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<div class="section" id="updatehdr-functions-for-updating-wcs-with-new-solutions">
<span id="updatehdr"></span><h1>UPDATEHDR: Functions for Updating WCS with New Solutions<a class="headerlink" href="#updatehdr-functions-for-updating-wcs-with-new-solutions" title="Permalink to this headline">¶</a></h1>
<p>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.</p>
<span class="target" id="module-drizzlepac.updatehdr"></span><dl class="function">
<dt id="drizzlepac.updatehdr.create_unique_wcsname">
<tt class="descclassname">drizzlepac.updatehdr.</tt><tt class="descname">create_unique_wcsname</tt><big>(</big><em>fimg</em>, <em>extnum</em>, <em>wcsname</em><big>)</big><a class="headerlink" href="#drizzlepac.updatehdr.create_unique_wcsname" title="Permalink to this definition">¶</a></dt>
<dd><p>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.</p>
<dl class="docutils">
<dt>fimg <span class="classifier-delimiter">:</span> <span class="classifier">obj</span></dt>
<dd>PyFITS object of image with WCS information to be updated</dd>
<dt>extnum <span class="classifier-delimiter">:</span> <span class="classifier">int</span></dt>
<dd>Index of extension with WCS information to be updated</dd>
<dt>wcsname <span class="classifier-delimiter">:</span> <span class="classifier">str</span></dt>
<dd>Value of WCSNAME specified by user for labelling the new WCS</dd>
</dl>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name" colspan="2">Returns:</th></tr>
<tr class="field-odd field"><td> </td><td class="field-body"><p class="first"><strong>uniqname</strong> : str</p>
<blockquote class="last">
<div><p>Unique WCSNAME value</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="drizzlepac.updatehdr.update_from_shiftfile">
<tt class="descclassname">drizzlepac.updatehdr.</tt><tt class="descname">update_from_shiftfile</tt><big>(</big><em>shiftfile</em>, <em>wcsname=None</em>, <em>force=False</em><big>)</big><a class="headerlink" href="#drizzlepac.updatehdr.update_from_shiftfile" title="Permalink to this definition">¶</a></dt>
<dd><p>Update headers of all images specified in shiftfile with shifts
from shiftfile.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name" colspan="2">Parameters:</th></tr>
<tr class="field-odd field"><td> </td><td class="field-body"><p class="first"><strong id="shiftfile">shiftfile</strong> : str</p>
<blockquote>
<div><p>Filename of shiftfile.</p>
</div></blockquote>
<p><strong id="wcsname">wcsname</strong> : str</p>
<blockquote>
<div><p>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]</p>
</div></blockquote>
<p><strong id="force">force</strong> : bool</p>
<blockquote class="last">
<div><p>Update header even though WCS already exists with this solution or
wcsname? [Default=False]</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="drizzlepac.updatehdr.update_wcs">
<tt class="descclassname">drizzlepac.updatehdr.</tt><tt class="descname">update_wcs</tt><big>(</big><em>image</em>, <em>extnum</em>, <em>new_wcs</em>, <em>wcsname=''</em>, <em>verbose=False</em><big>)</big><a class="headerlink" href="#drizzlepac.updatehdr.update_wcs" title="Permalink to this definition">¶</a></dt>
<dd><p>Updates the WCS of the specified extension number with the new WCS
after archiving the original WCS.</p>
<p>The value of ‘new_wcs’ needs to be the full
HSTWCS object.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name" colspan="2">Parameters:</th></tr>
<tr class="field-odd field"><td> </td><td class="field-body"><p class="first"><strong id="image">image</strong> : str</p>
<blockquote>
<div><p>Filename of image with WCS that needs to be updated</p>
</div></blockquote>
<p><strong id="extnum">extnum</strong> : int</p>
<blockquote>
<div><p>Extension number for extension with WCS to be updated/replaced</p>
</div></blockquote>
<p><strong id="new_wcs">new_wcs</strong> : object</p>
<blockquote>
<div><p>Full HSTWCS object which will replace/update the existing WCS</p>
</div></blockquote>
<p><strong id="wcsname">wcsname</strong> : str</p>
<blockquote>
<div><p>Label to give newly updated WCS</p>
</div></blockquote>
<p><strong id="verbose">verbose</strong> : bool, int</p>
<blockquote class="last">
<div><p>Print extra messages during processing? [Default: False]</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="drizzlepac.updatehdr.updatewcs_with_shift">
<tt class="descclassname">drizzlepac.updatehdr.</tt><tt class="descname">updatewcs_with_shift</tt><big>(</big><em>image</em>, <em>reference</em>, <em>wcsname=None</em>, <em>rot=0.0</em>, <em>scale=1.0</em>, <em>xsh=0.0</em>, <em>ysh=0.0</em>, <em>fit=None</em>, <em>xrms=None</em>, <em>yrms=None</em>, <em>verbose=False</em>, <em>force=False</em>, <em>sciext='SCI'</em><big>)</big><a class="headerlink" href="#drizzlepac.updatehdr.updatewcs_with_shift" title="Permalink to this definition">¶</a></dt>
<dd><p>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()’.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name" colspan="2">Parameters:</th></tr>
<tr class="field-odd field"><td> </td><td class="field-body"><p class="first"><strong id="image">image</strong> : str or PyFITS.HDUList object</p>
<blockquote>
<div><p>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.</p>
</div></blockquote>
<p><strong id="reference">reference</strong> : str</p>
<blockquote>
<div><p>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.</p>
</div></blockquote>
<p><strong id="wcsname">wcsname</strong> : str</p>
<blockquote>
<div><p>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. If a WCS has a name with this specific value, the code will
automatically append a version ID using the format ‘_n’, such as
‘TWEAK_1’, ‘TWEAK_2’,or ‘TWEAK_update_1’.
