lsst::meas::base::PsfFluxAlgorithm Class Reference

A measurement algorithm that estimates instFlux using a linear least-squares fit with the Psf model. More...

#include <PsfFlux.h>

Inheritance diagram for lsst::meas::base::PsfFluxAlgorithm:

Public Types
typedef PsfFluxControl	Control
	A typedef to the Control object for this algorithm, defined above.

Public Member Functions
	PsfFluxAlgorithm (Control const &ctrl, std::string const &name, afw::table::Schema &schema, std::string const &logName="")
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 Public Attributes
static FlagDefinition const	FAILURE = flagDefinitions.addFailureFlag()
static FlagDefinition const	NO_GOOD_PIXELS
static FlagDefinition const	EDGE

Protected Attributes
std::string	_logName

Detailed Description

A measurement algorithm that estimates instFlux using a linear least-squares fit with the Psf model.

The PsfFlux algorithm is extremely simple: we do a least-squares fit of the Psf model (evaluated at a given position) to the data. For point sources, this provides the optimal instFlux measurement in the limit where the Psf model is correct. We do not use per-pixel weights in the fit, as this results in bright stars being fit with a different effective profile than faint stairs.

Definition at line 69 of file PsfFlux.h.

Member Typedef Documentation

Control

typedef PsfFluxControl lsst::meas::base::PsfFluxAlgorithm::Control

A typedef to the Control object for this algorithm, defined above.

The control object contains the configuration parameters for this algorithm.

Definition at line 79 of file PsfFlux.h.

Constructor & Destructor Documentation

PsfFluxAlgorithm()

lsst::meas::base::PsfFluxAlgorithm::PsfFluxAlgorithm	(	Control const &	ctrl,
		std::string const &	name,
		afw::table::Schema &	schema,
		std::string const &	logName = "" )

Definition at line 53 of file PsfFlux.cc.

        : _ctrl(ctrl),
          _instFluxResultKey(FluxResultKey::addFields(
                  schema, name, "instFlux derived from linear least-squares fit of PSF model")),
          _areaKey(schema.addField<float>(name + "_area", "effective area of PSF", "pixel")),
          _chi2Key(schema.addField<float>(name + "_chi2", "chi2 of the fitted PSF")),
          _npixelsKey(schema.addField<int>(name + "_npixels",
                                           "number of pixels that were included in the PSF fit", "pixel")),
          _centroidExtractor(schema, name) {
    _logName = logName.size() ? logName : name;
    _flagHandler = FlagHandler::addFields(schema, name, getFlagDefinitions());
}

Member Function Documentation

fail()

void lsst::meas::base::PsfFluxAlgorithm::fail ( afw::table::SourceRecord & measRecord, MeasurementError * error = nullptr ) const

virtual

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 129 of file PsfFlux.cc.

                                                                                           {
    _flagHandler.handleFailure(measRecord, error);
}

getFlagDefinitions()

FlagDefinitionList const & lsst::meas::base::PsfFluxAlgorithm::getFlagDefinitions ( )

static

Definition at line 49 of file PsfFlux.cc.

{ return flagDefinitions; }

getLogName()

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

inlineinherited

Definition at line 66 of file Algorithm.h.

{ return _logName; }

measure()

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

virtual

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 67 of file PsfFlux.cc.

