diff options
Diffstat (limited to 'wcsutil/hstwcs.py')
| -rw-r--r-- | wcsutil/hstwcs.py | 35 |
1 files changed, 20 insertions, 15 deletions
diff --git a/wcsutil/hstwcs.py b/wcsutil/hstwcs.py index 9de9020..1d38f42 100644 --- a/wcsutil/hstwcs.py +++ b/wcsutil/hstwcs.py @@ -4,7 +4,7 @@ import os.path from pywcs import WCS import pyfits import instruments -from stwcs.distortion import models, coeff_converter +from stwcs.distortion import models, coeff_converter, utils import altwcs import numpy as np from pytools import fileutil @@ -335,24 +335,31 @@ class HSTWCS(WCS): y = np.zeros(3,dtype=np.float64) # define delta for comparison - err = 0.00001 + err = 0.0001 + + # Use linear WCS as frame in which to perform fit + # rather than on the sky + wcslin = utils.output_wcs([self]) # We can only transform 1 position at a time for r,d,n in zip(ra,dec,xrange(len(ra))): # First guess for output x[0],y[0] = self.wcs_sky2pix(r,d,origin) + # also convert RA,Dec into undistorted linear pixel positions + lx,ly = wcslin.wcs_sky2pix(r,d,origin) - # Loop around until we are close enough - still_iterating = True + # Loop around until we are close enough (max 20 iterations) ev_old = None - while still_iterating: + for i in xrange(20): x[1] = x[0] + 1.0 y[1] = y[0] x[2] = x[0] y[2] = y[0] + 1.0 # Perform full transformation on pixel position - xo,yo = self.all_pix2sky(x,y,1) - + rao,deco = self.all_pix2sky(x,y,origin) + # convert RA,Dec into linear pixel positions for fitting + xo,yo = wcslin.wcs_sky2pix(rao,deco,origin) + # Compute deltas between output and initial guess as # an affine transform then invert that transformation dxymat = np.array([[xo[1]-xo[0],yo[1]-yo[0]], @@ -360,18 +367,16 @@ class HSTWCS(WCS): invmat = np.linalg.inv(dxymat) # compute error in output position - delta_ra = r - xo[0] - delta_dec = d - yo[0] + dx = lx - xo[0] + dy = ly - yo[0] # record the old position xold = x[0] yold = y[0] # Update the initial guess position using the transform - delta_nx = delta_ra*dxymat[0][0] + delta_dec*dxymat[1][0] - delta_ny = delta_ra*dxymat[0][1] + delta_dec*dxymat[1][1] - x[0] = xold + delta_nx*3600*3600/self.pscale - y[0] = yold + delta_ny*3600*3600/self.pscale + x[0] = xold + dx*dxymat[0][0] + dy*dxymat[1][0] + y[0] = yold + dx*dxymat[0][1] + dy*dxymat[1][1] # Work out the error vector length ev = np.sqrt((x[0] - xold)**2 + (y[0] - yold)**2) @@ -379,11 +384,11 @@ class HSTWCS(WCS): # initialize record of previous error measurement during 1st iteration if ev_old is None: ev_old = ev + # Check to see whether we have reached the limit or # the new error is greater than error from previous iteration if ev < err or (np.abs(ev) > np.abs(ev_old)): - still_iterating = False - + break # remember error measurement from previous iteration ev_old = ev |