def test_combine(tmpdir):
"""Test ligo-skymap-combine."""
fn1 = str(tmpdir / 'skymap1.fits.gz')
fn2 = str(tmpdir / 'skymap2.fits.gz')
fn3 = str(tmpdir / 'joint_skymap.fits.gz')
# generate a hemisphere of constant probability
nside1 = 32
npix1 = ah.nside_to_npix(nside1)
m1 = np.zeros(npix1)
disc_idx = hp.query_disc(nside1, (1, 0, 0), np.pi / 2)
m1[disc_idx] = 1
m1 /= m1.sum()
hp.write_map(fn1,
m1,
column_names=['PROBABILITY'],
extra_header=[('INSTRUME', 'X1')])
# generate another hemisphere of constant probability
# but with higher resolution and rotated 90 degrees
nside2 = 64
npix2 = ah.nside_to_npix(nside2)
m2 = np.zeros(npix2)
disc_idx = hp.query_disc(nside2, (0, 1, 0), np.pi / 2)
m2[disc_idx] = 1
m2 /= m2.sum()
hp.write_map(fn2,
m2,
column_names=['PROBABILITY'],
extra_header=[('INSTRUME', 'Y1')])
run_entry_point('ligo-skymap-combine', fn1, fn2, fn3)
m3 = hp.read_map(fn3, nest=True)
npix3 = len(m3)
nside3 = ah.npix_to_nside(npix3)
pix_area3 = ah.nside_to_pixel_area(nside3).to_value(u.sr)
# resolution must match the highest original resolution
assert npix3 == npix2
# probability must be normalized to 1
assert m3.sum() == pytest.approx(1)
# support must be ¼ of the sphere
tolerance = 10 * ah.nside_to_pixel_area(nside1).to_value(u.sr)
assert sum(m3 > 0) * pix_area3 == pytest.approx(np.pi, abs=tolerance)
# generate a BAYESTAR-like map with mock distance information
d_mu = np.zeros_like(m1)
d_sigma = np.ones_like(m1)
d_norm = np.ones_like(m1)
io.write_sky_map(fn1, [m1, d_mu, d_sigma, d_norm])
run_entry_point('ligo-skymap-combine', fn1, fn2, fn3)
m3, meta3 = io.read_sky_map(fn3, nest=True, distances=True)
# check that marginal distance moments match what was simulated
mean, std, _ = distance.parameters_to_moments(d_mu[0], d_sigma[0])
assert meta3['distmean'] == pytest.approx(mean)
assert meta3['diststd'] == pytest.approx(std)
def test_from_valued_healpix_cells_bayestar():
from astropy.io import fits
fits_image_filename = './resources/bayestar.multiorder.fits'
with fits.open(fits_image_filename) as hdul:
hdul.info()
hdul[1].columns
data = hdul[1].data
uniq = data['UNIQ']
probdensity = data['PROBDENSITY']
import astropy_healpix as ah
import astropy.units as u
level, ipix = ah.uniq_to_level_ipix(uniq)
area = ah.nside_to_pixel_area(ah.level_to_nside(level)).to_value(
u.steradian)
prob = probdensity * area
cumul_to = np.linspace(0.01, 2.0, num=10)
for b in cumul_to:
MOC.from_valued_healpix_cells(uniq,
prob,
12,
cumul_from=0.0,
cumul_to=b)
def main(args=None):
p = parser()
opts = parser().parse_args(args)
import astropy_healpix as ah
import astropy.units as u
try:
from mocpy import MOC
except ImportError:
p.error('This command-line tool requires mocpy >= 0.8.2. '
'Please install it by running "pip install mocpy".')
from ..io import read_sky_map
# Read multi-order sky map
skymap = read_sky_map(opts.input.name, moc=True)
uniq = skymap['UNIQ']
probdensity = skymap['PROBDENSITY']
level, ipix = ah.uniq_to_level_ipix(uniq)
area = ah.nside_to_pixel_area(
ah.level_to_nside(level)).to_value(u.steradian)
prob = probdensity * area
# Create MOC
contour_decimal = opts.contour / 100
moc = MOC.from_valued_healpix_cells(
uniq, prob, cumul_from=0.0, cumul_to=contour_decimal)
# Write MOC
moc.write(opts.output, format='fits', overwrite=True)
def flat_bitmap(self):
"""Return flattened HEALPix representation."""
m = np.empty(ah.nside_to_npix(ah.level_to_nside(self.order)))
for nside, full_nside, ipix, ipix0, ipix1, samples in self.visit():
pixarea = ah.nside_to_pixel_area(nside).to_value(u.sr)
m[ipix0:ipix1] = len(samples) / pixarea
return m
def input_skymap(order1, d_order, fraction):
"""Construct a test multi-resolution sky map, with values that are
proportional to the NESTED pixel index.
