# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Ring background estimation."""
import itertools
import numpy as np
from astropy.convolution import Ring2DKernel, Tophat2DKernel
from astropy.coordinates import Angle
from gammapy.cube.fit import MapDatasetOnOff
from gammapy.maps import Map, scale_cube
__all__ = ["AdaptiveRingBackgroundMaker", "RingBackgroundMaker"]
[docs]class AdaptiveRingBackgroundMaker:
"""Adaptive ring background algorithm.
This algorithm extends the `RingBackgroundMaker` method by adapting the
size of the ring to achieve a minimum on / off exposure ratio (alpha) in regions
where the area to estimate the background from is limited.
Parameters
----------
r_in : `~astropy.units.Quantity`
Inner radius of the ring.
r_out_max : `~astropy.units.Quantity`
Maximal outer radius of the ring.
width : `~astropy.units.Quantity`
Width of the ring.
stepsize : `~astropy.units.Quantity`
Stepsize used for increasing the radius.
threshold_alpha : float
Threshold on alpha above which the adaptive ring takes action.
theta : `~astropy.units.Quantity`
Integration radius used for alpha computation.
method : {'fixed_width', 'fixed_r_in'}
Adaptive ring method.
exclusion_mask : `~gammapy.maps.WcsNDMap`
Exclusion mask
See Also
--------
RingBackgroundMaker, gammapy.detect.KernelBackgroundEstimator
"""
def __init__(
self,
r_in,
r_out_max,
width,
stepsize="0.02 deg",
threshold_alpha=0.1,
theta="0.22 deg",
method="fixed_width",
exclusion_mask=None,
):
if method not in ["fixed_width", "fixed_r_in"]:
raise ValueError("Not a valid adaptive ring method.")
self.r_in = Angle(r_in)
self.r_out_max = Angle(r_out_max)
self.width = Angle(width)
self.stepsize = Angle(stepsize)
self.threshold_alpha = threshold_alpha
self.theta = Angle(theta)
self.method = method
self.exclusion_mask = exclusion_mask
[docs] def kernels(self, image):
"""Ring kernels according to the specified method.
Parameters
----------
image : `~gammapy.maps.WcsNDMap`
Map specifying the WCS information.
Returns
-------
kernels : list
List of `~astropy.convolution.Ring2DKernel`
"""
scale = image.geom.pixel_scales[0]
r_in = (self.r_in / scale).to_value("")
r_out_max = (self.r_out_max / scale).to_value("")
width = (self.width / scale).to_value("")
stepsize = (self.stepsize / scale).to_value("")
if self.method == "fixed_width":
r_ins = np.arange(r_in, (r_out_max - width), stepsize)
widths = [width]
elif self.method == "fixed_r_in":
widths = np.arange(width, (r_out_max - r_in), stepsize)
r_ins = [r_in]
else:
raise ValueError(f"Invalid method: {self.method!r}")
kernels = []
for r_in, width in itertools.product(r_ins, widths):
kernel = Ring2DKernel(r_in, width)
kernel.normalize("peak")
kernels.append(kernel)
return kernels
@staticmethod
def _alpha_approx_cube(cubes):
acceptance = cubes["acceptance"]
acceptance_off = cubes["acceptance_off"]
with np.errstate(divide="ignore", invalid="ignore"):
alpha_approx = np.where(
acceptance_off > 0, acceptance / acceptance_off, np.inf
)
return alpha_approx
def _reduce_cubes(self, cubes, dataset):
"""Compute off and off acceptance map.
Calulated by reducing the cubes. The data is
iterated along the third axis (i.e. increasing ring sizes), the value
with the first approximate alpha < threshold is taken.
"""
threshold = self.threshold_alpha
alpha_approx_cube = self._alpha_approx_cube(cubes)
counts_off_cube = cubes["counts_off"]
acceptance_off_cube = cubes["acceptance_off"]
acceptance_cube = cubes["acceptance"]
shape = alpha_approx_cube.shape[:2]
counts_off = np.tile(np.nan, shape)
acceptance_off = np.tile(np.nan, shape)
acceptance = np.tile(np.nan, shape)
for idx in np.arange(alpha_approx_cube.shape[-1]):
mask = (alpha_approx_cube[:, :, idx] <= threshold) & np.isnan(counts_off)
counts_off[mask] = counts_off_cube[:, :, idx][mask]
acceptance_off[mask] = acceptance_off_cube[:, :, idx][mask]
acceptance[mask] = acceptance_cube[:, :, idx][mask]
counts = dataset.counts
acceptance = counts.copy(data=acceptance[np.newaxis, Ellipsis])
acceptance_off = counts.copy(data=acceptance_off[np.newaxis, Ellipsis])
counts_off = counts.copy(data=counts_off[np.newaxis, Ellipsis])
return acceptance, acceptance_off, counts_off
[docs] def make_cubes(self, dataset):
"""Make acceptance, off acceptance, off counts cubes
Parameters
----------
dataset : `~gammapy.cube.MapDataset`
Input map dataset.
Returns
-------
cubes : dict of `~gammapy.maps.WcsNDMap`
Dictionary containing ``counts_off``, ``acceptance`` and ``acceptance_off`` cubes.
