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)