lsst.meas.base  19.0.0-9-g463f923+12
Public Types | Public Member Functions | Static Public Member Functions | Static Public Attributes | Protected Attributes | List of all members
lsst::meas::base::BlendednessAlgorithm Class Reference

Compute metrics that measure how blended objects are. More...

#include <Blendedness.h>

Inheritance diagram for lsst::meas::base::BlendednessAlgorithm:
lsst::meas::base::SimpleAlgorithm lsst::meas::base::SingleFrameAlgorithm lsst::meas::base::ForcedAlgorithm lsst::meas::base::BaseAlgorithm lsst::meas::base::BaseAlgorithm

Public Types

typedef BlendednessControl Control
 

Public Member Functions

 BlendednessAlgorithm (Control const &ctrl, std::string const &name, afw::table::Schema &schema)
 
void measureChildPixels (afw::image::MaskedImage< float > const &image, afw::table::SourceRecord &child) const
 
void measureParentPixels (afw::image::MaskedImage< float > const &image, afw::table::SourceRecord &child) const
 
virtual void measure (afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure) const
 Called to measure a single child source in an image. More...
 
virtual void fail (afw::table::SourceRecord &measRecord, MeasurementError *error=nullptr) const
 Handle an exception thrown by the current algorithm by setting flags in the given record. More...
 
virtual void measureForced (afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure, afw::table::SourceRecord const &refRecord, afw::geom::SkyWcs const &refWcs) const
 Called to measure a single child source in an image. More...
 
virtual void measureNForced (afw::table::SourceCatalog const &measCat, afw::image::Exposure< float > const &exposure, afw::table::SourceCatalog const &refRecord, afw::geom::SkyWcs const &refWcs) const
 Called to simultaneously measure all children in a deblend family, in a single image. More...
 
virtual void measureN (afw::table::SourceCatalog const &measCat, afw::image::Exposure< float > const &exposure) const
 Called to simultaneously measure all children in a deblend family, in a single image. More...
 
std::string getLogName () const
 

Static Public Member Functions

static FlagDefinitionList const & getFlagDefinitions ()
 
static float computeAbsExpectation (float data, float variance)
 Compute the posterior expectation value of the true instrumental flux in a pixel from its (Gaussian) likelihood and a flat nonnegative prior. More...
 
static float computeAbsBias (float mu, float variance)
 Compute the bias induced by using the absolute value of a pixel instead of its value. More...
 

Static Public Attributes

static FlagDefinition const FAILURE = flagDefinitions.addFailureFlag()
 
static FlagDefinition const NO_CENTROID
 
static FlagDefinition const NO_SHAPE
 

Protected Attributes

std::string _logName
 

Detailed Description

Compute metrics that measure how blended objects are.

Blendedness is initialized once for a given Schema, then run repeatedly by calls to measureChildPixels and measureParentPixels (in any order, possibly with multiple sources interleaved). Since it needs access to both the image with with noise and the noise replaced children it cannot use the standard plugin interface.

Definition at line 66 of file Blendedness.h.

Member Typedef Documentation

◆ Control

Definition at line 74 of file Blendedness.h.

Constructor & Destructor Documentation

◆ BlendednessAlgorithm()

lsst::meas::base::BlendednessAlgorithm::BlendednessAlgorithm ( Control const &  ctrl,
std::string const &  name,
afw::table::Schema schema 
)

Definition at line 195 of file Blendedness.cc.

Member Function Documentation

◆ computeAbsBias()

float lsst::meas::base::BlendednessAlgorithm::computeAbsBias ( float  mu,
float  variance 
)
static

Compute the bias induced by using the absolute value of a pixel instead of its value.

The computation assumes the true distribution for the pixel is a Gaussian with mean mu and the given variance. To compute mu from the data, use computeAbsExpectation.

This computes

\[ \sqrt{\frac{2}{\pi}}\sigma e^{-\frac{\mu^2}{2\sigma^2}} - \mu\,\mathrm{erfc}\left(\frac{\mu}{\sqrt{2}\sigma}\right) \]

where \(\mu\) is the mean of the underlying distribution and \(\sigma^2\) is its variance. See section 4.9.11 of Bosch, J. et al. 2018, PASJ, 70, S5 for further details.

Definition at line 270 of file Blendedness.cc.

◆ computeAbsExpectation()

float lsst::meas::base::BlendednessAlgorithm::computeAbsExpectation ( float  data,
float  variance 
)
static

Compute the posterior expectation value of the true instrumental flux in a pixel from its (Gaussian) likelihood and a flat nonnegative prior.

This computes

\[ \frac{\int_0^\infty f \frac{1}{\sqrt{2\pi}\sigma} e^{-\frac{(f-z)^2}{2\sigma^2}} df} {\int_0^\infty \frac{1}{\sqrt{2\pi}\sigma} e^{-\frac{(f-z)^2}{2\sigma^2}} df} \]

where \(z\) is the (noisy) pixel value and \(\sigma^2\) is the pixel variance. This approaches \(z\) when \(z \gg \sigma\) and \(0\) when \(z \ll -\sigma\).

