[Difx-users] Handling lin-pol data with difx2fits

[Walter Brisken]

On Thu, 11 Apr 2019, Leonid Petrov wrote:

> Dear Walter,
>
>> It is true that the poltype is hard coded.  With some experimentation we
>> might be able to change that to X/Y as aspropriate.  At one point I
>> believe AIPS had trouble with other than R or L.  We can look into this
>> for DiFX 2.7.
>
>  If AIPS at the moment has troubles with other than R and L, we can
> ask Eric just to patch AIPS to treat X and Y or H and V as R and L on the flight
> temporarily until better time come, if it is necessary. It should not take more
> than 5 minutes. From the other hand, I got an impression that some folks
> already used AIPS for processing lin-pol data. Am I wrong? If yes, how did they
> do it?

Hi Leonid,

I just checked the code in DiFX trunk (which will become DiFX 2.6 
shortly).  The change to the poltype field is already in place -- was 
added in 2017.

 	-Walter

>  I have 6 lin-pol experiments on my table and a hundred or so to come within
> weeks. We have to fix it now, i.e. today.
>
>> As noted above, the FITS format is unable to describe such data, so this
>> is not possible.
>
>  Although I heard a combinations of words "possible" and "not", I still cannot
> grasp what do they mean together. We need amend FITS-IDI, I understand it.
> So what? Even the US Constitution was amended, and more than once. Let us
> discuss how to do it. And we need fix difx2fits: today it tells that it does not
> like a combination of lin- and cir- data and stops. Yes, we already have the
> lin-cir and cir-lin data that need to be processed, and we plan to get more data
> like that. I already rolled my sleeves up and ready to do it. If you or anybody
> else can provide ideas and/or guidance, warn about pitfalls, contribute code, etc,
> I will appreciate it. But I cannot just do nothing and say: "these are the data that
> I cannot process". Failure is not an option.
>
> Sincerely,
> Leonid
> 2019.04.11_15:38:06
>

-- 
-------------------------
Walter Brisken
NRAO
Deputy Assistant Director for VLBA Development
(575)-835-7133 (office)
(505)-234-5912 (cell)