"""
counts = dataset.counts
background = dataset.background_model.map
kernels = self.kernels(counts)
if self.exclusion_mask is not None:
# reproject exclusion mask
coords = counts.geom.get_coord()
data = self.exclusion_mask.get_by_coord(coords)
exclusion = Map.from_geom(geom=counts.geom, data=data)
else:
data = np.ones(counts.geom.data_shape, dtype=bool)
exclusion = Map.from_geom(geom=counts.geom, data=data)
cubes = {}
cubes["counts_off"] = scale_cube(
(counts.data * exclusion.data)[0, Ellipsis], kernels
)
cubes["acceptance_off"] = scale_cube(
(background.data * exclusion.data)[0, Ellipsis], kernels
)
scale = background.geom.pixel_scales[0].to("deg")
theta = self.theta * scale
tophat = Tophat2DKernel(theta.value)
tophat.normalize("peak")
acceptance = background.convolve(tophat.array)
acceptance_data = acceptance.data[0, Ellipsis]
cubes["acceptance"] = np.repeat(
acceptance_data[Ellipsis, np.newaxis], len(kernels), axis=2
)
return cubes
[docs] def run(self, dataset):
"""Run adaptive ring background maker
Parameters
----------
dataset : `~gammapy.cube.fit.MapDataset`
Input map dataset.
Returns
-------
dataset_on_off : `~gammapy.cube.fit.MapDatasetOnOff`
On off dataset.
"""
cubes = self.make_cubes(dataset)
acceptance, acceptance_off, counts_off = self._reduce_cubes(cubes, dataset)
mask_safe = dataset.mask_safe.copy()
not_has_off_acceptance = acceptance_off.data <= 0
mask_safe.data[not_has_off_acceptance] = 0
return MapDatasetOnOff(
counts=dataset.counts,
counts_off=counts_off,
acceptance=acceptance,
acceptance_off=acceptance_off,
exposure=dataset.exposure,
psf=dataset.psf,
name=dataset.name,
mask_safe=mask_safe,
gti=dataset.gti,
)
[docs]class RingBackgroundMaker:
"""Ring background method for cartesian coordinates.
- Step 1: apply exclusion mask
- Step 2: ring-correlate
Parameters
----------
r_in : `~astropy.units.Quantity`
Inner ring radius
width : `~astropy.units.Quantity`
Ring width
exclusion_mask : `~gammapy.maps.WcsNDMap`
Exclusion mask
See Also
--------
gammapy.detect.KernelBackgroundEstimator, AdaptiveRingBackgroundEstimator
"""
def __init__(self, r_in, width, exclusion_mask=None):
self.r_in = Angle(r_in)
self.width = Angle(width)
self.exclusion_mask = exclusion_mask
[docs] def kernel(self, image):
"""Ring kernel.
Parameters
----------
image : `~gammapy.maps.WcsNDMap`
Input Map
Returns
-------
ring : `~astropy.convolution.Ring2DKernel`
Ring kernel.
"""
scale = image.geom.pixel_scales[0].to("deg")
r_in = self.r_in.to("deg") / scale
width = self.width.to("deg") / scale
ring = Ring2DKernel(r_in.value, width.value)
ring.normalize("peak")
return ring
[docs] def make_maps_off(self, dataset):
"""Make off maps
Parameters
----------
dataset : `~gammapy.cube.fit.MapDataset`
Input map dataset.
Returns
-------
maps_off : dict of `~gammapy.maps.WcsNDMap`
Dictionary containing `counts_off` and `acceptance_off` maps.
"""
counts = dataset.counts
background = dataset.background_model.map
if self.exclusion_mask is not None:
# reproject exclusion mask
coords = counts.geom.get_coord()
data = self.exclusion_mask.get_by_coord(coords)
exclusion = Map.from_geom(geom=counts.geom, data=data)
else:
data = np.ones(counts.geom.data_shape, dtype=bool)
exclusion = Map.from_geom(geom=counts.geom, data=data)
maps_off = {}
ring = self.kernel(counts)
counts_excluded = counts * exclusion
maps_off["counts_off"] = counts_excluded.convolve(ring.array)
background_excluded = background * exclusion
maps_off["acceptance_off"] = background_excluded.convolve(ring.array)
return maps_off
[docs] def run(self, dataset):
"""Run ring background maker
Parameters
----------
dataset : `~gammapy.cube.fit.MapDataset`
Input map dataset.
Returns
-------
dataset_on_off : `~gammapy.cube.fit.MapDatasetOnOff`
On off dataset.
"""
maps_off = self.make_maps_off(dataset)
acceptance = dataset.background_model.map
mask_safe = dataset.mask_safe.copy()
not_has_off_acceptance = maps_off["acceptance_off"].data <= 0
mask_safe.data[not_has_off_acceptance] = 0
return MapDatasetOnOff(
counts=dataset.counts,
counts_off=maps_off["counts_off"],
acceptance=acceptance,
acceptance_off=maps_off["acceptance_off"],
exposure=dataset.exposure,
psf=dataset.psf,
name=dataset.name,
mask_safe=dataset.mask_safe,
gti=dataset.gti,
)
def __str__(self):
return (
"RingBackground parameters: \n"
f"r_in : {self.parameters['r_in']}\n"
f"width: {self.parameters['width']}\n"
f"Exclusion mask: {self.exclusion_mask}"
)