FitTanSipWcsTask

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

Processing summary

Measure the distortions in an image plane and express them a SIP polynomials.

Given a list of matching sources between a catalog and an image, and a linear Wcs that describes the mapping from pixel space in the image and ra/dec space in the catalog, calculate discrepancies between the two and compute SIP distortion polynomials to describe the discrepancy.

SIP polynomials are defined in Shupe at al. (2005) ASPC 347 491.

Note that the SIP standard insists (although it is only mentioned obliquely between Eqns 3 and 4) that the lowest three terms in the distortion polynomials be zero (A00, A10, A01, B00, etc.). To achieve this, we need to adjust the values of CD and CRPIX from the input wcs. This may not be the behavior you expect.

Python API summary

Retargetable subtasks

Configuration fields

Examples

See :lsst-task:`lsst.pipe.tasks.photoCal.PhotoCalTask` .. note:: Pipe task will require conversion before this link is usable.

Debugging

FitTanSipWcsTask does not support any debug variables.