To make the test more interesting by mixing together multiple resolutions,
part of the sky map is refined to a higher order.
Parameters
----------
order1 : int
The HEALPix resolution order.
d_order : int
The increase in orer for part of the sky map.
fraction : float
The fraction of the original pixels to refine.
"""
order2 = order1 + d_order
npix1 = ah.nside_to_npix(ah.level_to_nside(order1))
npix2 = ah.nside_to_npix(ah.level_to_nside(order2))
ipix1 = np.arange(npix1)
ipix2 = np.arange(npix2)
# Create a random sky map.
area = ah.nside_to_pixel_area(ah.level_to_nside(order1)).to_value(u.sr)
probdensity = np.random.uniform(0, 1, npix1)
prob = probdensity * area
normalization = prob.sum()
prob /= normalization
probdensity /= normalization
distmean = np.random.uniform(100, 110, npix1)
diststd = np.random.uniform(0, 1 / np.sqrt(3) - 0.1, npix1) * distmean
distmu, distsigma, distnorm = moments_to_parameters(distmean, diststd)
assert np.all(np.isfinite(distmu))
data1 = table.Table({
'UNIQ': moc.nest2uniq(order1, ipix1),
'PROBDENSITY': probdensity,
'DISTMU': distmu,
'DISTSIGMA': distsigma,
'DISTNORM': distnorm
})
# Add some upsampled pixels.
data2 = table.Table(np.repeat(data1, npix2 // npix1))
data2['UNIQ'] = moc.nest2uniq(order2, ipix2)
n = int(npix1 * (1 - fraction))
result = table.vstack((data1[:n], data2[n * npix2 // npix1:]))
# Add marginal distance mean and standard deviation.
rbar = (prob * distmean).sum()
r2bar = (prob * (np.square(diststd) + np.square(distmean))).sum()
result.meta['distmean'] = rbar
result.meta['diststd'] = np.sqrt(r2bar - np.square(rbar))
return result
def _build_moc_map(self):
pts = np.column_stack((self._grb_phi, self._grb_theta))
self._kde_map = Clustered2DSkyKDE(pts, jobs=12)
data = self._kde_map.as_healpix(top_nside=self._npix)
self._uniq = data["UNIQ"]
self._prob_density = data["PROBDENSITY"]
level, ipix = ah.uniq_to_level_ipix(self._uniq)
area = ah.nside_to_pixel_area(ah.level_to_nside(level)).to_value(
u.steradian)
self._prob = self._prob_density * area
def as_healpix(self, top_nside=16):
"""Return a HEALPix multi-order map of the posterior density."""
post, nside, ipix = zip(*self._bayestar_adaptive_grid(
top_nside=top_nside))
post = np.asarray(list(post))
nside = np.asarray(list(nside))
ipix = np.asarray(list(ipix))
# Make sure that sky map is normalized (it should be already)
post /= np.sum(post * ah.nside_to_pixel_area(nside).to_value(u.sr))
# Convert from NESTED to UNIQ pixel indices
order = np.log2(nside).astype(int)
uniq = moc.nest2uniq(order.astype(np.int8), ipix)
# Done!
return Table([uniq, post], names=['UNIQ', 'PROBDENSITY'], copy=False)
def unseen_pixels(cls, map_name, hires=False):
"""
Returns a list of UNSEEN healpix pixels contained in `map_name`.
Parameters
----------
map_name : ``str``
Name of the map to be plotted. Use ``show_maps`` method
to see a list of all available maps.
hires : ``boolean``, optional
Use high resolution map. If the map is not available locally,
it is downloaded. Defaults to ``False``.
