[daip] Re: UVFIX problem

[Eric Greisen]

Phil Edwards writes:

 > I'm helping a student reduce some archival VSOP data, and he seems to have
 > run into a problem. In his first reduction we found the delays and rates
 > were changing very rapidly on ground baselines, and checks revealed the
 > data was correlated with quite a large offset from the VCS position now
 > available: ~450 mas in RA and ~150 mas in dec(!). He corrected this in
 > uvfix and things looked good... except all the HALCA data disappeared!
 > Closer checkign of the uvfix parameters revealed uvfixprm(16), for
 > orbiting antennas. We assumed this should be 1, for HALCA, but have also
 > trialled 3, as three separate tracking stations are used for the HALCA
 > data in this observation. In both cases, though, UVFIX dies ("of unnatural
 > causes") with the message CMPUVW: UVWCAL ERROR 1. We tried reducing the
 > offset by a factor of 10 in ra and dec, on the off chance the relatively
 > large offset was the problem, but got the same message. He's using
 > the 31dec02 version of AIPS.
 > 
 > Are we missing a step somewhere? Do we need to run obtab?
 > Or whatever task links the three tracking station names together?
 > Is uvfixprm(1)=1 the correct value?
 > 
 > Any help you can provide would be most welcome. Please let us know if you
 > need any further details from us -- or would like the data to inspect
 > yourself.
 > 
Looking at the code - UVFIXP(16) must equal the antenna number of the
orbiting antenna - run PRTAB to see what that is and try it.  UVFIX is
a difficult task and I am unfamiliar with the orditing aspects of it,
but the rest has received work.  31DEC02 is getting a bit long in the
tooth however.

Eric Greisen