retrieving-and-selecting-data-in-casa.html

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      <a href="https://keflavich.github.io/blog/retrieving-and-selecting-data-in-casa.html" rel="bookmark"
         title="Permalink to Retrieving and Selecting Data in CASA">Retrieving and Selecting Data in CASA</a></h2>
 
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    <abbr class="published" title="2016-02-24T13:44:00-07:00">
      2016/02/24
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    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-ginsburg-adamgginsburggmailcom.html">Adam Ginsburg (Adam.G.Ginsburg@gmail.com)</a>
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    <p>I learned a few important things at the 7m+12m workshop in Garching:</p>
<ol class="arabic">
<li><p class="first"><tt class="docutils literal">clean</tt> treats input models in Jy/beam and Jy/pixel qualitatively (not
just quantitatively) differently.  Jy/pixel images are taken to be model
images exactly, where Jy/beam are... somehow interpreted differently, maybe
as clean component assemblies.  I don't know the details, but this is a
major caution.</p>
</li>
<li><p class="first">The <tt class="docutils literal">tbtool</tt> is not very good for extracting data for plotting.  The flags
are not guaranteed to be in a sane shape, which will lead to crashes if you
try <tt class="docutils literal"><span class="pre">tb.getcolumn('FLAG')</span></tt>.  <tt class="docutils literal">ms.msselect</tt>, however, allows you access
to most of the normal selection routines used in <tt class="docutils literal">clean</tt>, <tt class="docutils literal">split</tt>, etc.
It is tricky, though, because <tt class="docutils literal">ms.select</tt> does <em>not</em> allow you access to
the same selection.  Also, while <tt class="docutils literal">spw</tt>-based selection normally allows you
to select channels, in <tt class="docutils literal">ms.msselect</tt> it does not: instead you must use
<tt class="docutils literal">ms.selectchannel</tt>.  See <a class="reference external" href="https://github.com/radio-astro-tools/sandbox/blob/master/casa_7m12m_tools/weight_density_uv_plot.py">this example</a>.</p>
<p>Details about the selection are at this URL, but the documentation is
incomplete and, in places, incorrect:</p>
<p><a class="reference external" href="http://www.aoc.nrao.edu/~sbhatnag/misc/msselection/FrequencySelection.html">http://www.aoc.nrao.edu/~sbhatnag/misc/msselection/FrequencySelection.html</a></p>
<p>(for example, <tt class="docutils literal">chanspec</tt> is not valid in <tt class="docutils literal">msselect</tt>, or at least
it doesn't do anything)</p>
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