"""
hpmap, nside, _ = cls._load_map(map_name, hires)
unseen_pixels = np.where(np.isnan(hpmap))[0]
npixels = len(unseen_pixels)
if npixels:
bad_area = npixels * nside_to_pixel_area(nside).to(u.deg**2)
print("{} contains {} UNSEEN pixels ({})".format(
map_name, npixels, bad_area))
return unseen_pixels
def main(args=None):
opts = parser().parse_args(args)
# Late imports
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import rcParams
from ..io import fits
from .. import plot
from .. import postprocess
import astropy_healpix as ah
from astropy.coordinates import SkyCoord
from astropy.time import Time
from astropy import units as u
skymap, metadata = fits.read_sky_map(opts.input.name, nest=None)
nside = ah.npix_to_nside(len(skymap))
# Convert sky map from probability to probability per square degree.
deg2perpix = ah.nside_to_pixel_area(nside).to_value(u.deg**2)
probperdeg2 = skymap / deg2perpix
axes_args = {}
if opts.geo:
axes_args['projection'] = 'geo'
obstime = Time(metadata['gps_time'], format='gps').utc.isot
axes_args['obstime'] = obstime
else:
axes_args['projection'] = 'astro'
axes_args['projection'] += ' ' + opts.projection
if opts.projection_center is not None:
axes_args['center'] = SkyCoord(opts.projection_center)
if opts.zoom_radius is not None:
axes_args['radius'] = opts.zoom_radius
ax = plt.axes(**axes_args)
ax.grid()
# Plot sky map.
vmax = probperdeg2.max()
img = ax.imshow_hpx((probperdeg2, 'ICRS'),
nested=metadata['nest'],
vmin=0.,
vmax=vmax)
# Add colorbar.
if opts.colorbar:
cb = plot.colorbar(img)
cb.set_label(r'prob. per deg$^2$')
# Add contours.
if opts.contour:
cls = 100 * postprocess.find_greedy_credible_levels(skymap)
cs = ax.contour_hpx((cls, 'ICRS'),
nested=metadata['nest'],
colors='k',
linewidths=0.5,
levels=opts.contour)
fmt = r'%g\%%' if rcParams['text.usetex'] else '%g%%'
plt.clabel(cs, fmt=fmt, fontsize=6, inline=True)
# Add continents.
if opts.geo:
plt.plot(*plot.coastlines(),
color='0.5',
linewidth=0.5,
transform=ax.get_transform('world'))
radecs = opts.radec
if opts.inj_database:
query = '''SELECT DISTINCT longitude, latitude FROM sim_inspiral AS si
INNER JOIN coinc_event_map AS cm1
ON (si.simulation_id = cm1.event_id)
INNER JOIN coinc_event_map AS cm2
ON (cm1.coinc_event_id = cm2.coinc_event_id)
WHERE cm2.event_id = ?
AND cm1.table_name = 'sim_inspiral'
AND cm2.table_name = 'coinc_event'
'''
(ra,
dec), = opts.inj_database.execute(query,
(metadata['objid'], )).fetchall()
radecs.append(np.rad2deg([ra, dec]).tolist())
# Add markers (e.g., for injections or external triggers).
for ra, dec in radecs:
ax.plot_coord(SkyCoord(ra, dec, unit='deg'),
'*',
markerfacecolor='white',
markeredgecolor='black',
markersize=10)
# Add a white outline to all text to make it stand out from the background.
plot.outline_text(ax)
if opts.annotate:
text = []
try:
objid = metadata['objid']
except KeyError:
pass
else:
text.append('event ID: {}'.format(objid))
if opts.contour:
pp = np.round(opts.contour).astype(int)
ii = np.round(
np.searchsorted(np.sort(cls), opts.contour) *
deg2perpix).astype(int)
for i, p in zip(ii, pp):
# FIXME: use Unicode symbol instead of TeX '$^2$'
# because of broken fonts on Scientific Linux 7.
text.append('{:d}% area: {:,d} deg²'.format(p, i))
ax.text(1, 1, '\n'.join(text), transform=ax.transAxes, ha='right')
# Show or save output.
opts.output()
fits_image_filename = './../../resources/bayestar.multiorder.fits'
with fits.open(fits_image_filename) as hdul:
hdul.info()
hdul[1].columns
data = hdul[1].data
uniq=data['UNIQ']
probdensity=data['PROBDENSITY']
import astropy_healpix as ah
import astropy.units as u
level, ipix = ah.uniq_to_level_ipix(uniq)
area = ah.nside_to_pixel_area(ah.level_to_nside(level)).to_value(u.steradian)
prob = probdensity * area
from mocpy import MOC
import numpy as np
cumul_to = np.linspace(0.5, 0.9, 5)[::-1]
colors = ['blue', 'green', 'yellow', 'orange', 'red']
mocs = [MOC.from_valued_healpix_cells(uniq, prob, cumul_to=c) for c in cumul_to]
from mocpy import World2ScreenMPL
from astropy.coordinates import Angle, SkyCoord
import astropy.units as u
# Plot the MOC using matplotlib
def find_ellipse(prob, cl=90, projection='ARC', nest=False):
"""For a HEALPix map, find an ellipse that contains a given probability.
