ForcedMeasurementTask

ForcedMeasurementTask runs a set of (user-selectable) plugins, implementing particular measurement algorithms, to measure the properties of sources on a single image. A reference catalog, containing measurements made elsewere, is used to constrain some aspects of the algorithms.

Processing Summary

The set of plugins to run is set in the task configuration. Each plugin defines the values that it measures (which correspond to columns in the output table), and then conducts measurement on each detected source. See ForcedPlugin for details. This task intializes the set of plugins (thereby defining the catalog schema) from its configuration, then invokes each plugin on each source.

Most of the time, ForcedMeasurementTask will be used via one of the subclasses of lsst.meas.base.forcedPhotImage.ForcedPhotImageTask: lsst.meas.base.forcedPhotCcd.ForcedPhotCcdTask or lsst.meas.base.forcedPhotCoadd.ForcedPhotCoaddTask. These combine this measurement subtask with a references subtask (see lsst.meas.base.references.BaseReferencesTask and CoaddSrcReferencesTask) to perform forced measurement using measurements performed on another image as the references. There is generally little reason to use ForcedMeasurementTask outside of one of these drivers, unless it is necessary to avoid using the Butler for I/O.

Forced measurement means that the plugins are provided with a reference source containing centroid and/or shape measurements that they may use however they see fit. Some plugins can use these to set the location and size of apertures, but others may choose to ignore this information, essentially performing an unforced measurement starting at the position of the reference source (which may nevertheless be useful for certain investigations). Knowing how the plugin uses the reference information is essential to interpreting its resulting measurements. Typically, centroid and shape measurement plugins (e.g., SdssCentroid and SdssShape) are performing unforced measurements.

Python API summary

from lsst.meas.base.forcedMeasurement import ForcedMeasurementTask
classForcedMeasurementTask(refSchema, algMetadata=None, **kwds)

Measure sources on an image, constrained by a reference catalog...

attributeconfig

Access configuration fields and retargetable subtasks.

methodrun(measCat, exposure, refCat, refWcs, exposureId=None, beginOrder=None, endOrder=None)

Perform forced measurement...

See also

See the ForcedMeasurementTask API reference for complete details.

Configuration fields

checkUnitsParseStrict

Default
'raise'
Field type
str Field
Strictness of Astropy unit compatibility check, can be ‘raise’, ‘warn’ or ‘silent’

copyColumns

Default
{'id': 'objectId', 'parent': 'parentObjectId', 'deblend_nChild': 'deblend_nChild', 'coord_ra': 'coord_ra', 'coord_dec': 'coord_dec'}
Field type
DictField
Key type
str
Value type
str
Mapping of reference columns to source columns

doReplaceWithNoise

Default
True
Field type
bool Field
When measuring, replace other detected footprints with noise?

noiseReplacer

Data type
lsst.meas.base.noiseReplacer.NoiseReplacerConfig
Field type
ConfigField
configuration that sets how to replace neighboring sources with noise

slots

Data type
lsst.meas.base.baseMeasurement.SourceSlotConfig
Field type
ConfigField
Mapping from algorithms to special aliases in Source.

undeblendedPrefix

Default
'undeblended_'
Field type
str Field
Prefix to give undeblended plugins