""" Astropy coordinate class for the Sagittarius coordinate system """
# Third-party
import numpy as np
from astropy.coordinates import frame_transform_graph
import astropy.coordinates as coord
import astropy.units as u
from astropy.coordinates.matrix_utilities import rotation_matrix, matrix_product, matrix_transpose
__all__ = ["SagittariusLaw10", "Sagittarius"]
[docs]class SagittariusLaw10(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit
of the Sagittarius dwarf galaxy, as described in
http://adsabs.harvard.edu/abs/2003ApJ...599.1082M
and further explained in http://www.stsci.edu/~dlaw/Sgr/.
Parameters
----------
representation : `BaseRepresentation` or None
A representation object or None to have no data (or use the other
keywords).
Lambda : `Angle`, optional, must be keyword
The longitude-like angle corresponding to Sagittarius' orbit.
Beta : `Angle`, optional, must be keyword
The latitude-like angle corresponding to Sagittarius' orbit.
distance : `Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
pm_Lambda_cosBeta : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion along the stream in ``Lambda`` (including the
``cos(Beta)`` factor) for this object (``pm_Beta`` must also be given).
pm_Beta : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in Declination for this object (``pm_ra_cosdec`` must
also be given).
radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword
The radial velocity of this object.
"""
default_representation = coord.SphericalRepresentation
default_differential = coord.SphericalCosLatDifferential
frame_specific_representation_info = {
coord.SphericalRepresentation: [
coord.RepresentationMapping('lon', 'Lambda'),
coord.RepresentationMapping('lat', 'Beta'),
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)
if hasattr(r, "lon"):
r.lon.wrap_angle = self._default_wrap_angle
return r
represent_as.__doc__ = coord.BaseCoordinateFrame.represent_as.__doc__
# Define the Euler angles (from Law & Majewski 2010)
phi = (180+3.75) * u.degree
theta = (90-13.46) * u.degree
psi = (180+14.111534) * u.degree
# Generate the rotation matrix using the x-convention (see Goldstein)
D = rotation_matrix(phi, "z")
C = rotation_matrix(theta, "x")
B = rotation_matrix(psi, "z")
A = np.diag([1., 1., -1.])
R = matrix_product(A, B, C, D)
# Galactic to Sgr coordinates
@frame_transform_graph.transform(coord.StaticMatrixTransform, coord.Galactic,
SagittariusLaw10)
def galactic_to_sgr():
""" Compute the transformation from Galactic spherical to
heliocentric Sagittarius coordinates.
"""
return R
# Sgr to Galactic coordinates
@frame_transform_graph.transform(coord.StaticMatrixTransform, SagittariusLaw10,
coord.Galactic)
def sgr_to_galactic():
""" Compute the transformation from heliocentric Sagittarius coordinates to
spherical Galactic.
"""
return matrix_transpose(galactic_to_sgr())
# TODO: remove this in next version
class Sagittarius(SagittariusLaw10):
def __init__(self, *args, **kwargs):
import warnings
warnings.warn("This frame is deprecated. Use SagittariusLaw10 "
"instead.", DeprecationWarning)
super().__init__(*args, **kwargs)
trans = frame_transform_graph.get_transform(SagittariusLaw10,
coord.Galactic).transforms[0]
frame_transform_graph.add_transform(Sagittarius, coord.Galactic, trans)
trans = frame_transform_graph.get_transform(coord.Galactic,
SagittariusLaw10).transforms[0]
frame_transform_graph.add_transform(coord.Galactic, Sagittarius, trans)