The orientation is defined as the angle of the semimajor axis
counterclockwise from west on the plane of the sky. If you think of the
semimajor distance as the width of the ellipse, then the orientation is the
clockwise rotation relative to the image x-axis. Equivalently, the
orientation is the position angle of the semi-minor axis.
These conventions match the definitions used in DS9 region files [1]_ and
Aladin drawing commands [2]_.
Parameters
----------
prob : np.ndarray, astropy.table.Table
The HEALPix probability map, either as a full rank explicit array
or as a multi-order map.
cl : float
The desired credible level (default: 90).
projection : str, optional
The WCS projection (default: 'ARC', or zenithal equidistant).
For a list of possible values, see the Astropy documentation [3]_.
nest : bool
HEALPix pixel ordering (default: False, or ring ordering).
Returns
-------
ra : float
The ellipse center right ascension in degrees.
dec : float
The ellipse center right ascension in degrees.
a : float
The lenth of the semimajor axis in degrees.
b : float
The length of the semiminor axis in degrees.
pa : float
The orientation of the ellipse axis on the plane of the sky in degrees.
area : float
The area of the ellipse in square degrees.
Notes
-----
The center of the ellipse is the median a posteriori sky position. The
length and orientation of the semi-major and semi-minor axes are measured
as follows:
1. The sky map is transformed to a WCS projection that may be specified by
the caller. The default projection is ``ARC`` (zenithal equidistant), in
which radial distances are proportional to the physical angular
separation from the center point.
2. A 1-sigma ellipse is estimated by calculating the covariance matrix in
the projected image plane using three rounds of sigma clipping to reject
distant outlier points.
3. The 1-sigma ellipse is inflated until it encloses an integrated
probability of ``cl`` (default: 90%).
The function returns a tuple of the right ascension, declination,
semi-major distance, semi-minor distance, and orientation angle, all in
degrees.
References
----------
.. [1] http://ds9.si.edu/doc/ref/region.html
.. [2] http://aladin.u-strasbg.fr/java/AladinScriptManual.gml#draw
.. [3] http://docs.astropy.org/en/stable/wcs/index.html#supported-projections
Examples
--------
**Example 1**
First, we need some imports.
>>> from astropy.io import fits
>>> from astropy.utils.data import download_file
>>> from astropy.wcs import WCS
>>> import healpy as hp
>>> from reproject import reproject_from_healpix
>>> import subprocess
Next, we download the BAYESTAR sky map for GW170817 from the
LIGO Document Control Center.
>>> url = 'https://dcc.ligo.org/public/0146/G1701985/001/bayestar.fits.gz' # doctest: +SKIP
>>> filename = download_file(url, cache=True, show_progress=False) # doctest: +SKIP
>>> _, healpix_hdu = fits.open(filename) # doctest: +SKIP
>>> prob = hp.read_map(healpix_hdu, verbose=False) # doctest: +SKIP
Then, we calculate ellipse and write it to a DS9 region file.
>>> ra, dec, a, b, pa, area = find_ellipse(prob) # doctest: +SKIP
>>> print(*np.around([ra, dec, a, b, pa, area], 5)) # doctest: +SKIP
195.03732 -19.29358 8.66545 1.1793 63.61698 32.07665
>>> s = 'fk5;ellipse({},{},{},{},{})'.format(ra, dec, a, b, pa) # doctest: +SKIP
>>> open('ds9.reg', 'w').write(s) # doctest: +SKIP
Then, we reproject a small patch of the HEALPix map, and save it to a file.
