MeasurePsfTask

class lsst.pipe.tasks.measurePsf.MeasurePsfTask(schema=None, **kwargs)

Bases: Task

A task that selects stars from a catalog of sources and uses those to measure the PSF.

Parameters

schemalsst.sfw.table.Schema

An lsst.afw.table.Schema used to create the output lsst.afw.table.SourceCatalog.

**kwargs :

Keyword arguments passed to lsst.pipe.base.task.Task.__init__.

Notes

If schema is not None, ‘calib_psf_candidate’ and ‘calib_psf_used’ fields will be added to identify which stars were employed in the PSF estimation.

This task can add fields to the schema, so any code calling this task must ensure that these fields are indeed present in the input table.

The star selector is a subclass of lsst.meas.algorithms.starSelector.BaseStarSelectorTask “lsst.meas.algorithms.BaseStarSelectorTask” and the PSF determiner is a sublcass of lsst.meas.algorithms.psfDeterminer.BasePsfDeterminerTask “lsst.meas.algorithms.BasePsfDeterminerTask”

There is no establised set of configuration parameters for these algorithms, so once you start modifying parameters (as we do in @ref pipe_tasks_measurePsf_Example) your code is no longer portable.

Debugging:

display

If True, display debugging plots

displayExposure

display the Exposure + spatialCells

displayPsfCandidates

show mosaic of candidates

showBadCandidates

Include bad candidates

displayPsfMosaic

show mosaic of reconstructed PSF(xy)

displayResiduals

show residuals

normalizeResiduals

Normalise residuals by object amplitude

Additionally you can enable any debug outputs that your chosen star selector and psf determiner support.

Attributes Summary

usesMatches

Return True if this task makes use of the "matches" argument to the run method

Methods Summary

run(exposure, sources[, expId, matches])

Measure the PSF.

Attributes Documentation

usesMatches

Return True if this task makes use of the “matches” argument to the run method

Methods Documentation

run(exposure, sources, expId=0, matches=None)

Measure the PSF.

Parameters

exposurelsst.afw.image.Exposure

Exposure to process; measured PSF will be added.

sourcesUnknown

Measured sources on exposure; flag fields will be set marking stars chosen by the star selector and the PSF determiner if a schema was passed to the task constructor.

expIdint, optional

Exposure id used for generating random seed.

matcheslist, optional

A list of lsst.afw.table.ReferenceMatch objects (i.e. of lsst.afw.table.Match with @c first being of type lsst.afw.table.SimpleRecord and @c second type lsst.afw.table.SourceRecord — the reference object and detected object respectively) as returned by @em e.g. the AstrometryTask. Used by star selectors that choose to refer to an external catalog.

Returns

measurementlsst.pipe.base.Struct

PSF measurement as a struct with attributes:

psf

The measured PSF (also set in the input exposure).

cellSet

An lsst.afw.math.SpatialCellSet containing the PSF candidates as returned by the psf determiner.

Raises

NonfinitePsfShapeError

If the new PSF has NaN or Inf width.