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from __future__ import (absolute_import, unicode_literals, division, print_function)
import numpy as np
from astropy.io import fits
from astropy import wcs as pywcs
def sip2idc(wcs):
"""
Converts SIP style coefficients to IDCTAB coefficients.
Parameters
----------
wcs : `astropy.io.fits.Header` or `astropy.wcs.WCS` object
"""
if isinstance(wcs, fits.Header):
ocx10 = wcs.get('OCX10', None)
ocx11 = wcs.get('OCX11', None)
ocy10 = wcs.get('OCY10', None)
ocy11 = wcs.get('OCY11', None)
order = wcs.get('A_ORDER', None)
sipa, sipb = _read_sip_kw(wcs)
if None in [ocx10, ocx11, ocy10, ocy11, sipa, sipb]:
print('Cannot convert SIP to IDC coefficients.\n')
return None, None
elif isinstance(wcs, pywcs.WCS):
try:
ocx10 = wcs.ocx10
ocx11 = wcs.ocx11
ocy10 = wcs.ocy10
ocy11 = wcs.ocy11
except AttributeError:
print('First order IDCTAB coefficients are not available.\n')
print('Cannot convert SIP to IDC coefficients.\n')
return None, None
try:
sipa = wcs.sip.a
sipb = wcs.sip.b
except AttributeError:
print('SIP coefficients are not available.')
print('Cannot convert SIP to IDC coefficients.\n')
return None, None
try:
order = wcs.sip.a_order
except AttributeError:
print('SIP model order unknown, exiting ...\n')
return None, None
else:
print('Input to sip2idc must be a PyFITS header or a wcsutil.HSTWCS object\n')
return
if None in [ocx10, ocx11, ocy10, ocy11]:
print('First order IDC coefficients not found, exiting ...\n')
return None, None
idc_coeff = np.array([[ocx11, ocx10], [ocy11, ocy10]])
cx = np.zeros((order + 1, order + 1), dtype=np.double)
cy = np.zeros((order + 1, order + 1), dtype=np.double)
for n in range(order + 1):
for m in range(order + 1):
if n >= m and n >= 2:
sipval = np.array([[sipa[m, n - m]], [sipb[m, n - m]]])
idcval = np.dot(idc_coeff, sipval)
cx[n, m] = idcval[0]
cy[n, m] = idcval[1]
cx[1, 0] = ocx10
cx[1, 1] = ocx11
cy[1, 0] = ocy10
cy[1, 1] = ocy11
return cx, cy
def _read_sip_kw(header):
"""
Reads SIP header keywords and returns an array of coefficients.
If no SIP header keywords are found, None is returned.
"""
if "A_ORDER" in header:
if "B_ORDER" not in header:
raise ValueError(
"A_ORDER provided without corresponding B_ORDER "
"keyword for SIP distortion")
m = int(header["A_ORDER"])
a = np.zeros((m + 1, m + 1), np.double)
for i in range(m + 1):
for j in range(m - i + 1):
a[i, j] = header.get("A_%d_%d" % (i, j), 0.0)
m = int(header["B_ORDER"])
b = np.zeros((m + 1, m + 1), np.double)
for i in range(m + 1):
for j in range(m - i + 1):
b[i, j] = header.get("B_%d_%d" % (i, j), 0.0)
elif "B_ORDER" in header:
raise ValueError(
"B_ORDER provided without corresponding A_ORDER "
"keyword for SIP distortion")
else:
a = None
b = None
return a, b
"""
def idc2sip(wcsobj, idctab = None):
if isinstance(wcs,pywcs.WCS):
try:
cx10 = wcsobj.ocx10
cx11 = wcsobj.cx11
cy10 = wcsobj.cy10
cy11 = wcsobj.cy11
except AttributeError:
print
try:
order = wcs.sip.a_order
except AttributeError:
print 'SIP model order unknown, exiting ...\n'
return
else:
print 'Input to sip2idc must be a PyFITS header or a wcsutil.HSTWCS object\n'
return
if None in [ocx10, ocx11, ocy10, ocy11]:
print 'First order IDC coefficients not found, exiting ...\n'
return
idc_coeff = np.array([[wcsobj.cx11, wcsobj.cx10], [wcsobj.cy11, wcsobj.cy10]])
cx = numpy.zeros((order+1,order+1), dtype=numpy.double)
cy = numpy.zeros((order+1,order+1), dtype=numpy.double)
for n in range(order+1):
for m in range(order+1):
if n >= m and n>=2:
sipval = numpy.array([[wcsobj.sip.a[n,m]],[wcsobj.sip.b[n,m]]])
idcval = numpy.dot(idc_coeff, sipval)
cx[m,n-m] = idcval[0]
cy[m,n-m] = idcval[1]
return cx, cy
"""
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