[daip] Minor IMAGR.HLP issue

[Craig Walker]

Just thought I'd pass this on while I'm noticing it.

IMAGR.HLP says:
   ECHAN......Highest channel number to to include in image,
              0 => max   The actual # of output channels will be
                   (BCHAN-ECHAN+1-NCHAV)/CHINC + 1
The equation is surely wrong --- for most combinations of parameters, it 
will be negative.  Also I suspect that NCHAV is not in correctly (if it 
is, then I have totally misinterpreted what NCHAV does).

The correct equation depends how CHINC and NCHAV interact, which I don't 
feel I understand from the help file.  The help file says:  "If NCHAV>1, 
CHINC refers to the first plane going into the map.".  That still 
doesn't tell me if CHINC is applied to pre or post average channels.  In 
fact, I'm not sure what it does tell me.

What happens if ECHAN-BCHAN+1 is not divisible by NCHAV?

Here is a guess for the actual number of output channels, assuming any 
partial averages are skipped and CHINC applies to output channels.  I 
would not be surprised if these assumptions are wrong.

           ((ECHAN-BCHAN+1)/NCHAV)/CHINC

Cheers,

Craig

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     R. Craig Walker            Array Operations Center
     cwalker at nrao.edu           National Radio Astronomy Observatory
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