how do i use source extractor?

[YushengEdward]

Hi,
Last week i have downloaded the sex and tried to use it but there is something wrong. When i run cmd-line "--use-source-extractor", error message appeared as followed:
~/Astrometry.net-0.92$ ./demo.sh
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/hyayh/Astrometry.net-0.92/workdir/bin
Reading input file 1 of 1: "/home/hyayh/Astrometry.net-0.92/workdir/demo/demo.fits"...
Extracting sources...

WARNING: default.sex not found, using internal defaults

----- Source Extractor 2.25.0 started on 2023-08-07 at 10:56:51 with 1 thread

----- Measuring from: demo.fits
"Unnamed" / no ext. header / 2064x1386 / 16 bits (integers)
(M+D) Background: 4111.52 RMS: 224.21 / Threshold: 336.315
Objects: detected 2995 / sextracted 2060

All done (in 0.2 s: 6272.9 lines/s , 9323.3 detections/s)
Sorting brightness using MAG_AUTO and BACKGROUND columns failed; falling back to MAG_AUTO.
Reading sort column "MAG_AUTO"
Sorting sort column
mmapping input file
Copying table header.
Writing row 0
Done
Firstly. where the default.sex should i put into?
Secondly, it reminded me "the MAG_AUTO and BACKGROUND columns failed"，did it matter？ if it does matter，how do i make it right?
I will appreaciate if you can give me reply.THANKS！

[ebertin]

Hi @YushengEdward,
well this does not seem to be a SExtractor issue, as the extraction completed successfully. Unfortunately I cannot really provide support for astrometry.net, but I can tell you that the default.sex configuration file not being found is not an issue; it is not mandatory. Most probably astrometry.net runs SExtractor with configuration parameters set directly in the command line. Moreover the "MAG_AUTO and BACKGROUND columns failed" is not a SExtractor error message, this seems to be an astrometry.net issue. You might want to check with the astrometry.net people, but I am not sure one should worry about those warnings.
I hope this helps!

[YushengEdward]

Hi,
I managed to solve the problem above. But i have no idea where to find the filter file "default.conv" when try to change my configuration file to reduce the number of source extracted. Is there any way you can think out to help me solve it?
Thanks for any help!

[ebertin]

Hi @YushengEdward,
On Linux the filter file default.conv should be in /usr/share/sextractor/. Or you can grab it directly here.

[YushengEdward]

Hi,
I found it successfully. Actually, my goal is to minimize resolution time as much as possible.
May i change the information of default.sex, default.param or default.conv to make it happen? Or i can say, what information is related to the efficency of sex's extract source. I have tried to replace the default.conv with a laplace filter:
0 1 0
1 -4 1
0 1 0
It has achieved little. Do you have any advice for me?
Thanks always!

[ebertin]

Well if you want the code to run as fast as possible, I would suggest turning off detection filtering with the option FILTER N. You will also have to increase the detection threshold to ~3 sigma: DETECT_THRESH 3 to avoid detecting noise peaks. You might also want to turn off CLEANing: CLEAN N. Of course this will be at the expense of detection completeness and reliability.

[YushengEdward]

I really appreciate your help!