Source code for astropy.coordinates.builtin_frames.galactocentric

# Licensed under a 3-clause BSD style license - see LICENSE.rst

from __future__ import annotations

import copy
from import MappingView
from types import MappingProxyType

import numpy as np

from astropy import units as u
from astropy.coordinates import Angle
from astropy.coordinates import representation as r
from astropy.coordinates.attributes import (
from astropy.coordinates.baseframe import (
from astropy.coordinates.errors import ConvertError
from astropy.coordinates.matrix_utilities import matrix_transpose, rotation_matrix
from astropy.coordinates.transformations import AffineTransform
from astropy.utils.decorators import classproperty, format_doc
from astropy.utils.state import ScienceState

from .icrs import ICRS

__all__ = ["Galactocentric"]

# Measured by minimizing the difference between a plane of coordinates along
#   l=0, b=[-90,90] and the Galactocentric x-z plane
# This is not used directly, but accessed via `get_roll0`.  We define it here to
# prevent having to create new Angle objects every time `get_roll0` is called.
_ROLL0 = Angle(58.5986320306 *

class _StateProxy(MappingView):
    `` with a read-only ``getitem`` through


    def __init__(self, mapping):
        self._mappingproxy = MappingProxyType(self._mapping)  # read-only

    def __getitem__(self, key):
        """Read-only ``getitem``."""
        return self._mappingproxy[key]

    def __deepcopy__(self, memo):
        return copy.deepcopy(self._mapping, memo=memo)