>>> wcs = WCS() # doctest: +SKIP
>>> wcs.wcs.ctype = ['RA---ARC', 'DEC--ARC'] # doctest: +SKIP
>>> wcs.wcs.crval = [ra, dec] # doctest: +SKIP
>>> wcs.wcs.crpix = [128, 128] # doctest: +SKIP
>>> wcs.wcs.cdelt = [-0.1, 0.1] # doctest: +SKIP
>>> img, _ = reproject_from_healpix(healpix_hdu, wcs, [256, 256]) # doctest: +SKIP
>>> img_hdu = fits.ImageHDU(img, wcs.to_header()) # doctest: +SKIP
>>> img_hdu.writeto('skymap.fits') # doctest: +SKIP
Now open the image and region file in DS9. You should find that the ellipse
encloses the probability hot spot. You can load the sky map and region file
from the command line:
.. code-block:: sh
$ ds9 skymap.fits -region ds9.reg
Or you can do this manually:
1. Open DS9.
2. Open the sky map: select "File->Open..." and choose ``skymap.fits``
from the dialog box.
3. Open the region file: select "Regions->Load Regions..." and choose
``ds9.reg`` from the dialog box.
Now open the image and region file in Aladin.
1. Open Aladin.
2. Open the sky map: select "File->Load Local File..." and choose
``skymap.fits`` from the dialog box.
3. Open the sky map: select "File->Load Local File..." and choose
``ds9.reg`` from the dialog box.
You can also compare the original HEALPix file with the ellipse in Aladin:
1. Open Aladin.
2. Open the HEALPix file by pasting the URL from the top of this
example in the Command field at the top of the window and hitting
return, or by selecting "File->Load Direct URL...", pasting the URL,
and clicking "Submit."
3. Open the sky map: select "File->Load Local File..." and choose
``ds9.reg`` from the dialog box.
**Example 2**
This example shows that we get approximately the same answer for GW171087
if we read it in as a multi-order map.
>>> from ..io import read_sky_map # doctest: +SKIP
>>> skymap_moc = read_sky_map(healpix_hdu, moc=True) # doctest: +SKIP
>>> ellipse = find_ellipse(skymap_moc) # doctest: +SKIP
>>> print(*np.around(ellipse, 5)) # doctest: +SKIP
195.03709 -19.27589 8.67611 1.18167 63.60454 32.08015
**Example 3**
I'm not showing the `ra` or `pa` output from the examples below because
the right ascension is arbitary when dec=90° and the position angle is
arbitrary when a=b; their arbitrary values may vary depending on your math
library. Also, I add 0.0 to the outputs because on some platforms you tend
to get values of dec or pa that get rounded to -0.0, which is within
numerical precision but would break the doctests (see
https://stackoverflow.com/questions/11010683).
This is an example sky map that is uniform in sin(theta) out to a given
radius in degrees. The 90% credible radius should be 0.9 * radius. (There
will be deviations for small radius due to finite resolution.)
>>> def make_uniform_in_sin_theta(radius, nside=512):
... npix = ah.nside_to_npix(nside)
... theta, phi = hp.pix2ang(nside, np.arange(npix))
... theta_max = np.deg2rad(radius)
... prob = np.where(theta <= theta_max, 1 / np.sin(theta), 0)
... return prob / prob.sum()
...
>>> prob = make_uniform_in_sin_theta(1)
>>> ra, dec, a, b, pa, area = find_ellipse(prob)
>>> dec, a, b, area # doctest: +FLOAT_CMP
(89.90862520480792, 0.8703361458208101, 0.8703357768874356, 2.3788811576269793)
>>> prob = make_uniform_in_sin_theta(10)
>>> ra, dec, a, b, pa, area = find_ellipse(prob)
>>> dec, a, b, area # doctest: +FLOAT_CMP
(89.90827657529562, 9.024846562072119, 9.024842703023802, 255.11972196535515)
>>> prob = make_uniform_in_sin_theta(120)
>>> ra, dec, a, b, pa, area = find_ellipse(prob)
>>> dec, a, b, area # doctest: +FLOAT_CMP
(90.0, 107.9745037610576, 107.97450376105758, 26988.70467497216)
**Example 4**
These are approximately Gaussian distributions.
>>> from scipy import stats
>>> def make_gaussian(mean, cov, nside=512):
... npix = ah.nside_to_npix(nside)
... xyz = np.transpose(hp.pix2vec(nside, np.arange(npix)))
... dist = stats.multivariate_normal(mean, cov)
... prob = dist.pdf(xyz)
... return prob / prob.sum()
...
This one is centered at RA=45°, Dec=0° and has a standard deviation of ~1°.
