lsst.pipe.tasks.diffractionSpikeMask Namespace Reference

Classes
class	DiffractionSpikeMaskConfig
class	DiffractionSpikeMaskTask

Functions
	getRegion (exposure, margin=None)
	computePsfWidthFromMoments (psf, angle=0.)

Function Documentation

computePsfWidthFromMoments()

lsst.pipe.tasks.diffractionSpikeMask.computePsfWidthFromMoments	(		psf,
			angle = 0. )

Calculate the width of an elliptical PSF along a given direction.

Parameters
----------
psf : `lsst.afw.detection.Psf`
    The point spread function of the image.
angle : `float`, optional
    Rotation CCW from the +x axis to calculate the width of the PSF along.

Returns
-------
fwhm : `float`
    Full width at half maximum of the fitted shape of the PSF along the
    given `angle`. In pixels.

Definition at line 456 of file diffractionSpikeMask.py.

def computePsfWidthFromMoments(psf, angle=0.):
    """Calculate the width of an elliptical PSF along a given direction.
 
    Parameters
    ----------
    psf : `lsst.afw.detection.Psf`
        The point spread function of the image.
    angle : `float`, optional
        Rotation CCW from the +x axis to calculate the width of the PSF along.
 
    Returns
    -------
    fwhm : `float`
        Full width at half maximum of the fitted shape of the PSF along the
        given `angle`. In pixels.
    """
    psfShape = psf.computeShape(psf.getAveragePosition())
    c = np.cos(np.deg2rad(angle))
    s = np.sin(np.deg2rad(angle))
    sigma2 = c*c*psfShape.getIxx() + 2*c*s*psfShape.getIxy() + s*s*psfShape.getIyy()
    sigma = np.sqrt(max(sigma2, 0.0))   # rms width in pixels
 
    # 5) optional: Gaussian-equivalent FWHM along angle
    fwhm = 2.0 * np.sqrt(2.0 * np.log(2.0)) * sigma
    return fwhm

getRegion()

lsst.pipe.tasks.diffractionSpikeMask.getRegion	(		exposure,
			margin = None )

Calculate an enveloping region for an exposure.

Parameters
----------
exposure : `lsst.afw.image.Exposure`
    Exposure object with calibrated WCS.

Returns
-------
region : `lsst.sphgeom.Region`
    Region enveloping an exposure.

Definition at line 424 of file diffractionSpikeMask.py.

def getRegion(exposure, margin=None):
    """Calculate an enveloping region for an exposure.
 
    Parameters
    ----------
    exposure : `lsst.afw.image.Exposure`
        Exposure object with calibrated WCS.
 
    Returns
    -------
    region : `lsst.sphgeom.Region`
        Region enveloping an exposure.
    """
    # Bounding box needs to be a `Box2D` not a `Box2I` for `wcs.pixelToSky()`
    bbox = lsst.geom.Box2D(exposure.getBBox())
    wcs = exposure.getWcs()
 
    region = lsst.sphgeom.ConvexPolygon([pp.getVector() for pp in wcs.pixelToSky(bbox.getCorners())])
    if margin is not None:
        # This is an ad-hoc, approximate implementation. It should be good
        # enough for catalog loading, but is not a general-purpose solution.
        center = lsst.geom.SpherePoint(region.getCentroid())
        corners = [lsst.geom.SpherePoint(c) for c in region.getVertices()]
        # Approximate the region as a Euclidian square
        # geom.Angle(sphgeom.Angle) converter not pybind-wrapped???
        diagonal_margin = lsst.geom.Angle(margin.asRadians() * math.sqrt(2.0))
        padded = [c.offset(center.bearingTo(c), diagonal_margin) for c in corners]
        return lsst.sphgeom.ConvexPolygon.convexHull([c.getVector() for c in padded])
 
    return region