitude sampling distributions (examples of which are the Quadrilateralized Spherical Cube used for the NASA's COBE data, and any distribution based on the symmetries of the icosahedron). 

Applications of HEALPix to data processing and visualization have now spread well outside the original CMB field, as can be seen from the Resources and Gallery pages"

http://healpix.sourceforge.net/

spherelib - https://gitlab.in2p3.fr/spherelib/spherelib