PropagateVisitFlagsTask¶

class lsst.pipe.tasks.propagateVisitFlags.PropagateVisitFlagsTask(*args, **kwargs)¶

Bases: Task

Task to propagate flags from single-frame measurements to coadd measurements.

Parameters:

schemalsst.afw.table.Schema: The input schema for the reference source catalog, used to initialize the output schema.
**kwargs: Additional keyword arguments.

Notes

We want to be able to set a flag for sources on the coadds using flags that were determined from the individual visits. A common example is sources that were used for PSF determination, since we do not do any PSF determination on the coadd but use the individual visits. This requires matching the coadd source catalog to each of the catalogs from the inputs (see PropagateVisitFlagsConfig.matchRadius), and thresholding on the number of times a source is flagged on the input catalog.

An important consideration in this is that the flagging of sources in the individual visits can be somewhat stochastic, e.g., the same stars may not always be used for PSF determination because the field of view moves slightly between visits, or the seeing changed. We there threshold on the relative occurrence of the flag in the visits (see PropagateVisitFlagsConfig.flags). Flagging a source that is always flagged in inputs corresponds to a threshold of 1, while flagging a source that is flagged in any of the input corresponds to a threshold of 0. But neither of these extrema are really useful in practise.

Setting the threshold too high means that sources that are not consistently flagged (e.g., due to chip gaps) will not have the flag propagated. Setting that threshold too low means that random sources which are falsely flagged in the inputs will start to dominate. If in doubt, we suggest making this threshold relatively low, but not zero (e.g., 0.1 to 0.2 or so). The more confidence in the quality of the flagging, the lower the threshold can be. The relative occurrence accounts for the edge of the field-of-view of the camera, but does not include chip gaps, bad or saturated pixels, etc.

Initialization

Beyond the usual Task initialization, PropagateVisitFlagsTask also requires a schema for the catalog that is being constructed.

The ‘run’ method (described below) is the entry-point for operations. The ‘getCcdInputs’ staticmethod is provided as a convenience for retrieving the ‘ccdInputs’ (CCD inputs table) from an Exposure.

# Requires:
# * butler: data butler, for retrieving the CCD catalogs
# * coaddCatalog: catalog of source measurements on the coadd (lsst.afw.table.SourceCatalog)
# * coaddExposure: coadd (lsst.afw.image.Exposure)
from lsst.pipe.tasks.propagateVisitFlags import PropagateVisitFlagsTask, PropagateVisitFlagsConfig
config = PropagateVisitFlagsConfig()
config.flags["calib_psf_used"] = 0.3 # Relative threshold for this flag
config.matchRadius = 0.5 # Matching radius in arcsec
task = PropagateVisitFlagsTask(coaddCatalog.schema, config=config)
ccdInputs = task.getCcdInputs(coaddExposure)
task.run(butler, coaddCatalog, ccdInputs, coaddExposure.getWcs())

Deprecated since version v24.0: This task has been replaced with PropagateSourceFlagsTask

Methods Summary

`emptyMetadata`()	Empty (clear) the metadata for this Task and all sub-Tasks.
`getCcdInputs`(coaddExposure)	Convenience method to retrieve the CCD inputs table from a coadd exposure.
`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.
`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`(butler, coaddSources, ccdInputs, coaddWcs)	Propagate flags from individual visit measurements to coadd.
`timer`(name[, logLevel])	Context manager to log performance data for an arbitrary block of code.

Methods Documentation

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

static getCcdInputs(coaddExposure)¶

Convenience method to retrieve the CCD inputs table from a coadd exposure.

Parameters:

coaddExposurelsst.afw.image.Exposure: The exposure we need to retrieve the CCD inputs table from.

Returns:

ccdInputs``: CCD inputs table from a coadd exposure.

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

getTaskDict() → Dict[str, ReferenceType[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.

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(butler, coaddSources, ccdInputs, coaddWcs, visitCatalogs=None, wcsUpdates=None)¶

Propagate flags from individual visit measurements to coadd.

This requires matching the coadd source catalog to each of the catalogs from the inputs, and thresholding on the number of times a source is flagged on the input catalog. The threshold is made on the relative occurrence of the flag in each source. Flagging a source that is always flagged in inputs corresponds to a threshold of 1, while flagging a source that is flagged in any of the input corresponds to a threshold of 0. But neither of these extrema are really useful in practise.

Setting the threshold too high means that sources that are not consistently flagged (e.g., due to chip gaps) will not have the flag propagated. Setting that threshold too low means that random sources which are falsely flagged in the inputs will start to dominate. If in doubt, we suggest making this threshold relatively low, but not zero (e.g., 0.1 to 0.2 or so). The more confidence in the quality of the flagging, the lower the threshold can be.

The relative occurrence accounts for the edge of the field-of-view of the camera, but does not include chip gaps, bad or saturated pixels, etc.

Parameters:

butlerUnknown: Data butler, for retrieving the input source catalogs.
coaddSourceslsst.afw.image.SourceCatalog: Source catalog from the coadd.
ccdInputslsst.afw.table.ExposureCatalog: Table of CCDs that contribute to the coadd.
coaddWcslsst.afw.geom.SkyWcs: Wcs for coadd.
visitCatalogslist of lsst.afw.image.SourceCatalog, optional: List of loaded source catalogs for each input ccd in the coadd. If provided this is used instead of this method loading in the catalogs itself.
wcsUpdateslist of lsst.afw.geom.SkyWcs, optional: If visitCatalogs is a list of ccd catalogs, this should be a list of updated wcs to apply.

Raises:

ValueError: Raised if any of the following occur: - A list of wcs updates for each catalog is not supplied in the wcsUpdates parameter and ccdInputs is a list of src catalogs. - The visitCatalogs and ccdInput parameters are both None.

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.
logLevel: A logging level constant.

Navigation

PropagateVisitFlagsTask¶