We use single precision here for performance reasons; this function is called in a loop over single-precision pixels, and relies on a number of calls to exp and erfc, which are much faster in single precision.

Definition at line 260 of file Blendedness.cc.

◆ fail()

virtual void lsst::meas::base::BlendednessAlgorithm::fail ( afw::table::SourceRecord measRecord,
MeasurementError error = nullptr 
) const
inlinevirtual

Handle an exception thrown by the current algorithm by setting flags in the given record.

fail() is called by the measurement framework when an exception is allowed to propagate out of one the algorithm's measure() methods. It should generally set both a general failure flag for the algorithm as well as a specific flag indicating the error condition, if possible. To aid in this, if the exception was an instance of MeasurementError, it will be passed in, carrying information about what flag to set.

An algorithm can also to chose to set flags within its own measure() methods, and then just return, rather than throw an exception. However, fail() should be implemented even when all known failure modes do not throw exceptions, to ensure that unexpected exceptions thrown in lower-level code are properly handled.

Implements lsst::meas::base::BaseAlgorithm.

Definition at line 123 of file Blendedness.h.

◆ getFlagDefinitions()

FlagDefinitionList const & lsst::meas::base::BlendednessAlgorithm::getFlagDefinitions ( )
static

Definition at line 49 of file Blendedness.cc.

◆ getLogName()

std::string lsst::meas::base::BaseAlgorithm::getLogName ( ) const
inlineinherited

Definition at line 66 of file Algorithm.h.

◆ measure()

virtual void lsst::meas::base::BlendednessAlgorithm::measure ( afw::table::SourceRecord measRecord,
afw::image::Exposure< float > const &  exposure 
) const
inlinevirtual

Called to measure a single child source in an image.

Before this method is called, all neighbors will be replaced with noise, using the outputs of the deblender. Outputs should be saved in the given SourceRecord, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

Implements lsst::meas::base::SingleFrameAlgorithm.

Definition at line 120 of file Blendedness.h.

◆ measureChildPixels()

void lsst::meas::base::BlendednessAlgorithm::measureChildPixels ( afw::image::MaskedImage< float > const &  image,
afw::table::SourceRecord child 
) const

Definition at line 346 of file Blendedness.cc.

◆ measureForced()

virtual void lsst::meas::base::SimpleAlgorithm::measureForced ( afw::table::SourceRecord measRecord,
afw::image::Exposure< float > const &  exposure,
afw::table::SourceRecord const &  refRecord,
afw::geom::SkyWcs const &  refWcs 
) const
inlinevirtualinherited

Called to measure a single child source in an image.

Before this method is called, all neighbors will be replaced with noise, using the outputs of the deblender. Outputs should be saved in the given SourceRecord, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

Implements lsst::meas::base::ForcedAlgorithm.

Definition at line 172 of file Algorithm.h.

◆ measureN()

void lsst::meas::base::SingleFrameAlgorithm::measureN ( afw::table::SourceCatalog const &  measCat,
afw::image::Exposure< float > const &  exposure 
) const
virtualinherited

Called to simultaneously measure all children in a deblend family, in a single image.

Outputs should be saved in the given SourceCatalog, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

The default implementation simply throws an exception, indicating that simultaneous measurement is not supported.

Definition at line 31 of file Algorithm.cc.

◆ measureNForced()

virtual void lsst::meas::base::SimpleAlgorithm::measureNForced ( afw::table::SourceCatalog const &  measCat,
afw::image::Exposure< float > const &  exposure,
afw::table::SourceCatalog const &  refRecord,
afw::geom::SkyWcs const &  refWcs 
) const
inlinevirtualinherited

Called to simultaneously measure all children in a deblend family, in a single image.

Outputs should be saved in the given SourceCatalog, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

The default implementation simply throws an exception, indicating that simultaneous measurement is not supported.

Reimplemented from lsst::meas::base::ForcedAlgorithm.

Definition at line 179 of file Algorithm.h.

◆ measureParentPixels()

void lsst::meas::base::BlendednessAlgorithm::measureParentPixels ( afw::image::MaskedImage< float > const &  image,
afw::table::SourceRecord child 
) const

Definition at line 351 of file Blendedness.cc.

Member Data Documentation

◆ _logName

std::string lsst::meas::base::BaseAlgorithm::_logName
protectedinherited

Definition at line 69 of file Algorithm.h.

◆ FAILURE

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::FAILURE = flagDefinitions.addFailureFlag()
static

Definition at line 70 of file Blendedness.h.

◆ NO_CENTROID

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::NO_CENTROID
static
Initial value:
=
flagDefinitions.add("flag_noCentroid", "Object has no centroid")

Definition at line 71 of file Blendedness.h.

◆ NO_SHAPE

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::NO_SHAPE
static
Initial value:
=
flagDefinitions.add("flag_noShape", "Object has no shape")

Definition at line 72 of file Blendedness.h.


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