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<p>Locations.dat includes a text entry "FRAME". At least in the
older version I have on my computer, that tells where the data
came from - in the case I'm looking at, which solution from which
group. But that is just text and you would need to understand the
details of the solution to know which ITRF is involved. So the
information is (or should be) there to chase down the frame, but
it would be good to make it more formal. It doesn't seem that
FRAME got passed to the VEX file.<br>
</p>
<p>Years ago, we tried rather hard to be sure that the station and
source catalogs being used for Sched were the same as were being
used for the IOP observation. It took a while to get it right,
but I think we did. I can't speak for the last 10 years since I
retired.</p>
<p>Cheers,<br>
Craig</p>
<p>P.S. Chris, your previous email came in between when I started to
compose mine and when I sent it - without checking for anything
new. So it was not a response to yours.</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 7/4/25 8:37 PM, Phillips, Chris
(S&A, Marsfield) wrote:<br>
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<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Hi
Craig,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Yes I
think the main issue is if correlators use the location.dat
from sched as telescope positions, the bookkeeping is not
enough to know which ITRF frame was used. The rest of the
sched/calc mechanisms are fine.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Cheers<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Chris<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Difx-users
<a class="moz-txt-link-rfc2396E" href="mailto:difx-users-bounces@listmgr.nrao.edu"><difx-users-bounces@listmgr.nrao.edu></a> on
behalf of R. Craig Walker via Difx-users
<a class="moz-txt-link-rfc2396E" href="mailto:difx-users@listmgr.nrao.edu"><difx-users@listmgr.nrao.edu></a><br>
<b>Date: </b>Saturday, 5 July 2025 at 09:32<br>
<b>To: </b><a class="moz-txt-link-abbreviated" href="mailto:difx-users@listmgr.nrao.edu">difx-users@listmgr.nrao.edu</a>
<a class="moz-txt-link-rfc2396E" href="mailto:difx-users@listmgr.nrao.edu"><difx-users@listmgr.nrao.edu></a><br>
<b>Subject: </b>Re: [Difx-users] ITRF realisations
{External}<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><span style="font-size:11.0pt">Sched,
at least when I was the author and maintainer, never
claimed to
<br>
do geometric calculations at a level appropriate for
correlation. For <br>
scheduling of scans, typically many seconds long,
one can be more <br>
casual. So Sched never required the user to provide
EOP. The <br>
correlators needed to get measured EOP values for
best results. What <br>
Sched does provide to the correlator and get from
the users are the <br>
station and source coordinates in whatever reference
frames are being <br>
used. For this, it is important that the coordinate
values be in the <br>
same system used for the EOP measurements that the
correlator will use, <br>
whatever those are. After all, the EOP are a major
factor in defining <br>
the rotation between the terrestrial and celestial
reference frames at <br>
the time of the observations. So when scheduling,
you should learn <br>
which ITRF realization is being used for the EOP
observations and use <br>
that for astronomy observations. For geodetic
observations, it may not <br>
matter because the model will be bucked out and
replaced anyway.<br>
<br>
Cheers,<br>
<br>
Craig<br>
<br>
<br>
On 7/4/25 6:49 AM, Leonid Petrov via Difx-users
wrote:<br>
> Chris,<br>
><br>
> I looked at sched-12.0. I found that
internally it uses UTC(t)<br>
> function as time. It assumes UT1(t) = UTC(t),
see for instance<br>
> schgeo.f. This can introduce an error that is
equivalent to an<br>
> error in position of mid-latitude sites at a
level of several<br>
> hundreds meters.<br>
><br>
> In that context difference in several
centimeters between different<br>
> station catalogues is irrelevant.<br>
><br>
> Leonid<br>
> 2025.07.04_08:47:11<br>
><br>
>> On 2025-07-04 01:02, Phillips, Chris
(S&A, Marsfield) via Difx-users <br>
>> wrote:<br>
>> Hi all,<br>
>><br>
>> I have just learned that ITRF (which we use
as the XYZ coordinate<br>
>> system of our telescopes) has multiple
realisations (ITRF2000,<br>
>> ITRF2014 etc).<br>
>><br>
>> There was approx a 9cm change between
around ITRF2005, which is huge.<br>
>><br>
>> The “Frame” detail in Sched is light on
details and vex2difx make<br>
>> no mention of frame.<br>
>><br>
>> Does anyone know what ITRF frame Sched
expects?<br>
>><br>
>> Thanks<br>
>><br>
>> Chris<br>
>>
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