RingsSkyMap

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

Bases: CachingSkyMap

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

configlsst.skymap.RingsSkyMapConfig

The configuration for this SkyMap.

versionint, 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.

Methods Summary

findAllTracts(coord)	Find all tracts which include the specified coord.
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.
getRaDecRange(index)	Get the ra and dec ranges for the inner region of a specified tract index.
getRingIndices(index)	Calculate ring indices given a numerical index of a tract.
updateSha1(sha1)	Add subclass-specific state or configuration options to the SHA1.

Methods Documentation

findAllTracts(coord)

Find all tracts which include the specified coord.

Parameters

coordlsst.geom.SpherePoint

ICRS sky coordinate to search for.

Returns

tractListlist of TractInfo

The tracts which include the specified coord.

findTract(coord)

Find the tract whose center is nearest the specified coord.

Parameters

coordlsst.geom.SpherePoint

ICRS sky coordinate to search for.

Returns

resultTractInfo

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

ranumpy.ndarray

Array of Right Ascension. Units are radians unless degrees=True.

decnumpy.ndarray

Array of Declination. Units are radians unless degrees=True.

degreesbool, optional

Input ra, dec arrays are degrees if True.

Returns

tractIdnumpy.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

coordListlist of lsst.geom.SpherePoint

List of ICRS sky coordinates to search for.

Returns

reListlist 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.

getRaDecRange(index)

Get the ra and dec ranges for the inner region of a specified tract index.

Parameters

indexint

Tract index number.

Returns

raMin, raMax, decMin, decMaxlsst.geom.Angle

RA/Dec boundaries of the inner region.

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.

updateSha1(sha1)

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