defining-pointing-terminology.html

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         title="Permalink to Defining Pointing Terminology">Defining Pointing Terminology</a></h2>
 
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    <abbr class="published" title="2008-07-30T21:50:00-06:00">
      2008/07/30
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    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-adamgginsburggmailcom.html">Adam (adam.g.ginsburg@gmail.com)</a>
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    <p>There has been a lot of confusion about pointing terminology.</p>
<p>CSO pointing model: the telescope pointing model used and written as a
black box</p>
<ul class="simple">
<li>has already been corrected for aberration/nutation</li>
<li>is in current epoch coordinates (e.g. J2007.34)</li>
</ul>
<p>Instrument-specific correction to pointing model</p>
<ul class="simple">
<li>??? also referred to as 't terms'</li>
<li>is offset between CSO pointing model and real locations</li>
<li>should be a function of alt (and maybe az)</li>
<li>is recorded in &quot;RPC&quot; files</li>
<li>is in units of distance on the sky: delta-RA and delta-DEC, or
delta-ALT and delta-AZ will be in the same units, while if they were
in coordinate units delta-RA and delta-AZ would have to be scaled by
1/cos(DEC) or 1/cos(ALT) respectively</li>
</ul>
<p>FAZO and FZAO: Fixed Azimuth Offset and Fixed Zenith Angle Offset</p>
<ul class="simple">
<li>these are ambiguously defined in the pipeline code</li>
<li>???? FAZO/FZAO include both the functional instrument specific
pointing offset and any manual changes made at the telescope [manual
only relevant to 2007 observations]</li>
<li>???? or are these JUST fixed offsets, and the instrument specific
corrections are not included? Either way, how can I separate out
manually-applied fixed offsets from fitted-model offsets?</li>
</ul>

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