[daip] question about weights in FITS-IDI

[Eric Greisen]

Walter Brisken wrote:
> The weight vector that accompanies a visibility record stores weights on a 
> per IF / per polarization basis.  The documentation I have suggests that 
> this weight must be between 0 and 1.
> 
> Because of some subtleties in the DiFX software correlator, it is possible 
> for the data weight to be slightly greater than 1 (with a hypothetical 
> maximum of about 2).  This occurs when the integration time is not an 
> exact multiple of the subintegration time.  In these cases, some records 
> may have slightly less than full weight and some may have a bit more than 
> full weight.  The mean weight would be 1 in the case of perfect data 
> playback.
> 
> Will these weights that can exceed 1 cause any unexpected problems within 
> AIPS?

Weights in AIPS have any value whatsoever from enormous to very small in 
absolute value with negative or 0 implying flagged.  I do not know if 
FITLD cares other than to flag/delete all below some weight when reading 
in FITS IDI format.  It does not examine the value otherwise so weights 
larger than 1 will not cause a problem.  The wtthresh cannot be set > 1.

Eric