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.

See also

See the MatchOptimisticBTask API reference for complete details.

Retargetable subtasks

No subtasks.

Configuration fields

allowedNonperpDeg

Default
0.2
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
2.0
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
150
Field type

int RangeField

Range

[2,inf)

Maximum number of bright stars to use in fit.

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.