[daip] SDGRID convolution function

[Eric Greisen]

Glen Langston wrote:
> Thanks for the update.
> 
> Actually the Orion data do have spectral lines.  There
> are actually two lines at opposite ends of the bands (NH3 1-1
> at 23694 MHz and NH3 2-2 at 23722 MHz, and nothing much in the middle,
> the lines are about 8 km/sec wide or about 0.6 MHz, but there
> are several lines in the NH3 1-1 and 2-2 spectra, separated
> by about 0.3 MHz)
> 
> It takes running IMLIN to subtract out the continuum to see the
> lines.  See the figures at the top of page:
> 
> https://safe.nrao.edu/wiki/bin/view/Kbandfpa/WebHome
> 
> In that example, we'd averaged three channels (I'm not sure
> what data we gave you concerning averaging of channels, the
> original data set has 4096 channels)
> 
> I appreciate your points.  Its a tough problem, but I think
> the thing to check is for the "divide by zero problem" in the
> sum of weights.    Maybe perform a quality control check on the
> sum(wt), not just on the individual input "wt" weights input
> to the grid.   If "sum(wt)" falls inside some +/-threshold, then
> those data should be flagged as well.   This check threshold
> could be a new parameter or threshold = max(wt)*reweight(2) (?).
> or something similar.

The check is only on the sum of the weights not on the individual 
weights going into the sum.  That is why the process described by Bob 
can take place.

Eric