AstrometryTask¶

class lsst.meas.astrom.AstrometryTask(refObjLoader=None, schema=None, **kwargs)¶

Bases: RefMatchTask

Match an input source catalog with objects from a reference catalog and solve for the WCS.

This task is broken into two main subasks: matching and WCS fitting which are very interactive. The matching here can be considered in part a first pass WCS fitter due to the fitter’s sensitivity to outliers.

Parameters:

refObjLoaderlsst.meas.algorithms.ReferenceLoader: A reference object loader object; gen3 pipeline tasks will pass None and call setRefObjLoader in runQuantum.
schemalsst.afw.table.Schema: Used to set “calib_astrometry_used” flag in output source catalog.
**kwargs: Additional keyword arguments for pipe_base lsst.pipe.base.Task.__init__.

Methods Summary

`check`(exposure, sourceCat, nMatches)	Validate the astrometric fit against the maxMeanDistance threshold.
`emptyMetadata`()	Empty (clear) the metadata for this Task and all sub-Tasks.
`getFullMetadata`()	Get metadata for all tasks.
`getFullName`()	Get the task name as a hierarchical name including parent task names.
`getName`()	Get the name of the task.
`getTaskDict`()	Get a dictionary of all tasks as a shallow copy.
`loadAndMatch`(exposure, sourceCat)	Load reference objects overlapping an exposure and match to sources detected on that exposure.
`makeField`(doc)	Make a `lsst.pex.config.ConfigurableField` for this task.
`makeSubtask`(name, **keyArgs)	Create a subtask as a new instance as the `name` attribute of this task.
`run`(sourceCat, exposure)	Load reference objects, match sources and optionally fit a WCS.
`setRefObjLoader`(refObjLoader)	Sets the reference object loader for the task.
`solve`(exposure, sourceCat)	Load reference objects overlapping an exposure, match to sources and fit a WCS
`timer`(name[, logLevel])	Context manager to log performance data for an arbitrary block of code.

Methods Documentation

check(exposure, sourceCat, nMatches)¶

Validate the astrometric fit against the maxMeanDistance threshold.

If the distMean metric does not satisfy the requirement of being less than the value set in config.maxMeanDistanceArcsec, the WCS on the exposure will be set to None and the coordinate values in the source catalog will be set to NaN to reflect a failed astrometric fit.

Parameters:

exposurelsst.afw.image.Exposure: The exposure whose astrometric fit is being evaluated.
sourceCatlsst.afw.table.SourceCatalog: The catalog of sources associated with the exposure.
nMatchesint: The number of matches that were found and used during the astrometric fit (for logging purposes only).

Raises:

BadAstrometryFit: If the measured mean on-sky distance between the matched source and reference objects is greater than self.config.maxMeanDistanceArcsec.

emptyMetadata() → None¶: Empty (clear) the metadata for this Task and all sub-Tasks.

getFullMetadata() → TaskMetadata¶

Get metadata for all tasks.

Returns:

metadataTaskMetadata: The keys are the full task name. Values are metadata for the top-level task and all subtasks, sub-subtasks, etc.

Notes

The returned metadata includes timing information (if @timer.timeMethod is used) and any metadata set by the task. The name of each item consists of the full task name with . replaced by :, followed by . and the name of the item, e.g.:

topLevelTaskName:subtaskName:subsubtaskName.itemName

using : in the full task name disambiguates the rare situation that a task has a subtask and a metadata item with the same name.

getFullName() → str¶

Get the task name as a hierarchical name including parent task names.

Returns:

fullNamestr

The full name consists of the name of the parent task and each subtask separated by periods. For example:

The full name of top-level task “top” is simply “top”.
The full name of subtask “sub” of top-level task “top” is “top.sub”.
The full name of subtask “sub2” of subtask “sub” of top-level task “top” is “top.sub.sub2”.

getName() → str¶

Get the name of the task.

Returns:

taskNamestr: Name of the task.

See also

getFullName: Get the full name of the task.

getTaskDict() → dict[str, weakref.ReferenceType[lsst.pipe.base.task.Task]]¶

Get a dictionary of all tasks as a shallow copy.

