[daip] JMFIT/IMEAN booby trap

[Craig Walker]

Thanks.  That should help - it certainly would work in my case.  Of 
course, now I've become rather more careful about DOCAT.

Cheers,

Craig


On 07/11/2014 03:42 PM, Eric Greisen wrote:
> On 07/09/2014 10:21 PM, R. Craig Walker wrote:
>> I just stumbled on a booby trap for the unwary (like me).  Nothing is
>> formally being done wrong, but in practice, people could be led badly
>> astray.  Consider the following sequence, which is very common for me:
>>
>> IMEAN, full image, DOCAT=1
>>     Puts correct ACTNOISE in header.
>> IMEAN, tight window to measure flux density, DOCAT=1 because I'm not
>> paying
>>     attention to it - never did until very recently.
>>     Replaces ACTNOISE with a much higher value
>> JMFIT.  Uses bad ACTNOISE to calculate errors.
>>
>> I just did this.  Fortunately I noticed the statement about ACTNOISE
>> being
>> used and knew I had likely measured a flux density with a tight box.  I
>> reran
>> IMEAN with a wide open box, replacing ACTNOISE.  Then JMFIT came up with
>> much smaller errors.  My worry is that people will blunder into the bad
>> case very easily.  I suggest protecting against it somehow.  Is there any
>> reason not to default to recalculating the noise with a histogram fit?
>> Unfortunately RADIUS doesn't really have room for another option.
>
>
> I changed IMEAN to avoid writing ACTNOISE and ACTMEAN unless the area is
> at least 20% of a plane and the volume 10% of a cube.  DOCAT=2 says do
> it anyway.
>
> This should help.  But the fitting-task message about RMS remains
> significant.
>
> Eric

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