Source code for gala.coordinates.magellanic_stream

""" Astropy coordinate class for the Magellanic Stream coordinate system """

from astropy.coordinates.matrix_utilities import rotation_matrix
from astropy.coordinates.baseframe import (
    frame_transform_graph,
    BaseCoordinateFrame,
    RepresentationMapping,
)
from astropy.coordinates.transformations import StaticMatrixTransform
from astropy.coordinates import representation as r
from astropy.coordinates import Galactic

import astropy.units as u

__all__ = ["MagellanicStreamNidever08"]


class MagellanicStreamNidever08(BaseCoordinateFrame):
    """
    A coordinate or frame aligned with the Magellanic Stream,
    as defined by Nidever et al. (2008,
    see: `<http://adsabs.harvard.edu/abs/2008ApJ...679..432N>`_).

    For more information about this class, see the Astropy documentation
    on coordinate frames in :mod:`~astropy.coordinates`.

    Examples
    --------
    Converting the coordinates of the Large Magellanic Cloud:

        >>> from astropy import coordinates as coord
        >>> from astropy import units as u
        >>> from gala.coordinates import MagellanicStreamNidever08

        >>> c = coord.Galactic(l=280.4652*u.deg, b=-32.8884*u.deg)
        >>> ms = c.transform_to(MagellanicStreamNidever08())
        >>> print(ms)
        <MagellanicStreamNidever08 Coordinate: (L, B) in deg
            (-0.13686116, 2.42583948)>
    """

    frame_specific_representation_info = {
        r.SphericalRepresentation: [
            RepresentationMapping("lon", "L"),
            RepresentationMapping("lat", "B"),
        ]
    }

    default_representation = r.SphericalRepresentation
    default_differential = r.SphericalCosLatDifferential

    _ngp = Galactic(l=188.5 * u.deg, b=-7.5 * u.deg)
    _lon0 = Galactic(l=280.47 * u.deg, b=-32.75 * u.deg)

    _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, (r.UnitSphericalRepresentation, r.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
    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__ = BaseCoordinateFrame.represent_as.__doc__


@frame_transform_graph.transform(
    StaticMatrixTransform, Galactic, MagellanicStreamNidever08
)
def gal_to_mag():
    mat1 = rotation_matrix(57.275785782128686 * u.deg, "z")
    mat2 = rotation_matrix(90 * u.deg - MagellanicStreamNidever08._ngp.b, "y")
    mat3 = rotation_matrix(MagellanicStreamNidever08._ngp.l, "z")

    return mat1 @ mat2 @ mat3


@frame_transform_graph.transform(
    StaticMatrixTransform, MagellanicStreamNidever08, Galactic
)
def mag_to_gal():
    return gal_to_mag().T