Source code for gammapy.image.measure

# Licensed under a 3-clause BSD style license - see LICENSE.rst
import numpy as np
from scipy.optimize import brentq
from astropy.units import Quantity


__all__ = [
    "measure_containment_fraction",
    "measure_containment_radius",
    "measure_image_moments",
    "measure_containment",
    "measure_curve_of_growth",
]


[docs]def measure_image_moments(image): """ Compute 0th, 1st and 2nd moments of an image. NaN values are ignored in the computation. Parameters ---------- image : `gammapy.maps.Map` Image to measure on. Returns ------- image moments : list List of image moments: [A, x_cms, y_cms, x_sigma, y_sigma, sqrt(x_sigma * y_sigma)] """ data = image.quantity coords = image.geom.get_coord().skycoord x, y = coords.data.lon.wrap_at("180d"), coords.data.lat A = data[np.isfinite(data)].sum() # Center of mass x_cms = (x * data)[np.isfinite(data)].sum() / A y_cms = (y * data)[np.isfinite(data)].sum() / A # Second moments x_var = ((x - x_cms) ** 2 * data)[np.isfinite(data)].sum() / A y_var = ((y - y_cms) ** 2 * data)[np.isfinite(data)].sum() / A x_sigma = np.sqrt(x_var) y_sigma = np.sqrt(y_var) return A, x_cms, y_cms, x_sigma, y_sigma, np.sqrt(x_sigma * y_sigma)
[docs]def measure_containment(image, position, radius): """ Measure containment in a given circle around the source position. Parameters ---------- image :`gammapy.maps.Map` Image to measure on. position : `~astropy.coordinates.SkyCoord` Source position on the sky. radius : float Radius of the region to measure the containment in. """ coords = image.geom.get_coord() separation = coords.skycoord.separation(position) return measure_containment_fraction(image.quantity, radius, separation)
[docs]def measure_containment_radius(image, position, containment_fraction=0.8): """ Measure containment radius of a source. Uses `scipy.optimize.brentq`. Parameters ---------- image :`gammapy.maps.Map` Image to measure on. position : `~astropy.coordinates.SkyCoord` Source position on the sky. containment_fraction : float (default 0.8) Containment fraction Returns ------- containment_radius : Containment radius (pix) """ data = image.quantity coords = image.geom.get_coord() separation = coords.skycoord.separation(position) # Normalize image data = data / data[np.isfinite(data)].sum() def func(r): return ( measure_containment_fraction(data, r, separation.value) - containment_fraction ) containment_radius = brentq(func, a=0, b=separation.max().value) return Quantity(containment_radius, separation.unit)
[docs]def measure_containment_fraction(data, radius, separation): """Measure containment fraction. Parameters ---------- data :`~astropy.unit.Quantity` Image to measure on. radius : `~astropy.units.Quantity` Containment radius. separation : `~astropy.coordinates.Angle` Separation from the source position array. Returns ------- containment_fraction : float Containment fraction """ # Set up indices and containment mask containment_mask = separation < radius mask = np.isfinite(data) & containment_mask containment_fraction = data[mask].sum() return containment_fraction
[docs]def measure_curve_of_growth(image, position, radius_max=None, radius_n=10): """ Measure the curve of growth for a given source position. The curve of growth is determined by measuring the flux in a circle around the source and radius of this circle is increased Parameters ---------- image : `astropy.io.fits.ImageHDU` Image to measure on. position : `~astropy.coordinates.SkyCoord` Source position on the sky. radius_max : `~astropy.units.Quantity` Maximal radius, up to which the containment is measured (default 0.2 deg). radius_n : int Number of radius steps. Returns ------- radii : `~astropy.units.Quantity` Radii where the containment was measured. containment : `~astropy.units.Quantity` Corresponding contained flux. """ radius_max = radius_max if radius_max is not None else Quantity(0.2, "deg") containment = [] radii = Quantity(np.linspace(0, radius_max.value, radius_n), radius_max.unit) for radius in radii: containment.append(measure_containment(image, position, radius)) return radii, Quantity(containment)