# RingsSkyMap¶

class lsst.skymap.ringsSkyMap.RingsSkyMap(config, version=1)

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.

Attributes Summary

Methods Summary

 findAllTracts(coord) Find all tracts which include the specified coord. findClosestTractPatchList(coordList) Find closest tract and patches that overlap coordinates. findTract(coord) Find the tract whose center is nearest the specified coord. findTractIdArray(ra, dec[, degrees]) Find array of tract IDs with vectorized operations (where supported). findTractPatchList(coordList) Find tracts and patches that overlap a region. generateTract(index) Generate TractInfo for the specified tract index. getRingIndices(index) Calculate ring indices given a numerical index of a tract. getSha1() Return a SHA1 hash that uniquely identifies this SkyMap instance. logSkyMapInfo(log) Write information about a sky map to supplied log register(name, butler) Add skymap, tract, and patch Dimension entries to the given Gen3 Butler. updateSha1(sha1) Add subclass-specific state or configuration options to the SHA1.

Attributes Documentation

SKYMAP_DATASET_TYPE_NAME = 'skyMap'
SKYMAP_RUN_COLLECTION_NAME = 'skymaps'

Methods Documentation

findAllTracts(coord)

Find all tracts which include the specified coord.

Parameters: coord : lsst.geom.SpherePoint ICRS sky coordinate to search for. tractList : list of TractInfo The tracts which include the specified coord.
findClosestTractPatchList(coordList)

Find closest tract and patches that overlap coordinates.

Parameters: coordList : lsst.geom.SpherePoint List of ICRS sky coordinates to search for. retList : list 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.
findTract(coord)

Find the tract whose center is nearest the specified coord.

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

findTractIdArray(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. 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.

findTractPatchList(coordList)

Find tracts and patches that overlap a region.

Parameters: coordList : List of ICRS sky coordinates to search for. 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).
generateTract(index)

Generate TractInfo for the specified tract index.

getRingIndices(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.

getSha1()

Return a SHA1 hash that uniquely identifies this SkyMap instance.

Returns: sha1 : bytes A 20-byte hash that uniquely identifies this SkyMap instance.

Notes

Subclasses should almost always override updateSha1 instead of this function to add subclass-specific state to the hash.

logSkyMapInfo(log)

Write information about a sky map to supplied log

Parameters: log : lsst.log.Log Log object that information about skymap will be written
register(name, butler)

Add skymap, tract, and patch Dimension entries to the given Gen3 Butler.

Parameters: name : str The name of the skymap. butler : lsst.daf.butler.Butler The butler to add to. lsst.daf.butler.registry.ConflictingDefinitionError Raised if a different skymap exists with the same name.

Notes

Registering the same skymap multiple times (with the exact same definition) is safe, but inefficient; most of the work of computing the rows to be inserted must be done first in order to check for consistency between the new skymap and any existing one.

Re-registering a skymap with different tract and/or patch definitions but the same summary information may not be detected as a conflict but will never result in updating the skymap; there is intentionally no way to modify a registered skymap (aside from manual administrative operations on the database), as it is hard to guarantee that this can be done without affecting reproducibility.

updateSha1(sha1)

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