""" Astropy coordinate class for the Sagittarius coordinate system """
# Third-party
import numpy as np
import astropy.units as u
import astropy.coordinates as coord
from astropy.coordinates import frame_transform_graph
from astropy.coordinates.matrix_utilities import matrix_transpose
__all__ = ["GD1Koposov10", "GD1"]
[docs]class GD1Koposov10(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit
of the GD1 stream, as described in
Koposov et al. 2010 (see: `<http://arxiv.org/abs/0907.1085>`_).
For more information about this class, see the Astropy documentation
on coordinate frames in :mod:`~astropy.coordinates`.
Parameters
----------
representation : :class:`~astropy.coordinates.BaseRepresentation` or None
A representation object or None to have no data (or use the other keywords)
phi1 : angle_like, optional, must be keyword
The longitude-like angle corresponding to GD-1's orbit.
phi2 : angle_like, optional, must be keyword
The latitude-like angle corresponding to GD-1's orbit.
distance : :class:`~astropy.units.Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
pm_phi1_cosphi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the longitude-like direction corresponding to
the GD-1 stream's orbit.
pm_phi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the latitude-like direction perpendicular to the
GD-1 stream's orbit.
radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
"""
default_representation = coord.SphericalRepresentation
default_differential = coord.SphericalCosLatDifferential
frame_specific_representation_info = {
coord.SphericalRepresentation: [
coord.RepresentationMapping('lon', 'phi1'),
coord.RepresentationMapping('lat', 'phi2'),
coord.RepresentationMapping('distance', 'distance')],
}
_default_wrap_angle = 180*u.deg
def __init__(self, *args, **kwargs):
wrap = kwargs.pop('wrap_longitude', True)
super().__init__(*args, **kwargs)
if wrap and isinstance(self._data, (coord.UnitSphericalRepresentation,
coord.SphericalRepresentation)):
self._data.lon.wrap_angle = self._default_wrap_angle
# TODO: remove this. This is a hack required as of astropy v3.1 in order
# to have the longitude components wrap at the desired angle
[docs] def represent_as(self, base, s='base', in_frame_units=False):
r = super().represent_as(base, s=s, in_frame_units=in_frame_units)
r.lon.wrap_angle = self._default_wrap_angle
return r
represent_as.__doc__ = coord.BaseCoordinateFrame.represent_as.__doc__
# Rotation matrix as defined in the Appendix of Koposov et al. (2010)
R = np.array([[-0.4776303088, -0.1738432154, 0.8611897727],
[0.510844589, -0.8524449229, 0.111245042],
[0.7147776536, 0.4930681392, 0.4959603976]])
@frame_transform_graph.transform(coord.StaticMatrixTransform, coord.ICRS,
GD1Koposov10)
def icrs_to_gd1():
""" Compute the transformation from Galactic spherical to
heliocentric GD1 coordinates.
"""
return R
@frame_transform_graph.transform(coord.StaticMatrixTransform, GD1Koposov10,
coord.ICRS)
def gd1_to_icrs():
""" Compute the transformation from heliocentric GD1 coordinates to
spherical Galactic.
"""
return matrix_transpose(icrs_to_gd1())
# TODO: remove this in next version
class GD1(GD1Koposov10):
def __init__(self, *args, **kwargs):
import warnings
warnings.warn("This frame is deprecated. Use GD1Koposov10 instead.",
DeprecationWarning)
super().__init__(*args, **kwargs)
trans = frame_transform_graph.get_transform(GD1Koposov10,
coord.ICRS).transforms[0]
frame_transform_graph.add_transform(GD1, coord.ICRS, trans)
trans = frame_transform_graph.get_transform(coord.ICRS,
GD1Koposov10).transforms[0]
frame_transform_graph.add_transform(coord.ICRS, GD1, trans)