[daip] questions regarding prtan and imagr

[Eric Greisen]

Hiroko Shinnaga wrote:
> Dear AIPS experts,
> 
>    I'm Hiroko Shinnaga, a staff scientist at the Caltech Submillimeter
> Observatory.  I have two general questions regarding tasks of PRTAN
> and IMAGR.
> 
> Q1.   I'm dealing with some interferometric data that contains
> 10 antennas in total.  I first create FITS file using a calibration tool
> called MIR (IDL base) and generated a FITS file.  Then I read the
> FITS file to AIPS.  When I inspect the data using the task "UVPLT"
> for example, it looks like it contains all data of all baselines.   
> However,
> when I use the "PRTAN", I see only information of 8 antennas.  From
> the output of "PRTAN", it seems the antenna table seemed to not be
> transfered properly.  Could you let me know what kind of effect I
> should expect if I don't have a correct antenna table?
> 
> Q2.  When I tried to process the above image with IMAGR, I found
> I was able to make sensible image only when I use UVWTFN = ' '
> (uniform weighting).  Does this indicate that something may be
> wrong for the table that contains weighting information of each antenna?

Try the task PRTAB on your INEXT='AN' file.  My bet is that you have 
only 8 rows in that table.  The AN file is not used a great deal - it 
provides labels for antennas in plotting tasks but that is not essential 
and the tasks should run without them.  The only task that requires the 
AN table in a completely essential way is UVFIX.  You cannot run that 
task without an AN table that is correct.

I find your statement in Q2 hard to believe.  The weights are part of 
the visibility data (as real, imaginary, weight).  You can look at them 
with PRTUV, UVPRT, and even plot them with UVPLT et al.  If you attempt 
UVWTFN = 'NA' then you get the actual values present in the data.  If 
there is something really wrong with them, then the resulting image 
would be strange.  Really wrong means something like 10000 for one 
baseline and 0.001 for the others.  Weights that are <= 0.0 flag the 
associated data and so would not appear in any image independent of UVWTFN.

Eric Greisen