DirectMatchTask

DirectMatchTask implements a brute force nearest neighbor match between a input source catalog and a reference catalog.

The matching permits no rotation or scaling, but uses the existing sky positions in the source catalog. This is often useful for QA, as it allows validating the pipeline astrometry and photometry against the reference catalog.

Note that this DirectMatchTask is not currently suitable for use within the AstrometryTask, as it has a different interface and serves a different purpose.

Processing summary

DirectMatchTask runs this sequence of operations:

  • Finds an on sky circle covering the input source catalog.

  • Loads reference objects within the circle.

  • Performs a simple nearest neighbor assignment within a specified tolerance.

Python API summary

from lsst.meas.astrom.directMatch import DirectMatchTask
classDirectMatchTask(butler=None, refObjLoader=None, **kwargs)

Simple, brute force matching of a source catalog to a reference catalog...

attributeconfig

Access configuration fields and retargetable subtasks.

methodrun(catalog, filterName=None, epoch=None)

Load reference objects and match to them...

See also

See the DirectMatchTask API reference for complete details.

Retargetable subtasks

refObjLoader

Default

lsst.meas.algorithms.loadIndexedReferenceObjects.LoadIndexedReferenceObjectsTask

Field type

ConfigurableField

Load reference objects

referenceSelection

Default

lsst.meas.algorithms.sourceSelector.ReferenceSourceSelectorTask

Field type

ConfigurableField

Selection of reference sources

sourceSelection

Default

lsst.meas.algorithms.sourceSelector.ScienceSourceSelectorTask

Field type

ConfigurableField

Selection of science sources

Configuration fields

matchRadius

Default
0.25
Field type

float Field

Matching radius, arcsec

Examples

config = DirectMatchConfig()
task = DirectMatchTask(butler=butler, config=config)
matchResults = task.run(catalog)