[daip] Problem with SPLIT,SPLAT

[Michael Bietenholz]

Both SPLIT and SPLAT seem to calculate the average frequency of the
SPLIT/SPLAT file incorrectly when multiple IF's are averaged - they
both return the average freq. of only IF1.

This has the unfortunate consequence that your source gets
(apparently) moved towards or away from the phase center by the
relative change in the reference frequency, so is a problem for
astrometry.

Note: this is Dec 02 version, I haven't checked Dec 03, sorry if this
has been fixed.

           michael bietenholz

Header and FQ table of input file:

AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  TIME1  BASELINE
AIPS 1:            INTTIM  GATEID  CORR-ID
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      3   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 1: FREQ        16   8.4095212E+09       8.53  5.0000000E+05    0.00
AIPS 1: IF           4   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: RA           1    22 53 02.268       1.00       3600.000    0.00
AIPS 1: DEC          1    16 50 28.351       1.00       3600.000    0.00
AIPS 1: ----------------------------------------------------------------

Ncol   5  Nrow       1    Sort cols:
    Table has     1 keyword-value pairs:
   NO_IF    =            4
   Table format incompatable with FITS ASCII tables

ROW   FRQSEL       IF FREQ           CH WIDTH         TOTAL BANDWI    SIDEBAND
NUMBER                  HZ                HZ                HZ
1         1     0.0000000000D+00    5.000000E+05      8.000000E+06          1
1               7.9687500000D+06    5.000000E+05      8.000000E+06          1
1               1.6000000000D+07    5.000000E+05      8.000000E+06          1
1               2.3968750000D+07    5.000000E+05      8.000000E+06          1

So the output file should have a mean frequency of about 8409 MHz + 12 MHz,
or 8421 MHz, but, after I run SPLIT, I get the following 8409 MHz again.

Header of SPLIT, aparm(1)=3 output file:

AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      3   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00    0.00
AIPS 1: FREQ         1   8.4095056E+09       1.00  3.2000000E+07    0.00
AIPS 1: IF           1   1.0000000E+00       1.00  1.0000000E+00    0.00
AIPS 1: RA           1    22 53 02.268       1.00       3600.000    0.00
AIPS 1: DEC          1    16 50 28.351       1.00       3600.000    0.00
AIPS 1: ----------------------------------------------------------------


ROW    FRQSEL    IF FREQ           CH WIDTH        TOTAL BANDWI      SIDEBAND
NUMBER               HZ                 HZ              HZ
1         1    0.0000000000D+00    3.200000E+07    3.200000E+07          1