def _make_wcs_3D(shape, galactic=False):
"""
Create a simple celestial WCS object in either the ICRS or Galactic
coordinate frame.
Parameters
----------
shape : 3-tuple of int
The shape of the 3D array to be used with the output
`~astropy.wcs.WCS` object.
galactic : bool, optional
If `True`, then the output WCS will be in the Galactic
coordinate frame. If `False` (default), then the output WCS
will be in the ICRS coordinate frame.
Returns
-------
wcs : `~astropy.wcs.WCS` object
The world coordinate system (WCS) transformation.
See Also
--------
make_imagehdu
Examples
--------
>>> from photutils.datasets import make_wcs
>>> shape = (1000, 100, 100)
>>> wcs = make_wcs(shape)
>>> print(wcs.wcs.crpix) # doctest: +FLOAT_CMP
[50. 50. 500.]
>>> print(wcs.wcs.crval) # doctest: +FLOAT_CMP
[197.8925 -1.36555556 4861.]
"""
wcs = WCS(naxis=3)
rho = np.pi / 3.
scale = 0.1 / 3600.
delta_wave = 0.5
wcs._naxis1 = shape[2] # nx
wcs._naxis2 = shape[1] # ny
wcs._naxis3 = shape[0] # nz
wcs.wcs.crpix = [shape[2] / 2, shape[1] / 2, shape[0] / 2] # 1-indexed (x, y, z)
wcs.wcs.crval = [197.8925, -1.36555556, 4861.]
wcs.wcs.cunit = ['deg', 'deg', 'nm']
wcs.wcs.cd = [[-scale * np.cos(rho), scale * np.sin(rho), 0.],
[ scale * np.sin(rho), scale * np.cos(rho), 0.],
[ 0., 0., delta_wave]]
if not galactic:
wcs.wcs.radesys = 'ICRS'
wcs.wcs.ctype = ['RA---TAN', 'DEC--TAN', 'WAVE']
else:
wcs.wcs.ctype = ['GLON-CAR', 'GLAT-CAR', 'WAVE']
return wcs
