mainGNU Astronomy Utilities - Support: sr #110649, Clumps with S/N smaller than...


sr #110649: Clumps with S/N smaller than threshold consider as a true clumps

Submitter:  Sepideh Eskandarlou <sepideh>
Submitted:  Thu 12 May 2022 03:20:33 PM UTC
Category:  Segment Priority:  5 - Normal
Severity:  3 - Normal Item Group:  * Output not reasonable
Status:  In Progress Privacy:  Public
Assigned to:  makhlaghi Open/Closed:  Open
Operating System:  GNU/Linux
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Mon 16 May 2022 12:08:37 AM UTC, comment #1: 

Thanks a lot for reporting this Sepideh!

Just for completeness, when you say "flat(3*3)", do you mean that 'flat.txt' is simply a plain-text file with 9 values of '1' like below?

$ cat flat.txt
1  1  1
1  1  1
1  1  1

Now to my question: when I ran the same series of commands, and visually inspected 'seg.fits', I couldn't visually find any bad clumps. In the P.S. you can see the output of my Segment command. Do you also find 2811 objects and clumps? If so, when you run with '--checksegmentation' and '--checksn', can you tell me which clump has an S/N below 1.3337?

By the way, when you put multi-line commands (like the 'astcrop' and 'wget' commands of your first post), don't forget to put the back-slask (\) at the end of the line, otherwise, its hard to copy-paste the commands ;-).


$ astsegment nc.fits --kernel=kernel.fits --snquant=0.99 --gthresh=1000 --grownclumps --output=seg.fits
Segment 0.17.30-e5c4 started on Mon May 16 02:00:10 2022
  - Using 12 CPU threads.
  - Input: nc.fits (hdu: 1)
  - Sky STD: nc.fits (hdu: SKY_STD)
  - Kernel: kernel.fits (hdu: 1)
  - Detection: nc.fits (hdu: DETECTIONS)
  - Convolved with given kernel.                       0.150609 seconds
  - Input number of connected components: 218
  - Finding true clumps...
  ---- Clump peak S/N: 1.3337 (0.990 quant of 4339).   0.022486 seconds
  - 2811 objects containing 2811 clumps found.         1.656154 seconds
  - Output written to 'seg.fits'.
Segment finished in:  2.340592 seconds

Mohammad Akhlaghi <makhlaghi>
Group administrator
Thu 12 May 2022 03:20:33 PM UTC, original submission:  

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

I expected the S/N of main object (which did not consider as a clump) became smaller the S/N threshold and S/N of faint objects (which considered as clump) was larger than S/N threshold. While S/N of both of them were smaller than the S/N threshold.

But why the fainter objects considered as clump, they should be ignored because the S/N of these objects were smaller than S/N threshold. I think this is a bug and it should be solved.

For producing this problem I put all the command use for making this segment below.

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


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

Sepideh Eskandarlou <sepideh>
Group Member


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    Date Changed by Updated Field Previous Value => Replaced by
    2022-05-16 makhlaghi StatusNone In Progress
        Assigned toNone makhlaghi

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