utils.py

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#
# LSST Data Management System
# Copyright 2017 AURA/LSST
#
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# LSST Project (http://www.lsst.org/).
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__all__ = ('InitialSkyWcsError', 'createInitialSkyWcs', 'bboxFromIraf')

import re
import lsst.geom as geom

from lsst.afw.cameraGeom import PIXELS, FIELD_ANGLE
from lsst.afw.image import RotType
from lsst.afw.geom.skyWcs import makeSkyWcs
import lsst.pex.exceptions


class InitialSkyWcsError(Exception):
    """For handling failures when creating a SkyWcs from a camera geometry and
    boresight.

    Typically used as a chained exception from a lower level exception.
    """
    pass


def createInitialSkyWcs(visitInfo, detector, flipX=False):
    """Create a SkyWcs from the telescope boresight and detector geometry.

    A typical usecase for this is to create the initial WCS for a newly-read
    raw exposure.


    Parameters
    ----------
    visitInfo : `lsst.afw.image.VisitInfo`
        Where to get the telescope boresight and rotator angle from.
    detector : `lsst.afw.cameraGeom.Detector`
        Where to get the camera geomtry from.
    flipX : `bool`, optional
        If False, +X is along W, if True +X is along E.

    Returns
    -------
    skyWcs : `lsst.afw.geom.SkyWcs`
        The new composed WCS.

    Raises
    ------
    InitialSkyWcsError
        Raised if there is an error generating the SkyWcs, chained from the
        lower-level exception if available.
    """
    if visitInfo.getRotType() != RotType.SKY:
        msg = (f"Cannot create SkyWcs from camera geometry: rotator angle defined using "
               f"RotType={visitInfo.getRotType()} instead of SKY.")
        raise InitialSkyWcsError(msg)
    orientation = visitInfo.getBoresightRotAngle()
    boresight = visitInfo.getBoresightRaDec()
    try:
        pixelsToFieldAngle = detector.getTransform(detector.makeCameraSys(PIXELS),
                                                   detector.makeCameraSys(FIELD_ANGLE))
    except lsst.pex.exceptions.InvalidParameterError as e:
        raise InitialSkyWcsError("Cannot compute PIXELS to FIELD_ANGLE Transform.") from e
    return makeSkyWcs(pixelsToFieldAngle, orientation, flipX, boresight)


def bboxFromIraf(irafBBoxStr):
    """Return a Box2I corresponding to an IRAF-style BBOX

    [x0:x1,y0:y1] where x0 and x1 are the one-indexed start and end columns, and correspondingly
    y0 and y1 are the start and end rows.
    """

    mat = re.search(r"^\[([-\d]+):([-\d]+),([-\d]+):([-\d]+)\]$", irafBBoxStr)
    if not mat:
        raise RuntimeError("Unable to parse IRAF-style bbox \"%s\"" % irafBBoxStr)
    x0, x1, y0, y1 = [int(_) for _ in mat.groups()]

    return geom.BoxI(geom.PointI(x0 - 1, y0 - 1), geom.PointI(x1 - 1, y1 - 1))