Class SdssShapeAlgorithm

Inheritance Relationships

Base Type

Class Documentation

class SdssShapeAlgorithm : public lsst::meas::base::SimpleAlgorithm

Measure the image moments of source using adaptive Gaussian weights.

This algorithm measures the weighted second moments of an image using a Gaussian weight function, which is iteratively updated to match the current weights. If this iteration does not converge, it can fall back to using unweighted moments, which can be significantly noisier.

See Bernstein & Jarvis, 2002, for more information on this type of algorithm. Note that the code here makes no attempt to correct for the PSF; for PSF corrected ellipticities using weighted moments please use the shapeHSM package.

Public Types

typedef SdssShapeControl Control
typedef SdssShapeResult Result
typedef SdssShapeResultKey ResultKey

Public Functions

SdssShapeAlgorithm(Control const &ctrl, std::string const &name, afw::table::Schema &schema)
virtual void measure(afw::table::SourceRecord &measRecord, afw::image::Exposure<float> const &exposure) const

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.

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.

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.

Public Static Functions

static FlagDefinitionList const &getFlagDefinitions()
template<typename ImageT>
static Result computeAdaptiveMoments(ImageT const &image, geom::Point2D const &position, bool negative = false, Control const &ctrl = Control())

Compute the adaptive Gaussian-weighted moments of an image.

Parameters

  • [in] image: An Image or MaskedImage instance with int, float, or double pixels. This need not be a small postage stamp (the pixel region actually used in the fit will be a subset of this image determined automatically).

  • [in] position: Center position of the object to be measured, in the image’s PARENT coordinates.

  • [in] negative: Boolean, specify if the source is in negative instFlux space

  • [in] ctrl: Control object specifying the details of how the object is to be measured.

template<typename ImageT>
static FluxResult computeFixedMomentsFlux(ImageT const &image, afw::geom::ellipses::Quadrupole const &shape, geom::Point2D const &position)

Compute the instFlux within a fixed Gaussian aperture.

Parameters

  • [in] image: An Image or MaskedImage instance with int, float, or double pixels. This need not be a small postage stamp (the pixel region actually used in the fit will be a subset of this image determined automatically).

  • [in] shape: Ellipse object specifying the 1-sigma contour of the Gaussian.

  • [in] position: Center position of the object to be measured, in the image’s PARENT coordinates.

Public Static Attributes

unsigned int const N_FLAGS = 6
FlagDefinition const FAILURE
FlagDefinition const UNWEIGHTED_BAD
FlagDefinition const UNWEIGHTED
FlagDefinition const SHIFT
FlagDefinition const MAXITER
FlagDefinition const PSF_SHAPE_BAD