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
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class
GbdesAstrometricFitTask(**kwargs) Calibrate the WCS across multiple visits of the same field using the GBDES package
...
- attributeconfig
Access configuration fields and retargetable subtasks.
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method
run(inputCatalogRefs, inputVisitSummaries, instrumentName='', refEpoch=None, refObjectLoader=None, inputCameraModel=None, colorCatalog=None) Run the WCS fit for a given set of visits
...
See also
See the GbdesAstrometricFitTask API reference for complete details.
Retargetable subtasks¶
referenceSelector¶
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'null'lsst.meas.algorithms.sourceSelector.NullSourceSelectorTask'objectSize'lsst.meas.algorithms.objectSizeStarSelector.ObjectSizeStarSelectorTask'flagged'lsst.meas.algorithms.flaggedSourceSelector.FlaggedSourceSelectorTask'astrometry'lsst.meas.algorithms.astrometrySourceSelector.AstrometrySourceSelectorTask'matcher'lsst.meas.algorithms.matcherSourceSelector.MatcherSourceSelectorTask
How to select sources for cross-matching.
Configuration fields¶
allowSelfMatches¶
Allow multiple sources from the same visit to be associated with the same object.
applyRefCatProperMotion¶
Apply proper motion to shift reference catalog to epoch of observations.
color¶
The bands to use for calculating color.
connections¶
- Data type
lsst.pipe.base.config.GbdesAstrometricFitConfigConnections- Field type
Configurations describing the connections of the PipelineTask to datatypes
deviceModel¶
List of mappings to apply to transform from detector pixels to intermediate frame. Map namesshould match the format ‘BAND/DEVICE/<map name>’.
devicePolyOrder¶
Order of device polynomial model.
excludeNonPMObjects¶
Exclude reference objects without proper motion/parallax information.
exposureModel¶
List of mappings to apply to transform from intermediate frame to sky coordinates. Map namesshould match the format ‘EXPOSURE/<map name>’.
exposurePolyOrder¶
Order of exposure polynomial model.
fitProperMotion¶
Fit the proper motions of the objects.
fitReserveFraction¶
Fraction of objects to reserve from fit for validation.
fitReserveRandomSeed¶
Set the random seed for selecting data points to reserve from the fit for validation.
matchRadius¶
Matching tolerance between associated objects (arcseconds).
minMatches¶
Number of matches required to keep a source object.
modelComponents¶
List of mappings to apply to transform from pixels to sky, in order of their application.Supported options are ‘INSTRUMENT/DEVICE’ and ‘EXPOSURE’.
referenceColor¶
The color for which DCR is defined as zero.
referenceFilter¶
Name of filter to load from reference catalog. This is a required argument, although the valuesreturned are not used.
referenceSystematicError¶
Systematic error padding added in quadrature for the reference catalog (marcsec).
saveCameraModel¶
Save the ‘device’ part of the model to be used as input in future runs.
saveLogOutput¶
Flag to enable/disable saving of log output for a task, enabled by default.
saveModelParams¶
Save the parameters and covariance of the WCS model. Default to false because this can be very large.
sourceFluxType¶
Source flux field to use in source selection and to get fluxes from the catalog.
systematicError¶
Systematic error padding added in quadrature for the science catalogs (marcsec). The defaultvalue is equivalent to 0.02 pixels for HSC.
useColor¶
Use color information to correct for differential chromatic refraction.
useInputCameraModel¶
Use a preexisting model for the ‘device’ part of the model. When true, the device part of the model will be held fixed in the fitting process.