approximateWcs

lsst.meas.astrom.approximateWcs(wcs, bbox, order=3, nx=20, ny=20, iterations=3, skyTolerance=4.84814e-09 rad, pixelTolerance=0.02, useTanWcs=False)

Approximate an existing WCS as a TAN-SIP WCS

The fit is performed by evaluating the WCS at a uniform grid of points within a bounding box.

Parameters:
wcs : lsst.afw.geom.SkyWcs

wcs to approximate

bbox : lsst.geom.Box2I

the region over which the WCS will be fit

order : int

order of SIP fit

nx : int

number of grid points along x

ny : int

number of grid points along y

iterations : int

number of times to iterate over fitting

skyTolerance : lsst.geom.Angle

maximum allowed difference in world coordinates between input wcs and approximate wcs (default is 0.001 arcsec)

pixelTolerance : float

maximum allowed difference in pixel coordinates between input wcs and approximate wcs (default is 0.02 pixels)

useTanWcs : bool

send a TAN version of wcs to the fitter? It is documented to require that, but I don’t think the fitter actually cares

Returns:
fitWcs : lsst.afw.geom.SkyWcs

the fit TAN-SIP WCS