[daip] forwarded message from Harro Verkouter

[Leonia Kogan]

Hi  all,

I wrote the last version of UVFIX . At that time I discovered that that 
the old version of UVFIX interpreted
POLRX, POLRY ( as they were read from the header of AN table) in meters!!!!

Having looked at the output of th task PRTAN I found  that POLRX, POLRY 
are in arcsec
That is why I changed  POLRX, POLRY from meters to arcsec inside of  UVFIX.

Today I decided to check whether the numbers printed in the AN table 
header (by PRTAN) are actually
in arcsec.

For this purpose

1. I run UVFIX with VLBA data with debugger and looked what the ANTINI 
sibroutine actually reproduces
    for  POLRX, POLRY. Those number coincide with the AN table header 
printed by PRTAN

2. I called to my friend Leonid Petrov ( Goddard Space Center) and asked 
him to look what are the numbers
    for POLRX, POLRY for the date of my VLBA data. His numbers in arcsec 
coincide with numbers
    given at the AN table header..

CONCLUSION:

The VLBI correlator records POLRX, POLRY into AN table header INARCSEC, 
not in METER !!!!!!!!
UVFIX (last version) is CORRECT interpreting numbers given at the AN 
header in arcsec, not in meter!!!!!!!!

Leonid Kogan


Eric Greisen wrote:

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>From: Harro Verkouter <verkouter at jive.nl>
>To: Eric Greisen <egreisen at nrao.edu>
>CC: Huib Jan van Langevelde <langevelde at jive.nl>
>Subject: Re: [daip] bug in AIPS 'tst"/ POLARX/Y
>Date: Thu, 10 Aug 2006 08:30:30 +0200
>
>
>Ok so I changed the subject to incorporate POLARX/Y.
>
>To summarize: it is a matter of units. IDI says it should be 'meters', 
>VLBA s/w writes in units of 'arcseconds'. This breaks (at least) the 
>UVFIX task - UVWs are way off since apparently UVFIX *expects* 
>arcseconds rather than meters.
>
>Our original question to you was: do you know if AIPS has an internal 
>unit associated with the POLARX/Y values and if so, which one is it? 
>Other tasks besides UVFIX may be affected by this.
>
>Depending on if/what AIPS internally thinks we may or may not have to 
>fix FITLD to recompute the value of the POLARX/Y keyword in order to 
>represent it in the units which are internally used.
>
>Browsing through 31DEC06 sources I found POLARX/Y referenced in a few 
>places and mostly in the comments it is taken to be in units of meters 
>save in the file APL/SUB/JPOLAR.FOR where it is assumed to be in units 
>of arcsec....
>
>
>The fix in itself would be a no-brainer for any of us - VLBA, JIVE, AIPS 
>  - I'd say.
>However, the more difficult thing we're faced with is the question of: 
>how can we fix this in such a way that it is somehow consistent and 
>hopefully not break existing archive data... it would be quite a 
>nuisance to have to retro-edit FITS files to modify the values of the 
>POLARX/Y keywords. That would definitely not be a no-brainer I hope 
>you'll agree with me.
>
>By the way - answer these issues at your own convenience...
>
>Cheers,
>
>harro verkouter
>
>Eric Greisen wrote:
>  
>
>>I can get the info eventually if you will remind me of the POLARX/Y
>>problem.  The VLBA is run by expert scientists not me - all aips does
>>is use whatever the correlator writes which may or may not be
>>correct.  Craig Walket, John Romney are ones who might change what is
>>written.  I cannot find the previous e-mail - either I lost it or it
>>was not from you and it does not say POLAR in its subject.
>>
>>Eric Greisen
>>    
>>
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