lsst.obs.base  19.0.0-9-ge91d8c4+1
exposureIdInfo.py
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1 #
2 # LSST Data Management System
3 # Copyright 2016 LSST Corporation.
4 #
5 # This product includes software developed by the
6 # LSST Project (http://www.lsst.org/).
7 #
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21 #
22 
23 __all__ = ["ExposureIdInfo"]
24 
25 
26 class ExposureIdInfo(object):
27  """Exposure ID and number of bits used.
28 
29  Attributes include:
30 
31  expId
32  exposure ID as an int
33  expBits
34  maximum number of bits allowed for exposure IDs
35  maxBits
36  maximum number of bits available for values that combine exposure ID
37  with other information, such as source ID
38  unusedBits
39  maximum number of bits available for non-exposure info (maxBits - expBits)
40 
41  One common use is creating an ID factory for making a source table.
42  For example, given a data butler `butler` and a data ID `dataId`::
43 
44  from lsst.afw.table import IdFactory, SourceTable
45  exposureIdInfo = butler.get("expIdInfo", dataId)
46  sourceIdFactory = IdFactory.makeSource(exposureIdInfo.expId, exposureIdInfo.unusedBits)
47  schema = SourceTable.makeMinimalSchema()
48  #...add fields to schema as desired, then...
49  sourceTable = SourceTable.make(self.schema, sourceIdFactory)
50 
51  At least one bit must be reserved, even if there is no exposure ID, for reasons
52  that are not entirely clear (this is DM-6664).
53  """
54 
55  def __init__(self, expId=0, expBits=1, maxBits=64):
56  """Construct an ExposureIdInfo
57 
58  See the class doc string for an explanation of the arguments.
59  """
60  expId = int(expId)
61  expBits = int(expBits)
62  maxBits = int(maxBits)
63 
64  if expId.bit_length() > expBits:
65  raise RuntimeError("expId=%s uses %s bits > expBits=%s" % (expId, expId.bit_length(), expBits))
66  if maxBits < expBits:
67  raise RuntimeError("expBits=%s > maxBits=%s" % (expBits, maxBits))
68 
69  self.expId = expId
70  self.expBits = expBits
71  self.maxBits = maxBits
72 
73  @property
74  def unusedBits(self):
75  return self.maxBits - self.expBits
def __init__(self, expId=0, expBits=1, maxBits=64)