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.forcedPhotCcd.ForcedPhotCcdTask or lsst.meas.base.forcedPhotCoadd.ForcedPhotCoaddTask. These combine this measurement subtask with a references subtask (see lsst.meas.base.references.BaseReferencesTask and ~lsst.meas.base.references.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...

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

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