lsst.ip.diffim.dcrModel Namespace Reference

Classes
class	DcrModel

Functions
def	applyDcr (image, dcr, useInverse=False, splitSubfilters=False, kwargs)
def	calculateDcr (visitInfo, wcs, filterInfo, dcrNumSubfilters, splitSubfilters=False)
def	calculateImageParallacticAngle (visitInfo, wcs)
def	wavelengthGenerator (filterInfo, dcrNumSubfilters)

Function Documentation

applyDcr()

def lsst.ip.diffim.dcrModel.applyDcr	(		image,
			dcr,
			useInverse = False,
			splitSubfilters = False,
			kwargs
	)

Shift an image along the X and Y directions.

Parameters
----------
image : `numpy.ndarray`
    The input image to shift.
dcr : `tuple`
    Shift calculated with ``calculateDcr``.
    Uses numpy axes ordering (Y, X).
    If ``splitSubfilters`` is set, each element is itself a `tuple`
    of two `float`, corresponding to the DCR shift at the two wavelengths.
    Otherwise, each element is a `float` corresponding to the DCR shift at
    the effective wavelength of the subfilter.
useInverse : `bool`, optional
    Apply the shift in the opposite direction. Default: False
splitSubfilters : `bool`, optional
    Calculate DCR for two evenly-spaced wavelengths in each subfilter,
    instead of at the midpoint. Default: False
kwargs
    Additional keyword parameters to pass in to
    `scipy.ndimage.interpolation.shift`

Returns
-------
shiftedImage : `numpy.ndarray`
    A copy of the input image with the specified shift applied.

Definition at line 582 of file dcrModel.py.

def applyDcr(image, dcr, useInverse=False, splitSubfilters=False, **kwargs):
    """Shift an image along the X and Y directions.

    Parameters
    ----------
    image : `numpy.ndarray`
        The input image to shift.
    dcr : `tuple`
        Shift calculated with ``calculateDcr``.
        Uses numpy axes ordering (Y, X).
        If ``splitSubfilters`` is set, each element is itself a `tuple`
        of two `float`, corresponding to the DCR shift at the two wavelengths.
        Otherwise, each element is a `float` corresponding to the DCR shift at
        the effective wavelength of the subfilter.
    useInverse : `bool`, optional
        Apply the shift in the opposite direction. Default: False
    splitSubfilters : `bool`, optional
        Calculate DCR for two evenly-spaced wavelengths in each subfilter,
        instead of at the midpoint. Default: False
    kwargs
        Additional keyword parameters to pass in to
        `scipy.ndimage.interpolation.shift`

    Returns
    -------
    shiftedImage : `numpy.ndarray`
        A copy of the input image with the specified shift applied.
    """
    if splitSubfilters:
        if useInverse:
            shift = [-1.*s for s in dcr[0]]
            shift1 = [-1.*s for s in dcr[1]]
        else:
            shift = dcr[0]
            shift1 = dcr[1]
        shiftedImage = ndimage.interpolation.shift(image, shift, **kwargs)
        shiftedImage += ndimage.interpolation.shift(image, shift1, **kwargs)
        shiftedImage /= 2.
    else:
        if useInverse:
            shift = [-1.*s for s in dcr]
        else:
            shift = dcr
        shiftedImage = ndimage.interpolation.shift(image, shift, **kwargs)
    return shiftedImage

calculateDcr()

def lsst.ip.diffim.dcrModel.calculateDcr	(		visitInfo,
			wcs,
			filterInfo,
			dcrNumSubfilters,
			splitSubfilters = False
	)

Calculate the shift in pixels of an exposure due to DCR.

Parameters
----------
visitInfo : `lsst.afw.image.VisitInfo`
    Metadata for the exposure.
wcs : `lsst.afw.geom.SkyWcs`
    Coordinate system definition (wcs) for the exposure.
filterInfo : `lsst.afw.image.Filter`
    The filter definition, set in the current instruments' obs package.
dcrNumSubfilters : `int`
    Number of sub-filters used to model chromatic effects within a band.
splitSubfilters : `bool`, optional
    Calculate DCR for two evenly-spaced wavelengths in each subfilter,
    instead of at the midpoint. Default: False

Returns
-------
dcrShift : `tuple` of two `float`
    The 2D shift due to DCR, in pixels.
    Uses numpy axes ordering (Y, X).

Definition at line 629 of file dcrModel.py.

def calculateDcr(visitInfo, wcs, filterInfo, dcrNumSubfilters, splitSubfilters=False):
    """Calculate the shift in pixels of an exposure due to DCR.

    Parameters
    ----------
    visitInfo : `lsst.afw.image.VisitInfo`
        Metadata for the exposure.
    wcs : `lsst.afw.geom.SkyWcs`
        Coordinate system definition (wcs) for the exposure.
    filterInfo : `lsst.afw.image.Filter`
        The filter definition, set in the current instruments' obs package.
    dcrNumSubfilters : `int`
        Number of sub-filters used to model chromatic effects within a band.
    splitSubfilters : `bool`, optional
        Calculate DCR for two evenly-spaced wavelengths in each subfilter,
        instead of at the midpoint. Default: False

