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<html>
   
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
      <link rel="stylesheet" type="text/css" href="sun-style.css">
      <title>skyerr:
         Sky Matching with Per-Object Errors
      </title>
   </head>
   
   <body>
      <hr>
      <a href="EllipseSkyMatchEngine.html">Next</a> <a href="SkyMatchEngine.html">Previous</a> <a href="MatchEngine.html">Up</a> <a href="index.html">Contents</a> <br> <b>Next: </b><a href="EllipseSkyMatchEngine.html">skyellipse:
         Sky Matching of Elliptical Regions</a><br>
       <b>Up: </b><a href="MatchEngine.html">Match Criteria</a><br>
       <b>Previous: </b><a href="SkyMatchEngine.html">sky: Sky Matching</a><br>
      
      <hr>
      <h4><a name="SkyMatchEngine-err">7.1.2 <code>skyerr</code>:
            Sky Matching with Per-Object Errors</a></h4>
      <p><pre>matcher=skyerr values*='&lt;ra/degrees&gt; &lt;dec/degrees&gt; &lt;error/arcsec&gt;'
               params='&lt;scale/arcsec&gt;'
               tuning='&lt;healpix-k&gt;'</pre>
         <blockquote>
            
            <dl>
               <dt><strong><code>values*</code>:</strong></dt>
               <dd>
                  
                  <ul>
                     <li><code>ra/degrees</code>: Right Ascension
                     </li>
                     <li><code>dec/degrees</code>: Declination
                     </li>
                     <li><code>error/arcsec</code>: Per-object error radius along a great circle
                     </li>
                  </ul>
                  
               </dd>
               <dt><strong><code>params</code>:</strong></dt>
               <dd>
                  
                  <ul>
                     <li><code>scale/arcsec</code>: Rough average of per-object error distance; just used for tuning to set default
                        pixel size
                     </li>
                  </ul>
                  
               </dd>
               <dt><strong><code>tuning</code>:</strong></dt>
               <dd>
                  
                  <ul>
                     <li><code>healpix-k</code>: Controls sky pixel size. Legal range 0 - 20. 0 is 60deg, 20 is 0.2".
                     </li>
                  </ul>
                  
               </dd>
            </dl>
            
         </blockquote>
         
      </p>
      <p>The <code>skyerr</code> matcher compares positions on the celestial 
         sphere using error radii which can be different for each row.
         Rows are considered to match when the separation between the
         two <code>ra</code>, <code>dec</code> positions is no larger than 
         the sum of the two per-row <code>error</code> values.
         
      </p>
      <p>The <code>scale</code> parameter should be a rough average value
         of the error distances.  It is used only to set a sensible default for 
         <code>healpix-k</code> tuning parameter, and its value does not affect
         the result.  If you set <code>healpix-k</code> directly, its value is ignored.
         
      </p>
      <p>As with <a href="SkyMatchEngine.html"><code>sky</code></a> matching,
         other longitude/latitude coordinate pairs may be used in place of
         right ascension and declination.
         
      </p>
      <p><strong>Note:</strong> the semantics of this matcher have changed
         slightly at version 2.4 of STILTS.
         In earlier versions the single parameter was named <code>max-error</code>
         and provided an additional constraint on the maximum accepted separation
         between matched objects.  For most uses, the old and new behaviours are
         expected to give the same results, but in cases of difference, the new
         behaviour is more likely what you want.
         
      </p>
      <hr><a href="EllipseSkyMatchEngine.html">Next</a> <a href="SkyMatchEngine.html">Previous</a> <a href="MatchEngine.html">Up</a> <a href="index.html">Contents</a> <br> <b>Next: </b><a href="EllipseSkyMatchEngine.html">skyellipse:
         Sky Matching of Elliptical Regions</a><br>
       <b>Up: </b><a href="MatchEngine.html">Match Criteria</a><br>
       <b>Previous: </b><a href="SkyMatchEngine.html">sky: Sky Matching</a><br>
      
      <hr><i>STILTS - Starlink Tables Infrastructure Library Tool Set<br>Starlink User Note256<br>STILTS web page:
         <a href="http://www.starlink.ac.uk/stilts/">http://www.starlink.ac.uk/stilts/</a><br>Author email:
         <a href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a><br>Mailing list:
         <a href="mailto:topcat-user@jiscmail.ac.uk">topcat-user@jiscmail.ac.uk</a><br></i></body>
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