MatchOptimisticBTask¶

MatchOptimisticBTask matches sources to reference objects. This is often done as a preliminary step to fitting an astrometric or photometric solution.

Optimistic Pattern Matching is described in [Tabur2007]

Processing summary¶

MatchOptimisticBTask runs this sequence of operations:

Flags sources with bad centroids and low signal to noise and remove them from the matching.
Match the usable sources with an input reference catalog using the V. Tabur 2007 algorithm.
Further remove sources detected on the edge of the image and those that are saturated.
Return these sources matched to the references.

Python API summary¶

from lsst.meas.astrom.matchOptimisticBTask import MatchOptimisticBTask

classMatchOptimisticBTask(**kwargs): Match sources to reference objects using the Optimistic Pattern Matcher B algorithm of Tabur 2007...

attributeconfig: Access configuration fields and retargetable subtasks.

Retargetable subtasks¶

No subtasks.

Configuration fields¶

allowedNonperpDeg¶

Default: 3.0
Field type: float RangeField
Range: [-inf,45.0)

Allowed non-perpendicularity of x and y (degree)

maxDeterminant¶

Default: 0.02
Field type: float Field

maximum determinant of linear transformation matrix for a usable solution

maxMatchDistArcSec¶

Default: 3
Field type: float RangeField
Range: [0,inf)

Maximum separation between reference objects and sources beyond which they will not be considered a match (arcsec)

maxOffsetPix¶

Default: 250
Field type: int RangeField
Range: [-inf,4000)

Maximum allowed shift of WCS, due to matching (pixel). When changing this value, the LoadReferenceObjectsConfig.pixelMargin should also be updated.

maxRotationDeg¶

Default: 1.0
Field type: float RangeField
Range: [-inf,6.0)

Rotation angle allowed between sources and position reference objects (degrees)

minFracMatchedPairs¶

Default: 0.3
Field type: float RangeField
Range: [0,1)

Minimum number of matched pairs as a fraction of the smaller of the number of reference stars or the number of good sources; the actual minimum is the smaller of this value or minMatchedPairs

minMatchedPairs¶

Default: 30
Field type: int RangeField
Range: [2,inf)

Minimum number of matched pairs; see also minFracMatchedPairs

numBrightStars¶

Default: 50
Field type: int RangeField
Range: [2,inf)

Number of bright stars to use

numPointsForShape¶

Default: 6
Field type: int Field

number of points to define a shape for matching

Debugging¶

The lsst.pipe.base.cmdLineTask.CmdLineTask command line task interface supports a flag -d to import debug.py from your PYTHONPATH; see lsstDebug for more about debug.py files.

The available variables in MatchOptimisticB are

display (bool): If True display information at three stages: after finding reference objects, after matching sources to reference objects, and after fitting the WCS; defaults to False
frame (int): frame to use to display the reference objects; the next two frames are used to display the match list and the results of the final WCS; defaults to 0

To investigate the meas_astrom_astrometry_Debug, put something like

import lsstDebug
def DebugInfo(name):
    debug = lsstDebug.getInfo(name) # N.b. lsstDebug.Info(name) would call us recursively
    if name == "lsst.meas.astrom.astrometry":
        debug.display = True

    return debug

lsstDebug.Info = DebugInfo

into your debug.py file and run this task with the --debug flag.

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