draw_psf.yaml

# Copyright (c) 2012-2026 by the GalSim developers team on GitHub
# https://github.com/GalSim-developers
#
# This file is part of GalSim: The modular galaxy image simulation toolkit.
# https://github.com/GalSim-developers/GalSim
#
# GalSim is free software: redistribution and use in source and binary forms,
# with or without modification, are permitted provided that the following
# conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice, this
#    list of conditions, and the disclaimer given in the accompanying LICENSE
#    file.
# 2. Redistributions in binary form must reproduce the above copyright notice,
#    this list of conditions, and the disclaimer given in the documentation
#    and/or other materials provided with the distribution.
#
#
# Draw DES PSFs at the locations of observed galaxies.  To run it type:
#
#     galsim draw_psf.yaml
#
# This demo probably isn't so useful as an actual program, but it does showcase how to
# use the DES module that comes with GalSim, which can be modified to do what you actually
# need.
#
# It works on a full DES exposure with 62 chip images and the files that are output by the
# DESDM and WL pipelines.  We don't include these files in the repo, since they total about
# 700 MB.  You can download a tarball with the files used by this script at:
#
#     http://www.sas.upenn.edu/~mjarvis/des_data.html
#
# The DESDM pipeline produces a catalog of detected objects for each image, and also an
# interpolated PSF using Emmanuel Bertin's PSFEx code, which are stored in *_psfcat.psf files.
# The WL pipeline produces a different estimate of the PSF using Mike Jarvis's shapelet code,
# which are stored in *_fitpsf.fits files.
#
# This script reads the appropriate files for each chip and builds two images, one for each kind
# of PSF estimate, and draws an image of the PSF at the location of each galaxy.  Normally, you
# would probably want to draw these with no noise on individual postage stamps or something like
# that.

# First define the aspects of the configuration that are common to both tasks

# We define a few variables here that will be used multiple times below.
# Also, it's convenient to define them near the top to make them easy to change to run on
# different exposures in other directories, etc.
eval_variables :
    # Note: the s at the start of sroot means the variable is a str.
    # This will be used as simply root in the Eval items below that use it.
    sroot : &root 'DECam_00154912_'

    # Directories in the Galsim repo
    sdata_dir : &data_dir 'des_data'

    # Set which chips to run on
    ifirst_chip : &first_chip 1
    ilast_chip : &last_chip 62
    #ifirst_chip : &first_chip 12
    #ilast_chip : &last_chip 12

# This uses the galsim.des module, which is not loaded by default, so we need to tell it
# to import that module to get the des-specific types.
modules :
    - galsim.des

# Define the PSF profile.  For now, just the items common to both shapelet and PSFEx PSFs.
psf :
    skip : { type : Catalog, col : 'FLAGS' }
    flux : { type : Catalog, col : 'FLUX_AUTO' }


# Setup input files
input :
    catalog :
        dir : *data_dir
        file_name :
            type : NumberedFile
            root : *root
            digits : 2
            ext : '_cat.fits'
            num : { type : Sequence, first : *first_chip }
        hdu : 2

    fits_header :
        dir : *data_dir
        file_name :
            type : NumberedFile
            root : *root
            digits : 2
            ext : '.fits.fz'
            num : { type : Sequence, first : *first_chip }



# Define some other information about the images
image :
    type : Scattered

    xsize : { type : FitsHeader , key : 'NAXIS1' }
    ysize : { type : FitsHeader , key : 'NAXIS2' }
    pixel_scale : { type : FitsHeader , key : 'PIXSCAL1' }
    sky_level_pixel : { type : FitsHeader , key : 'SKYBRITE' }

    noise :
        type : CCD
        gain :
            # This is an approximation, since GAINA, GAINB are missing in SV files.
            type : Eval
            str : 'sky / sig**2'
            fsky : { type : FitsHeader , key : 'SKYBRITE' }
            fsig : { type : FitsHeader , key : 'SKYSIGMA' }

    image_pos :
        type : XY
        x : { type : Catalog , col : 'X_IMAGE' }
        y : { type : Catalog , col : 'Y_IMAGE' }

    draw_method : no_pixel  # The PSFs here already include the pixel response.

    wcs :
        type : Fits
        dir : *data_dir
        file_name :
            type : Current
            key : input.fits_header.file_name

    random_seed : 1339201


# Define the names and format of the output files
output :
    nfiles : { type : Eval, str : 'last_chip - first_chip + 1' }

    file_name :
        type : NumberedFile
        root : *root
        digits : 2
        num : { type : Sequence, first : *first_chip }
        # ext is defined below, since it is different for the two runs

    dir : 'output_yaml'

    nproc : -1

---
# Next the particulars that are specific to the shapelet PSFs

psf :
    type : DES_Shapelet

input :
    des_shapelet :
        # Can't use *data_dir here, since the anchors don't follow across yaml documents.
        dir : { type : Eval, str : 'data_dir' }
        file_name :
            type : NumberedFile
            root : { type : Eval, str : 'root' }
            digits : 2
            ext : '_fitpsf.fits'
            num : { type : Sequence, first : { type : Eval, str : 'first_chip' } }

output :
    file_name :
        ext : '_fitpsf_image.fits'

---
# Now the particulars that are specific to PSFEx

psf :
    type : DES_PSFEx

input :
    des_psfex :
        dir : { type : Eval, str : 'data_dir' }
        file_name :
            type : NumberedFile
            root : { type : Eval, str : 'root' }
            digits : 2
            ext : '_psfcat.psf'
            num : { type : Sequence, first : { type : Eval, str : 'first_chip' } }
        image_file_name :
            type : Current
            key : input.fits_header.file_name

output :
    file_name :
        ext : '_psfex_image.fits'