Hi Nathan

Unfortunately I believe David Berry is on vacation for the next week
or two, so you may have to wait till he's back to get a more useful
insight.

If you have any interest in looking into the code in more detail to
see if you can see what's happning, the code that converts the Beam
FWHM into a minimum pixel (using the minimum detection level and the
noise level) is in:

cupid/cupidsub/cupiddefminpix.c
https://github.com/Starlink/starlink/blob/master/applications/cupid/cupidsub/cupiddefminpix.c

And for the clumpfind algorithm its called within:

cupid/cupidsub/cupidclumpfind.c
https://github.com/Starlink/starlink/blob/master/applications/cupid/cupidsub/cupidclumpfind.c

Cheers,

Sarah

On 11 August 2017 at 10:49, Nathan Brunetti <[log in to unmask]> wrote:
> Hi
>
> As part of putting together some completeness estimation code I'm trying to get ClumpFind to find a gaussian source in a blank image whose FWHM is the same as my ClumpFind.FWHMBeam input. I would expect that since the source is the same size as the input beam size it should find it but instead ClumpFind complains about the source being smaller than the spatial beam width. I have TLow=3*RMS and DeltaT=2*RMS so I thought since I'm using a 20*RMS peak source it would count up all the pixels above 3*RMS and that would be well above MinPix.
>
> I've attached a tar file with a test 2D FITS map and a Python script that populates the map and outputs the ClumpFind configuration file I'm using. To run things the way I am just untar the tar file, run "python prep.py" and then these Starlink commands
>
> convert
> fits2ndf template.fits template.sdf
> cupid
> findclumps backoff=FALSE config='^test.conf' deconv=FALSE msg_filter=2 in='template.sdf' logfile='test.cuplog' method='ClumpFind' out='test' outcat='test' rms=0.000330365670379 shape='None' wcspar=FALSE
> ndf2fits test.FIT test.fits
>
> That will try finding the source that has the same FWHM as the input to ClumpFind. I have found that if I increase the standard deviation of the gaussian by around 30% then ClumpFind finds the source without rejecting it. You can test that by multiplying the "sigma" variable in prep.py by 1.3 and rerunning it to repopulate the map and then do the clump finding again.
>
> I'm using Starlink version 2017A on 64-bit Mageia 6 (basically RHEL/Fedora). Any help/insight would be greatly appreciated.
>
> Thank you,
> Nathan
>
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-- 
Dr Sarah Graves
Scientific Programmer
East Asian Observatory/JCMT
[log in to unmask]

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