healpix.py 文件源码

def _calc_hpx_indexes(nside):
    """Calculate HEALPix element indexes for the HPX projection scheme.

    Parameters
    ----------
    nside : int
        Nside of the input/output HEALPix data

    Returns
    -------
    indexes : 2D `~numpy.ndarray`
        2D integer array of same size as the input/output HPX FITS image,
        with elements tracking the indexes of the HPX pixels in the
        HEALPix 1D array, while elements with value "-1" indicating
        null/empty HPX pixels.

    NOTE
    ----
    * The indexes are 0-based;
    * Currently only HEALPix RING ordering supported;
    * The null/empty elements in the HPX projection are filled with "-1".
    """
    # number of horizontal/vertical facet
    nfacet = 5
    # Facets layout of the HPX projection scheme.
    # Note that this appears to be upside-down, and the blank facets
    # are marked with "-1".
    # Ref: ref.[2], Fig.4
    #
    # XXX:
    # Cannot use the nested list here, which fails with ``numba`` error:
    # ``NotImplementedError: unsupported nested memory-managed object``
    FACETS_LAYOUT = np.zeros((nfacet, nfacet), dtype=np.int64)
    FACETS_LAYOUT[0, :] = [6,   9, -1, -1, -1]
    FACETS_LAYOUT[1, :] = [1,   5,  8, -1, -1]
    FACETS_LAYOUT[2, :] = [-1,  0,  4, 11, -1]
    FACETS_LAYOUT[3, :] = [-1, -1,  3,  7, 10]
    FACETS_LAYOUT[4, :] = [-1, -1, -1,  2,  6]
    #
    shape = (nfacet*nside, nfacet*nside)
    indexes = -np.ones(shape, dtype=np.int64)
    #
    # Loop vertically facet-by-facet
    for jfacet in range(nfacet):
        # Loop row-by-row
        for j in range(nside):
            row = jfacet * nside + j
            # Loop horizontally facet-by-facet
            for ifacet in range(nfacet):
                facet = FACETS_LAYOUT[jfacet, ifacet]
                if facet < 0:
                    # blank facet
                    pass
                else:
                    idx = _calc_hpx_row_idx(nside, facet, j)
                    col = ifacet * nside
                    indexes[row, col:(col+nside)] = idx
    #
    return indexes