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LSST Data Management Base Package
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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.
 
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.
 
void measureForced (afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure, afw::table::SourceRecord const &refRecord, afw::geom::SkyWcs const &refWcs) const override
 Called to measure a single child source in an image.
 
void measureNForced (afw::table::SourceCatalog const &measCat, afw::image::Exposure< float > const &exposure, afw::table::SourceCatalog const &refRecord, afw::geom::SkyWcs const &refWcs) const override
 Called to simultaneously measure all children in a deblend family, in a single image.
 
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.
 
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.
 
static float computeAbsBias (float mu, float variance)
 Compute the bias induced by using the absolute value of a pixel instead of its value.
 

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.

197 : _ctrl(ctrl) {
198 if (_ctrl.doOld) {
199 _old = schema.addField<double>(
200 schema.join(name, "old"),
201 "Blendedness from dot products: (child.dot(parent)/child.dot(child) - 1)");
202 }
203 if (_ctrl.doFlux) {
204 _raw = schema.addField<double>(
205 schema.join(name, "raw"),
206 "Measure of how much the flux is affected by neighbors: "
207 "(1 - child_instFlux/parent_instFlux). Operates on the \"raw\" pixel values.");
208 _instFluxChildRaw = schema.addField<double>(
209 schema.join(name, "raw_child_instFlux"),
210 "Instrumental flux of the child, measured with a Gaussian weight matched to the child. "
211 "Operates on the \"raw\" pixel values.", "count");
212 _instFluxParentRaw = schema.addField<double>(
213 schema.join(name, "raw_parent_instFlux"),
214 "Instrumental flux of the parent, measured with a Gaussian weight matched to the child. "
215 "Operates on the \"raw\" pixel values.", "count");
216 _abs = schema.addField<double>(
217 schema.join(name, "abs"),
218 "Measure of how much the flux is affected by neighbors: "
219 "(1 - child_instFlux/parent_instFlux). "
220 "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value. "
221 "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.");
222 _instFluxChildAbs = schema.addField<double>(
223 schema.join(name, "abs_child_instFlux"),
224 "Instrumental flux of the child, measured with a Gaussian weight matched to the child. "
225 "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value. "
226 "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.", "count");
227 _instFluxParentAbs = schema.addField<double>(
228 schema.join(name, "abs_parent_instFlux"),
229 "Instrumental flux of the parent, measured with a Gaussian weight matched to the child. "
230 "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value. "
231 "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.", "count");
232 }
233 if (_ctrl.doShape) {
234 _shapeChildRaw = ShapeResultKey::addFields(
235 schema, schema.join(name, "raw_child"),
236 "Shape of the child, measured with a Gaussian weight matched to the child. "
237 "Operates on the \"raw\" pixel values.", NO_UNCERTAINTY);
238 _shapeParentRaw = ShapeResultKey::addFields(
239 schema, schema.join(name, "raw_parent"),
240 "Shape of the parent, measured with a Gaussian weight matched to the child. "
241 "Operates on the \"raw\" pixel values.", NO_UNCERTAINTY);
242 _shapeChildAbs = ShapeResultKey::addFields(
243 schema, schema.join(name, "abs_child"),
244 "Shape of the child, measured with a Gaussian weight matched to the child. "
245 "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value. "
246 "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.",
248 _shapeParentAbs = ShapeResultKey::addFields(
249 schema, schema.join(name, "abs_parent"),
250 "Shape of the parent, measured with a Gaussian weight matched to the child. "
251 "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value. "
252 "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.",
254 }
255 if (_ctrl.doShape || _ctrl.doFlux) {
256 _flagHandler = FlagHandler::addFields(schema, name, getFlagDefinitions());
257 }
258}
static FlagDefinitionList const & getFlagDefinitions()
bool doOld
"Whether to compute HeavyFootprint dot products (the old deblend.blendedness parameter)" ;
Definition Blendedness.h:44
bool doShape
"Whether to compute quantities related to the Gaussian-weighted shape" ;
Definition Blendedness.h:48
bool doFlux
"Whether to compute quantities related to the Gaussian-weighted flux" ;
Definition Blendedness.h:46
static FlagHandler addFields(afw::table::Schema &schema, std::string const &prefix, FlagDefinitionList const &flagDefs, FlagDefinitionList const &exclDefs=FlagDefinitionList::getEmptyList())
Add Flag fields to a schema, creating a FlagHandler object to manage them.
static ShapeResultKey addFields(afw::table::Schema &schema, std::string const &name, std::string const &doc, UncertaintyEnum uncertainty, afw::table::CoordinateType coordType=afw::table::CoordinateType::PIXEL)
Add the appropriate fields to a Schema, and return a ShapeResultKey that manages them.
@ NO_UNCERTAINTY
Algorithm provides no uncertainy information at all.
Definition constants.h:44

