Source code for gammapy.utils.regions

# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Regions helper functions.

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

https://astropy-regions.readthedocs.io

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 Bounds, minimize
from astropy import units as u
from astropy.coordinates import SkyCoord
from regions import (
    CircleAnnulusSkyRegion,
    CircleSkyRegion,
    CompoundSkyRegion,
    EllipseSkyRegion,
    RectangleSkyRegion,
    Regions,
    PolygonSkyRegion,
    PolygonPixelRegion,
)

from regions.core.pixcoord import PixCoord
from regions.core.metadata import RegionMeta, RegionVisual
from regions._utils.wcs_helpers import pixel_scale_angle_at_skycoord

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


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 : `~astropy.coordinates.SkyCoord`
        Geometric median of the positions of the individual regions.
    """
    regions = compound_region_to_regions(compound_region)

    if len(regions) == 1:
        return regions[0].center

    positions = SkyCoord([region.center.icrs 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.ra.wrap_at("180d").deg, positions.dec.deg

    ub = np.array([np.max(ra), np.max(dec)])
    lb = np.array([np.min(ra), np.min(dec)])

    if np.all(ub == lb):
        bounds = None
    else:
        bounds = Bounds(ub=ub, lb=lb)

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

    return SkyCoord(result.x[0], result.x[1], 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[0] for region in regions[1:]: region_union = region_union.union(region) return region_union
def get_centroid(vertices): """Compute centroid of a polygon. Implicitly assumes a flat cartesian projection, will probably break for very large polygons. Code comes from: https://stackoverflow.com/questions/75699024/finding-the-centroid-of-a-polygon-in-python Parameters ---------- vertices : `~astropy.coordinates.SkyCoord` List of vertices. Returns ------- centroid : `~astropy.coordinates.SkyCoord` Centroid of the polygon. """ polygon = [] for vertex in vertices: polygon.append((vertex.ra.degree, vertex.dec.degree)) polygon = np.array(polygon) # Same polygon, but with vertices cycled around. Now the polygon # decomposes into triangles of the form origin-polygon[i]-polygon2[i] polygon2 = np.roll(polygon, -1, axis=0) # Compute signed area of each triangle signed_areas = 0.5 * np.cross(polygon, polygon2) # Compute centroid of each triangle centroids = (polygon + polygon2) / 3.0 # Get average of those centroids, weighted by the signed areas. centroid = np.average(centroids, axis=0, weights=signed_areas) return SkyCoord(centroid[0] * u.deg, centroid[1] * u.deg, frame=vertices.frame) 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 class PolygonPointsSkyRegion(PolygonSkyRegion): """Polygon sky region defined by a list of points.""" def __init__(self, vertices, meta=None, visual=None): """Create a polygon sky region. Parameters ---------- vertices : `~astropy.coordinates.SkyCoord` List of vertices. meta : `~regions.RegionMeta`, optional Region meta data. visual : `~regions.RegionVisual`, optional Region visual meta data. """ self.vertices = vertices self.meta = meta or RegionMeta() self.center = get_centroid(vertices) self.visual = visual or RegionVisual() def to_pixel(self, wcs): """Convert to pixel region.""" x, y = wcs.world_to_pixel(self.vertices) center, _, _ = pixel_scale_angle_at_skycoord(self.center, wcs) vertices_pix = PixCoord(x, y) return PolygonPointsPixelRegion( vertices_pix, center=center, meta=self.meta.copy(), visual=self.visual.copy(), ) class PolygonPointsPixelRegion(PolygonPixelRegion): """Polygon pixel region defined by a list of points.""" def __init__(self, vertices, center=None, meta=None, visual=None, origin=None): """Create a polygon pixel region. Parameters ---------- vertices : `~regions.PixCoord` List of vertices. center : `~regions.PixCoord`, optional Center of the region. meta : `~regions.RegionMeta`, optional Region meta data. visual : `~regions.RegionVisual`, optional Region visual meta data. origin : `~regions.PixCoord`, optional Origin of the region. Default is `PixCoord(0, 0)` """ if origin is None: origin = PixCoord(0, 0) self._vertices = vertices self.meta = meta or RegionMeta() self.visual = visual or RegionVisual() self.origin = origin self.vertices = vertices + origin self.center = center def to_sky(self, wcs): """Convert to sky region. Parameters ---------- wcs : `~astropy.wcs.WCS` WCS transformation object. """ vertices_sky = wcs.pixel_to_world(self.vertices.x, self.vertices.y) return PolygonPointsSkyRegion( vertices=vertices_sky, meta=self.meta.copy(), visual=self.visual.copy() ) def rotate(self, center, angle): """ Rotate the region. Positive ``angle`` corresponds to counter-clockwise rotation. Parameters ---------- center : `~regions.PixCoord` The rotation center point. angle : `~astropy.coordinates.Angle` The rotation angle. Returns ------- region : `PolygonPixelRegion` The rotated region (which is an independent copy). """ vertices = self.vertices.rotate(center, angle) center = self.center.rotate(center, angle) return self.copy(vertices=vertices, center=center)
[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, optional Number of boxes along the line. Default is 1. 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[0], centers[1], 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, radius_min=1e-5 * u.deg, nbin=11 ): """Make a list of concentric annulus regions. Parameters ---------- center : `~astropy.coordinates.SkyCoord` Center coordinate. radius_max : `~astropy.units.Quantity` Maximum radius. radius_min : `~astropy.units.Quantity`, optional Minimum radius. Default is 1e-5 deg. nbin : int, optional Number of boxes along the line. Default is 11. Returns ------- regions : list of `~regions.RectangleSkyRegion` Regions in which the profiles are made. """ regions = [] edges = np.linspace(radius_min, 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
[docs] def region_to_frame(region, frame): """Convert a region to a different frame. Parameters ---------- region : `~regions.SkyRegion` Region to transform. frame : {"icrs", "galactic"} Frame to transform the region into. Returns ------- region_new : `~regions.SkyRegion` Region in the given frame. """ from gammapy.maps import WcsGeom wcs = WcsGeom.create(skydir=region.center, binsz=0.01, frame=frame).wcs region_new = region.to_pixel(wcs).to_sky(wcs) return region_new
def region_circle_to_ellipse(region): """Convert a CircleSkyRegion to an EllipseSkyRegion. Parameters ---------- region : `~regions.CircleSkyRegion` Region to transform. Returns ------- region_new : `~regions.EllipseSkyRegion` Elliptical region with same major and minor axis. """ region_new = EllipseSkyRegion( center=region.center, width=region.radius, height=region.radius ) return region_new