lsst.skymap.ringsSkyMap.RingsSkyMap Class Reference

Inheritance diagram for lsst.skymap.ringsSkyMap.RingsSkyMap:

Public Member Functions
def	__init__ (self, config, version=1)
def	getRingIndices (self, index)
def	generateTract (self, index)
def	findTract (self, coord)
def	findTractIdArray (self, ra, dec, degrees=False)
def	findAllTracts (self, coord)
def	findTractPatchList (self, coordList)
def	updateSha1 (self, sha1)

Static Public Attributes
	ConfigClass = RingsSkyMapConfig

Detailed Description

Rings sky map pixelization.

We divide the sphere into N rings of Declination, plus the two polar
caps, which sets the size of the individual tracts.  The rings are
divided in RA into an integral number of tracts of this size; this
division is made at the Declination closest to zero so as to ensure
full overlap.

Rings are numbered in the rings from south to north. The south pole cap is
``tract=0``, then the tract at ``raStart`` in the southernmost ring is
``tract=1``. Numbering continues (in the positive RA direction) around that
ring and then continues in the same fashion with the next ring north, and
so on until all reaching the north pole cap, which is
``tract=len(skymap) - 1``.

However, ``version=0`` had a bug in the numbering of the tracts: the first
and last tracts in the first (southernmost) ring were identical, and the
first tract in the last (northernmost) ring was missing. When using
``version=0``, these tracts remain missing in order to preserve the
numbering scheme.

Parameters
----------
config : `lsst.skymap.RingsSkyMapConfig`
    The configuration for this SkyMap.
version : `int`, optional
    Software version of this class, to retain compatibility with old
    verisons. ``version=0`` covers the period from first implementation
    until DM-14809, at which point bugs were identified in the numbering
    of tracts (affecting only tracts at RA=0). ``version=1`` uses the
    post-DM-14809 tract numbering.

Definition at line 42 of file ringsSkyMap.py.

Constructor & Destructor Documentation

__init__()

def lsst.skymap.ringsSkyMap.RingsSkyMap.__init__	(		self,
			config,
			version = 1
	)

Reimplemented from lsst.skymap.cachingSkyMap.CachingSkyMap.

Definition at line 78 of file ringsSkyMap.py.

    def __init__(self, config, version=1):
        assert version in (0, 1), "Unrecognised version: %s" % (version,)
        # We count rings from south to north
        # Note: pole caps together count for one additional ring when calculating the ring size
        self._ringSize = math.pi / (config.numRings + 1)  # Size of a ring in Declination (radians)
        self._ringNums = []  # Number of tracts for each ring
        for i in range(config.numRings):
            startDec = self._ringSize*(i + 0.5) - 0.5*math.pi
            stopDec = startDec + self._ringSize
            dec = min(math.fabs(startDec), math.fabs(stopDec))  # Declination for determining division in RA
            self._ringNums.append(int(2*math.pi*math.cos(dec)/self._ringSize) + 1)
        numTracts = sum(self._ringNums) + 2
        super(RingsSkyMap, self).__init__(numTracts, config, version)
        self._raStart = self.config.raStart*geom.degrees
 

Member Function Documentation

findAllTracts()

def lsst.skymap.ringsSkyMap.RingsSkyMap.findAllTracts	(		self,
			coord
	)

Find all tracts which include the specified coord.

Parameters
----------
coord : `lsst.geom.SpherePoint`
    ICRS sky coordinate to search for.

Returns
-------
tractList : `list` of `TractInfo`
    The tracts which include the specified coord.

Definition at line 252 of file ringsSkyMap.py.

    def findAllTracts(self, coord):
        """Find all tracts which include the specified coord.
 
        Parameters
        ----------
        coord : `lsst.geom.SpherePoint`
            ICRS sky coordinate to search for.
 
        Returns
        -------
        tractList : `list` of `TractInfo`
            The tracts which include the specified coord.
        """
        ringNum = self._decToRingNum(coord.getLatitude())
 
        tractList = list()
        # ringNum denotes the closest ring to the specified coord
        # I will check adjacent rings which may include the specified coord
        for r in [ringNum - 1, ringNum, ringNum + 1]:
            if r < 0 or r >= self.config.numRings:
                # Poles will be checked explicitly outside this loop
                continue
            tractNum = self._raToTractNum(coord.getLongitude(), r)
            # Adjacent tracts will also be checked.
            for t in [tractNum - 1, tractNum, tractNum + 1]:
                # Wrap over raStart
                if t < 0:
                    t = t + self._ringNums[r]
                elif t > self._ringNums[r] - 1:
                    t = t - self._ringNums[r]
 
                extra = 0
                if self._version == 0 and t == 0 and r != 0:
                    # Account for off-by-one error in getRingIndices
                    # Note that this means that tract 1 gets duplicated.
                    extra = 1
 
                index = sum(self._ringNums[:r + extra], t + 1)  # Allow 1 for south pole
                tract = self[index]
                if tract.contains(coord):
                    tractList.append(tract)
 
        # Always check tracts at poles
        # Southern cap is 0, Northern cap is the last entry in self
        for entry in [0, len(self)-1]:
            tract = self[entry]
            if tract.contains(coord):
                tractList.append(tract)
 
        return tractList
 

findTract()

def lsst.skymap.ringsSkyMap.RingsSkyMap.findTract	(		self,
			coord
	)

Find the tract whose center is nearest the specified coord.

