[sr #110648] Do not select a clump with significant peak

[Sepideh Eskandarlou]

URL:
  <https://savannah.gnu.org/support/?110648>

                 Summary: Do not select a clump with significant peak
                 Project: GNU Astronomy Utilities
            Submitted by: sepideh
            Submitted on: Thu 12 May 2022 02:26:39 PM UTC
                Category: Segment
                Priority: 5 - Normal
                Severity: 3 - Normal
              Item Group: Output not reasonable
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
        Operating System: GNU/Linux

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Details:

I was attempting to make catalog for one of the Frontier-fields cluster. But I
realized some faint objects are not in my catalog.

I saw Segmentation map and realized this object did not consider as true
clump, while, the fainter objects considered as a clump.

When I run _Segment_ with _--checksegmentation_ and _--checksn_, I expected
number of difference between the clump’s peak value and the highest valued
river pixel around that clump when divided by the Sky standard deviation under
the river pixel, for main objects become smaller than the faint objects which
considered as clumps. 
Because the criteria to select true from false clumps is the peak
significance.

Unfortunately, this value was approximately similar for main clump and fainter
object's clump and both of them should not consider as true clump. I do not
know where is problem.

I think this is a bug. For producing this result and check problem, I write my
complete commands in below.

At first, I downloaded a frontier-fields cluster by below command:


wget
https://archive.stsci.edu/pub/hlsp/frontier/abell2744/images/hst/v1.0/hlsp_frontier_hst_wfc3-60mas_abell2744_f160w_v1.0_drz.fits
-Oabell2744-f160w.fits


Secondly, based on the below command I crop the deeper part:


astcrop abell2744-f160w.fits -h0 --polygon="3.6034055,-30.4165889:3.5655321,-
30.4135259:3.5722988,-30.3765434:3.6103451,-30.3816284" --mode=wcs
--output=crop.fits


Then I run _NiseChisel_ on output of the _astcrop_:


astnoisechisel crop.fits --output=nc.fits 


Finally, I have make a flat(3*3) kernel and based on this kernel _Segment_ was
built.


astconvert flat.txt --output=kernel.fits
astsegment nc.fits --kernel=kernel.fits --snquant=0.99 --gthresh=1000
--grownclumps --output=seg.fits


I would be thankful if you check this problem.





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