makePixelToTanPixel.py

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# This file is part of afw.
#
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__all__ = ["makePixelToTanPixel"]
 
import lsst.geom
import lsst.afw.geom
 
 
def makePixelToTanPixel(bbox, orientation, focalPlaneToField, pixelSizeMm):
    """Make a Transform whose forward direction converts PIXELS to TAN_PIXELS
    for one detector.
 
    Parameters
    ----------
    bbox : `lsst.geom.Box2I`
        Detector bounding box.
    orientation : `lsst.afw.cameraGeom.Orientation`
        Orientation of detector in focal plane.
    focalPlaneToField : `lsst.afw.geom.TransformPoint2ToPoint2`
        A transform that converts from focal plane (mm) to field angle
        coordinates (radians) in the forward direction.
    pixelSizeMm : `lsst.geom.Extent2D`
        Size of the pixel in mm in X and Y.
 
    Returns
    -------
    transform : `lsst.afw.geom.TransformPoint2ToPoint2`
        A transform whose forward direction converts PIXELS to TAN_PIXELS.
 
    Notes
    -----
    PIXELS and TAN_PIXELS are described in the CameraGeom documentation under
    :ref:`camera coordinate systems<section_Camera_Coordinate_Systems>`.
    """
    pixelToFocalPlane = orientation.makePixelFpTransform(pixelSizeMm)
    pixelToField = pixelToFocalPlane.then(focalPlaneToField)
    # fieldToTanPix is affine and matches fieldToPix at field center
    # Note: focal plane to field angle is typically a radial transform,
    # and linearizing the inverse transform of that may fail,
    # so linearize the forward direction instead. (pixelToField is pixelToFocalPlane,
    # an affine transform, followed by focalPlaneToField,
    # so the same consideration applies to pixelToField)
    pixAtFieldCtr = pixelToField.applyInverse(lsst.geom.Point2D(0, 0))
    tanPixToFieldAffine = lsst.afw.geom.linearizeTransform(pixelToField, pixAtFieldCtr)
    fieldToTanPix = lsst.afw.geom.makeTransform(tanPixToFieldAffine.inverted())
 
    return pixelToField.then(fieldToTanPix)