>>> prob = make_gaussian(
... [1/np.sqrt(2), 1/np.sqrt(2), 0],
... np.square(np.deg2rad(1)))
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(45.0, 0.0, 2.1424077148886744, 2.1420790721225518, 90.0, 14.467701995920123)
This one is centered at RA=45°, Dec=0°, and is elongated in the north-south
direction.
>>> prob = make_gaussian(
... [1/np.sqrt(2), 1/np.sqrt(2), 0],
... np.diag(np.square(np.deg2rad([1, 1, 10]))))
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(44.99999999999999, 0.0, 13.58768882719899, 2.0829846178241853, 90.0, 88.57796576937031)
This one is centered at RA=0°, Dec=0°, and is elongated in the east-west
direction.
>>> prob = make_gaussian(
... [1, 0, 0],
... np.diag(np.square(np.deg2rad([1, 10, 1]))))
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(0.0, 0.0, 13.583918022027149, 2.0823769912401433, 0.0, 88.54622940628761)
This one is centered at RA=0°, Dec=0°, and has its long axis tilted about
10° to the west of north.
>>> prob = make_gaussian(
... [1, 0, 0],
... [[0.1, 0, 0],
... [0, 0.1, -0.15],
... [0, -0.15, 1]])
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(0.0, 0.0, 64.7713312709293, 33.50754131182681, 80.78231196786838, 6372.344658663038)
This one is centered at RA=0°, Dec=0°, and has its long axis tilted about
10° to the east of north.
>>> prob = make_gaussian(
... [1, 0, 0],
... [[0.1, 0, 0],
... [0, 0.1, 0.15],
... [0, 0.15, 1]])
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(0.0, 0.0, 64.77133127093047, 33.50754131182745, 99.21768803213159, 6372.344658663096)
This one is centered at RA=0°, Dec=0°, and has its long axis tilted about
80° to the east of north.
>>> prob = make_gaussian(
... [1, 0, 0],
... [[0.1, 0, 0],
... [0, 1, 0.15],
... [0, 0.15, 0.1]])
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(0.0, 0.0, 64.7756448603915, 33.509863018519894, 170.78252287327365, 6372.425731592412)
This one is centered at RA=0°, Dec=0°, and has its long axis tilted about
80° to the west of north.
>>> prob = make_gaussian(
... [1, 0, 0],
... [[0.1, 0, 0],
... [0, 1, -0.15],
... [0, -0.15, 0.1]])
...
>>> find_ellipse(prob) # doctest: +FLOAT_CMP
(0.0, 0.0, 64.77564486039148, 33.50986301851987, 9.217477126726322, 6372.42573159241)
""" # noqa: E501
try:
prob['UNIQ']
except (IndexError, KeyError, ValueError):
npix = len(prob)
nside = ah.npix_to_nside(npix)
ipix = range(npix)
area = ah.nside_to_pixel_area(nside).to_value(u.deg**2)
else:
order, ipix = moc.uniq2nest(prob['UNIQ'])
nside = 1 << order.astype(int)
ipix = ipix.astype(int)
area = ah.nside_to_pixel_area(nside).to_value(u.sr)
prob = prob['PROBDENSITY'] * area
area *= np.square(180 / np.pi)
nest = True
# Find median a posteriori sky position.
xyz0 = [
quantile(x, 0.5, weights=prob)
for x in hp.pix2vec(nside, ipix, nest=nest)
]
(ra, ), (dec, ) = hp.vec2ang(np.asarray(xyz0), lonlat=True)
# Construct WCS with the specified projection
# and centered on mean direction.
w = WCS()
w.wcs.crval = [ra, dec]
w.wcs.ctype = ['RA---' + projection, 'DEC--' + projection]
# Transform HEALPix to zenithal equidistant coordinates.
xy = w.wcs_world2pix(
np.transpose(hp.pix2ang(nside, ipix, nest=nest, lonlat=True)), 1)
# Keep only values that were inside the projection.
keep = np.logical_and.reduce(np.isfinite(xy), axis=1)
xy = xy[keep]
prob = prob[keep]
if not np.isscalar(area):
area = area[keep]
# Find covariance matrix, performing three rounds of sigma-clipping
# to reject outliers.
keep = np.ones(len(xy), dtype=bool)
for _ in range(3):
c = np.cov(xy[keep], aweights=prob[keep], rowvar=False)
nsigmas = np.sqrt(np.sum(xy.T * np.linalg.solve(c, xy.T), axis=0))
keep &= (nsigmas < 3)
