lsst.skymap gd8df4e7cf5+7c00d642d4
healpixSkyMap.py
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2# LSST Data Management System
3# Copyright 2008, 2009, 2010, 2012 LSST Corporation.
4#
5# This product includes software developed by the
6# LSST Project (http://www.lsst.org/).
7#
8# This program is free software: you can redistribute it and/or modify
9# it under the terms of the GNU General Public License as published by
10# the Free Software Foundation, either version 3 of the License, or
11# (at your option) any later version.
12#
13# This program is distributed in the hope that it will be useful,
14# but WITHOUT ANY WARRANTY; without even the implied warranty of
15# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16# GNU General Public License for more details.
17#
18# You should have received a copy of the LSST License Statement and
19# the GNU General Public License along with this program. If not,
20# see <http://www.lsstcorp.org/LegalNotices/>.
21#
22
23__all__ = ['HealpixSkyMapConfig', 'HealpixSkyMap']
24
25import struct
26import numpy
27
28# We want to register the HealpixSkyMap, but want "healpy" to be an
29# optional dependency. However, the HealpixSkyMap requires the use
30# of healpy. Therefore, we'll only raise an exception on the healpy
31# import when it comes time to using it.
32try:
33 import healpy
34except Exception as e:
36 """An object which blows up when we try to read it"""
37
38 def __getattr__(self, name, e=e):
39 raise RuntimeError("Was unable to import healpy: %s" % e)
40 healpy = DummyHealpy()
41
42from lsst.pex.config import Field
43import lsst.geom as geom
44from .cachingSkyMap import CachingSkyMap
45from .tractInfo import TractInfo
46
47
48def angToCoord(thetaphi):
49 """Convert healpy's ang to an lsst.geom.SpherePoint
50
51 The ang is provided as a single object, thetaphi, so the output
52 of healpy functions can be directed to this function without
53 additional translation.
54 """
55 return geom.SpherePoint(float(thetaphi[1]), float(thetaphi[0] - 0.5*numpy.pi), geom.radians)
56
57
58def coordToAng(coord):
59 """Convert an lsst.geom.SpherePoint to a healpy ang (theta, phi)
60
61 The Healpix convention is that 0 <= theta <= pi, 0 <= phi < 2pi.
62 """
63 return (coord.getLatitude().asRadians() + 0.5*numpy.pi, coord.getLongitude().asRadians())
64
65
67 """Tract for the HealpixSkyMap"""
68
69 def __init__(self, nSide, ident, nest, tractBuilder, ctrCoord, tractOverlap, wcs):
70 """Set vertices from nside, ident, nest"""
71 theta, phi = healpy.vec2ang(numpy.transpose(healpy.boundaries(nSide, ident, nest=nest)))
72 vertexList = [angToCoord(thetaphi) for thetaphi in zip(theta, phi)]
73 super(HealpixTractInfo, self).__init__(ident, tractBuilder, ctrCoord,
74 vertexList, tractOverlap, wcs)
75
76
77class HealpixSkyMapConfig(CachingSkyMap.ConfigClass):
78 """Configuration for the HealpixSkyMap"""
79 log2NSide = Field(dtype=int, default=0, doc="Number of sides, expressed in powers of 2")
80 nest = Field(dtype=bool, default=False, doc="Use NEST ordering instead of RING?")
81
82 def setDefaults(self):
83 self.rotationrotation = 45 # HEALPixels are oriented at 45 degrees
84
85
87 """HEALPix-based sky map pixelization.
88
89 We put a Tract at the position of each HEALPixel.
90
91
92 Parameters
93 ----------
95 The configuration for this SkyMap.
96 version : `int` or `tuple` of `int` (optional)
97 Software version of this class, to retain compatibility with old
98 instances.
99 """
100 ConfigClass = HealpixSkyMapConfig
101 _version = (1, 0) # for pickle
102 numAngles = 4 # Number of angles for vertices
103
104 def __init__(self, config, version=0):
105 self._nside_nside = 1 << config.log2NSide
106 numTracts = healpy.nside2npix(self._nside_nside)
107 super(HealpixSkyMap, self).__init__(numTracts, config, version)
108
109 def findTract(self, coord):
110 """Find the tract whose inner region includes the coord.
111
112 Parameters
113 ----------
114 coord : `lsst.geom.SpherePoint`
115 ICRS sky coordinate to search for.
116
117 Returns
118 -------
119 tractInfo : `TractInfo`
120 Info for tract whose inner region includes the coord.
121 """
122 theta, phi = coordToAng(coord)
123 index = healpy.ang2pix(self._nside_nside, theta, phi, nest=self.configconfig.nest)
124 return self[index]
125
126 def generateTract(self, index):
127 """Generate TractInfo for the specified tract index."""
128 center = angToCoord(healpy.pix2ang(self._nside_nside, index, nest=self.configconfig.nest))
129 wcs = self._wcsFactory_wcsFactory.makeWcs(crPixPos=geom.Point2D(0, 0), crValCoord=center)
130 return HealpixTractInfo(self._nside_nside, index, self.configconfig.nest, self._tractBuilder_tractBuilder,
131 center, self.configconfig.tractOverlap*geom.degrees,
132 wcs)
133
134 def updateSha1(self, sha1):
135 """Add subclass-specific state or configuration options to the SHA1."""
136 sha1.update(struct.pack("<i?", self.configconfig.log2NSide, self.configconfig.nest))
def __init__(self, config, version=0)
def __init__(self, nSide, ident, nest, tractBuilder, ctrCoord, tractOverlap, wcs)