[daip] additional SWTIN output in UVWAIT ?

[Olaf Wucknitz]

Hello again,

when running IMAGR with non-natural weighting, the subroutine UVWAIT 
determines some relevant noise parameters. One of them is logged as 
"UVWAIT: Noise is increased by a factor XXX due to weighting". This one 
(variable NOISR) is also written to the data file header as keyword 
WTNOISE, which is very helpful.
Would it be possible to add a few lines to do the same with the variable 
SWTIN as some appropriate (unused) keyword?

If the weights are calibrated and normalised to reflect 1/sigma^2, one 
could then directly use this number to estimate the expected image noise 
for natural weighting as 1/sqrt(SWTIN), or scale with NOISR to obtain the 
noise for the current weighting.
I know that this number is logged as "UVWAIT: Sum of weights in XXX", but 
writing in into the header would make it easily accessible for scripts.

By the way: Is there a (moderately easy) way to determine the ungridded uv 
chi^2, say from a residual uv data set created by IMAGR? I am currently 
doing this with my own software or in DIFMAP and wonder if it can be done 
with AIPS.



Cheers,
Olaf