FitSipDistortionTask

class lsst.meas.astrom.FitSipDistortionTask(**kwargs)

Bases: Task

Fit a TAN-SIP WCS given a list of reference object/source matches.

Methods Summary

display(revFitter[, exposure, bbox, frame, ...])	Display positions and outlier status overlaid on an image.
fitWcs(matches, initWcs[, bbox, refCat, ...])	Fit a TAN-SIP WCS from a list of reference object/source matches.
makeInitialWcs(matches, wcs)	Generate a guess Wcs from the astrometric matches

Methods Documentation

display(revFitter, exposure=None, bbox=None, frame=0, pause=True)

Display positions and outlier status overlaid on an image.

This method is called by fitWcs when display debugging is enabled. It always drops into pdb before returning to allow interactive inspection, and hence it should never be called in non-interactive contexts.

Parameters

revFitterlsst::meas::astrom::ScaledPolynomialTransformFitter

Fitter object initialized with fromMatches for fitting a “reverse” distortion: the mapping from intermediate world coordinates to pixels.

exposurelsst::afw::image::Exposure

An Exposure or other displayable image on which matches can be overplotted.

bboxlsst::afw::geom::Box2I

Bounding box of the region on which matches should be plotted.

fitWcs(matches, initWcs, bbox=None, refCat=None, sourceCat=None, exposure=None)

Fit a TAN-SIP WCS from a list of reference object/source matches.

Parameters

matcheslist of lsst.afw.table.ReferenceMatch

A sequence of reference object/source matches. The following fields are read: - match.first (reference object) coord - match.second (source) centroid

The following fields are written: - match.first (reference object) centroid - match.second (source) centroid - match.distance (on sky separation, in radians)

initWcslsst.afw.geom.SkyWcs

An initial WCS whose CD matrix is used as the final CD matrix.

bboxlsst.geom.Box2I

The region over which the WCS will be valid (PARENT pixel coordinates); if None or an empty box then computed from matches

refCatlsst.afw.table.SimpleCatalog

Reference object catalog, or None. If provided then all centroids are updated with the new WCS, otherwise only the centroids for ref objects in matches are updated. Required fields are “centroid_x”, “centroid_y”, “coord_ra”, and “coord_dec”.

sourceCatlsst.afw.table.SourceCatalog

Source catalog, or None. If provided then coords are updated with the new WCS; otherwise only the coords for sources in matches are updated. Required input fields are “slot_Centroid_x”, “slot_Centroid_y”, “slot_Centroid_xErr”, “slot_Centroid_yErr”, and optionally “slot_Centroid_x_y_Cov”. The “coord_ra” and “coord_dec” fields will be updated but are not used as input.

exposurelsst.afw.image.Exposure

An Exposure or other displayable image on which matches can be overplotted. Ignored (and may be None) if display-based debugging is not enabled via lsstDebug.

Returns

An lsst.pipe.base.Struct with the following fields:

• wcslsst.afw.geom.SkyWcs

  The best-fit WCS.

• scatterOnSkylsst.geom.Angle

  The median on-sky separation between reference objects and sources in “matches”, as an lsst.geom.Angle

makeInitialWcs(matches, wcs)

Generate a guess Wcs from the astrometric matches

We create a Wcs anchored at the center of the matches, with the scale of the input Wcs. This is necessary because the Wcs may have a very approximation position (as is common with telescoped-generated Wcs). We’re using the best of each: positions from the matches, and scale from the input Wcs.

Parameters

matcheslist of lsst::afw::table::ReferenceMatch

A sequence of reference object/source matches. The following fields are read:

• match.first (reference object) coord

• match.second (source) centroid

wcslsst::afw::geom::SkyWcs

An initial WCS whose CD matrix is used as the CD matrix of the result.

Returns

newWcslsst.afw.geom.SkyWcs

A new WCS guess.