[daip] SPECR + UVFRE: Combining VLA datasets with different frequency axes.

[Nissim Kanekar]

Hi Eric,

I've run into a problem with combining two VLA datasets with different frequency 
axes, using SPECR and UVFRE in 31DEC17. One dataset is from the VLA and has a 
bandwidth of 3.125 MHz and 128 channels (i.e. channel resolution of 24.41 kHz), 
while the other is from the JVLA and has a bandwidth of 4 MHz and 256 channels 
(i.e. channel resolution of 24.41 kHz). The bands are also centred at different 
frequencies.

I first used SPECR with NPOINTS 160 to convert the JVLA dataset to a channel 
resolution of 25 kHz, and then SPECR with NPOINTS 125 to convert the VLA dataset 
to the same resolution. The VLA.SPECR dataset has a frequency of 1418.4974 MHz 
at channel 63 and 125 channels. I then SPLIT the JVLA.SPECR dataset to produce a 
dataset with 125 channels and 25 kHz resolution, and with a central frequency 
of 1418.8454 MHz (within half a channel of the value in the VLA dataset). And 
then ran UVFRE to regrid the JVLA.SPECR dataset to the VLA.SPECR dataset. The 
JVLA.UVFRE file now appears to have the same frequency structure as the 
VLA.SPECR dataset, i.e. 125 channels, with a frequency of 1418.4974 MHz at 
channel 63, and a channel resolution of 25 kHz. However, when I next run DBCON 
to combine the two files (keeping the VLA.SPECR file first and the JVLA.UVFRE 
file second), I get the following error message:

JEEVES> DBCON1: Copied WX file from vol/cno/vers  1    8   1 to  1   11   1
JEEVES> DBCON1: Copied OF file from vol/cno/vers  1    8   1 to  1   11   1
JEEVES> DBCON1: Copied FO file from vol/cno/vers  1    8   1 to  1   11   1
JEEVES> DBCON1: TABINI: KEY COUNTS     51     51 OR COLS     13     11 DON'T MAT
JEEVES>         CH
JEEVES> DBCON1: DBCAPP: ERROR    1 OPENING INPUT TABLE
JEEVES> DBCON1: Appears to have ended successfully
JEEVES> DBCON1: jeeves 31DEC17 TST: Cpu=     14.5  Real=     15  IO=     12065


The DBCON output file now only contains the first datafile (the VLA dataset), 
when plotted with VPLOT.

If I try changing the order in DBCON, with the JVLA.UVFRE file first and the 
VLA.SPECR dataset second, I get a different error:


JEEVES> DBCON1: Task DBCON  (release of 31DEC17) begins
JEEVES> DBCON1: WARNING: COMBINING VISIBILITY DATA WITH DATAOF UNKNOWN TYPE
JEEVES> DBCON1: RA does not match, will shift second
JEEVES> DBCON1: DEC does not match, will shift second
JEEVES> DBCON1: Create ESO 461-36  .DBCON .   1 (UV)  on disk  1  cno   11
JEEVES> DBCON1: Copied AN file from vol/cno/vers  1    7   1 to  1   11   1
JEEVES> DBCON1: Copied AN file from vol/cno/vers  1    4   1 to  1   11   2
JEEVES> DBCON1: DBMNGL: at output record     50000
.....
JEEVES> DBCON1: DBMNGL: at output record   2050000
JEEVES> DBCON1: Copied WX file from vol/cno/vers  1    7   1 to  1   11   1
JEEVES> DBCON1: DBCAPP: INPUT TABLES DO NOT MATCH
JEEVES> DBCON1: Appears to have ended successfully

This time, the DBCON output appears to contain only the JVLA.UVFRE data (when 
plotted with VPLOT).

I'm not sure whether I'm making a mistake when combining the two files, or if 
there's some sort of a bug in UVFRE. Do you happen to know what's going on?

Many thanks indeed!

Best wishes,
Nissim