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.

270 {
271 return (std::sqrt(2.0f * variance / boost::math::constants::pi<float>()) *
272 std::exp(-0.5f * (mu * mu) / variance)) -
273 mu * std::erfc(mu / std::sqrt(2.0f * variance));
274}
afw::table::Key< afw::table::Array< VariancePixelT > > variance
T erfc(T... args)
T exp(T... args)
T sqrt(T... args)

◆ 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.

260 {
261 float normalization = 0.5f * std::erfc(-data / std::sqrt(2.0f * variance));
262 if (!(normalization > 0)) {
263 // avoid division by zero; we know the limit at data << -sigma -> 0.
264 return 0.0;
265 }
266 return data + (std::sqrt(0.5f * variance / boost::math::constants::pi<float>()) *
267 std::exp(-0.5f * (data * data) / variance) / normalization);
268}
char * data
Definition BaseRecord.cc:61

◆ 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.

123{}

◆ getFlagDefinitions()

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

Definition at line 49 of file Blendedness.cc.

49{ return flagDefinitions; }

◆ getLogName()

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

Definition at line 66 of file Algorithm.h.

66{ return _logName; }

◆ 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.

121 {}

◆ 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.

347 {
348 _measureMoments(image, child, _instFluxChildRaw, _instFluxChildAbs, _shapeChildRaw, _shapeChildAbs);
349}

◆ measureForced()

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
inlineoverridevirtualinherited

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.

Reimplemented in lsst::meas::extensions::photometryKron::KronFluxAlgorithm.

Definition at line 172 of file Algorithm.h.

175 {
176 measure(measRecord, exposure);
177 }
virtual void measure(afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure) const =0
Called to measure a single child source in an image.

◆ 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.

32 {
33 throw LSST_EXCEPT(pex::exceptions::LogicError, "measureN not implemented for this algorithm");
34}
#define LSST_EXCEPT(type,...)
Create an exception with a given type.
Definition Exception.h:48

◆ measureNForced()

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
inlineoverridevirtualinherited

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.

182 {
183 measureN(measCat, exposure);
184 }
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.
Definition Algorithm.cc:31

◆ 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.

352 {
353 if (_ctrl.doOld) {
354 child.set(_old, computeOldBlendedness(child.getFootprint(), *image.getImage()));
355 }
356 _measureMoments(image, child, _instFluxParentRaw, _instFluxParentAbs, _shapeParentRaw, _shapeParentAbs);
357 if (_ctrl.doFlux) {
358 child.set(_raw, 1.0 - child.get(_instFluxChildRaw) / child.get(_instFluxParentRaw));
359 child.set(_abs, 1.0 - child.get(_instFluxChildAbs) / child.get(_instFluxParentAbs));
360 if (child.get(_instFluxParentAbs) == 0.0) {
361 // We can get NaNs in the absolute measure if both parent and child have only negative
362 // biased-corrected instFluxes (which we clip to zero). We can't really recover from this,
363 // so we should set the flag.
364 _flagHandler.setValue(child, FAILURE.number, true);
365 }
366 }
367}
static FlagDefinition const FAILURE
Definition Blendedness.h:70
void setValue(afw::table::BaseRecord &record, std::size_t i, bool value) const
Set the flag field corresponding to the given flag index.

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: