lsst.meas.base.plugins.VariancePlugin Class Reference

Inheritance diagram for lsst.meas.base.plugins.VariancePlugin:

Public Member Functions
	getExecutionOrder (cls)
	__init__ (self, config, name, schema, metadata)
	measure (self, measRecord, exposure, center)
	fail (self, measRecord, error=None)

Public Attributes
	varValue
	emptyFootprintFlag
	FAILURE_BAD_CENTROID
	FAILURE_EMPTY_FOOTPRINT

Static Public Attributes
	ConfigClass = VarianceConfig
int	FAILURE_BAD_CENTROID = 1
int	FAILURE_EMPTY_FOOTPRINT = 2

Detailed Description

Compute the median variance corresponding to a footprint.

The aim here is to measure the background variance, rather than that of
the object itself. In order to achieve this, the variance is calculated
over an area scaled up from the shape of the input footprint.

Parameters
----------
config : `VarianceConfig`
    Plugin configuraion.
name : `str`
    Plugin name.
schema : `lsst.afw.table.Schema`
    The schema for the measurement output catalog. New fields will be
    added to hold measurements produced by this plugin.
metadata : `lsst.daf.base.PropertySet`
    Plugin metadata that will be attached to the output catalog

Definition at line 234 of file plugins.py.

Constructor & Destructor Documentation

__init__()

lsst.meas.base.plugins.VariancePlugin.__init__	(		self,
			config,
			name,
			schema,
			metadata )

Reimplemented from lsst.meas.base.wrappers.GenericPlugin.

Definition at line 268 of file plugins.py.

    def __init__(self, config, name, schema, metadata):
        GenericPlugin.__init__(self, config, name, schema, metadata)
        self.varValue = schema.addField(name + '_value', type="D", doc="Variance at object position")
        self.emptyFootprintFlag = schema.addField(name + '_flag_emptyFootprint', type="Flag",
                                                  doc="Set to True when the footprint has no usable pixels")
 
        # Alias the badCentroid flag to that which is defined for the target
        # of the centroid slot.  We do not simply rely on the alias because
        # that could be changed post-measurement.
        schema.getAliasMap().set(name + '_flag_badCentroid', schema.getAliasMap().apply("slot_Centroid_flag"))
 

Member Function Documentation

fail()

lsst.meas.base.plugins.VariancePlugin.fail	(		self,
			measRecord,
			error = None )

Record a measurement failure.

This default implementation simply records the failure in the source
record.

Parameters
----------
measRecord : `lsst.afw.table.SourceRecord`
    Catalog record for the source being measured.
error : `Exception`
    Error causing failure, or `None`.

Reimplemented from lsst.meas.base.wrappers.GenericPlugin.

Definition at line 307 of file plugins.py.

    def fail(self, measRecord, error=None):
        # Check that we have an error object and that it is of type
        # MeasurementError
        if isinstance(error, MeasurementError):
            assert error.getFlagBit() in (self.FAILURE_BAD_CENTROID, self.FAILURE_EMPTY_FOOTPRINT)
            # FAILURE_BAD_CENTROID handled by alias to centroid record.
            if error.getFlagBit() == self.FAILURE_EMPTY_FOOTPRINT:
                measRecord.set(self.emptyFootprintFlag, True)
        measRecord.set(self.varValue, np.nan)
        GenericPlugin.fail(self, measRecord, error)
 
 

getExecutionOrder()

lsst.meas.base.plugins.VariancePlugin.getExecutionOrder

(

cls

)

Get the relative execution order of this plugin.

Must be reimplemented as a class method by concrete derived classes.

Reimplemented from lsst.meas.base.wrappers.GenericPlugin.

Definition at line 265 of file plugins.py.

    def getExecutionOrder(cls):
        return BasePlugin.FLUX_ORDER
 

measure()

lsst.meas.base.plugins.VariancePlugin.measure	(		self,
			measRecord,
			exposure,
			center )

Measure a single source.

It is the responsibility of this method to perform the desired
measurement and record the result in the `measRecord`.

Parameters
----------
measRecord : `lsst.afw.table.SourceRecord`
    Catalog record for the source being measured.
exposure : `lsst.afw.image.Exposure`
    Exposure on which the source is being measured.
center : `lsst.geom.Point2D`
    Pixel coordinates of the object.

Raises
------
MeasurementError
    Raised if the measurement fails for a known/justifiable reason.

Reimplemented from lsst.meas.base.wrappers.GenericPlugin.

Definition at line 279 of file plugins.py.

    def measure(self, measRecord, exposure, center):
        # Create an aperture and grow it by scale value defined in config to
        # ensure there are enough pixels around the object to get decent
        # statistics
        if not np.all(np.isfinite(measRecord.getCentroid())):
            raise MeasurementError("Bad centroid and/or shape", self.FAILURE_BAD_CENTROID)
        aperture = lsst.afw.geom.Ellipse(measRecord.getShape(), measRecord.getCentroid())
        aperture.scale(self.config.scale)
        ellipse = lsst.afw.geom.SpanSet.fromShape(aperture)
        foot = lsst.afw.detection.Footprint(ellipse)
        foot.clipTo(exposure.getBBox(lsst.afw.image.PARENT))
        # Filter out any pixels which have mask bits set corresponding to the
        # planes to be excluded (defined in config.mask)
        maskedImage = exposure.getMaskedImage()
        pixels = lsst.afw.detection.makeHeavyFootprint(foot, maskedImage)
        maskBits = maskedImage.getMask().getPlaneBitMask(self.config.mask)
        logicalMask = np.logical_not(pixels.getMaskArray() & maskBits)
        # Compute the median variance value for each pixel not excluded by the
        # mask and write the record.  Numpy median is used here instead of
        # afw.math makeStatistics because of an issue with data types being
        # passed into the C++ layer (DM-2379).
        if np.any(logicalMask):
            medVar = np.median(pixels.getVarianceArray()[logicalMask])
            measRecord.set(self.varValue, medVar)
        else:
            raise MeasurementError("Footprint empty, or all pixels are masked, can't compute median",
                                   self.FAILURE_EMPTY_FOOTPRINT)
 

Member Data Documentation

ConfigClass

lsst.meas.base.plugins.VariancePlugin.ConfigClass = VarianceConfig

static

Definition at line 254 of file plugins.py.

emptyFootprintFlag

lsst.meas.base.plugins.VariancePlugin.emptyFootprintFlag

Definition at line 271 of file plugins.py.

FAILURE_BAD_CENTROID [1/2]

int lsst.meas.base.plugins.VariancePlugin.FAILURE_BAD_CENTROID = 1

static

Definition at line 256 of file plugins.py.

FAILURE_BAD_CENTROID [2/2]

lsst.meas.base.plugins.VariancePlugin.FAILURE_BAD_CENTROID

Definition at line 284 of file plugins.py.

FAILURE_EMPTY_FOOTPRINT [1/2]

int lsst.meas.base.plugins.VariancePlugin.FAILURE_EMPTY_FOOTPRINT = 2

static

Definition at line 260 of file plugins.py.

FAILURE_EMPTY_FOOTPRINT [2/2]

lsst.meas.base.plugins.VariancePlugin.FAILURE_EMPTY_FOOTPRINT

Definition at line 305 of file plugins.py.

varValue

lsst.meas.base.plugins.VariancePlugin.varValue

Definition at line 270 of file plugins.py.

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The documentation for this class was generated from the following file:

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-8.0.0/Linux64/meas_base/gf18bd8381d+7268b93478/python/lsst/meas/base/plugins.py