makeSipIwcToPixel¶
- lsst.afw.geom.testUtils.makeSipIwcToPixel(metadata)¶
Make an IWC to pixel 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 inverse SIP coefficients
- Returns:
- lsst.afw.geom.TransformPoint2ToPoint2
Transform from IWC position to pixel position (zero-based) in the forward direction. The inverse direction is not defined.
Notes
The inverse SIP terms APn_m, BPn_m are polynomial coefficients x^n y^m for computing transformed x, y respectively. If we call the resulting polynomial inverseSipPolynomial, the returned transformation is:
pixelPosition = pixel origin + uv + inverseSipPolynomial(uv) where uv = inverseCdMatrix * iwcPosition