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LSST Data Management Base Package
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gaussianPsfFactory.py
Go to the documentation of this file.
2# LSST Data Management System
3#
4# Copyright 2008-2017 AURA/LSST.
5#
6# This product includes software developed by the
7# LSST Project (http://www.lsst.org/).
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 LSST License Statement and
20# the GNU General Public License along with this program. If not,
21# see <https://www.lsstcorp.org/LegalNotices/>.
22#
23
24__all__ = ["GaussianPsfFactory", "SigmaPerFwhm"]
25
26import math
27
28from lsst.pex.config import Config, Field, ConfigurableField
29from ._algorithmsLib import DoubleGaussianPsf, SingleGaussianPsf
30
31SigmaPerFwhm = 1.0 / (2.0 * math.sqrt(2.0 * math.log(2.0)))
32
33
35 return x > 0
36
37
39 """Factory for simple Gaussian PSF models
40
41 Provides a high-level interface to DoubleGaussianPsf and SingleGaussianPsf
42 by specifying Gaussian PSF model width in FWHM instead of sigma,
43 and supporting computing kernel size as a multiple of PSF width.
44 This makes it suitable for tasks where PSF width is not known in advance.
45 """
46 size = Field(
47 doc="Kernel size (width and height) (pixels); if None then sizeFactor is used",
48 dtype=int,
49 optional=True,
50 default=None,
51 check=isPositive,
52 )
53 sizeFactor = Field(
54 doc="Kernel size as a factor of fwhm (dimensionless); "
55 "size = sizeFactor * fwhm; ignored if size is not None",
56 dtype=float,
57 optional=False,
58 default=3.0,
59 check=isPositive,
60 )
61 minSize = Field(
62 doc="Minimum kernel size if using sizeFactor (pixels); ignored if size is not None",
63 dtype=int,
64 optional=True,
65 default=5,
66 check=isPositive,
67 )
68 maxSize = Field(
69 doc="Maximum kernel size if using sizeFactor (pixels); ignored if size is not None",
70 dtype=int,
71 optional=True,
72 default=None,
73 check=isPositive,
74 )
75 defaultFwhm = Field(
76 doc="Default FWHM of Gaussian model of core of star (pixels)",
77 dtype=float,
78 default=3.0,
79 check=isPositive,
80 )
81 addWing = Field(
82 doc="Add a Gaussian to represent wings?",
83 dtype=bool,
84 optional=False,
85 default=True,
86 )
87 wingFwhmFactor = Field(
88 doc="wing width, as a multiple of core width (dimensionless); ignored if addWing false",
89 dtype=float,
90 optional=False,
91 default=2.5,
92 check=isPositive,
93 )
94 wingAmplitude = Field(
95 doc="wing amplitude, as a multiple of core amplitude (dimensionless); ignored if addWing false",
96 dtype=float,
97 optional=False,
98 default=0.1,
99 check=isPositive,
100 )
101
102 def computeSizeAndSigma(self, fwhm=None):
103 """Compute kernel size and star width as sigma. The kernel size will be
104 odd unless minSize or maxSize is used and that value is even. Assumes
105 a valid config.
106
107 Parameters
108 ----------
109 fwhm : `float`
110 FWHM of core star (pixels); if None then defaultFwhm is used
111
112 Returns
113 -------
114 size : `int`
115 Kernel size (width == height) in pixels
116 sigma : `float`
117 Sigma equivalent to supplied FWHM, assuming a Gaussian (pixels)
118 """
119 if fwhm is None:
120 fwhm = self.defaultFwhm
121
122 if self.size is not None:
123 size = self.size
124 else:
125 desSize = (int(self.sizeFactor * fwhm) // 2) * 2 + 1 # make result odd
126 if self.minSize and self.minSize > desSize:
127 size = self.minSize
128 elif self.maxSize and self.maxSize < desSize:
129 size = self.maxSize
130 else:
131 size = desSize
132
133 return size, fwhm * SigmaPerFwhm
134
135 def validate(self):
136 Config.validate(self)
137 if self.minSize and self.maxSize and self.minSize > self.maxSize:
138 raise RuntimeError("minSize=%s > maxSize=%s" % (self.minSize, self.maxSize))
139
140 def apply(self, fwhm=None):
141 """Construct a GaussianPsf
142
143 Parameters
144 ----------
145 fwhm : `float`
146 FWHM of core of star (pixels); if None then self.defaultFwhm is used
147
148 Returns
149 -------
150 DoubleGaussianPsf : ``lsst.meas.algorithms.DoubleGaussianPsf``
151 Returns if self.addWing is True
152 SingleGaussianPsf : ``lsst.meas.algorithms.SingleGaussianPsf``
153 Returns if self.addWing is False
154 """
155 kernelSize, sigma = self.computeSizeAndSigma(fwhm)
156 if self.addWing:
157 wingsSigma = sigma * self.wingFwhmFactor
158 return DoubleGaussianPsf(kernelSize, kernelSize, sigma, wingsSigma, self.wingAmplitude)
159 else:
160 return SingleGaussianPsf(kernelSize, kernelSize, sigma)
161
162 @classmethod
163 def makeField(cls, doc):
164 """Make an lsst.pex.config.ConfigurableField
165 """
166 def applyWrapper(config, **kwargs):
167 """Construct a Gaussian PSF
168
169 Parameters
170 ----------
171 config : instance of ``GaussianPsfFactory``
172 """
173 return config.apply(**kwargs)
174 return ConfigurableField(
175 doc=doc,
176 target=applyWrapper,
177 ConfigClass=cls
178 )