Parameters
----------
coord : `lsst.geom.SpherePoint`
    ICRS sky coordinate to search for.

Returns
-------
result : `TractInfo`
    TractInfo of tract whose center is nearest the specified coord.

Notes
-----
- If coord is equidistant between multiple sky tract centers then one
  is arbitrarily chosen.

- The default implementation is not very efficient; subclasses may wish
  to override.

**Warning:**
If tracts do not cover the whole sky then the returned tract may not
include the coord.

Reimplemented from lsst.skymap.baseSkyMap.BaseSkyMap.

Definition at line 187 of file ringsSkyMap.py.

    def findTract(self, coord):
        ringNum = self._decToRingNum(coord.getLatitude())
        if ringNum == -1:
            # Southern cap
            return self[0]
        if ringNum == self.config.numRings:
            # Northern cap
            return self[self._numTracts - 1]
        tractNum = self._raToTractNum(coord.getLongitude(), ringNum)
 
        if self._version == 0 and tractNum == 0 and ringNum != 0:
            # Account for off-by-one error in getRingIndices
            # Note that this means that tract 1 gets duplicated.
            ringNum += 1
 
        index = sum(self._ringNums[:ringNum], tractNum + 1)  # Allow 1 for south pole
        return self[index]
 

findTractIdArray()

def lsst.skymap.ringsSkyMap.RingsSkyMap.findTractIdArray	(		self,
			ra,
			dec,
			degrees = False
	)

Find array of tract IDs with vectorized operations (where supported).

If a given sky map does not support vectorized operations, then a loop
over findTract will be called.

Parameters
----------
ra : `np.ndarray`
    Array of Right Ascension.  Units are radians unless
    degrees=True.
dec : `np.ndarray`
    Array of Declination.  Units are radians unless
    degrees=True.
degrees : `bool`, optional
    Input ra, dec arrays are degrees if True.

Returns
-------
tractId : `np.ndarray`
    Array of tract IDs

Notes
-----
- If coord is equidistant between multiple sky tract centers then one
  is arbitrarily chosen.

**Warning:**
If tracts do not cover the whole sky then the returned tract may not
include the given ra/dec.

Reimplemented from lsst.skymap.baseSkyMap.BaseSkyMap.

Definition at line 205 of file ringsSkyMap.py.

    def findTractIdArray(self, ra, dec, degrees=False):
        if degrees:
            _ra = np.deg2rad(ra)
            _dec = np.deg2rad(dec)
        else:
            _ra = np.atleast_1d(ra)
            _dec = np.atleast_1d(dec)
 
        # Set default to -1 to distinguish from polar tracts
        indexes = np.full(_ra.size, -1, dtype=np.int32)
 
        # Do the dec search
        firstRingStart = self._ringSize*0.5 - 0.5*np.pi
        ringNums = np.zeros(len(_dec), dtype=np.int32)
 
        ringNums[_dec < firstRingStart] = -1
        ringNums[_dec > -1*firstRingStart] = self.config.numRings
 
        mid = (_dec >= firstRingStart) & (_dec <= -1*firstRingStart)
        ringNums[mid] = ((_dec[mid] - firstRingStart)/self._ringSize).astype(np.int32)
 
        indexes[ringNums == -1] = 0
        indexes[ringNums == self.config.numRings] = self._numTracts - 1
 
        # We now do the full lookup for all non-polar tracts that have not been set.
        inRange, = np.where(indexes < 0)
 
        # Do the ra search
        _ringNumArray = np.array(self._ringNums)
        _ringCumulative = np.cumsum(np.insert(_ringNumArray, 0, 0))
 
        deltaWrap = (_ra[inRange] - self._raStart.asRadians()) % (2.*np.pi)
        tractNum = (deltaWrap/(2.*np.pi/_ringNumArray[ringNums[inRange]]) + 0.5).astype(np.int32)
        # Allow wraparound
        tractNum[tractNum == _ringNumArray[ringNums[inRange]]] = 0
 
        if self._version == 0:
            # Account for off-by-one error in getRingIndices
            # Note that this means tract 1 gets duplicated
            offByOne, = np.where((tractNum == 0)
                                 & (ringNums[inRange] != 0))
            ringNums[inRange[offByOne]] += 1
 
        indexes[inRange] = _ringCumulative[ringNums[inRange]] + tractNum + 1
 
        return indexes
 

findTractPatchList()

def lsst.skymap.ringsSkyMap.RingsSkyMap.findTractPatchList	(		self,
			coordList
	)

Find tracts and patches that overlap a region.

