Source code for lsst.obs.base.exposureIdInfo

#
# LSST Data Management System
# Copyright 2016 LSST Corporation.
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# LSST Project (http://www.lsst.org/).
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from past.builtins import long

__all__ = ["ExposureIdInfo"]


[docs]class ExposureIdInfo(object): """Exposure ID and number of bits used. Attributes include: expId exposure ID as a long 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). """ def __init__(self, expId=0, expBits=1, maxBits=64): """Construct an ExposureIdInfo See the class doc string for an explanation of the arguments. """ expId = long(expId) expBits = int(expBits) maxBits = int(maxBits) if expId.bit_length() > expBits: raise RuntimeError("expId=%s uses %s bits > expBits=%s" % (expId, expId.bit_length(), expBits)) if maxBits < expBits: raise RuntimeError("expBits=%s > maxBits=%s" % (expBits, maxBits)) self.expId = expId self.expBits = expBits self.maxBits = maxBits @property def unusedBits(self): return self.maxBits - self.expBits