[daip] forwarded message from Harro Verkouter

[Eric Greisen]

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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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