Parameters
----------
coordList : `list` of `lsst.geom.SpherePoint`
    List of ICRS sky coordinates to search for.

Returns
-------
reList : `list` of (`TractInfo`, `list` of `PatchInfo`)
    For tracts and patches that contain, or may contain, the specified
    region. The list will be empty if there is no overlap.

Notes
-----
**warning:**
    This uses a naive algorithm that may find some tracts and patches
    that do not overlap the region (especially if the region is not a
    rectangle aligned along patch x, y).

Reimplemented from lsst.skymap.baseSkyMap.BaseSkyMap.

Definition at line 303 of file ringsSkyMap.py.

    def findTractPatchList(self, coordList):
        retList = []
        for coord in coordList:
            for tractInfo in self.findAllTracts(coord):
                patchList = tractInfo.findPatchList(coordList)
                if patchList and not (tractInfo, patchList) in retList:
                    retList.append((tractInfo, patchList))
        return retList
 

generateTract()

def lsst.skymap.ringsSkyMap.RingsSkyMap.generateTract	(		self,
			index
	)

Generate TractInfo for the specified tract index.

Reimplemented from lsst.skymap.cachingSkyMap.CachingSkyMap.

Definition at line 124 of file ringsSkyMap.py.

    def generateTract(self, index):
        """Generate TractInfo for the specified tract index."""
        ringNum, tractNum = self.getRingIndices(index)
        if ringNum == -1:  # South polar cap
            ra, dec = 0, -0.5*math.pi
        elif ringNum == self.config.numRings:  # North polar cap
            ra, dec = 0, 0.5*math.pi
        else:
            dec = self._ringSize*(ringNum + 1) - 0.5*math.pi
            ra = ((2*math.pi*tractNum/self._ringNums[ringNum])*geom.radians
                  + self._raStart).wrap().asRadians()
 
        center = geom.SpherePoint(ra, dec, geom.radians)
        wcs = self._wcsFactory.makeWcs(crPixPos=geom.Point2D(0, 0), crValCoord=center)
        return ExplicitTractInfo(index, self._tractBuilder, center,
                                 0.5*self._ringSize*geom.radians, self.config.tractOverlap*geom.degrees,
                                 wcs)
 

getRingIndices()

def lsst.skymap.ringsSkyMap.RingsSkyMap.getRingIndices	(		self,
			index
	)

Calculate ring indices given a numerical index of a tract.

The ring indices are the ring number and the tract number within
the ring.

The ring number is -1 for the south polar cap and increases to the
north.  The north polar cap has ring number = numRings.  The tract
number is zero for either of the polar caps.

Definition at line 93 of file ringsSkyMap.py.

    def getRingIndices(self, index):
        """Calculate ring indices given a numerical index of a tract.
 
        The ring indices are the ring number and the tract number within
        the ring.
 
        The ring number is -1 for the south polar cap and increases to the
        north.  The north polar cap has ring number = numRings.  The tract
        number is zero for either of the polar caps.
        """
        if index == 0:  # South polar cap
            return -1, 0
        if index == self._numTracts - 1:  # North polar cap
            return self.config.numRings, 0
        if index < 0 or index >= self._numTracts:
            raise IndexError("Tract index %d is out of range [0, %d]" % (index, len(self) - 1))
        ring = 0  # Ring number
        tractNum = index - 1  # Tract number within ring
        if self._version == 0:
            # Maintain the off-by-one bug in version=0 (DM-14809).
            # This means that the first tract in the first ring is duplicated
            # and the first tract in the last ring is missing.
            while ring < self.config.numRings and tractNum > self._ringNums[ring]:
                tractNum -= self._ringNums[ring]
                ring += 1
        else:
            while ring < self.config.numRings and tractNum >= self._ringNums[ring]:
                tractNum -= self._ringNums[ring]
                ring += 1
        return ring, tractNum
 

updateSha1()

def lsst.skymap.ringsSkyMap.RingsSkyMap.updateSha1	(		self,
			sha1
	)

Add subclass-specific state or configuration options to the SHA1.

Reimplemented from lsst.skymap.baseSkyMap.BaseSkyMap.

Definition at line 312 of file ringsSkyMap.py.

    def updateSha1(self, sha1):
        """Add subclass-specific state or configuration options to the SHA1."""
        sha1.update(struct.pack("<id", self.config.numRings, self.config.raStart))

Member Data Documentation

ConfigClass

lsst.skymap.ringsSkyMap.RingsSkyMap.ConfigClass = RingsSkyMapConfig

static

Definition at line 75 of file ringsSkyMap.py.

---

The documentation for this class was generated from the following file:

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-4.0.1/Linux64/skymap/gdb4cecd868+6f279b5b48/python/lsst/skymap/ringsSkyMap.py