How to convert and save healpy map to another coordinate system?

Question

I have a healpix map with a galactic coordinate. I would like to convert this map to an equatorial coordinate system. I know that I could build a map in the equatorial coordinate using the mollview () function. Do you have a way to save such a converted map?

Thanks Vinu

Answer 1

The following function changes the coordinate system of the map.

def change_coord(m, coord):
    """ Change coordinates of a HEALPIX map

    Parameters
    ----------
    m : map or array of maps
      map(s) to be rotated
    coord : sequence of two character
      First character is the coordinate system of m, second character
      is the coordinate system of the output map. As in HEALPIX, allowed
      coordinate systems are 'G' (galactic), 'E' (ecliptic) or 'C' (equatorial)

    Example
    -------
    The following rotate m from galactic to equatorial coordinates.
    Notice that m can contain both temperature and polarization.
    >>>> change_coord(m, ['G', 'C']
    """
    # Basic HEALPix parameters
    npix = m.shape[-1]
    nside = hp.npix2nside(npix)
    ang = hp.pix2ang(nside, np.arange(npix))

    # Select the coordinate transformation
    rot = hp.Rotator(coord=reversed(coord))

    # Convert the coordinates
    new_ang = rot(*ang)
    new_pix = hp.ang2pix(nside, *new_ang)

    return m[..., new_pix]

Example of your case