I'm sorry, I'm here to bother you again about pst photometry

[xiao yezhu]

The  official website say :

The configuration files for SExtractor and PSFEx that were used for a given iteration of the Legacy Surveys legacypipe codebase are available on our GitHub page.

but i not found SExtractor .psf config ,only have .psfex  .

The .psf  should used on SExtractor , .psfex should  used on SExtractor PSFEx.

I want to pst photometry use  SExtractor .

Did I understand wrong?

Thank you very much again!

[Dustin Lang]

The config files used for Source Extractor are named *.se, eg,

https://github.com/legacysurvey/legacypipe/blob/main/py/legacypipe/config/common.se

and the config files used for PsfEx are named *.psfex, eg,

https://github.com/legacysurvey/legacypipe/blob/main/py/legacypipe/config/common.psfex

These are only used during photometric calibration, so the sigma levels are set to detect fairly bright stars.

cheers,

dustin

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[xiao yezhu]

Thank you for your reply,

sorry,
I don't seem to see the related configuration of sextractor PSF metering?
Does this contain  sextractor   PSF -related configuration?

Thank you very much again!

[Dustin Lang]

Hi,

I don't know what you are asking :)  All the config files for Source Extractor and PsfEx are here, https://github.com/legacysurvey/legacypipe/tree/main/py/legacypipe/config

We run only

Source Extractor

then

PsfEx

but we don't then run Source Extractor using the PsfEx PSF models.  We only use the PsfEx models in the later Tractor fitting.

cheers,

dustin

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[xiao yezhu]

Hi, dustin

I have a few questions for you

1. I see a lot of  config files  about Source Extractor
Is the value of DR9 aperture metering calculated according to Source Extractor?

2.The words 'These are only used during photometric calibration, so the sigma levels are set to detect fairly bright stars '

In the official website(https://www.legacysurvey.org/dr9/description/) I see this description 

I don't understand
In DR9, Is PSF metering using PSFex or is it just photometric calibration as you said above

3.The  https://www.legacysurvey.org/dr9/catalogs/

The config files for Source Extractor 
https://github.com/legacysurvey/legacypipe/blob/main/py/legacypipe/config/common.se

Why aperture of radius *2 != diameters of [] arcsec? Why is it different?

4.In the file https://github.com/legacysurvey/legacypipe/blob/main/py/legacypipe/config/common.psfex 
PHOTFLUX_KEY FLUX_APER(4) Is equal to  diameters  7 srcsec(26.71 pix)

I have a bit too many questions!
Thank you very much for your reply dustin !

[Dustin Lang]

Hi,

I made a mistake in what I wrote earlier:  We only use Source Extractor + PsfEx to generate the PSF models (not for photometric calibration).

We then use those PsfEx PSF models in the "legacypipe" / "tractor" code to do the photometric calibration of each image, and then in the photometry.

The aperture photometry is measured using the "photutils" package, on the coadded images.

I hope that helps!

cheers,

dustin

To view this discussion on the web visit https://groups.google.com/d/msgid/decam-legacy-survey/b36576e4-9f60-4c39-8c80-4367946e6e4an%40googlegroups.com.

[xiao yezhu]

This is very helpful for me!

I understood how to get the mag(or flux).

I still have questions about question 3 and question 4, can you help me with them?

Thank you for all that you do here!

[Dustin Lang]

Hi,

For 3 and 4 - we don't use the Source Extractor aperture photometry at all any more.  (We used to, back in... DR3? DR5?)

In the Legacy Surveys catalogs, the "apflux" measurements are made using the "photutils" python package.

cheers,

dustin

To view this discussion on the web visit https://groups.google.com/d/msgid/decam-legacy-survey/d219608d-070a-4506-91d9-175154612b8bn%40googlegroups.com.

[xiao yezhu]

I get it.

Thank you for all that you do here!

Have a great day!