Source code for astropy.coordinates.angle_utilities

# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
This module contains utility functions for working with angles. These are both
used internally in astropy.coordinates.angles, and of possible
"""

__all__ = ['angular_separation', 'position_angle', 'offset_by',
           'golden_spiral_grid', 'uniform_spherical_random_surface',
           'uniform_spherical_random_volume']

# Third-party
import numpy as np

# Astropy
import astropy.units as u
from astropy.coordinates.representation import (
    UnitSphericalRepresentation,
    SphericalRepresentation)


[docs]def angular_separation(lon1, lat1, lon2, lat2): """ Angular separation between two points on a sphere. Parameters ---------- lon1, lat1, lon2, lat2 : `~astropy.coordinates.Angle`, `~astropy.units.Quantity` or float Longitude and latitude of the two points. Quantities should be in angular units; floats in radians. Returns ------- angular separation : `~astropy.units.Quantity` ['angle'] or float Type depends on input; ``Quantity`` in angular units, or float in radians. Notes ----- The angular separation is calculated using the Vincenty formula [1]_, which is slightly more complex and computationally expensive than some alternatives, but is stable at at all distances, including the poles and antipodes. .. [1] https://en.wikipedia.org/wiki/Great-circle_distance """ sdlon = np.sin(lon2 - lon1) cdlon = np.cos(lon2 - lon1) slat1 = np.sin(lat1) slat2 = np.sin(lat2) clat1 = np.cos(lat1) clat2 = np.cos(lat2) num1 = clat2 * sdlon num2 = clat1 * slat2 - slat1 * clat2 * cdlon denominator = slat1 * slat2 + clat1 * clat2 * cdlon return np.arctan2(np.hypot(num1, num2), denominator)
[docs]def position_angle(lon1, lat1, lon2, lat2): """ Position Angle (East of North) between two points on a sphere. Parameters ---------- lon1, lat1, lon2, lat2 : `~astropy.coordinates.Angle`, `~astropy.units.Quantity` or float Longitude and latitude of the two points. Quantities should be in angular units; floats in radians. Returns ------- pa : `~astropy.coordinates.Angle` The (positive) position angle of the vector pointing from position 1 to position 2. If any of the angles are arrays, this will contain an array following the appropriate `numpy` broadcasting rules. """ from .angles import Angle deltalon = lon2 - lon1 colat = np.cos(lat2) x = np.sin(lat2) * np.cos(lat1) - colat * np.sin(lat1) * np.cos(deltalon) y = np.sin(deltalon) * colat return Angle(np.arctan2(y, x), u.radian).wrap_at(360*u.deg)
[docs]def offset_by(lon, lat, posang, distance): """ Point with the given offset from the given point. Parameters ---------- lon, lat, posang, distance : `~astropy.coordinates.Angle`, `~astropy.units.Quantity` or float Longitude and latitude of the starting point, position angle and distance to the final point. Quantities should be in angular units; floats in radians. Polar points at lat= +/-90 are treated as limit of +/-(90-epsilon) and same lon. Returns ------- lon, lat : `~astropy.coordinates.Angle` The position of the final point. If any of the angles are arrays, these will contain arrays following the appropriate `numpy` broadcasting rules. 0 <= lon < 2pi. Notes ----- """ from .angles import Angle # Calculations are done using the spherical trigonometry sine and cosine rules # of the triangle A at North Pole, B at starting point, C at final point # with angles A (change in lon), B (posang), C (not used, but negative reciprocal posang) # with sides a (distance), b (final co-latitude), c (starting colatitude) # B, a, c are knowns; A and b are unknowns # https://en.wikipedia.org/wiki/Spherical_trigonometry cos_a = np.cos(distance) sin_a = np.sin(distance) cos_c = np.sin(lat) sin_c = np.cos(lat) cos_B = np.cos(posang) sin_B = np.sin(posang) # cosine rule: Know two sides: a,c and included angle: B; get unknown side b cos_b = cos_c * cos_a + sin_c * sin_a * cos_B # sin_b = np.sqrt(1 - cos_b**2) # sine rule and cosine rule for A (using both lets arctan2 pick quadrant). # multiplying both sin_A and cos_A by x=sin_b * sin_c prevents /0 errors # at poles. Correct for the x=0 multiplication a few lines down. # sin_A/sin_a == sin_B/sin_b # Sine rule xsin_A = sin_a * sin_B * sin_c # cos_a == cos_b * cos_c + sin_b * sin_c * cos_A # cosine rule xcos_A = cos_a - cos_b * cos_c A = Angle(np.arctan2(xsin_A, xcos_A), u.radian) # Treat the poles as if they are infinitesimally far from pole but at given lon small_sin_c = sin_c < 1e-12 if small_sin_c.any(): # For south pole (cos_c = -1), A = posang; for North pole, A=180 deg - posang A_pole = (90*u.deg + cos_c*(90*u.deg-Angle(posang, u.radian))).to(u.rad) if A.shape: # broadcast to ensure the shape is like that of A, which is also # affected by the (possible) shapes of lat, posang, and distance. small_sin_c = np.broadcast_to(small_sin_c, A.shape) A[small_sin_c] = A_pole[small_sin_c] else: A = A_pole outlon = (Angle(lon, u.radian) + A).wrap_at(360.0*u.deg).to(u.deg) outlat = Angle(np.arcsin(cos_b), u.radian).to(u.deg) return outlon, outlat
[docs]def golden_spiral_grid(size): """Generate a grid of points on the surface of the unit sphere using the Fibonacci or Golden Spiral method. .. seealso:: `Evenly distributing points on a sphere <https://stackoverflow.com/questions/9600801/evenly-distributing-n-points-on-a-sphere>`_ Parameters ---------- size : int The number of points to generate. Returns ------- rep : `~astropy.coordinates.UnitSphericalRepresentation` The grid of points. """ golden_r = (1 + 5**0.5) / 2 grid = np.arange(0, size, dtype=float) + 0.5 lon = 2*np.pi / golden_r * grid * u.rad lat = np.arcsin(1 - 2 * grid / size) * u.rad return UnitSphericalRepresentation(lon, lat)
[docs]def uniform_spherical_random_surface(size=1): """Generate a random sampling of points on the surface of the unit sphere. Parameters ---------- size : int The number of points to generate. Returns ------- rep : `~astropy.coordinates.UnitSphericalRepresentation` The random points. """ rng = np.random # can maybe switch to this being an input later - see #11628 lon = rng.uniform(0, 2*np.pi, size) * u.rad lat = np.arcsin(rng.uniform(-1, 1, size=size)) * u.rad return UnitSphericalRepresentation(lon, lat)
[docs]def uniform_spherical_random_volume(size=1, max_radius=1): """Generate a random sampling of points that follow a uniform volume density distribution within a sphere. Parameters ---------- size : int The number of points to generate. max_radius : number, quantity-like, optional A dimensionless or unit-ful factor to scale the random distances. rng : `numpy.random.Generator`, optional A random number generator instance. Returns ------- rep : `~astropy.coordinates.SphericalRepresentation` The random points. """ rng = np.random # can maybe switch to this being an input later - see #11628 usph = uniform_spherical_random_surface(size=size) r = np.cbrt(rng.uniform(size=size)) * u.Quantity(max_radius, copy=False) return SphericalRepresentation(usph.lon, usph.lat, r)
# # below here can be deleted in v5.0 from astropy.utils.decorators import deprecated from astropy.coordinates import angle_formats __old_angle_utilities_funcs = ['check_hms_ranges', 'degrees_to_dms', 'degrees_to_string', 'dms_to_degrees', 'format_exception', 'hms_to_degrees', 'hms_to_dms', 'hms_to_hours', 'hms_to_radians', 'hours_to_decimal', 'hours_to_hms', 'hours_to_radians', 'hours_to_string', 'parse_angle', 'radians_to_degrees', 'radians_to_dms', 'radians_to_hms', 'radians_to_hours', 'sexagesimal_to_string'] for funcname in __old_angle_utilities_funcs: vars()[funcname] = deprecated(name='astropy.coordinates.angle_utilities.' + funcname, alternative='astropy.coordinates.angle_formats.' + funcname, since='v4.3')(getattr(angle_formats, funcname))