Source code for gammapy.utils.regions

"""Regions helper functions.

Throughout Gammapy, we use regions to represent and work with regions.

We might add in other conveniences and features here, e.g. sky coord contains
without a WCS (see "sky and pixel regions" in PIG 10), or some HEALPix integration.

TODO: before Gammapy v1.0, discuss what to do about gammapy.utils.regions.
Options: keep as-is, hide from the docs, or to remove it completely
(if the functionality is available in astropy-regions directly.
"""
import operator
import numpy as np
from scipy.optimize import minimize
from astropy import units as u
from astropy.coordinates import SkyCoord
from regions import (
CircleAnnulusSkyRegion,
CircleSkyRegion,
CompoundSkyRegion,
RectangleSkyRegion,
Regions,
)

__all__ = [
"make_orthogonal_rectangle_sky_regions",
"make_concentric_annulus_sky_regions",
"compound_region_to_regions",
"regions_to_compound_region",
]

def compound_region_center(compound_region):
"""Compute center for a CompoundRegion

The center of the compound region is defined here as the geometric median
of the individual centers of the regions. The geometric median is defined
as the point the minimises the distance to all other points.

Parameters
----------
compound_region : CompoundRegion
Compound region

Returns
-------
center : SkyCoord
Geometric median of the positions of the individual regions
"""
regions = compound_region_to_regions(compound_region)
positions = SkyCoord([region.center for region in regions])

def f(x, coords):
"""Function to minimize"""
lon, lat = x
center = SkyCoord(lon * u.deg, lat * u.deg)
return np.sum(center.separation(coords).deg)

ra, dec = positions.icrs.ra.wrap_at("180d").deg, positions.icrs.dec.deg

result = minimize(
f,
x0=[np.mean(ra), np.mean(dec)],
args=(positions,),
bounds=[(np.min(ra), np.max(ra)), (np.min(dec), np.max(dec))],
method="L-BFGS-B",
)

return SkyCoord(result.x, result.x, frame="icrs", unit="deg")

[docs]def compound_region_to_regions(region): """Create list of regions from compound regions. Parameters ---------- region : ~regions.CompoundSkyRegion or ~regions.SkyRegion Compound sky region Returns ------- regions : ~regions.Regions List of regions. """ regions = Regions([]) if isinstance(region, CompoundSkyRegion): if region.operator is operator.or_: regions_1 = compound_region_to_regions(region.region1) regions.extend(regions_1) regions_2 = compound_region_to_regions(region.region2) regions.extend(regions_2) else: raise ValueError("Only union operator supported") else: return Regions([region]) return regions
[docs]def regions_to_compound_region(regions): """Create compound region from list of regions, by creating the union. Parameters ---------- regions : ~regions.Regions List of regions. Returns ------- compound : ~regions.CompoundSkyRegion or ~regions.CompoundPixelRegion Compound sky region """ region_union = regions for region in regions[1:]: region_union = region_union.union(region) return region_union
class SphericalCircleSkyRegion(CircleSkyRegion): """Spherical circle sky region. TODO: is this separate class a good idea? - If yes, we could move it to the regions package? - If no, we should implement some other solution. Probably the alternative is to add extra methods to the CircleSkyRegion class and have that support both planar approximation and spherical case? Or we go with the approach to always make a TAN WCS and not have true cone select at all? """ def contains(self, skycoord, wcs=None): """Defined by spherical distance.""" separation = self.center.separation(skycoord) return separation < self.radius
[docs]def make_orthogonal_rectangle_sky_regions(start_pos, end_pos, wcs, height, nbin=1): """Utility returning an array of regions to make orthogonal projections Parameters ---------- start_pos : ~astropy.regions.SkyCoord First sky coordinate defining the line to which the orthogonal boxes made end_pos : ~astropy.regions.SkyCoord Second sky coordinate defining the line to which the orthogonal boxes made height : ~astropy.quantity.Quantity Height of the rectangle region. wcs : ~astropy.wcs.WCS WCS projection object nbin : int Number of boxes along the line Returns -------- regions : list of ~regions.RectangleSkyRegion Regions in which the profiles are made """ pix_start = start_pos.to_pixel(wcs) pix_stop = end_pos.to_pixel(wcs) points = np.linspace(start=pix_start, stop=pix_stop, num=nbin + 1).T centers = 0.5 * (points[:, :-1] + points[:, 1:]) coords = SkyCoord.from_pixel(centers, centers, wcs) width = start_pos.separation(end_pos).to("rad") / nbin angle = end_pos.position_angle(start_pos) - 90 * u.deg regions = [] for center in coords: reg = RectangleSkyRegion( center=center, width=width, height=u.Quantity(height), angle=angle ) regions.append(reg) return regions
[docs]def make_concentric_annulus_sky_regions(center, radius_max, nbin=11): """Make a list of concentric annulus regions. Parameters ---------- center : ~astropy.coordinates.SkyCoord Center coordinate radius_max : ~astropy.units.Quantity Maximum radius. nbin : int Number of boxes along the line Returns ------- regions : list of ~regions.RectangleSkyRegion Regions in which the profiles are made """ regions = [] edges = np.linspace(0 * u.deg, u.Quantity(radius_max), nbin) for r_in, r_out in zip(edges[:-1], edges[1:]): region = CircleAnnulusSkyRegion( center=center, inner_radius=r_in, outer_radius=r_out, ) regions.append(region) return regions