<div dir="ltr"><div>I don't see any need to deviate from what is currently available (linear motion within a date range), I think it is just a case of adding a text field that includes some metadata on where that comes from, and passing that through to vex and onwards to FITS via difx2fits.</div><div><br></div><div>Leonid: the position that is in the vex file can always be overridden in vex2difx if a different station position is desired for correlation, and I'm not suggesting additional positions/keywords. As you suggested, post-processing is the place to do anything meticulous. I view this as simply ensuring that the origin of the coordinates used for correlation can be more easily ascertained when one has the FITS file.</div><div><br></div><div>Cheers,</div><div>Adam</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, 8 Jul 2025 at 02:50, Jay Blanchard via Difx-users <<a href="mailto:difx-users@listmgr.nrao.edu">difx-users@listmgr.nrao.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">SCHED is currently maintained enough to put in a little bit of work if <br>
more metadata on the frame used is requested in the VEX.<br>
I don't envisage us being able to put in the work to do anything super <br>
complicated (non-linear etc).<br>
We'd need a clear idea of how/where though :)<br>
<br>
Jay<br>
<br>
On 7/7/25 10:30, R. Craig Walker via Difx-users wrote:<br>
> SCHED locations.dat file has date ranges. SCHED uses the appropriate <br>
> entry. This allows accounting for steps (earthquakes), but nothing <br>
> more complicated. For example, there are three entries for MK-VLBA <br>
> with different date ranges.<br>
><br>
> Cheers<br>
> Craig<br>
><br>
><br>
> On 7/7/25 5:08 AM, Leonid Petrov via Difx-users wrote:<br>
>> Adam,<br>
>><br>
>> Vex schedule has some positions, although these are not necessarily<br>
>> the positions actually used for scheduling. Sched (as as three other<br>
>> scheduling programs) has no mechanism to account for non-linear site<br>
>> motion, which in case of Japanese station may reach a meter level.<br>
>><br>
>> We have section ARRAY_GEOMETRY with a keyword STABXYZ.<br>
>> Do you suggest to have two keywords for station positions?<br>
>><br>
>> Leonid<br>
>> 2025.07.07_07:06:00<br>
>><br>
>><br>
>>> On 2025-07-06 23:32, Adam Deller wrote:<br>
>>> Hi everyone,<br>
>>><br>
>>> It sounds like there is a desire that some metadata relevant to the<br>
>>> station positions propagates through from the sched station catalogue<br>
>>> through to the vex file and thence into the FITS-IDI output. That<br>
>>> seems a reasonable thing to aim for, regardless of what one thinks of<br>
>>> the provenance of said station positions (and how one deals with the<br>
>>> delay model that has been generated from them and applied at the<br>
>>> correlator).<br>
>>><br>
>>> Cheers,<br>
>>> Adam<br>
>>><br>
>>> On Sat, 5 Jul 2025 at 12:56, Leonid Petrov via Difx-users<br>
>>> <<a href="mailto:difx-users@listmgr.nrao.edu" target="_blank">difx-users@listmgr.nrao.edu</a>> wrote:<br>
>>><br>
>>>> Dear Chris,<br>
>>>><br>
>>>>> but the sched catalogue as what most people use as the positions<br>
>>>> used<br>
>>>>> for Calc.<br>
>>>><br>
>>>> Pity!<br>
>>>><br>
>>>> Coordinates are not measurable quantities. The is is the<br>
>>>> essence of geodesy. Path delay is invariant to a group<br>
>>>> of rotations and translations. As a result, one cannot determine<br>
>>>> station positions using only observations. One needs to apply<br>
>>>> constraint equations with some arbitrary constants right hand sides.<br>
>>>> You can select these constants whichever way you like, for set to<br>
>>>> a telephone number of your spouse, but usually, these constants<br>
>>>> are chosen in such a way that the origin of the coordinate system<br>
>>>> is not too far from the place where nobody traveled -- I mean the<br>
>>>> geocenter, and orientation is not too different then the EOP time<br>
>>>> series maintained by Christian Bizouard. "Too far", "too different"<br>
>>>> sounds subjective. In my view, 10 cm is not too far.<br>
>>>><br>
>>>> Reference frame is just a synonym to station position catalogue.<br>
>>>> If one determines position of ATCA pad XXX with respect, say<br>
>>>> ATCA-104,<br>
>>>> using total station, then that geodesist uses solution gsf_2025b,<br>
>>>> then that guy can write: position of ATCA pad XXX in the gsfc_2025b<br>
>>>> reference frame is A.<br>
>>>><br>
>>>> ITRF is not consistent with anything. The latter versions are<br>
>>>> worse<br>
>>>> than the previous one. I do not recommend of using it all.<br>
>>>><br>
>>>> I know users AIPS got used to a concept that the correlator would<br>
>>>> provide them a perfect model and then they can work with residuals.<br>
>>>> At NASA we have never used that approach at least since 1975.<br>
>>>> Instead, we compute our model that is orders of magnitude more<br>
>>>> accurate<br>
