makeSipPixelToIwc

lsst.afw.geom.testUtils.makeSipPixelToIwc(metadata)

Make a pixel to IWC transform with SIP distortion from FITS-WCS metadata

This function is primarily intended for unit tests. IWC is intermediate world coordinates, as described in the FITS papers.

Parameters:

metadatalsst.daf.base.PropertySet

FITS metadata describing a WCS with forward SIP coefficients

Returns:

lsst.afw.geom.TransformPoint2ToPoint2

Transform from pixel position (zero-based) to IWC position in the forward direction. The inverse direction is not defined.

Notes

The forward SIP terms An_m, Bn_m are polynomial coefficients x^n y^m for computing transformed x, y respectively. If we call the resulting polynomial sipPolynomial, the returned transformation is:

iwcPosition = cdMatrix * (dxy + sipPolynomial(dxy)) where dxy = pixelPosition - pixelOrigin