def compute_scale(wcs: WCS, fiducial: Union[tuple, np.ndarray]) -> float:
"""Compute scaling transform.
Parameters
----------
wcs : `~gwcs.wcs.WCS`
Reference WCS object from which to compute a scaling factor.
fiducial : tuple
Input fiducial of (RA, DEC) used in calculating reference points.
Returns
-------
scale : float
Scaling factor for x and y.
"""
if len(fiducial) != 2:
raise ValueError(f'Input fiducial must contain only (RA, DEC); Instead recieved: {fiducial}')
crpix = np.array(wcs.invert(*fiducial))
crpix_with_offsets = np.vstack((crpix, crpix + (1, 0), crpix + (0, 1))).T
crval_with_offsets = wcs(*crpix_with_offsets)
coords = SkyCoord(ra=crval_with_offsets[0], dec=crval_with_offsets[1], unit="deg")
xscale = np.abs(coords[0].separation(coords[1]).value)
yscale = np.abs(coords[0].separation(coords[2]).value)
return np.sqrt(xscale * yscale)
def compute_scale(wcs: WCS,
fiducial: Union[tuple, np.ndarray],
disp_axis: int = None,
pscale_ratio: float = None) -> float:
"""Compute scaling transform.
Parameters
----------
wcs : `~gwcs.wcs.WCS`
Reference WCS object from which to compute a scaling factor.
fiducial : tuple
Input fiducial of (RA, DEC) or (RA, DEC, Wavelength) used in calculating reference points.
disp_axis : int
Dispersion axis integer. Assumes the same convention as `wcsinfo.dispersion_direction`
pscale_ratio : int
Ratio of input to output pixel scale
Returns
-------
scale : float
Scaling factor for x and y or cross-dispersion direction.
"""
spectral = 'SPECTRAL' in wcs.output_frame.axes_type
if spectral and disp_axis is None:
raise ValueError('If input WCS is spectral, a disp_axis must be given')
crpix = np.array(wcs.invert(*fiducial))
delta = np.zeros_like(crpix)
spatial_idx = np.where(
np.array(wcs.output_frame.axes_type) == 'SPATIAL')[0]
delta[spatial_idx[0]] = 1
crpix_with_offsets = np.vstack(
(crpix, crpix + delta, crpix + np.roll(delta, 1))).T
crval_with_offsets = wcs(*crpix_with_offsets)
coords = SkyCoord(ra=crval_with_offsets[spatial_idx[0]],
dec=crval_with_offsets[spatial_idx[1]],
unit="deg")
xscale = np.abs(coords[0].separation(coords[1]).value)
yscale = np.abs(coords[0].separation(coords[2]).value)
if pscale_ratio is not None:
xscale = xscale * pscale_ratio
yscale = yscale * pscale_ratio
if spectral:
# Assuming scale doesn't change with wavelength
# Assuming disp_axis is consistent with DataModel.meta.wcsinfo.dispersion.direction
return yscale if disp_axis == 1 else xscale
return np.sqrt(xscale * yscale)