>>>> than that the correlator used and add to theoreticals the quantity<br>
>>>> new_path_delay minus old_path_delay. And we do not care about<br>
>>>> TRF, EOP used by the correlator. I offered 5 or 6 times to the AIPS<br>
>>>> maintainer to add this feature to AIPS and always heard "no!".<br>
>>>> Personally, I have PIMA for VLBI data analysis instead of AIPS and<br>
>>>> I am not affected by this problem.<br>
>>>><br>
>>>>> So what frame used likely does not matter, but for normal<br>
>>>> astronomical<br>
>>>>> use cases my worry is that we as a whole are not careful enough.<br>
>>>><br>
>>>> If you really want to have a precise theoretical model, use<br>
>>>> open-source<br>
>>>> NASA SGDASS that has station positions, source positions, EOP,<br>
>>>> non-linear<br>
>>>> station motion updated on a quarterly basis, various loading<br>
>>>> applied,<br>
>>>> the ionospheric model, path delay through the atmosphere computed<br>
>>>> by integration of equations of wave propagation using the output of<br>
>>>> NASA<br>
>>>> numerical model, etc. The right place for this refined model is<br>
>>>> the post-processing stage, not correlation. Though, you can run<br>
>>>> difxvtd<br>
>>>> if you like.<br>
>>>><br>
>>>> Leonid<br>
>>>> 2025.07.04_22:46:50<br>
>>>><br>
>>>>> On 2025-07-04 22:26, Phillips, Chris (S&A, Marsfield) wrote:<br>
>>>>> Hi Leonid,<br>
>>>>><br>
>>>>> My concern with sched was that the catalogue have no frame info<br>
>>>>> recorded into the positions. Sched does not do much with<br>
>>>> positions, so<br>
>>>>> I agree for sched it does not matter but the sched catalogue as<br>
>>>> what<br>
>>>>> most people use as the positions used for Calc.<br>
>>>>><br>
>>>>> I have chatted to Cormac offline, who points out that the absolute<br>
>>>>> difference between frames would only affect stuff like ionospheric<br>
>>>>> corrections, which will make difference at all. However the<br>
>>>> different<br>
>>>>> frames have many cm difference between them so if inconsistent<br>
>>>> frames<br>
>>>>> are used in the catalogues, that *will* have an effect.<br>
>>>>><br>
>>>>> So what frame used likely does not matter, but for normal<br>
>>>> astronomical<br>
>>>>> use cases my worry is that we as a whole are not careful enough.<br>
>>>>><br>
>>>>> Cheers<br>
>>>>><br>
>>>>> Chris<br>
>>>>><br>
>>>>> From: Leonid Petrov <<a href="mailto:Leonid.Petrov@lpetrov.net" target="_blank">Leonid.Petrov@lpetrov.net</a>><br>
>>>>> Date: Friday, 4 July 2025 at 19:49<br>
>>>>> To: Phillips, Chris (S&A, Marsfield) <<a href="mailto:Chris.Phillips@csiro.au" target="_blank">Chris.Phillips@csiro.au</a>><br>
>>>>> Cc: Difx-users <<a href="mailto:difx-users@listmgr.nrao.edu" target="_blank">difx-users@listmgr.nrao.edu</a>><br>
>>>>> Subject: Re: [Difx-users] ITRF realisations {External}<br>
>>>>><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<br>
>>>> 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<br>
>>>> Difx-users<br>
>>>>><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<br>
>>>>> huge.<br>
>>>>>><br>
>>>>>> The “Frame” detail in Sched is light on details and vex2difx<br>
>>>>> make<br>
>>>>>> no mention of frame.<br>
>>>>>><br>
>>>>>> Does anyone know what ITRF frame Sched expects?<br>
>>>>>><br>
>>>>>> Thanks<br>
>>>>>><br>
>>>>>> Chris<br>
>>>>>> _______________________________________________<br>
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>>>>>> <a href="mailto:Difx-users@listmgr.nrao.edu" target="_blank">Difx-users@listmgr.nrao.edu</a><br>
>>>>>> <a href="https://listmgr.nrao.edu/mailman/listinfo/difx-users" rel="noreferrer" target="_blank">https://listmgr.nrao.edu/mailman/listinfo/difx-users</a><br>
>>>><br>
>>>> _______________________________________________<br>
>>>> Difx-users mailing list<br>
>>>> <a href="mailto:Difx-users@listmgr.nrao.edu" target="_blank">Difx-users@listmgr.nrao.edu</a><br>
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>>><br>
>>> -- <br>
>>><br>
>>> !=============================================================!<br>
>>> Prof. Adam Deller<br>
>>> Centre for Astrophysics & Supercomputing<br>
>>> Swinburne University of Technology<br>
>>> John St, Hawthorn VIC 3122 Australia<br>
>>> phone: +61 3 9214 5307<br>
>>> fax: +61 3 9214 8797<br>
>>> !=============================================================!<br>
>><br>
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</blockquote></div><div><br clear="all"></div><br><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================================================!<br><div dir="ltr" style="font-size:12.8px">Prof. Adam Deller </div></div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: +61 3 9214 5307</div><div style="font-size:12.8px">fax: +61 3 9214 8797</div><div style="font-size:12.8px">!=============================================================!</div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>