[daip] question about aips tasks

[Eric Greisen]

Hiroko Shinnaga writes:

 > 1. I found a disagreement between LISTR statements
 >    and the plot made with VPLOT for a data set.
 >    The situation is as follows.  Although LISTR reports
 >    data on some specific object were taken during some
 >    specific time periods, the plot created by VPLOT is
 >    shifted about 15 min from the LISTR statements. Namely,
 >    the observing periods has a time lag roughly about 15
 >    minutes between LISTR and VPLOT.  I checked the observing
 >    script which was run during the period.  Comparing with
 >    the script, it seems that LISTR output looks correct
 >    and VPLOT looks not correct.  With UVPLOT, the
 >    plot of time vs. phase (or amp) agrees with
 >    LISTR results.  So, it seems VPLOT creates wrong plot.
 >    I tried to specify time using the BPARM option.  However,
 >    the results were the same.  Could you let me know
 >    possible reasons why this is happening?  Have you
 >    seen this problem before?

      No and I do not see it when I try right now.  I would need to
see the inputs used to VPLOT.  Note that time is BPARM(1)=12 in VPLOT
and =11 in UVPLT.  BPARM(1)=11 is Greenwich time but that should
differ by an integer number of hours.

 > 
 > 2.  Using the same data set, when I set xinc as 3
 >     or 2 on vplot, I couldn't see almost any point on many
 >     baselines (such as antenna 1, 8, 11, 17, 18,19,
 >     etc).  However, when I set xinc as 1, I could see
 >     all the data points including baselines of antenna
 >     1 etc, which looked missing using xinc = 2 or 3.
 >     Could you let me know possible reasons why this is
 >     happening?

     If XINC=3 then only every 3rd point is considered for plotting.
If the number of baselines selected with the adverbs is a multiple of
3 then you should see lots of points for some baselines and virtually
none for others.  Editing and other vagueries usually make XINC
reasonable but in small data sets you could easily see the effect you
are reporting.  Use XINC=1, modern computers are fast enough.

 > 
 > 3.  Above two issues are  happening only on a specific
 >      data set. I created this AIPS data file using
 >      multiple(four) tape files with FILLM.  For the
 >      other data set that I created from one tape file
 >      with FILLM, with the same options, I didn't have
 >      the above problems.  Do you think these are related?
 >      (Please note that both data sets were taken using
 >      fast switching.  I don't know if these are related.
 >      But just as a info. )
 > 
 >    I would like to appreciate your response soon,
 > if possible.  I have my next VLA run this week
 > Thursday.  In case the data itself have some problem,
 > I need to investigate my script to avoid these issues.

Did you run FILLM 4 times and use DBCON or did you run FILLM once with
all 4 files read?  The latter may end up with times offset by 5 days.
The former could get interesting too if the four files are from very
different dates.  Times are kept in single-precision floating days and
would get inaccurate if many days were involved.  But UVPLT and VPLOT
should see the same times since the data are handed to both of them
from the same subroutines.

So far as I can tell you should have no problem in your data, but I
have no idea what VPLOT appears to be doing or why.

If you provide more information I might be able to look more deeply.

Eric Greisen