GbdesAstrometricFitTask¶

GbdesAstrometricFitTask fits an astrometric solution, or world coordinate system (WCS), for a series of visits. Sources in science images are matched with a reference catalog, which allows the fitting algorithm to break degeneracies in the astrometric model. The fit model is a series of mappings, which can include (but are not limited to) a per-detector polynomial mapping and a per-visit polynomial mapping. The fit is done using the WCSFit class from the gbdes package (https://github.com/lsst/gbdes/tree/lsst-dev), which is an implementation of the method described in Bernstein et al. (2017).

This task requires source catalogs for the input images, a reference catalog, and a visit summary table, which provides a starting point for the WCS fit. The task produces the fitted WCSs, which are described in AST format and are held in lsst.afw.table.ExposureCatalogs called outputWcs. The task also outputs a table for debugging, outputCatalog, which contains the sources used in the fit, along with their residuals with the best-fit model.

Processing summary¶

GbdesAstrometricFitTask runs this sequence of operations:

Gathers information on the visit epochs, RAs and Decs, etc.
Associates sources in science images and the reference catalog to make matched objects using a friends-of-friends algorithm.

#. Uses the associated objects to fit the astrometric solution, which is a configurable sequence of mappings from the detector pixels to the sky. This uses WCSFit from the gbdes package (https://github.com/lsst/gbdes/tree/lsst-dev).

#. Converts the internal astrometric mappings to AST format. The output is in the form of one lsst.afw.table.ExposureCatalog for each visit, with a row for each detector. The fit WCS is accessed by calling getWCS() on the catalog row corresponding to the desired visit and detector.

Python API summary¶

from lsst.drp.tasks.gbdesAstrometricFit import GbdesAstrometricFitTask

classGbdesAstrometricFitTask(**kwargs): Calibrate the WCS across multiple visits of the same field using the GBDES package...

attributeconfig: Access configuration fields and retargetable subtasks.

methodrun(inputCatalogRefs, inputVisitSummaries, instrumentName='', refEpoch=None, refObjectLoader=None): Run the WCS fit for a given set of visits...

Retargetable subtasks¶

referenceSelector¶

Default: lsst.meas.algorithms.sourceSelector.ReferenceSourceSelectorTask
Field type: ConfigurableField

How to down-select the loaded astrometry reference catalog.

sourceSelector¶

Default

'science'

Field type

Single-selection RegistryField

Choices

'science': lsst.meas.algorithms.sourceSelector.ScienceSourceSelectorTask
'references': lsst.meas.algorithms.sourceSelector.ReferenceSourceSelectorTask
'objectSize': lsst.meas.algorithms.objectSizeStarSelector.ObjectSizeStarSelectorTask
'flagged': lsst.meas.algorithms.flaggedSourceSelector.FlaggedSourceSelectorTask
'astrometry': lsst.meas.algorithms.astrometrySourceSelector.AstrometrySourceSelectorTask
'matcher': lsst.meas.algorithms.matcherSourceSelector.MatcherSourceSelectorTask
'diaCatalog': lsst.ip.diffim.diaCatalogSourceSelector.DiaCatalogSourceSelectorTask

How to select sources for cross-matching.

Configuration fields¶

allowSelfMatches¶

Default: False
Field type: bool Field

Allow multiple sources from the same visit to be associated with the same object.

connections¶

Data type: lsst.pipe.base.config.Connections
Field type: ConfigField

Configurations describing the connections of the PipelineTask to datatypes

deviceModel¶

Default: ['BAND/DEVICE/poly']
Field type: str ListField

List of mappings to apply to transform from detector pixels to intermediate frame. Map namesshould match the format ‘BAND/DEVICE/<map name>’.

devicePolyOrder¶

Default: 4
Field type: int Field

Order of device polynomial model.

excludeNonPMObjects¶

Default: True
Field type: bool Field

Exclude reference objects without proper motion/parallax information.

exposureModel¶

Default: ['EXPOSURE/poly']
Field type: str ListField

List of mappings to apply to transform from intermediate frame to sky coordinates. Map namesshould match the format ‘EXPOSURE/<map name>’.

exposurePolyOrder¶

Default: 6
Field type: int Field

Order of exposure polynomial model.

fitProperMotion¶

Default: False
Field type: bool Field

Fit the proper motions of the objects.

fitReserveFraction¶

Default: 0.2
Field type: float Field

Fraction of objects to reserve from fit for validation.

fitReserveRandomSeed¶

Default: 1234
Field type: int Field

Set the random seed for selecting data points to reserve from the fit for validation.

matchRadius¶

Default: 1.0
Field type: float Field

Matching tolerance between associated objects (arcseconds).

minMatches¶

Default: 2
Field type: int Field

Number of matches required to keep a source object.

modelComponents¶

Default: ['INSTRUMENT/DEVICE', 'EXPOSURE']
Field type: str ListField

List of mappings to apply to transform from pixels to sky, in order of their application.Supported options are ‘INSTRUMENT/DEVICE’ and ‘EXPOSURE’.

referenceSystematicError¶

Default: 0.0
Field type: float Field

Systematic error padding added in quadrature for the reference catalog (marcsec).

saveLogOutput¶

Default: True
Field type: bool Field

Flag to enable/disable saving of log output for a task, enabled by default.

saveMetadata¶

Default: True
Field type: bool Field

Flag to enable/disable metadata saving for a task, enabled by default.

sourceFluxType¶

Default: 'apFlux_12_0'
Field type: str Field

Source flux field to use in source selection and to get fluxes from the catalog.

systematicError¶

Default: 0.0034
Field type: float Field

Systematic error padding added in quadrature for the science catalogs (marcsec). The defaultvalue is equivalent to 0.02 pixels for HSC.

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