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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>skyellipse</title>
   </head>
   
   <body>
      <hr>
      <a href="layer-skycorr.html">Next</a> <a href="layer-skyvector.html">Previous</a> <a href="LayerType.html">Up</a> <a href="index.html">Contents</a> <br> <b>Next: </b><a href="layer-skycorr.html">skycorr</a><br>
       <b>Up: </b><a href="LayerType.html">Layer Types</a><br>
       <b>Previous: </b><a href="layer-skyvector.html">skyvector</a><br>
      
      <hr>
      <h4><a name="layer-skyellipse">8.3.24 <code>skyellipse</code></a></h4>
      <p>Plots an ellipse (or rectangle, triangle,
         or other similar figure)
         defined by two principal radii and
         an optional angle of rotation,
         the so-called position angle.
         This angle, if specified, is in degrees and
         gives the angle from the North pole towards the
         direction of increasing longitude on the longitude axis.
         
      </p>
      <p>The dimensions of the plotted ellipses
         are given by the
         <code>ra</code> and <code>rb</code>
         coordinates.
         The units of these values are specified using the
         <code>unit</code> option.
         If only the relative rather than the absolute sizes
         are required on the plot,
         or if the units are not known,
         the special value
         <code>unit=scaled</code>
         may be used;
         this applies a non-physical scaling factor
         to make the ellipses appear at some reasonable size
         in the plot.
         When <code>unit=scaled</code>
         
         ellipses will keep approximately the same screen size
         during zoom operations;
         when one of the angular units is chosen, they will keep
         the same size in data coordinates.
         
      </p>
      <p>Additionally, the
         <code>scale</code> option
         may be used to scale all the plotted ellipses
         by a given factor to make them all larger or smaller.
         
      </p>
      <p>
         <strong>Usage Overview:</strong>
         <pre>
   layerN=skyellipse ellipseN=ellipse|crosshair_ellipse|...
                     unitN=scaled|degree|minute|arcsec|mas|uas scaleN=&lt;number&gt;
                     shadingN=auto|flat|translucent|transparent|density|aux|weighted &lt;shade-paramsN&gt;
                     lonN=&lt;deg-expr&gt; latN=&lt;deg-expr&gt; raN=&lt;num-expr&gt;
                     rbN=&lt;num-expr&gt; posangN=&lt;deg-expr&gt; inN=&lt;table&gt;
                     ifmtN=&lt;in-format&gt; istreamN=true|false icmdN=&lt;cmds&gt;
</pre>
         </p>
      <p>All the parameters listed here
         affect only the relevant layer,
         identified by the suffix
         <code>N</code>.
         
      </p>
      <p>
         <strong>Example:</strong>
         
      </p>
      <div align="center"><img src="plot2-layer-skyellipse.png" alt="" align="middle"></div>
      <p><pre>   stilts plot2sky <strong>in=mgc_ok.fits</strong>
                   <strong>lon=mgc_alpha_j2000</strong> <strong>lat=mgc_delta_j2000</strong>
                   <strong>ra=bulge_re</strong> <strong>rb=bulge_re*bulge_e</strong> <strong>unit=arcsec</strong> <strong>posang=bulge_pa</strong>
                   <strong>scale=10</strong> <strong>color=#cc00ff</strong>
                   <strong>layer1=skyellipse</strong> <strong>ellipse1=filled_ellipse</strong> <strong>shading1=transparent</strong> <strong>opaque1=4</strong>
                   <strong>layer2=skyellipse</strong> <strong>ellipse2=crosshair_ellipse</strong>
                   clon=180.1 clat=0 radius=0.25</pre></p>
      <p>
         <dl>
            <dt><strong><code>ellipseN = ellipse|crosshair_ellipse|...</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot/ErrorRenderer.html">ErrorRenderer</a>)</em></strong></dt>
            <dd>How ellipses are represented.
               