    Returns
    -------
    dcrShift : `tuple` of two `float`
        The 2D shift due to DCR, in pixels.
        Uses numpy axes ordering (Y, X).
    """
    rotation = calculateImageParallacticAngle(visitInfo, wcs)
    dcrShift = []
    weight = [0.75, 0.25]
    lambdaEff = filterInfo.getFilterProperty().getLambdaEff()
    for wl0, wl1 in wavelengthGenerator(filterInfo, dcrNumSubfilters):
        # Note that diffRefractAmp can be negative, since it's relative to the midpoint of the full band
        diffRefractAmp0 = differentialRefraction(wavelength=wl0, wavelengthRef=lambdaEff,
                                                 elevation=visitInfo.getBoresightAzAlt().getLatitude(),
                                                 observatory=visitInfo.getObservatory(),
                                                 weather=visitInfo.getWeather())
        diffRefractAmp1 = differentialRefraction(wavelength=wl1, wavelengthRef=lambdaEff,
                                                 elevation=visitInfo.getBoresightAzAlt().getLatitude(),
                                                 observatory=visitInfo.getObservatory(),
                                                 weather=visitInfo.getWeather())
        if splitSubfilters:
            diffRefractPix0 = diffRefractAmp0.asArcseconds()/wcs.getPixelScale().asArcseconds()
            diffRefractPix1 = diffRefractAmp1.asArcseconds()/wcs.getPixelScale().asArcseconds()
            diffRefractArr = [diffRefractPix0*weight[0] + diffRefractPix1*weight[1],
                              diffRefractPix0*weight[1] + diffRefractPix1*weight[0]]
            shiftX = [diffRefractPix*np.sin(rotation.asRadians()) for diffRefractPix in diffRefractArr]
            shiftY = [diffRefractPix*np.cos(rotation.asRadians()) for diffRefractPix in diffRefractArr]
            dcrShift.append(((shiftY[0], shiftX[0]), (shiftY[1], shiftX[1])))
        else:
            diffRefractAmp = (diffRefractAmp0 + diffRefractAmp1)/2.
            diffRefractPix = diffRefractAmp.asArcseconds()/wcs.getPixelScale().asArcseconds()
            shiftX = diffRefractPix*np.sin(rotation.asRadians())
            shiftY = diffRefractPix*np.cos(rotation.asRadians())
            dcrShift.append((shiftY, shiftX))
    return dcrShift

calculateImageParallacticAngle()

def lsst.ip.diffim.dcrModel.calculateImageParallacticAngle	(		visitInfo,
			wcs
	)

Calculate the total sky rotation angle of an exposure.

Parameters
----------
visitInfo : `lsst.afw.image.VisitInfo`
    Metadata for the exposure.
wcs : `lsst.afw.geom.SkyWcs`
    Coordinate system definition (wcs) for the exposure.

Returns
-------
`lsst.geom.Angle`
    The rotation of the image axis, East from North.
    Equal to the parallactic angle plus any additional rotation of the
    coordinate system.
    A rotation angle of 0 degrees is defined with
    North along the +y axis and East along the +x axis.
    A rotation angle of 90 degrees is defined with
    North along the +x axis and East along the -y axis.

Definition at line 683 of file dcrModel.py.

def calculateImageParallacticAngle(visitInfo, wcs):
    """Calculate the total sky rotation angle of an exposure.

    Parameters
    ----------
    visitInfo : `lsst.afw.image.VisitInfo`
        Metadata for the exposure.
    wcs : `lsst.afw.geom.SkyWcs`
        Coordinate system definition (wcs) for the exposure.

    Returns
    -------
    `lsst.geom.Angle`
        The rotation of the image axis, East from North.
        Equal to the parallactic angle plus any additional rotation of the
        coordinate system.
        A rotation angle of 0 degrees is defined with
        North along the +y axis and East along the +x axis.
        A rotation angle of 90 degrees is defined with
        North along the +x axis and East along the -y axis.
    """
    parAngle = visitInfo.getBoresightParAngle().asRadians()
    cd = wcs.getCdMatrix()
    if wcs.isFlipped:
        cdAngle = (np.arctan2(-cd[0, 1], cd[0, 0]) + np.arctan2(cd[1, 0], cd[1, 1]))/2.
    else:
        cdAngle = (np.arctan2(cd[0, 1], -cd[0, 0]) + np.arctan2(cd[1, 0], cd[1, 1]))/2.
    rotAngle = (cdAngle + parAngle)*radians
    return rotAngle

wavelengthGenerator()

def lsst.ip.diffim.dcrModel.wavelengthGenerator	(		filterInfo,
			dcrNumSubfilters
	)

Iterate over the wavelength endpoints of subfilters.

Parameters
----------
filterInfo : `lsst.afw.image.Filter`
    The filter definition, set in the current instruments' obs package.
dcrNumSubfilters : `int`
    Number of sub-filters used to model chromatic effects within a band.

Yields
------
`tuple` of two `float`
    The next set of wavelength endpoints for a subfilter, in nm.

Definition at line 714 of file dcrModel.py.

def wavelengthGenerator(filterInfo, dcrNumSubfilters):
    """Iterate over the wavelength endpoints of subfilters.

    Parameters
    ----------
    filterInfo : `lsst.afw.image.Filter`
        The filter definition, set in the current instruments' obs package.
    dcrNumSubfilters : `int`
        Number of sub-filters used to model chromatic effects within a band.

    Yields
    ------
    `tuple` of two `float`
        The next set of wavelength endpoints for a subfilter, in nm.
    """
    lambdaMin = filterInfo.getFilterProperty().getLambdaMin()
    lambdaMax = filterInfo.getFilterProperty().getLambdaMax()
    wlStep = (lambdaMax - lambdaMin)/dcrNumSubfilters
    for wl in np.linspace(lambdaMin, lambdaMax, dcrNumSubfilters, endpoint=False):
        yield (wl, wl + wlStep)

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