def _is_skysys_consistent(ctype, sky_inmap):
""" Determine if the sky axes in CTYPE match to form a standard celestial system."""
if len(sky_inmap) != 2:
raise ValueError("{} sky coordinate axes found. "
"There must be exactly 2".format(len(sky_inmap)))
for item in sky_pairs.values():
if ctype[sky_inmap[0]] == item[0]:
if ctype[sky_inmap[1]] != item[1]:
raise ValueError(
"Inconsistent ctype for sky coordinates {0} and {1}".format(*ctype))
break
elif ctype[sky_inmap[1]] == item[0]:
if ctype[sky_inmap[0]] != item[1]:
raise ValueError(
"Inconsistent ctype for sky coordinates {0} and {1}".format(*ctype))
sky_inmap.reverse()
break
def get_axes(header):
"""
Matches input with spectral and sky coordinate axes.
Parameters
----------
header : `astropy.io.fits.Header` or dict
FITS Header (or dict) with basic WCS information.
Returns
-------
sky_inmap, spectral_inmap, unknown : list
indices in the output representing sky and spectral coordinates.
"""
if isinstance(header, fits.Header):
wcs_info = read_wcs_from_header(header)
elif isinstance(header, dict):
wcs_info = header
else:
raise TypeError("Expected a FITS Header or a dict.")
# Split each CTYPE value at "-" and take the first part.
# This should represent the coordinate system.
ctype = [ax.split('-')[0].upper() for ax in wcs_info['CTYPE']]
sky_inmap = []
spec_inmap = []
unknown = []
skysystems = np.array(list(sky_pairs.values())).flatten()
for ax in ctype:
ind = ctype.index(ax)
if ax in specsystems:
spec_inmap.append(ind)
elif ax in skysystems:
sky_inmap.append(ind)
else:
unknown.append(ind)
if sky_inmap:
_is_skysys_consistent(ctype, sky_inmap)
return sky_inmap, spec_inmap, unknown