               <p>The available options are:
                  
                  <ul>
                     <li><code>ellipse</code></li>
                     <li><code>crosshair_ellipse</code></li>
                     <li><code>filled_ellipse</code></li>
                     <li><code>rectangle</code></li>
                     <li><code>crosshair_rectangle</code></li>
                     <li><code>filled_rectangle</code></li>
                     <li><code>open_triangle</code></li>
                     <li><code>filled_triangle</code></li>
                     <li><code>lines</code></li>
                     <li><code>capped_lines</code></li>
                     <li><code>arrows</code></li>
                  </ul>
                  
               </p>
               <p>[Default: <code>ellipse</code>]
               </p>
            </dd>
            <dt><strong><code>icmdN = &lt;cmds&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/filter/ProcessingStep.html">ProcessingStep[]</a>)</em></strong></dt>
            <dd>Specifies processing to be performed on
               the layer N input table as specified by parameter <code>inN</code>.
               The value of this parameter is one or more of the filter
               commands described in <a href="filterSteps.html">Section 6.1</a>.
               If more than one is given, they must be separated by
               semicolon characters (";").
               This parameter can be repeated multiple times on the same
               command line to build up a list of processing steps.
               The sequence of commands given in this way
               defines the processing pipeline which is performed on the table.
               
               <p>Commands may alteratively be supplied in an external file,
                  by using the indirection character '@'.
                  Thus a value of "<code>@filename</code>"
                  causes the file <code>filename</code> to be read for a list
                  of filter commands to execute.  The commands in the file
                  may be separated by newline characters and/or semicolons.
                  
               </p>
            </dd>
            <dt><strong><code>ifmtN = &lt;in-format&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Specifies the format of the input table as specified by parameter <code>inN</code>.
               The known formats are listed in <a href="inFormats.html">Section 5.2.1</a>.
               This flag can be used if you know what format your
               table is in.
               If it has the special value
               <code>(auto)</code> (the default),
               then an attempt will be
               made to detect the format of the table automatically.
               This cannot always be done correctly however, in which case
               the program will exit with an error explaining which
               formats were attempted.
               
               <p>[Default: <code>(auto)</code>]
               </p>
            </dd>
            <dt><strong><code>inN = &lt;table&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(<a href="http://www.starlink.ac.uk/stil/javadocs/uk/ac/starlink/table/StarTable.html">StarTable</a>)</em></strong></dt>
            <dd>The location of the input table.
               This may take one of the following forms:
               
               <ul>
                  <li>A filename.</li>
                  <li>A URL.</li>
                  <li>The special value "<code>-</code>",
                     meaning standard input.
                     In this case the input format must be given explicitly
                     using the <code>ifmtN</code>
                     parameter.
                     Note that not all formats can be streamed in this way.
                  </li>
                  <li>A system command line with
                     either a "<code>&lt;</code>" character at the start,
                     or a "<code>|</code>" character at the end
                     ("<code>&lt;syscmd</code>" or
                     "<code>syscmd|</code>").
                     This executes the given pipeline and reads from its
                     standard output.
                     This will probably only work on unix-like systems.
                  </li>
               </ul>
               
               In any case, compressed data in one of the supported compression
               formats (gzip, Unix compress or bzip2) will be decompressed
               transparently.
               
            </dd>
            <dt><strong><code>istreamN = true|false</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(Boolean)</em></strong></dt>
            <dd>If set true, the input table
               specified by the <code>inN</code> parameter
               will be read as a stream.
               It is necessary to give the 
               <code>ifmtN</code> parameter
               in this case.
               Depending on the required operations and processing mode,
               this may cause the read to fail (sometimes it is necessary
               to read the table more than once).
               It is not normally necessary to set this flag;
               in most cases the data will be streamed automatically
               if that is the best thing to do.
               However it can sometimes result in less resource usage when
               processing large files in certain formats (such as VOTable).
               
               <p>[Default: <code>false</code>]
               </p>
            </dd>
            <dt><strong><code>latN = &lt;deg-expr&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Latitude in decimal degrees.
               <p>The value is a numeric algebraic expression based on column names
                  as described in <a href="jel.html">Section 10</a>.
                  
               </p>
            </dd>
            <dt><strong><code>lonN = &lt;deg-expr&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Longitude in decimal degrees.
               <p>The value is a numeric algebraic expression based on column names
                  as described in <a href="jel.html">Section 10</a>.
                  
               </p>
            </dd>
            <dt><strong><code>posangN = &lt;deg-expr&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Orientation of the ellipse.
               The value is the angle in degrees from the North pole
               to the primary axis of the ellipse
               in the direction of increasing longitude.
               
               <p>The value is a numeric algebraic expression based on column names
                  as described in <a href="jel.html">Section 10</a>.
                  