                                                                              {
    std::shared_ptr<afw::detection::Psf const> psf = exposure.getPsf();
    if (!psf) {
        LOGL_ERROR(getLogName(), "PsfFlux: no psf attached to exposure");
        throw LSST_EXCEPT(FatalAlgorithmError, "PsfFlux algorithm requires a Psf with every exposure");
    }
    geom::Point2D position = _centroidExtractor(measRecord, _flagHandler);
    std::shared_ptr<afw::detection::Psf::Image> psfImage = psf->computeImage(position);
    geom::Box2I fitBBox = psfImage->getBBox();
    fitBBox.clip(exposure.getBBox());
    if (fitBBox != psfImage->getBBox()) {
        _flagHandler.setValue(measRecord, FAILURE.number,
                              true);  // if we had a suspect flag, we'd set that instead
        _flagHandler.setValue(measRecord, EDGE.number, true);
    }
    auto fitRegionSpans = std::make_shared<afw::geom::SpanSet>(fitBBox);
    afw::detection::Footprint fitRegion(fitRegionSpans);
    if (!_ctrl.badMaskPlanes.empty()) {
        afw::image::MaskPixel badBits = 0x0;
        for (std::vector<std::string>::const_iterator i = _ctrl.badMaskPlanes.begin();
             i != _ctrl.badMaskPlanes.end(); ++i) {
            badBits |= exposure.getMaskedImage().getMask()->getPlaneBitMask(*i);
        }
        fitRegion.setSpans(fitRegion.getSpans()
                                   ->intersectNot(*exposure.getMaskedImage().getMask(), badBits)
                                   ->clippedTo(exposure.getMaskedImage().getMask()->getBBox()));
    }
    if (fitRegion.getArea() == 0) {
        _flagHandler.setValue(measRecord, NO_GOOD_PIXELS.number, true);
        _flagHandler.setValue(measRecord, FAILURE.number, true);
        return;
    }
    typedef afw::detection::Psf::Pixel PsfPixel;
    // SpanSet::flatten returns a new ndarray::Array, which must stay in scope
    // while we use an Eigen::Map view of it
    auto modelNdArray = fitRegion.getSpans()->flatten(psfImage->getArray(), psfImage->getXY0());
    auto dataNdArray = fitRegion.getSpans()->flatten(exposure.getMaskedImage().getImage()->getArray(),
                                                     exposure.getXY0());
    auto varianceNdArray = fitRegion.getSpans()->flatten(exposure.getMaskedImage().getVariance()->getArray(),
                                                         exposure.getXY0());
    auto model = ndarray::asEigenMatrix(modelNdArray);
    auto data = ndarray::asEigenMatrix(dataNdArray);
    auto variance = ndarray::asEigenMatrix(varianceNdArray);
    PsfPixel alpha = model.squaredNorm();
    FluxResult result;
    result.instFlux = model.dot(data.cast<PsfPixel>()) / alpha;
    // If we're not using per-pixel weights to compute the instFlux, we'll still want to compute the
    // variance as if we had, so we'll apply the weights to the model now, and update alpha.
    result.instFluxErr = std::sqrt(model.array().square().matrix().dot(variance.cast<PsfPixel>())) / alpha;
    measRecord.set(_areaKey, model.sum() / alpha);
    measRecord.set(_npixelsKey, fitRegion.getSpans()->getArea());
    if (!std::isfinite(result.instFlux) || !std::isfinite(result.instFluxErr)) {
        throw LSST_EXCEPT(PixelValueError, "Invalid pixel value detected in image.");
    }
    measRecord.set(_instFluxResultKey, result);
    auto chi2 = ((data.cast<PsfPixel>() - result.instFlux * model).array().square() /
                 variance.cast<PsfPixel>().array())
                        .sum();
    measRecord.set(_chi2Key, chi2);
}

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.

                                                                           {
        measure(measRecord, exposure);
    }

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.

                                                                                   {
    throw LSST_EXCEPT(pex::exceptions::LogicError, "measureN not implemented for this algorithm");
}

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.

                                                                            {
        measureN(measCat, exposure);
    }

Member Data Documentation

_logName

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

protectedinherited

Definition at line 69 of file Algorithm.h.

EDGE

FlagDefinition const lsst::meas::base::PsfFluxAlgorithm::EDGE

static

Initial value:

= flagDefinitions.add(
        "flag_edge", "object was too close to the edge of the image to use the full PSF model")

Definition at line 75 of file PsfFlux.h.

FAILURE

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

static

Definition at line 73 of file PsfFlux.h.

NO_GOOD_PIXELS

FlagDefinition const lsst::meas::base::PsfFluxAlgorithm::NO_GOOD_PIXELS

static

Initial value:

=
        flagDefinitions.add("flag_noGoodPixels", "not enough non-rejected pixels in data to attempt the fit")

Definition at line 74 of file PsfFlux.h.

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

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-8.0.0/Linux64/meas_base/g48712c4677+3bf1020dcb/include/lsst/meas/base/PsfFlux.h
• /j/snowflake/release/lsstsw/stack/lsst-scipipe-8.0.0/Linux64/meas_base/g48712c4677+3bf1020dcb/src/PsfFlux.cc