wcsUtilsContinued.py

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#
# LSST Data Management System
# Copyright 2017 LSST Corporation.
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__all__ = ["getSipMatrixFromMetadata", "computePixelToDistortedPixel"]
 
import lsst.geom
from ..transformFactory import linearizeTransform, makeTransform
from .wcsUtils import _getSipMatrixFromMetadata
 
 
def getSipMatrixFromMetadata(metadata, name):
    """Extract a SIP matrix from FITS TAN-SIP WCS metadata.
 
    Omitted coefficients are set to 0 and all coefficients may be omitted.
 
    Parameters
    ----------
    metadata : `lsst.daf.base.PropertySet`
        FITS metadata.
    name : `str`
        Name of TAN-SIP matrix (``"A"``, ``"B"``, ``"Ap"``, or ``"Bp"``).
 
    Returns
    -------
    `numpy.array`
        The SIP matrix.
 
    Raises
    ------
    TypeError
        If the order keyword ``<name>_ORDER`` (e.g. ``AP_ORDER``) is not found,
        the value of the order keyword cannot be read as an integer,
        the value of the order keyword is negative,
        or if a matrix parameter (e.g. ``AP_5_0``) cannot be read as a float.
    """
    arr = _getSipMatrixFromMetadata(metadata, name)
    if arr.shape == ():  # order=0
        arr.shape = (1, 1)
    return arr
 
 
def computePixelToDistortedPixel(pixelToFocalPlane, focalPlaneToFieldAngle):
    """Compute the transform ``pixelToDistortedPixel``, which applies optical
    distortion specified by ``focalPlaneToFieldAngle``.
 
    The resulting transform is designed to be used to convert a pure TAN WCS
    to a WCS that includes a model for optical distortion. In detail,
    the initial WCS will contain these frames and transforms::
 
        PIXELS frame -> pixelToIwc -> IWC frame ->  gridToIwc -> SkyFrame
 
    To produce the WCS with distortion, replace ``pixelToIwc`` with::
 
        pixelToDistortedPixel -> pixelToIwc
 
    Parameters
    ----------
    pixelToFocalPlane : `lsst.afw.geom.TransformPoint2ToPoint2`
        Transform parent pixel coordinates to focal plane coordinates
    focalPlaneToFieldAngle : `lsst.afw.geom.TransformPoint2ToPoint2`
        Transform focal plane coordinates to field angle coordinates
 
    Returns
    -------
    pixelToDistortedPixel : `lsst.afw.geom.TransformPoint2ToPoint2`
        A transform that applies the effect of the optical distortion model.
    """
    # return pixelToFocalPlane -> focalPlaneToFieldAngle -> tanFieldAngleToocalPlane -> focalPlaneToPixel
    focalPlaneToTanFieldAngle = makeTransform(linearizeTransform(focalPlaneToFieldAngle,
                                                                 lsst.geom.Point2D(0, 0)))
    return pixelToFocalPlane.then(focalPlaneToFieldAngle) \
        .then(focalPlaneToTanFieldAngle.inverted()) \
        .then(pixelToFocalPlane.inverted())