AstrometryTask

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

Bases: lsst.meas.astrom.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:

refObjLoader : lsst.meas.algorithms.ReferenceLoader

A reference object loader object

schema : lsst.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

emptyMetadata()	Empty (clear) the metadata for this Task and all sub-Tasks.
getAllSchemaCatalogs()	Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.
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.
getSchemaCatalogs()	Get the schemas generated by this 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

emptyMetadata()

Empty (clear) the metadata for this Task and all sub-Tasks.

getAllSchemaCatalogs()

Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.

Returns:

schemacatalogs : dict

Keys are butler dataset type, values are a empty catalog (an instance of the appropriate lsst.afw.table Catalog type) for all tasks in the hierarchy, from the top-level task down through all subtasks.

Notes

This method may be called on any task in the hierarchy; it will return the same answer, regardless.

The default implementation should always suffice. If your subtask uses schemas the override Task.getSchemaCatalogs, not this method.

getFullMetadata()

Get metadata for all tasks.

Returns:

metadata : lsst.daf.base.PropertySet or TaskMetadata

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()

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

Returns:

fullName : str

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()

Get the name of the task.

Returns:

taskName : str

Name of the task.

See also

getFullName

getSchemaCatalogs()

Get the schemas generated by this task.

Returns:

schemaCatalogs : dict

Keys are butler dataset type, values are an empty catalog (an instance of the appropriate lsst.afw.table Catalog type) for this task.

See also

Task.getAllSchemaCatalogs

Notes

Warning

Subclasses that use schemas must override this method. The default implementation returns an empty dict.

This method may be called at any time after the Task is constructed, which means that all task schemas should be computed at construction time, not when data is actually processed. This reflects the philosophy that the schema should not depend on the data.

Returning catalogs rather than just schemas allows us to save e.g. slots for SourceCatalog as well.

getTaskDict()

Get a dictionary of all tasks as a shallow copy.

Returns:

taskDict : dict

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:

exposure : lsst.afw.image.Exposure

exposure that the sources overlap

sourceCat : lsst.afw.table.SourceCatalog.

catalog of sources detected on the exposure

Returns:

result : lsst.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)

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

Parameters:

doc : str

Help text for the field.

Returns:

configurableField : lsst.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, **keyArgs)

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

Parameters:

name : str

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:

exposure : lsst.afw.image.Exposure

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

• bbox
• photoCalib (may be absent)
• 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)

sourceCat : lsst.afw.table.SourceCatalog

catalog of sources detected on the exposure

Returns:

result : lsst.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:

result : lsst.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:

TaskError

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, logLevel=10)

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

Parameters:

name : str

Name of code being timed; data will be logged using item name: Start and End.

logLevel

A logging level constant.

See also

timer.logInfo

Examples

Creating a timer context:

with self.timer("someCodeToTime"):
    pass  # code to time