Returns:

taskDictdict: Dictionary containing full task name: task object for the top-level task and all subtasks, sub-subtasks, etc.

loadAndMatch(exposure, sourceCat)¶

Load reference objects overlapping an exposure and match to sources detected on that exposure.

Parameters:

exposurelsst.afw.image.Exposure: exposure that the sources overlap
sourceCatlsst.afw.table.SourceCatalog.: catalog of sources detected on the exposure

Returns:

resultlsst.pipe.base.Struct

Result struct with Components:

refCat : reference object catalog of objects that overlap the exposure (lsst.afw.table.SimpleCatalog)
matches : Matched sources and references (list of lsst.afw.table.ReferenceMatch)
matchMeta : metadata needed to unpersist matches (lsst.daf.base.PropertyList)

Notes

ignores config.matchDistanceSigma

classmethod makeField(doc: str) → ConfigurableField¶

Make a lsst.pex.config.ConfigurableField for this task.

Parameters:

docstr: Help text for the field.

Returns:

configurableFieldlsst.pex.config.ConfigurableField: A ConfigurableField for this task.

Examples

Provides a convenient way to specify this task is a subtask of another task.

Here is an example of use:

class OtherTaskConfig(lsst.pex.config.Config):
    aSubtask = ATaskClass.makeField("brief description of task")

makeSubtask(name: str, **keyArgs: Any) → None¶

Create a subtask as a new instance as the name attribute of this task.

Parameters:

namestr

Brief name of the subtask.

**keyArgs

Extra keyword arguments used to construct the task. The following arguments are automatically provided and cannot be overridden:

config.
parentTask.

Notes

The subtask must be defined by Task.config.name, an instance of ConfigurableField or RegistryField.

run(sourceCat, exposure)¶

Load reference objects, match sources and optionally fit a WCS.

This is a thin layer around solve or loadAndMatch, depending on config.forceKnownWcs.

Parameters:

exposurelsst.afw.image.Exposure

exposure whose WCS is to be fit The following are read only:

bbox
filter (may be unset)
detector (if wcs is pure tangent; may be absent)

The following are updated:

wcs (the initial value is used as an initial guess, and is required)

sourceCatlsst.afw.table.SourceCatalog

catalog of sources detected on the exposure

Returns:

resultlsst.pipe.base.Struct

with these fields:

refCat : reference object catalog of objects that overlap the exposure (with some margin) (lsst.afw.table.SimpleCatalog).
matches : astrometric matches (list of lsst.afw.table.ReferenceMatch).
scatterOnSky : median on-sky separation between reference objects and sources in “matches” (lsst.afw.geom.Angle) or None if config.forceKnownWcs True
matchMeta : metadata needed to unpersist matches (lsst.daf.base.PropertyList)

setRefObjLoader(refObjLoader)¶

Sets the reference object loader for the task.

Parameters:

refObjLoader: An instance of a reference object loader task or class.

solve(exposure, sourceCat)¶

Load reference objects overlapping an exposure, match to sources and fit a WCS

Returns:

resultlsst.pipe.base.Struct

Result struct with components:

refCat : reference object catalog of objects that overlap the exposure (with some margin) (lsst::afw::table::SimpleCatalog).
matches : astrometric matches (list of lsst.afw.table.ReferenceMatch).
scatterOnSky : median on-sky separation between reference objects and sources in “matches” (lsst.geom.Angle)
matchMeta : metadata needed to unpersist matches (lsst.daf.base.PropertyList)

Raises:

BadAstrometryFit: If the measured mean on-sky distance between the matched source and reference objects is greater than self.config.maxMeanDistanceArcsec.

Notes

ignores config.forceKnownWcs

timer(name: str, logLevel: int = 10) → Iterator[None]¶

Context manager to log performance data for an arbitrary block of code.

Parameters:

namestr: Name of code being timed; data will be logged using item name: Start and End.
logLevelint: A logging level constant.

Navigation

AstrometryTask¶