               </p>
            </dd>
            <dt><strong><code>raN = &lt;num-expr&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Ellipse first principal radius.
               The units of this angular extent are determined by the <code>unit</code> option.
               
               <p>The value is a numeric algebraic expression based on column names
                  as described in <a href="jel.html">Section 10</a>.
                  
               </p>
            </dd>
            <dt><strong><code>rbN = &lt;num-expr&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(String)</em></strong></dt>
            <dd>Ellipse second principal radius.
               The units of this angular extent are determined by the <code>unit</code> option.
               If this value is blank, the two radii will be assumed equal,
               i.e. the ellipses will be circles.
               
               <p>The value is a numeric algebraic expression based on column names
                  as described in <a href="jel.html">Section 10</a>.
                  
               </p>
            </dd>
            <dt><strong><code>scaleN = &lt;number&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(Double)</em></strong></dt>
            <dd>Scales the size of variable-sized markers
               like vectors and ellipses.
               The default value is 1, smaller or larger values
               multiply the visible sizes accordingly.
               
               <p>The main purpose of this option is to tweak
                  the visible sizes of the plotted markers for better visibility.
                  The <code>unit</code> option
                  is more convenient to account for the units in which the
                  angular extent coordinates are supplied.
                  If the markers are supposed to be plotted with their
                  absolute angular extents visible, this option should be set
                  to its default value of 1.
                  
               </p>
               <p>[Default: <code>1</code>]
               </p>
            </dd>
            <dt><strong><code>shadingN = auto|flat|translucent|transparent|density|aux|weighted &lt;shade-paramsN&gt;</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot2/layer/ShapeMode.html">ShapeMode</a>)</em></strong></dt>
            <dd>Determines how plotted objects in layer N
               are coloured.
               This may be influenced by how many objects are plotted
               over each other as well as the values of other parameters.
               Available options (<a href="ShapeMode.html">Section 8.4</a>) are:
               
               <ul>
                  <li><code><a href="shading-auto.html">auto</a></code></li>
                  <li><code><a href="shading-flat.html">flat</a></code></li>
                  <li><code><a href="shading-translucent.html">translucent</a></code></li>
                  <li><code><a href="shading-transparent.html">transparent</a></code></li>
                  <li><code><a href="shading-density.html">density</a></code></li>
                  <li><code><a href="shading-aux.html">aux</a></code></li>
                  <li><code><a href="shading-weighted.html">weighted</a></code></li>
               </ul>
               Each of these options comes with its own set of parameters
               to specify the details of how colouring is done.
               
               <p>[Default: <code>auto</code>]
               </p>
            </dd>
            <dt><strong><code>unitN = scaled|degree|minute|arcsec|mas|uas</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<em>(<a href="http://andromeda.star.bris.ac.uk/starjavadocs/uk/ac/starlink/ttools/plot2/layer/AngleUnit.html">AngleUnit</a>)</em></strong></dt>
            <dd>Defines the units in which the angular extents are specified.
               Options are degrees, arcseconds etc.
               If the special value <code>scaled</code> is given
               then a non-physical scaling is applied to the
               input values to make the the largest markers
               appear at a reasonable size (a few tens of pixels)
               in the plot.
               
               <p>Note that the actual plotted size of the markers
                  can also be scaled using the
                  <code>scale</code> option;
                  these two work together to determine the actual plotted sizes.
                  
               </p>
               <p>The available options are:
                  
                  <ul>
                     <li><code>scaled</code>: a non-physical scaling is applied
                        based on the size of values present
                        
                     </li>
                     <li><code>degree</code>: degrees
                     </li>
                     <li><code>minute</code>: arcminutes
                     </li>
                     <li><code>arcsec</code>: arcseconds
                     </li>
                     <li><code>mas</code>: milli-arcseconds
                     </li>
                     <li><code>uas</code>: micro-arcseconds
                     </li>
                  </ul>
                  
               </p>
               <p>[Default: <code>degree</code>]
               </p>
            </dd>
         </dl>
      </p>
      <hr><a href="layer-skycorr.html">Next</a> <a href="layer-skyvector.html">Previous</a> <a href="LayerType.html">Up</a> <a href="index.html">Contents</a> <br> <b>Next: </b><a href="layer-skycorr.html">skycorr</a><br>
       <b>Up: </b><a href="LayerType.html">Layer Types</a><br>
       <b>Previous: </b><a href="layer-skyvector.html">skyvector</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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