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LSST Data Management Base Package
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reserveIsolatedStars.py
Go to the documentation of this file.
1# This file is part of pipe_tasks.
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"""Task to make a flexible and repeatable selection of reserve stars.
23"""
24
25__all__ = ['ReserveIsolatedStarsConfig',
26 'ReserveIsolatedStarsTask']
27
28import numpy as np
29import hashlib
30
31import lsst.pex.config as pexConfig
32import lsst.pipe.base as pipeBase
33
34
35class ReserveIsolatedStarsConfig(pexConfig.Config):
36 """Configuration for ReserveIsolatedStarsTask."""
37 reserve_name = pexConfig.Field(
38 doc='Name to use for random seed selection hash.',
39 dtype=str,
40 default='reserved',
41 )
42 reserve_fraction = pexConfig.RangeField(
43 doc='Fraction of stars to reserve. None if == 0.',
44 dtype=float,
45 default=0.1,
46 min=0.0,
47 max=1.0,
48 inclusiveMin=True,
49 inclusiveMax=True,
50 )
51
52
53class ReserveIsolatedStarsTask(pipeBase.Task):
54 """Reserve isolated stars with repeatable hash."""
55 ConfigClass = ReserveIsolatedStarsConfig
56 _DefaultName = 'reserve_isolated_stars'
57
58 def run(self, nstar, extra=''):
59 """Retrieve a selection of reserved stars.
60
61 Parameters
62 ----------
63 nstar : `int`
64 Number of stars to select from.
65 extra : `str`, optional
66 Extra name to appended to reserve_name, often tract or pixel,
67 and may be combined with band name.
68
69 Returns
70 -------
71 selection : `np.ndarray` (N,)
72 Boolean index array, with ``True`` for reserved stars.
73 """
74 selection = np.zeros(nstar, dtype=bool)
75
76 if self.config.reserve_fraction == 0.0:
77 return selection
78
79 # Full name combines the configured reserve name and the tract.
80 name = self.config.reserve_name + '_' + extra
81 # Random seed is the lower 32 bits of the hashed name.
82 # We use hashlib.sha256 for guaranteed repeatability.
83 hex_hash = hashlib.sha256(name.encode('UTF-8')).hexdigest()
84 seed = int('0x' + hex_hash, 0) & 0xFFFFFFFF
85
86 rng = np.random.default_rng(seed)
87
88 selection[:int(nstar*self.config.reserve_fraction)] = True
89 rng.shuffle(selection)
90
91 return selection