[Difx-users] Getting difx working on VDIF files - newbie {External}

[Adam Deller]

Hi Hugh,

Can I ask the context in which you want to make this substitution? I.e.,
where did you get the VDIF files, what observation are they from, etc?
Generally I usually find it easier to provide sched with a key file that
describes the observation correctly, and have sched produce a vex file that
describes the observation correctly, and then just use that - rather than
hacking vex files, which is error prone.

That said, the information on fanout on this page may be relevant:
https://www.atnf.csiro.au/people/Tasso.Tzioumis/vlbi/dokuwiki/doku.php/difx/fanoutdef
.

Cheers,
Adam

On Sat, 22 Jun 2024 at 02:47, Hugh Garsden via Difx-users <
difx-users at listmgr.nrao.edu> wrote:

> Hello all,
>
> I'm new to difx and I want to run it on VDIF files. I've seen some recent
> mails about VDIF files so they are obviously being used, but I was looking
> at the manual <https://github.com/difx/difx/wiki/vex2difx#vdif-issues> for
> VDIF information it seems to be incomplete: "TO BE ADDED". I wondered if I
> could get more info or example files or something.
>
> Here is a much longer story of what I'm up to:
>
> I have difx running on the example files in the vf252 dataset here
> <https://www.atnf.csiro.au/vlbi/dokuwiki/doku.php/difx/datasets>. I
> stripped down the vex/v2d files to correlate only one file each of the
> PARKES and ATCA data. That works. So for PARKES I have this filelist:
>
>     /home/jbcaadmin/work/v252f/v252f_Pk_161_012830.lba
>
> and for ATCA this filelist:
>
>     /home/jbcaadmin/work/v252f/v252f_At_161_012830.lba
>
> and the vex/v2d files contain the minimum neccessary to make everything
> work.
>
> Now I want to replace the above files with two VDIF files, and make the
> necessary changes to the vex/v2d files to run difx. There will be changes
> to timing, sampling rate etc., to accomodate the new files, but the VDIF
> files don't contain all the information necessary for  vex/v2d files, so
> I'm going to "pretend" that it some of it is the same as for the LBA files
> above. (The VDIF files are just test files and not actually from an
> observation, but they are valid.)
>
> I made all the changes that I think are necessary, but vex2difx gives me
> this error:
>
> Warning: job y_1 not written since it correlates no data
> This is often due to media not being specified, all frequency Ids being
> unselected, or too many antennas being explicitly unselected by time.
> It is also possible that the vex file is faulty and missing, e.g., an $IF
> section, leading to missing polarisation information.
> nBaseline=0  minSubarraySize=2
>
> I think this is something to do with the $TRACKS block in the vex file. I
> have this in the $TRACKS:
>
> $TRACKS;
> *
> def LBA_.4Ch2bit1to1;
>      track_frame_format = VDIF/8032/4;
> enddef;
>
> but from the manual I think more is needed, because it says:
>
> As a concrete example, a complete $TRACKS section may resemble:
>
> TOBEADDED
>
> so I'm wondering what I'm missing. I tried adding some fanout_def
> statements, based on there being a single 4 bit data stream in the VDIF.
> Then vex2difx was happy, and vex2difx and calcif2 ran successfully, and the
> correlator difx started ok, but seemed to be quite confused about the input
> data streams. Also the manual says that fanout_def is not used for VDIF.
>
> I've attached vex/v2d files of the set that works (LBA files) and the set
> that doesn't work (VDIF files).
>
>
> Thanks,
>
>
>                Hugh
>
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>


-- 
!=============================================================!
Prof. Adam Deller
Centre for Astrophysics & Supercomputing
Swinburne University of Technology
John St, Hawthorn VIC 3122 Australia
phone: +61 3 9214 5307
fax: +61 3 9214 8797
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