chealpy is a minimal Python package for HealPix.

  HealPix embeds S2 (sphere / vectors with |r| = 1) into a plane, conserving
  the area.

  chealpix is the C implementation of HealPix.

  You will need numpy > 1.6.
  
  To install:

    python setup.py install

  Refer to HealPix manual for usage.

  Two precisions are provided:

    - chealpy.high : upto nside=1<<29
    - chealpy.low : upto nside=8192

  chealpy.low is somewhat faster, but chealpy allows higher resolutions.

  Functions under the namespace chealpy are imported from chealpy.high.

  high.MAX_NSIDES and low.MAX_NSIDES is the upper limit of nsides.

  Wrappers are automatically generated Cython code, making use of the NpyIter C-API.
  There are probably cleaner ways of achiving the same nowadays; this mechanism was
  was crafted 2012.

Plans:

  - Add sparse maps and lossy compression.
  compression = low pass filter / downsample + sparse map.
  efficient if the high frequency modes are spatially localized.

  - binning / histograms stats (from mpl_aea)

  - visualization Integration with Cartopy and matplotlib.axes. 
    mostly from http://github.com/rainwoodman/mpl_aea, but needs some rewrites.
    may need to rewrite chealpix.c / or add new routines to upstream.

  Probably should never support transforms (anafast). For a feature-rich
  Healpix C++ binding, take a look at healpy.


Author: Yu Feng 2012 <yfeng1@andrew.cmu.edu>
        Yu Feng 2020 <yfeng1@berkeley.edu>/<feyu@google.com>


List of Functions (all propertly vectorized for numpy):

    def ang2pix_ring (nside,theta,phi,i pix = None)
    def ang2pix_nest (nside,theta,phi, ipix = None)
    def pix2ang_ring (nside,ipix, theta = None,phi = None)
    def pix2ang_nest (nside,ipix, theta = None,phi = None)
    def vec2pix_ring (nside,vec, ipix = None)
    def vec2pix_nest (nside,vec, ipix = None)
    def pix2vec_ring (nside,ipix, vec = None)
    def pix2vec_nest (nside,ipix, vec = None)
    def nest2ring (nside,ipnest, ipring = None)
    def ring2nest (nside,ipring, ipnest = None)
    def npix2nside (npix, nside = None)
    def nside2npix (nside, npix = None)
    def ang2vec (theta,phi, vec = None)
    def vec2ang (vec, theta = None, phi = None)