FitAffineWcsTask#

class lsst.meas.astrom.FitAffineWcsTask(config: Config | None = None, *, name: str | None = None, parentTask: Task | None = None, log: logging.Logger | lsst.utils.logging.LsstLogAdapter | None = None)#

Bases: Task

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

This WCS fitter should be used on top of a cameraGeom distortion model as the model assumes that only a shift the WCS center position and a small affine transform are required.

Methods Summary

fitWcs(matches, initWcs[, bbox, refCat, ...])

Fit a simple Affine transform with a shift to the matches and update the WCS.

Methods Documentation

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

Fit a simple Affine transform with a shift to the matches and update the WCS.

This method assumes that the distortion model of the telescope is applied correctly and is accurate with only a slight rotation, rotation, and “squish” required to fit to the reference locations.

Parameters#

matcheslist of lsst.afw.table.ReferenceMatch

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

initial WCS

bboxlsst.geom.Box2I

Ignored; present for consistency with FitSipDistortionTask.

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 fields are “slot_Centroid_x”, “slot_Centroid_y”, and “coord_ra”, and “coord_dec”.

exposurelsst.afw.image.Exposure

Ignored; present for consistency with FitSipDistortionTask.

Returns#

resultlsst.pipe.base.Struct

with the following fields:

  • wcs : the fit WCS (lsst.afw.geom.SkyWcs)

  • scatterOnSky : median on-sky separation between reference objects and sources in “matches” (lsst.afw.geom.Angle)