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<title>Contours</title>
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<h3><img alt="" src="../sun.gif" height="98" align="middle"
width="100"> Contours</h3>
<blockquote>
<p>DS9 can create and display contours as an overlay on an image.
The Analysis Contours menu is used to display contours. To
create, copy, paste, and configure contours, use the
Analysis Contour Parameters menu.</p>
<p><b>Contour Parameters </b></p>
<p>When creating a new contour, a dialog box appears, in which the
user selects the number of contour levels, smoothness, and the
distribution of the contours. </p>
<p><b> Contour Levels</b></p>
<p>Specifies the number of contour levels to be generated. A
typical number is between 1 and 10. Note: large numbers of
contours can take a long time to generate. </p>
<p><b> Contour Smoothness</b></p>
<p>Specifies how smooth the contours are. A smoothness level of 1
will evaluate the contour at each image pixel. A level of 2 will
evaluate the contour at every other pixel. The larger the
number, the quicker the contour will be generated, and the less
detail will be available. </p>
<p><b> Contour Scale</b></p>
<p>Specifies the distribution of the contour levels. <br>
</p>
<p><b> Contour Method</b></p>
<p>There are two methods that are available to calculate the
contour lines. The first, BLOCK, blocks down the image, by the
smoothness factor, before contours are calculated. As a result,
the larger the smoothness, the faster the result. The second
method, SMOOTH, smooths the image before calculating contours.
As a result, the larger the smoothness, the slower the result.<br>
</p>
<p><b> <a name="ContourFiles"></a>Contour Files</b></p>
<p>A contour file is an ASCII file containing a header, global
properties, coordinate system, contour levels, and contour
points. <br>
</p>
<blockquote>
<p><b> Header</b></p>
<p>A DS9 contour file may start with the following optional
header: </p>
<blockquote> <tt># Contour file format: DS9 version 7.5<br>
</tt></blockquote>
<p><b> Global Properties</b></p>
<p>Global properties affect all contour levels unless a line
level attribute is specified. The <tt>global</tt> keyword is
first, followed by a list of keyword = value pairs. Multiple
global property lines may be used within a region file. </p>
<blockquote> <tt>global color=green width=1 dash=1 dashlist=8 3<br>
</tt></blockquote>
<p><b> Coordinate Systems</b></p>
<p>For each contour file, it is important to specify the
coordinate system used to interpret the contour points, i.e.,
to set the context in which the positions are interpreted. For
this purpose, the following keywords are recognized: </p>
<blockquote> <tt>PHYSICAL
#
pixel coords of original file using LTM/LTV</tt> <br>
<tt>IMAGE
#
pixel coords of current file</tt> <br>
<tt><tt><tt>FK4,B1950
# sky coordinate systems</tt> <br>
FK5,J2000
#
sky coordinate systems</tt> <br>
</tt><tt><tt><tt>ICRS
#
sky coordinate systems</tt> <br>
</tt>GALACTIC
#
sky coordinate systems</tt> <br>
<tt>ECLIPTIC
#
sky coordinate systems</tt> <br>
<tt>WCS
# primary WCS<br>
</tt><tt>WCSA
#
secondary WCS<br>
</tt><tt>LINEAR
#
linear primary WCS</tt> <tt><br>
</tt></blockquote>
</blockquote>
<blockquote>
<p><b> Contour Level</b></p>
<p>Each contour level is composed of a line value, line
attributes and one or more contours. Line attributes are
specified at the start of a new level and only affect contours
within that level . </p>
<blockquote> <tt>level=15.78775 color=pink width=2 dash=yes dashlist=2
2<br>
</tt></blockquote>
<p><b> Contour</b></p>
<p>Each contour is composed of one or more X,Y coordinates, with
a deliminator of space or comma, starting with "(" and
ending with ")". Contours are not closed.<br>
</p>
</blockquote>
<blockquote>
<blockquote><tt>(</tt><tt>202.4836468 47.22380226</tt><tt><br>
</tt><tt> 202.4833538 47.2239185</tt><tt><br>
</tt><tt> 202.4831634 47.22409874</tt><tt><br>
</tt><tt> 202.4829883 47.22428858</tt><tt>)</tt><br>
</blockquote>
</blockquote>
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<p><br>
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