Exposure ID and number of bits used.
Attributes include:
expId
exposure ID as an int
expBits
maximum number of bits allowed for exposure IDs
maxBits
maximum number of bits available for values that combine exposure ID
with other information, such as source ID
unusedBits
maximum number of bits available for non-exposure info (maxBits - expBits)
One common use is creating an ID factory for making a source table.
For example, given a data butler `butler` and a data ID `dataId`::
from lsst.afw.table import IdFactory, SourceTable
exposureIdInfo = butler.get("expIdInfo", dataId)
sourceIdFactory = IdFactory.makeSource(exposureIdInfo.expId, exposureIdInfo.unusedBits)
schema = SourceTable.makeMinimalSchema()
#...add fields to schema as desired, then...
sourceTable = SourceTable.make(self.schema, sourceIdFactory)
At least one bit must be reserved, even if there is no exposure ID, for reasons
that are not entirely clear (this is DM-6664).
Definition at line 25 of file exposureIdInfo.py.