psfSelectionFromMatchList.py

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# This file is part of meas_algorithms.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (https://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
__all__ = ["selectPsfSources"]
 
import numpy as np
import lsst.afw.math as afwMath
import lsst.meas.algorithms as measAlg
import lsst.afw.display as afwDisplay
 
args = [None, "MatchList", None]        # allow the user to probe for this signature
 
 
def selectPsfSources(exposure, matches, psfPolicy):
    """Get a list of suitable stars to construct a PSF."""
 
    import lsstDebug
    display = lsstDebug.Info(__name__).display
    displayExposure = lsstDebug.Info(__name__).displayExposure     # display the Exposure + spatialCells
    #
    # Unpack policy
    #
    kernelSize = psfPolicy.get("kernelSize")
    borderWidth = psfPolicy.get("borderWidth")
    sizePsfCellX = psfPolicy.get("sizeCellX")
    sizePsfCellY = psfPolicy.get("sizeCellY")
    #
    mi = exposure.getMaskedImage()
 
    if display and displayExposure:
        disp = afwDisplay.Display(frame=0)
        disp.mtv(mi, title="PSF candidates")
 
    psfCellSet = afwMath.SpatialCellSet(mi.getBBox(), sizePsfCellX, sizePsfCellY)
    psfStars = []
 
    for val in matches:
        ref, source = val[0:2]
        if not (ref.getFlagForDetection() & measAlg.Flags.STAR) or \
               (source.getFlagForDetection() & measAlg.Flags.BAD):
            continue
 
        try:
            cand = measAlg.makePsfCandidate(source, mi)
            #
            # The setXXX methods are class static, but it's convenient to call them on
            # an instance as we don't know Exposure's pixel type (and hence cand's exact type)
            if cand.getWidth() == 0:
                cand.setBorderWidth(borderWidth)
                cand.setWidth(kernelSize + 2*borderWidth)
                cand.setHeight(kernelSize + 2*borderWidth)
 
            im = cand.getMaskedImage().getImage()
            max = afwMath.makeStatistics(im, afwMath.MAX).getValue()
            if not np.isfinite(max):
                continue
 
            psfCellSet.insertCandidate(cand)
 
            if display and displayExposure:
                disp.dot("+", source.getXAstrom() - mi.getX0(), source.getYAstrom() - mi.getY0(),
                         size=4, ctype=afwDisplay.CYAN)
                disp.dot("o", source.getXAstrom() - mi.getX0(), source.getYAstrom() - mi.getY0(),
                         size=4, ctype=afwDisplay.CYAN)
        except Exception:
            continue
 
        source.setFlagForDetection(source.getFlagForDetection() | measAlg.Flags.STAR)
        psfStars += [source]
 
    return psfStars, psfCellSet