BaseSkyMap

class lsst.skymap.BaseSkyMap(config=None)

Bases: object

A collection of overlapping Tracts that map part or all of the sky.

See TractInfo for more information.

Parameters:
config : BaseSkyMapConfig or None (optional)

The configuration for this SkyMap; if None use the default config.

Notes

BaseSkyMap is an abstract base class. Subclasses must do the following: define __init__ and have it construct the TractInfo objects and put them in __tractInfoList__ define __getstate__ and __setstate__ to allow pickling (the butler saves sky maps using pickle); see DodecaSkyMap for an example of how to do this. (Most of that code could be moved into this base class, but that would make it harder to handle older versions of pickle data.) define updateSha1 to add any subclass-specific state to the hash.

All SkyMap subclasses must be conceptually immutable; they must always refer to the same set of mathematical tracts and patches even if the in- memory representation of those objects changes.

Methods Summary

findClosestTractPatchList(coordList) Find closest tract and patches that overlap coordinates.
findTract(coord) Find the tract whose center is nearest the specified coord.
findTractPatchList(coordList) Find tracts and patches that overlap a region.
getSha1() Return a SHA1 hash that uniquely identifies this SkyMap instance.
register(name, registry) Add SkyMap, Tract, and Patch Dimension entries to the given Gen3 Butler Registry.
updateSha1(sha1) Add subclass-specific state or configuration options to the SHA1.

Methods Documentation

findClosestTractPatchList(coordList)

Find closest tract and patches that overlap coordinates.

Parameters:
coordList : lsst.geom.SpherePoint

List of ICRS sky coordinates to search for.
Returns:
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.
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.

findTractPatchList(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).
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.

register(name, registry)

Add SkyMap, Tract, and Patch Dimension entries to the given Gen3 Butler Registry.

Parameters:
name : str

The name of the skymap.

registry : lsst.daf.butler.Registry

The registry to add to.
updateSha1(sha1)

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

Parameters:
sha1 : hashlib.sha1

A hashlib object on which update can be called to add additional state to the hash.

Notes

This method is conceptually “protected” : it should be reimplemented by all subclasses, but called only by the base class implementation of getSha1 .