psfDeterminer.py

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# This file is part of meas_algorithms.
#
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# (https://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
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__all__ = ["BasePsfDeterminerConfig", "BasePsfDeterminerTask", "psfDeterminerRegistry"]
 
import abc
import numpy as np
 
import lsst.pipe.base as pipeBase
import lsst.pex.config as pexConfig
 
 
class BasePsfDeterminerConfig(pexConfig.Config):
    """Configuration that is likely to be shared by all PSF determiners
 
    This is fairly sparse; more fields can be moved here once it is clear they are universal.
    """
    stampSize = pexConfig.Field[int](
        doc="Size of the postage stamp (in native pixels) to render the PSF model. Should be odd.",
        default=None,
        optional=True,
        check=lambda x: (x > 0) & (x % 2 == 1),
    )
    maxCandidates = pexConfig.Field[int](
        doc="Maximum number of candidates to consider. Will down-sample if given more.",
        default=300,
    )
    downsampleRandomSeed = pexConfig.Field[int](
        doc="Random seed to use to downsample candidates.",
        default=98765,
    )
 
 
class BasePsfDeterminerTask(pipeBase.Task, metaclass=abc.ABCMeta):
    """Base class for PSF determiners
 
    Register all PSF determiners with the psfDeterminerRegistry using:
        psfDeterminerRegistry.register(name, class)
 
    Parameters
    ----------
    config : `lsst.pexConfig.Config`
        Input for configuring the algorithm
    schema : `lsst.afw.table.Schema`
        Schema used for sources; passing a schema allows the
        determiner to reserve a flag field to mark stars used in
        PSF measurement, but some PSF determiners ignore this argument.
    """
 
    usesMatches = False  # Does the PSF determiner use the "matches" argument in the "run method? Few do.
    ConfigClass = BasePsfDeterminerConfig
    _DefaultName = "psfDeterminer"
 
    def __init__(self, config, schema=None, **kwds):
        pipeBase.Task.__init__(self, config=config, **kwds)
 
    def downsampleCandidates(self, inputCandidateList):
        """Down-sample candidates from the input candidate list.
 
        Parameters
        ----------
        inputCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
            Input candidate list.
 
        Returns
        -------
        outputCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
            Down-selected candidate list.
        """
        if len(inputCandidateList) <= self.config.maxCandidates:
            return inputCandidateList
 
        rng = np.random.RandomState(seed=self.config.downsampleRandomSeed)
 
        self.log.info(
            "Down-sampling from %d to %d psf candidates.",
            len(inputCandidateList),
            self.config.maxCandidates,
        )
 
        selection = rng.choice(len(inputCandidateList), size=self.config.maxCandidates, replace=False)
        selection = np.sort(selection)
 
        outputCandidateList = [inputCandidateList[index] for index in selection]
 
        return outputCandidateList
 
    @abc.abstractmethod
    def determinePsf(self, exposure, psfCandidateList, metadata=None, flagKey=None):
        """Determine a PSF model.
 
        Parameters
        ----------
        exposure : `lsst.afw.Exposure`
            Exposure containing the psf candidates.
        psdCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
            A sequence of PSF candidates; typically obtained by
            detecting sources and then running them through a star
            selector.
        metadata : `str`, optional
            A place to save interesting items.
        flagKey: `lsst.afw.table.Key`, optional
            Schema key used to mark sources actually used in PSF determination.
 
        Returns
        -------
        psf : `lsst.afw.detection.Psf`
            The fit PSF.
        cellSet : `lsst.afw.math.SpatialCellSet`
            The spatial cell set used to determine the PSF
        """
        raise NotImplementedError("BasePsfDeterminerTask is abstract, subclasses must override this method")
 
 
psfDeterminerRegistry = pexConfig.makeRegistry(
    doc="A registry of PSF determiners (subclasses of BasePsfDeterminerTask)",
)