# Licensed under a 3-clause BSD style license - see LICENSE.rst
import numpy as np
import astropy.units as u
from astropy.coordinates import Angle
from astropy.coordinates.angle_utilities import angular_separation
from gammapy.irf import TablePSF
from gammapy.maps import Map, WcsGeom
from gammapy.utils.gauss import Gauss2DPDF
__all__ = ["PSFKernel"]
def _make_kernel_geom(geom, max_radius):
# Create a new geom object with an odd number of pixel and a maximum size
# This is useful for PSF kernel creation.
center = geom.center_skydir
binsz = Angle(np.abs(geom.wcs.wcs.cdelt[0]), "deg")
max_radius = Angle(max_radius)
npix = 2 * int(max_radius.deg / binsz.deg) + 1
return WcsGeom.create(
skydir=center,
binsz=binsz,
npix=npix,
proj=geom.projection,
frame=geom.frame,
axes=geom.axes,
)
def _compute_kernel_separations(geom, factor):
# utility function used for preparing distance to the center of the upsampled geom
# TODO : take into account non regular geometry for energy dependent PSF kernel size
if geom.is_regular is False:
raise ValueError("Non regular geometries are not supported yet.")
upsampled_image_geom = geom.to_image().upsample(factor)
# get center coordinate
center_coord = upsampled_image_geom.center_coord * u.deg
# get coordinates
map_c = upsampled_image_geom.get_coord()
# compute distances to map center
separations = angular_separation(
center_coord[0], center_coord[1], map_c.lon, map_c.lat
)
# Create map
kernel_map = Map.from_geom(geom=upsampled_image_geom.to_cube(axes=geom.axes))
return kernel_map, separations
def table_psf_to_kernel_map(table_psf, geom, factor=4):
"""Compute a PSF kernel on a given Geom.
If the Geom is not an image, the same kernel will be present on all axes.
The PSF is estimated by oversampling defined by a given factor.
The PSF kernel is normalized
Parameters
----------
table_psf : `~gammapy.irf.TablePSF`
the input table PSF
geom : `~gammapy.maps.Geom`
the target geometry. The PSF kernel will be centered on the spatial center.
factor : int
the oversample factor to compute the PSF
"""
# prepare map and compute distances to map center
kernel_map, rads = _compute_kernel_separations(geom, factor)
vals = table_psf.evaluate(rad=rads).value
norm = vals.sum()
for img, idx in kernel_map.iter_by_image():
img += vals.reshape(img.shape) / norm
return kernel_map.downsample(factor, preserve_counts=True)
def energy_dependent_table_psf_to_kernel_map(table_psf, geom, factor=4):
"""Compute an energy dependent PSF kernel on a given Geom.
The PSF is estimated by oversampling defined by a given factor.
Parameters
----------
table_psf : `~gammapy.irf.EnergyDependentTablePSF`
the input table PSF
geom : `~gammapy.maps.Geom`
the target geometry.
The PSF kernel will be centered on the spatial centre.
the geometry axes should contain an "energy" axis.
The kernel will be duplicated along other axes.
factor : int
the oversample factor to compute the PSF
"""
energy_axis = geom.get_axis_by_name("energy")
energy_idx = geom.axes.index(energy_axis)
# prepare map and compute distances to map center
kernel_map, rads = _compute_kernel_separations(geom, factor)
# loop over images
for img, idx in kernel_map.iter_by_image():
# TODO: this is super complex. Find or invent a better way!
energy = energy_axis.center[idx[energy_idx]]
vals = table_psf.evaluate(energy=energy, rad=rads).reshape(img.shape)
img += vals.value / vals.sum().value
return kernel_map.downsample(factor, preserve_counts=True)
[docs]class PSFKernel:
"""PSF kernel for `~gammapy.maps.Map`.
This is a container class to store a PSF kernel
that can be used to convolve `~gammapy.maps.WcsNDMap` objects.
It is usually computed from an `~gammapy.irf.EnergyDependentTablePSF`.