[Default =None]</p>
</div></blockquote>
<p><strong id="rot">rot</strong> : float</p>
<blockquote>
<div><p>Amount of rotation measured in fit to be applied.
[Default=0.0]</p>
</div></blockquote>
<p><strong id="scale">scale</strong> : float</p>
<blockquote>
<div><p>Amount of scale change measured in fit to be applied.
[Default=1.0]</p>
</div></blockquote>
<p><strong id="xsh">xsh</strong> : float</p>
<blockquote>
<div><p>Offset in X pixels from defined tangent plane to be applied to image.
[Default=0.0]</p>
</div></blockquote>
<p><strong id="ysh">ysh</strong> : float</p>
<blockquote>
<div><p>Offset in Y pixels from defined tangent plane to be applied to image.
[Default=0.0]</p>
</div></blockquote>
<p><strong id="fit">fit</strong> : arr</p>
<blockquote>
<div><p>Linear coefficients for fit
[Default = None]</p>
</div></blockquote>
<p><strong id="xrms">xrms</strong> : float</p>
<blockquote>
<div><p>RMS of fit in RA (in decimal degrees) that will be recorded as
CRDER1 in WCS and header
[Default = None]</p>
</div></blockquote>
<p><strong id="yrms">yrms</strong> : float</p>
<blockquote>
<div><p>RMS of fit in Dec (in decimal degrees) that will be recorded as
CRDER2 in WCS and header
[Default = None]</p>
</div></blockquote>
<p><strong id="verbose">verbose</strong> : bool</p>
<blockquote>
<div><p>Print extra messages during processing? [Default=False]</p>
</div></blockquote>
<p><strong id="force">force</strong> : bool</p>
<blockquote>
<div><p>Update header even though WCS already exists with this solution or
wcsname? [Default=False]</p>
</div></blockquote>
<p><strong id="sciext">sciext</strong> : string</p>
<blockquote class="last">
<div><p>Value of FITS EXTNAME keyword for extensions with WCS headers to
be updated with the fit values. [Default=’SCI’]</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
<p class="rubric">Notes</p>
<p>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:</p>
<ol class="arabic">
<li><dl class="first docutils">
<dt>compute RA/Dec with full distortion correction for</dt>
<dd><p class="first last">reference point as (Rc_i,Dc_i)</p>
</dd>
</dl>
</li>
<li><dl class="first docutils">
<dt>find the Xc,Yc for each Rc_i,Dc_i and get the difference from the</dt>
<dd><p class="first last">CRPIX position for the reference WCS as (dXc_i,dYc_i)</p>
</dd>
</dl>
</li>
<li><dl class="first docutils">
<dt>apply fit (rot&scale) to (dXc_i,dYc_i) then apply shift, then add</dt>
<dd><p class="first last">CRPIX back to get new (Xcs_i,Ycs_i) position</p>
</dd>
</dl>
</li>
<li><p class="first">compute (Rcs_i,Dcs_i) as the sky coordinates for (Xcs_i,Ycs_i)</p>
</li>
<li><p class="first">compute delta of (Rcs_i-Rc_i, Dcs_i-Dcs_i) as (dRcs_i,dDcs_i)</p>
</li>
<li><dl class="first docutils">
<dt>apply the fit to the chip’s undistorted CD matrix, the apply linear</dt>
<dd><p class="first last">distortion terms back in to create a new CD matrix</p>
</dd>
</dl>
</li>
<li><p class="first">add (dRcs_i,dDcs_i) to CRVAL of the reference chip’s WCS</p>
</li>
<li><p class="first">update header with new WCS values</p>
</li>
</ol>
</dd></dl>
</div>
</div>
</div>
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