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LSST Data Management Base Package
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psfDeterminer.py
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1# This file is part of meas_algorithms.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (https://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <https://www.gnu.org/licenses/>.
21
22__all__ = ["BasePsfDeterminerConfig", "BasePsfDeterminerTask", "psfDeterminerRegistry"]
23
24import abc
25import numpy as np
26
27import lsst.pipe.base as pipeBase
28import lsst.pex.config as pexConfig
29
30
31class BasePsfDeterminerConfig(pexConfig.Config):
32 """Configuration that is likely to be shared by all PSF determiners
33
34 This is fairly sparse; more fields can be moved here once it is clear they are universal.
35 """
36 stampSize = pexConfig.Field[int](
37 doc="Size of the postage stamp (in native pixels) to render the PSF model. Should be odd.",
38 default=None,
39 optional=True,
40 check=lambda x: (x > 0) & (x % 2 == 1),
41 )
42 maxCandidates = pexConfig.Field[int](
43 doc="Maximum number of candidates to consider. Will down-sample if given more.",
44 default=300,
45 )
46 downsampleRandomSeed = pexConfig.Field[int](
47 doc="Random seed to use to downsample candidates.",
48 default=98765,
49 )
50
51
52class BasePsfDeterminerTask(pipeBase.Task, metaclass=abc.ABCMeta):
53 """Base class for PSF determiners
54
55 Register all PSF determiners with the psfDeterminerRegistry using:
56 psfDeterminerRegistry.register(name, class)
57
58 Parameters
59 ----------
60 config : `lsst.pexConfig.Config`
61 Input for configuring the algorithm
62 schema : `lsst.afw.table.Schema`
63 Schema used for sources; passing a schema allows the
64 determiner to reserve a flag field to mark stars used in
65 PSF measurement, but some PSF determiners ignore this argument.
66 """
67
68 usesMatches = False # Does the PSF determiner use the "matches" argument in the "run method? Few do.
69 ConfigClass = BasePsfDeterminerConfig
70 _DefaultName = "psfDeterminer"
71
72 def __init__(self, config, schema=None, **kwds):
73 pipeBase.Task.__init__(self, config=config, **kwds)
74
75 def downsampleCandidates(self, inputCandidateList):
76 """Down-sample candidates from the input candidate list.
77
78 Parameters
79 ----------
80 inputCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
81 Input candidate list.
82
83 Returns
84 -------
85 outputCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
86 Down-selected candidate list.
87 """
88 if len(inputCandidateList) <= self.config.maxCandidates:
89 return inputCandidateList
90
91 rng = np.random.RandomState(seed=self.config.downsampleRandomSeed)
92
93 self.log.info(
94 "Down-sampling from %d to %d psf candidates.",
95 len(inputCandidateList),
96 self.config.maxCandidates,
97 )
98
99 selection = rng.choice(len(inputCandidateList), size=self.config.maxCandidates, replace=False)
100 selection = np.sort(selection)
101
102 outputCandidateList = [inputCandidateList[index] for index in selection]
103
104 return outputCandidateList
105
106 @abc.abstractmethod
107 def determinePsf(self, exposure, psfCandidateList, metadata=None, flagKey=None):
108 """Determine a PSF model.
109
110 Parameters
111 ----------
112 exposure : `lsst.afw.Exposure`
113 Exposure containing the psf candidates.
114 psdCandidateList : `list` [`lsst.meas.algorithms.PsfCandidate`]
115 A sequence of PSF candidates; typically obtained by
116 detecting sources and then running them through a star
117 selector.
118 metadata : `str`, optional
119 A place to save interesting items.
120 flagKey: `lsst.afw.table.Key`, optional
121 Schema key used to mark sources actually used in PSF determination.
122
123 Returns
124 -------
125 psf : `lsst.afw.detection.Psf`
126 The fit PSF.
127 cellSet : `lsst.afw.math.SpatialCellSet`
128 The spatial cell set used to determine the PSF
129 """
130 raise NotImplementedError("BasePsfDeterminerTask is abstract, subclasses must override this method")
131
132
133psfDeterminerRegistry = pexConfig.makeRegistry(
134 doc="A registry of PSF determiners (subclasses of BasePsfDeterminerTask)",
135)
determinePsf(self, exposure, psfCandidateList, metadata=None, flagKey=None)