Parameters
----------
psf_kernel_map : `~gammapy.maps.Map`
PSF kernel stored in a Map
Examples
--------
::
import numpy as np
from gammapy.maps import Map, WcsGeom, MapAxis
from gammapy.irf import EnergyDependentMultiGaussPSF
from gammapy.cube import PSFKernel
from astropy import units as u
# Define energy axis
energy_axis = MapAxis.from_edges(np.logspace(-1., 1., 4), unit='TeV', name='energy')
# Create WcsGeom and map
geom = WcsGeom.create(binsz=0.02*u.deg, width=2.0*u.deg, axes=[energy_axis])
some_map = Map.from_geom(geom)
# Fill map at two positions
some_map.fill_by_coord([[0.2,0.4],[-0.1,0.6],[0.5,3.6]])
# Extract EnergyDependentTablePSF from CTA 1DC IRF
filename = '$GAMMAPY_DATA/cta-1dc/caldb/data/cta/1dc/bcf/South_z20_50h/irf_file.fits'
psf = EnergyDependentMultiGaussPSF.read(filename, hdu='POINT SPREAD FUNCTION')
table_psf = psf.to_energy_dependent_table_psf(theta=0.5*u.deg)
psf_kernel = PSFKernel.from_table_psf(table_psf,geom, max_radius=1*u.deg)
# Do the convolution
some_map_convolved = some_map.convolve(psf_kernel)
some_map_convolved.get_image_by_coord(dict(energy=0.6*u.TeV)).plot()
"""
def __init__(self, psf_kernel_map):
self._psf_kernel_map = psf_kernel_map
@property
def data(self):
"""Access the PSFKernel numpy array"""
return self._psf_kernel_map.data
@property
def psf_kernel_map(self):
"""The map object holding the kernel (`~gammapy.maps.Map`)"""
return self._psf_kernel_map
[docs] @classmethod
def read(cls, *args, **kwargs):
"""Read kernel Map from file."""
psf_kernel_map = Map.read(*args, **kwargs)
return cls(psf_kernel_map)
[docs] @classmethod
def from_table_psf(cls, table_psf, geom, max_radius=None, factor=4):
"""Create a PSF kernel from a TablePSF or an EnergyDependentTablePSF on a given Geom.
If the Geom is not an image, the same kernel will be present on all axes.
The PSF is estimated by oversampling defined by a given factor.
Parameters
----------
table_psf : `~gammapy.irf.TablePSF` or `~gammapy.irf.EnergyDependentTablePSF`
the input table PSF
geom : `~gammapy.maps.WcsGeom`
the target geometry. The PSF kernel will be centered on the central pixel.
The geometry axes should contain an axis with name "energy"
max_radius : `~astropy.coordinates.Angle`
the maximum radius of the PSF kernel.
factor : int
the oversample factor to compute the PSF
Returns
-------
kernel : `~gammapy.cube.PSFKernel`
the kernel Map with reduced geometry according to the max_radius
"""
# TODO : use PSF containment radius if max_radius is None
if max_radius is not None:
geom = _make_kernel_geom(geom, max_radius)
if isinstance(table_psf, TablePSF):
return cls(table_psf_to_kernel_map(table_psf, geom, factor))
else:
return cls(
energy_dependent_table_psf_to_kernel_map(table_psf, geom, factor)
)
[docs] @classmethod
def from_gauss(
cls, geom, sigma, max_radius=None, containment_fraction=0.99, factor=4
):
"""Create Gaussian PSF.
This is used for testing and examples.
The map geometry parameters (pixel size, energy bins) are taken from ``geom``.
The Gaussian width ``sigma`` is a scalar,
TODO : support array input if it should vary along the energy axis.
Parameters
----------
geom : `~gammapy.maps.WcsGeom`
Map geometry
sigma : `~astropy.coordinates.Angle`
Gaussian width.
max_radius : `~astropy.coordinates.Angle`
Desired kernel map size.
factor : int
Oversample factor to compute the PSF
Returns
-------
kernel : `~gammapy.cube.PSFKernel`
the kernel Map with reduced geometry according to the max_radius
"""
sigma = Angle(sigma)
if max_radius is None:
max_radius = (
Gauss2DPDF(sigma.deg).containment_radius(
containment_fraction=containment_fraction
)
* u.deg
)
max_radius = Angle(max_radius)
# Create a new geom according to given input
geom = _make_kernel_geom(geom, max_radius)
rad = Angle(np.linspace(0.0, max_radius.deg, 200), "deg")
table_psf = TablePSF.from_shape(shape="gauss", width=sigma, rad=rad)
return cls(table_psf_to_kernel_map(table_psf, geom, factor))
[docs] def write(self, *args, **kwargs):
"""Write the Map object which contains the PSF kernel to file."""
self.psf_kernel_map.write(*args, **kwargs)