[daip] Wrong (u,v) coordinates?

[Eric Greisen]

On 07/07/2014 09:00 AM, Arnaud Collioud wrote:
>> Can you look at files from earlier in the processing to see when this issue arose?  I changed many tasks to shift the frequency reference to the center, but I see that you have not done that.  This shift does require a re-scaling of the uvw's but a very minor one.  Were the X and S data in the same file at one time?  There could be an issue then if the header had the X band frequency because the u,v,w should then be in wavelengths at X band even on the S band data.  Then, splitting out S band would lead to a really big correction and I wonder if it happened in some way twice???
>
> Yes, originally X and S frequencies were together (even if there were no X data). I split the 2 using UVCOP with the following parameters:
>
> AIPS 1: UVCOP     Task to copy selected times and channels of uv data.
> AIPS 1: Adverbs     Values                 Comments
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: INNAME     'IYA09_S.3'             Input UV file name (name)
> AIPS 1: INCLASS    'UV'                    Input UV file name (class)
> AIPS 1: INSEQ         1                    Input UV file name (seq. #)
> AIPS 1: INDISK        1                    Input UV file disk unit #
> AIPS 1: OUTNAME    'IYA09_S.CLN'           Output UV file name (name)
> AIPS 1: OUTCLASS   'UV'                    Output UV file name (class)
> AIPS 1: OUTSEQ        1                    Output UV file name (seq. #)
> AIPS 1: OUTDISK       1                    Output UV file disk unit #.
> AIPS 1: SELBAND      -1                    Bandwidth to select (kHz)
> AIPS 1: SELFREQ      -1                    Frequency to select (MHz)
> AIPS 1: FREQID        2                    Freq. ID to select. 0=> all
> AIPS 1: BCHAN         1                    First channel selected.
> AIPS 1: ECHAN         0                    Last channel selected.
> AIPS 1: BIF           0                    Lowest IF number 0=>all
> AIPS 1: EIF           0                    Highest IF number 0=>all
> AIPS 1: SOURCES    *all ' '                Source list
> AIPS 1: QUAL         -1                    Source qualifier -1=>all
> AIPS 1: UVRANGE       0           0        Annulus in uv plane selected
> AIPS 1:                                     (thousands of wavelengths)
> AIPS 1: TIMERANG   *all 0                  Timerange:
> AIPS 1:                                     1-4 = start day,hr,min,sec
> AIPS 1:                                     5-8 = end   day,hr,min,sec
> AIPS 1: ANTENNAS   *all 0                  Antennas to copy 0=>all
> AIPS 1: BASELINE   *all 0                  Baselines with ANTENNAS
> AIPS 1: SUBARRAY      0                    Limit copy to one subarray
> AIPS 1:                                    0 => all.
> AIPS 1: FLAGVER      -1                    FG table to apply to data
> AIPS 1:                                    <= 0 => do not apply
> AIPS 1: UVCOPPRM      1           0        Flags:
> AIPS 1:               0           1         1 > 0 => keep flagged data
> AIPS 1:               0           0         2 > 0 => drop subarray info
> AIPS 1:              -1        *rest 0      3 = 0 => copy xc and ac data
> AIPS 1:                                       = 1 => copy only xc data
> AIPS 1:                                       = 2 => copy only ac data
> AIPS 1:                                          of antennas, named in
> AIPS 1:                                          antenna list. Baseline
> AIPS 1:                                          list must be zero.
> AIPS 1:                                     4 > 0 => report progress
> AIPS 1:                                     5 => flag data with weights
> AIPS 1:                                          below this limit
> AIPS 1:                                     6 = 1,3 -> do NOT flag TY/SY
> AIPS 1:                                       = 2,3 -> do NOT flag SN
> AIPS 1:                                     7 = extend copy of tables
> AIPS 1:                                         by UVCO(7) min, 0 -> 15
> AIPS 1: NCOUNT        0                    If UVCOPPRM(3) = 2 then
> AIPS 1:                                    NCOUNT is the approximate
> AIPS 1:                                    ratio of AC to XC in file.
> AIPS 1: FQCENTER      0                    >= 0 -> center frequency axis
>
> I did not change FQCENTER because I was not sure about what it will do (I was also not aware of the importance of it).
>
> As you said, the initial file has the X-band frequency as reference in the header:
>> imh
> AIPS 1: Image=MULTI     (UV)         Filename=IYA09_S.3   .UV    .   1
> AIPS 1: Telescope=VLBI               Receiver=MKIV
> AIPS 1: Observer=Bonn Cor            User #=    4
> AIPS 1: Observ. date=18-NOV-2009     Map date=03-JUL-2014
> AIPS 1: # visibilities   4848965     Sort order  TB
> AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
> AIPS 1:            SOURCE  FREQSEL  INTTIM  WEIGHT  SCALE
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
> AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: FREQ        32   8.4059900E+09       1.00  2.5000000E+05    0.00
> AIPS 1: STOKES       1  -1.0000000E+00       1.00 -1.0000000E+00    0.00
> AIPS 1: IF           4   1.0000000E+00       1.00  1.0000000E+00    0.00
> AIPS 1: RA           1    00 00 00.000       1.00       3600.000    0.00
> AIPS 1: DEC          1    00 00 00.000       1.00       3600.000    0.00
> AIPS 1: ----------------------------------------------------------------
> AIPS 1: Coordinate equinox 2000.00
> AIPS 1: Maximum version number of extension files of type HI is   1
> AIPS 1: Maximum version number of extension files of type BS is   1
> AIPS 1: Maximum version number of extension files of type CL is   1
> AIPS 1: Maximum version number of extension files of type SU is   1
> AIPS 1: Maximum version number of extension files of type AN is   1
> AIPS 1: Maximum version number of extension files of type FQ is   1
>
> What should I do?
> Set FQCENTER to '1' in UVCOP?  Could you explain to me what this parameter is for?

I would leave FQCENTER false for now - let's not complicate things 
(although my code changes for FQCENTER may be the cause of the problem).

Try UVPLT and PRTUV on the initial data set.  Also PRTAB on the FQ 
table.  What do these tests show?

Thanks

Eric