UPDATEHDR: Functions for Updating WCS with New Solutions

The functions in this module support updating the WCS information in distorted images with the alignment solution determined by TweakReg or saved in a shiftfile.

Authors:

Warren Hack, Mihai Cara

License:

License

drizzlepac.updatehdr.create_unique_wcsname(fimg, extnum, wcsname)[source]

This function evaluates whether the specified wcsname value has already been used in this image. If so, it automatically modifies the name with a simple version ID using wcsname_NNN format.

Parameters:
fimgobj

PyFITS object of image with WCS information to be updated

extnumint

Index of extension with WCS information to be updated

wcsnamestr

Value of WCSNAME specified by user for labelling the new WCS

Returns:
uniqnamestr

Unique WCSNAME value

drizzlepac.updatehdr.interpret_wcsname_type(wcsname)[source]

Interpret WCSNAME as a standardized human-understandable description

drizzlepac.updatehdr.linearize(wcsim, wcsima, wcsref, imcrpix, f, shift, hx=1.0, hy=1.0)[source]

linearization using 5-point formula for first order derivative

drizzlepac.updatehdr.update_from_shiftfile(shiftfile, wcsname=None, force=False)[source]

Update headers of all images specified in shiftfile with shifts from shiftfile.

Parameters:
shiftfilestr

Filename of shiftfile.

wcsnamestr

Label to give to new WCS solution being created by this fit. If a value of None is given, it will automatically use ‘TWEAK’ as the label. [Default =None]

forcebool

Update header even though WCS already exists with this solution or wcsname? [Default=False]

drizzlepac.updatehdr.update_refchip_with_shift(chip_wcs, wcslin, fitgeom='rscale', rot=0.0, scale=1.0, xsh=0.0, ysh=0.0, fit=None, xrms=None, yrms=None)[source]

Compute the matrix for the scale and rotation correction

Parameters:
chip_wcs: wcs object

HST of the input image

wcslin: wcs object

Reference WCS from which the offsets/rotations are determined

fitgeom: str

NOT USED

rotfloat

Amount of rotation measured in fit to be applied. [Default=0.0]

scalefloat

Amount of scale change measured in fit to be applied. [Default=1.0]

xshfloat

Offset in X pixels from defined tangent plane to be applied to image. [Default=0.0]

yshfloat

Offset in Y pixels from defined tangent plane to be applied to image. [Default=0.0]

fitarr

Linear coefficients for fit [Default = None]

xrmsfloat

RMS of fit in RA (in decimal degrees) that will be recorded as CRDER1 in WCS and header [Default = None]

yrmsfloat

RMS of fit in Dec (in decimal degrees) that will be recorded as CRDER2 in WCS and header [Default = None]

drizzlepac.updatehdr.update_wcs(image, extnum, new_wcs, wcsname='', reusename=False, verbose=False)[source]

Updates the WCS of the specified extension number with the new WCS after archiving the original WCS.

The value of ‘new_wcs’ needs to be the full HSTWCS object.

Parameters:
imagestr

Filename of image with WCS that needs to be updated

extnumint

Extension number for extension with WCS to be updated/replaced

new_wcsobject

Full HSTWCS object which will replace/update the existing WCS

wcsnamestr

Label to give newly updated WCS

reusenamebool

User can choose whether to over-write WCS with same name or not. [Default: False]

verbosebool, int

Print extra messages during processing? [Default: False]

drizzlepac.updatehdr.updatewcs_with_shift(image, reference, wcsname='TWEAK', reusename=False, fitgeom='rscale', rot=0.0, scale=1.0, xsh=0.0, ysh=0.0, fit=None, xrms=None, yrms=None, verbose=False, force=False, sciext='SCI')[source]

Update the SCI headers in ‘image’ based on the fit provided as determined in the WCS specified by ‘reference’. The fit should be a 2-D matrix as generated for use with ‘make_vector_plot()’.

Parameters:
imagestr or PyFITS.HDUList object

Filename, or PyFITS object, of image with WCS to be updated. All extensions with EXTNAME matches the value of the ‘sciext’ parameter value (by default, all ‘SCI’ extensions) will be updated.

referencestr

Filename of image/headerlet (FITS file) which contains the WCS used to define the tangent plane in which all the fit parameters (shift, rot, scale) were measured.

wcsnamestr, None, optional

Label to give to new WCS solution being created by this fit. If a value of None is given, it will automatically use ‘TWEAK’ as the label. [Default =None]

reusenamebool

User can specify whether or not to over-write WCS with same name. [Default: False]

rotfloat

Amount of rotation measured in fit to be applied. [Default=0.0]

scalefloat

Amount of scale change measured in fit to be applied. [Default=1.0]

xshfloat

Offset in X pixels from defined tangent plane to be applied to image. [Default=0.0]

yshfloat

Offset in Y pixels from defined tangent plane to be applied to image. [Default=0.0]

fitarr

Linear coefficients for fit [Default = None]

xrmsfloat

RMS of fit in RA (in decimal degrees) that will be recorded as CRDER1 in WCS and header [Default = None]

yrmsfloat

RMS of fit in Dec (in decimal degrees) that will be recorded as CRDER2 in WCS and header [Default = None]

verbosebool

Print extra messages during processing? [Default=False]

forcebool

Update header even though WCS already exists with this solution or wcsname? [Default=False]

sciextstring

Value of FITS EXTNAME keyword for extensions with WCS headers to be updated with the fit values. [Default=’SCI’]

Notes

The algorithm used to apply the provided fit solution to the image involves applying the following steps to the WCS of each of the input image’s chips:

  1. compute RA/Dec with full distortion correction for

    reference point as (Rc_i,Dc_i)

  2. find the Xc,Yc for each Rc_i,Dc_i and get the difference from the

    CRPIX position for the reference WCS as (dXc_i,dYc_i)

  3. apply fit (rot&scale) to (dXc_i,dYc_i) then apply shift, then add

    CRPIX back to get new (Xcs_i,Ycs_i) position

  4. compute (Rcs_i,Dcs_i) as the sky coordinates for (Xcs_i,Ycs_i)

  5. compute delta of (Rcs_i-Rc_i, Dcs_i-Dcs_i) as (dRcs_i,dDcs_i)

  6. apply the fit to the chip’s undistorted CD matrix, the apply linear

    distortion terms back in to create a new CD matrix

  7. add (dRcs_i,dDcs_i) to CRVAL of the reference chip’s WCS

  8. update header with new WCS values