HigherOrderMomentsPSFPlugin

class lsst.meas.extensions.shapeHSM.HigherOrderMomentsPSFPlugin(config, name, schema, metadata, logName=None)

Bases: HigherOrderMomentsPlugin

Plugin for Higher Order Moments measurement of PSF models.

The moments are measured in normalized coordinates, where the normalized x axis is along the major axis and the normalized y axis along the minor. The moments are dependent only on the light profile, and does not scale with the size or orientation of the object.

For any well-sampled image, the zeroth order moment is 1, the first order moments are 0, and the second order moments are 0.5 for xx and yy and 0 for xy. For a symmetric profile, the moments are zeros if either of the indices is odd.

Notes

This plugin requires the ext_shapeHSM_HsmPsfMoments plugin to be enabled in order to measure the higher order moments, and raises a FatalAlgorithmError otherwise. The weight function is parametrized by the shape measured from ext_shapeHSM_HsmPsfMoments but for efficiency reasons, uses the slot centroid to evaluate the PSF model.

The only known failure mode of this plugin is if ext_shapeHSM_HsmPsfMoments measurement failed. The flags of that plugin are informative here as well and should be used to filter out unreliable measurements.

Methods Summary

measure(record, exposure)

Measure the properties of a source on a single image.

Methods Documentation

measure(record, exposure)

Measure the properties of a source on a single image.

The image may be from a single epoch, or it may be a coadd.

Parameters

measRecordlsst.afw.table.SourceRecord

Record describing the object being measured. Previously-measured quantities may be retrieved from here, and it will be updated in-place tih the outputs of this plugin.

exposurelsst.afw.image.ExposureF

The pixel data to be measured, together with the associated PSF, WCS, etc. All other sources in the image should have been replaced by noise according to deblender outputs.