# Find the number of sigma that enclose the cl% credible level.
i = np.argsort(nsigmas)
nsigmas = nsigmas[i]
cls = np.cumsum(prob[i])
if np.isscalar(area):
careas = np.arange(1, len(i) + 1) * area
else:
careas = np.cumsum(area[i])
nsigma = np.interp(1e-2 * cl, cls, nsigmas)
area = np.interp(1e-2 * cl, cls, careas)
# If the credible level is not within the projection,
# then stop here and return all nans.
if 1e-2 * cl > cls[-1]:
return np.nan, np.nan, np.nan, np.nan, np.nan
# Find the eigendecomposition of the covariance matrix.
w, v = np.linalg.eigh(c)
# Find the semi-minor and semi-major axes.
b, a = nsigma * np.sqrt(w)
# Find the position angle.
pa = np.rad2deg(np.arctan2(*v[0]))
# An ellipse is symmetric under rotations of 180°.
# Return the smallest possible positive position angle.
pa %= 180
# Done!
return ra, dec, a, b, pa, area
def contour(m, levels, nest=False, degrees=False, simplify=True):
"""Calculate contours from a HEALPix dataset.
Parameters
----------
m : `numpy.ndarray`
The HEALPix dataset.
levels : list
The list of contour values.
nest : bool, default=False
Indicates whether the input sky map is in nested rather than
ring-indexed HEALPix coordinates (default: ring).
degrees : bool, default=False
Whether the contours are in degrees instead of radians.
simplify : bool, default=True
Whether to simplify the paths.
Returns
-------
list
A list with the same length as `levels`.
Each item is a list of disjoint polygons, of which each item is a
list of points, of which each is a list consisting of the right
ascension and declination.
Examples
--------
A very simply example sky map...
>>> nside = 32
>>> npix = ah.nside_to_npix(nside)
>>> ra, dec = hp.pix2ang(nside, np.arange(npix), lonlat=True)
>>> m = dec
>>> contour(m, [10, 20, 30], degrees=True)
[[[[..., ...], ...], ...], ...]
"""
# Infrequently used import
import networkx as nx
# Determine HEALPix resolution.
npix = len(m)
nside = ah.npix_to_nside(npix)
min_area = 0.4 * ah.nside_to_pixel_area(nside).to_value(u.sr)
neighbors = hp.get_all_neighbours(nside, np.arange(npix), nest=nest).T
# Loop over the requested contours.
paths = []
for level in levels:
# Find credible region.
indicator = (m >= level)
# Find all faces that lie on the boundary.
# This speeds up the doubly nested ``for`` loop below by allowing us to
# skip the vast majority of faces that are on the interior or the
# exterior of the contour.
tovisit = np.flatnonzero(
np.any(indicator.reshape(-1, 1) != indicator[neighbors[:, ::2]],
axis=1))
# Construct a graph of the edges of the contour.
graph = nx.Graph()
face_pairs = set()
for ipix1 in tovisit:
neighborhood = neighbors[ipix1]
for _ in range(4):
neighborhood = np.roll(neighborhood, 2)
ipix2 = neighborhood[4]
# Skip this pair of faces if we have already examined it.
new_face_pair = frozenset((ipix1, ipix2))
if new_face_pair in face_pairs:
continue
face_pairs.add(new_face_pair)
# Determine if this pair of faces are on a boundary of the
# credible level.
if indicator[ipix1] == indicator[ipix2]:
continue
# Add the common edge of this pair of faces.
# Label each vertex with the set of faces that they share.
graph.add_edge(frozenset((ipix1, *neighborhood[2:5])),
frozenset((ipix1, *neighborhood[4:7])))
graph = nx.freeze(graph)
# Find contours by detecting cycles in the graph.
cycles = nx.cycle_basis(graph)
# Construct the coordinates of the vertices by averaging the
# coordinates of the connected faces.
cycles = [[
np.sum(hp.pix2vec(nside, [i for i in v if i != -1], nest=nest), 1)
for v in cycle
] for cycle in cycles]
# Simplify paths if requested.
if simplify:
cycles = [_simplify(cycle, min_area) for cycle in cycles]
cycles = [cycle for cycle in cycles if len(cycle) > 2]
# Convert to angles.
cycles = [
_vec2radec(cycle, degrees=degrees).tolist() for cycle in cycles
]
# Add to output paths.
paths.append([cycle + [cycle[0]] for cycle in cycles])
return paths
