DecorrelateALKernelMapper

class lsst.ip.diffim.DecorrelateALKernelMapper(*args, **kwargs)

Bases: lsst.ip.diffim.DecorrelateALKernelTask, lsst.ip.diffim.ImageMapper

Task to be used as an ImageMapper for performing A&L decorrelation on subimages on a grid across a A&L difference image.

This task subclasses DecorrelateALKernelTask in order to implement all of that task’s configuration parameters, as well as its run method.

Methods Summary

computeCorrectedDiffimPsf(kappa, psf[, …])	Compute the (decorrelated) difference image’s new PSF.
computeVarianceMean(exposure)
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.
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(subExposure, expandedSubExposure, …[, …])	Perform decorrelation operation on subExposure, using expandedSubExposure to allow for invalid edge pixels arising from convolutions.
timer(name[, logLevel])	Context manager to log performance data for an arbitrary block of code.

Methods Documentation

static computeCorrectedDiffimPsf(kappa, psf, svar=0.04, tvar=0.04)

Compute the (decorrelated) difference image’s new PSF. new_psf = psf(k) * sqrt((svar + tvar) / (svar + tvar * kappa_ft(k)**2))

Parameters

kappanumpy.ndarray

A matching kernel array derived from Alard & Lupton PSF matching

psfnumpy.ndarray

The uncorrected psf array of the science image (and also of the diffim)

svarfloat, optional

Average variance of science image used for PSF matching

tvarfloat, optional

Average variance of template image used for PSF matching

Returns

pcfnumpy.ndarray

a 2-d numpy.array containing the new PSF

computeVarianceMean(exposure)

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

schemacatalogsdict

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

metadatalsst.daf.base.PropertySet

The PropertySet 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

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()

Get the name of the task.

Returns

taskNamestr

Name of the task.

See also

getFullName

getSchemaCatalogs()

Get the schemas generated by this task.

Returns

schemaCatalogsdict

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 implemenation 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

taskDictdict

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

classmethod makeField(doc)

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("a brief description of what this task does")

makeSubtask(name, **keyArgs)

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 pex_config ConfigurableField or RegistryField.

run(subExposure, expandedSubExposure, fullBBox, template, science, alTaskResult=None, psfMatchingKernel=None, preConvKernel=None, **kwargs)

Perform decorrelation operation on subExposure, using expandedSubExposure to allow for invalid edge pixels arising from convolutions.

This method performs A&L decorrelation on subExposure using local measures for image variances and PSF. subExposure is a sub-exposure of the non-decorrelated A&L diffim. It also requires the corresponding sub-exposures of the template (template) and science (science) exposures.

Parameters

subExposurelsst.afw.image.Exposure

the sub-exposure of the diffim

expandedSubExposurelsst.afw.image.Exposure

the expanded sub-exposure upon which to operate

fullBBoxlsst.geom.Box2I

the bounding box of the original exposure

templatelsst.afw.image.Exposure

the corresponding sub-exposure of the template exposure

sciencelsst.afw.image.Exposure

the corresponding sub-exposure of the science exposure

alTaskResultlsst.pipe.base.Struct

the result of A&L image differencing on science and template, importantly containing the resulting psfMatchingKernel. Can be None, only if psfMatchingKernel is not None.

psfMatchingKernelAlternative parameter for passing the

A&L psfMatchingKernel directly.

preConvKernelIf not None, then pre-filtering was applied

to science exposure, and this is the pre-convolution kernel.

kwargs :

additional keyword arguments propagated from ImageMapReduceTask.run.

Returns

A `pipeBase.Struct` containing:

• subExposure : the result of the subExposure processing.

• decorrelationKernelthe decorrelation kernel, currently

  not used.

Notes

This run method accepts parameters identical to those of ImageMapper.run, since it is called from the ImageMapperTask. See that class for more information.

timer(name, logLevel=10000)

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 lsst.log level constant.

See also

timer.logInfo

Examples

Creating a timer context:

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