[docs] class galactocentric_frame_defaults(ScienceState): """Global setting of default values for the frame attributes in the `~astropy.coordinates.Galactocentric` frame. These constancts may be updated in future versions of ``astropy``. Note that when using `~astropy.coordinates.Galactocentric`, changing values here will not affect any attributes that are set explicitly by passing values in to the `~astropy.coordinates.Galactocentric` initializer. Modifying these defaults will only affect the frame attribute values when using the frame as, e.g., ``Galactocentric`` or ``Galactocentric()`` with no explicit arguments. This class controls the parameter settings by specifying a string name, with the following pre-specified options: - 'pre-v4.0': The current default value, which sets the default frame attribute values to their original (pre-astropy-v4.0) values. - 'v4.0': The attribute values as updated in Astropy version 4.0. - 'latest': An alias of the most recent parameter set (currently: 'v4.0') Alternatively, user-defined parameter settings may be registered, with :meth:`~astropy.coordinates.galactocentric_frame_defaults.register`, and used identically as pre-specified parameter sets. At minimum, registrations must have unique names and a dictionary of parameters with keys "galcen_coord", "galcen_distance", "galcen_v_sun", "z_sun", "roll". See examples below. This class also tracks the references for all parameter values in the attribute ``references``, as well as any further information the registry. The pre-specified options can be extended to include similar state information as user-defined parameter settings -- for example, to add parameter uncertainties. The preferred method for getting a parameter set and metadata, by name, is :meth:`~astropy.coordinates.galactocentric_frame_defaults.get_from_registry` since it ensures the immutability of the registry. See :ref:`astropy:astropy-coordinates-galactocentric-defaults` for more information. Examples -------- The default `~astropy.coordinates.Galactocentric` frame parameters can be modified globally:: >>> from astropy.coordinates import galactocentric_frame_defaults >>> _ = galactocentric_frame_defaults.set('v4.0') # doctest: +SKIP >>> Galactocentric() # doctest: +SKIP <Galactocentric Frame (galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.122 kpc, galcen_v_sun=(12.9, 245.6, 7.78) km / s, z_sun=20.8 pc, roll=0.0 deg)> >>> _ = galactocentric_frame_defaults.set('pre-v4.0') # doctest: +SKIP >>> Galactocentric() # doctest: +SKIP <Galactocentric Frame (galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.3 kpc, galcen_v_sun=(11.1, 232.24, 7.25) km / s, z_sun=27.0 pc, roll=0.0 deg)> The default parameters can also be updated by using this class as a context manager:: >>> with galactocentric_frame_defaults.set('pre-v4.0'): ... print(Galactocentric()) # doctest: +FLOAT_CMP <Galactocentric Frame (galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.3 kpc, galcen_v_sun=(11.1, 232.24, 7.25) km / s, z_sun=27.0 pc, roll=0.0 deg)> Again, changing the default parameter values will not affect frame attributes that are explicitly specified:: >>> import astropy.units as u >>> with galactocentric_frame_defaults.set('pre-v4.0'): ... print(Galactocentric(galcen_distance=8.0*u.kpc)) # doctest: +FLOAT_CMP <Galactocentric Frame (galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.0 kpc, galcen_v_sun=(11.1, 232.24, 7.25) km / s, z_sun=27.0 pc, roll=0.0 deg)> Additional parameter sets may be registered, for instance to use the Dehnen & Binney (1998) measurements of the solar motion. We can also add metadata, such as the 1-sigma errors. In this example we will modify the required key "parameters", change the recommended key "references" to match "parameters", and add the extra key "error" (any key can be added):: >>> state = galactocentric_frame_defaults.get_from_registry("v4.0") >>> state["parameters"]["galcen_v_sun"] = (10.00, 225.25, 7.17) * ( / u.s) >>> state["references"]["galcen_v_sun"] = "" >>> state["error"] = {"galcen_v_sun": (0.36, 0.62, 0.38) * ( / u.s)} >>> galactocentric_frame_defaults.register(name="DB1998", **state) Just as in the previous examples, the new parameter set can be retrieved with:: >>> state = galactocentric_frame_defaults.get_from_registry("DB1998") >>> print(state["error"]["galcen_v_sun"]) # doctest: +FLOAT_CMP [0.36 0.62 0.38] km / s """ _latest_value = "v4.0" _value = None _references = None _state = {} # all other data # Note: _StateProxy() produces read-only view of enclosed mapping. _registry = { "v4.0": { "parameters": _StateProxy( { "galcen_coord": ICRS( ra=266.4051 *, dec=-28.936175 * ), "galcen_distance": 8.122 * u.kpc, "galcen_v_sun": r.CartesianDifferential( [12.9, 245.6, 7.78] * ( / u.s) ), "z_sun": 20.8 * u.pc, "roll": 0 * u.deg, } ), "references": _StateProxy( { "galcen_coord": ( "" ), "galcen_distance": ( "" ), "galcen_v_sun": [ "", "", "", ], "z_sun": "", "roll": None, } ), }, "pre-v4.0": { "parameters": _StateProxy( { "galcen_coord": ICRS( ra=266.4051 *, dec=-28.936175 * ), "galcen_distance": 8.3 * u.kpc, "galcen_v_sun": r.CartesianDifferential( [11.1, 220 + 12.24, 7.25] * ( / u.s) ), "z_sun": 27.0 * u.pc, "roll": 0 * u.deg, } ), "references": _StateProxy( { "galcen_coord": ( "" ), "galcen_distance": ( "" ), "galcen_v_sun": [ "", "", ], "z_sun": "", "roll": None, } ), }, } @classproperty # read-only def parameters(cls): return cls._value @classproperty # read-only def references(cls): return cls._references
[docs] @classmethod def get_from_registry(cls, name: str) -> dict[str, dict]: """ Return Galactocentric solar parameters and metadata given string names for the parameter sets. This method ensures the returned state is a mutable copy, so any changes made do not affect the registry state. Returns ------- state : dict Copy of the registry for the string name. Should contain, at minimum: - "parameters": dict Galactocentric solar parameters - "references" : Dict[str, Union[str, Sequence[str]]] References for "parameters". Fields are str or sequence of str. Raises ------ KeyError If invalid string input to registry to retrieve solar parameters for Galactocentric frame. """ # Resolve the meaning of 'latest': latest parameter set is from v4.0 # - update this as newer parameter choices are added if name == "latest": name = cls._latest_value # Get the state from the registry. # Copy to ensure registry is immutable to modifications of "_value". # Raises KeyError if `name` is invalid string input to registry # to retrieve solar parameters for Galactocentric frame. state = copy.deepcopy(cls._registry[name]) # ensure mutable return state
[docs] @classmethod def validate(cls, value): if value is None: value = cls._latest_value if isinstance(value, str): state = cls.get_from_registry(value) cls._references = state["references"] cls._state = state parameters = state["parameters"] elif isinstance(value, dict): parameters = value elif isinstance(value, Galactocentric): # turn the frame instance into a dict of frame attributes parameters = {} for k in value.frame_attributes: parameters[k] = getattr(value, k) cls._references = value.frame_attribute_references.copy() cls._state = {"parameters": parameters, "references": cls._references} else: raise ValueError( "Invalid input to retrieve solar parameters for Galactocentric frame:" " input must be a string, dict, or Galactocentric instance" ) return parameters
[docs] @classmethod def register( cls, name: str, parameters: dict, references=None, **meta: dict ) -> None: """Register a set of parameters. Parameters ---------- name : str The registration name for the parameter and metadata set. parameters : dict The solar parameters for Galactocentric frame. references : dict or None, optional References for contents of `parameters`. None becomes empty dict. **meta : dict, optional Any other properties to register. """ # check on contents of `parameters` must_have = {"galcen_coord", "galcen_distance", "galcen_v_sun", "z_sun", "roll"} missing = must_have.difference(parameters) if missing: raise ValueError(f"Missing parameters: {missing}") references = references or {} # None -> {} state = {"parameters": parameters, "references": references} state.update(meta) # meta never has keys "parameters" or "references" cls._registry[name] = state
doc_components = """ x : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`x` position component. y : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`y` position component. z : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`z` position component. v_x : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`v_x` velocity component. v_y : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`v_y` velocity component. v_z : `~astropy.units.Quantity`, optional Cartesian, Galactocentric :math:`v_z` velocity component. """ doc_footer = """ Other parameters ---------------- galcen_coord : `~astropy.coordinates.ICRS`, optional, keyword-only The ICRS coordinates of the Galactic center. galcen_distance : `~astropy.units.Quantity`, optional, keyword-only The distance from the sun to the Galactic center. galcen_v_sun : `~astropy.coordinates.CartesianDifferential`, `~astropy.units.Quantity` ['speed'], optional, keyword-only The velocity of the sun *in the Galactocentric frame* as Cartesian velocity components. z_sun : `~astropy.units.Quantity` ['length'], optional, keyword-only The distance from the sun to the Galactic midplane. roll : `~astropy.coordinates.Angle`, optional, keyword-only The angle to rotate about the final x-axis, relative to the orientation for Galactic. For example, if this roll angle is 0, the final x-z plane will align with the Galactic coordinates x-z plane. Unless you really know what this means, you probably should not change this! Examples -------- To transform to the Galactocentric frame with the default frame attributes, pass the uninstantiated class name to the ``transform_to()`` method of a `~astropy.coordinates.SkyCoord` object:: >>> import astropy.units as u >>> import astropy.coordinates as coord >>> c = coord.SkyCoord(ra=[158.3122, 24.5] *, ... dec=[-17.3, 81.52] *, ... distance=[11.5, 24.12] * u.kpc, ... frame='icrs') >>> c.transform_to(coord.Galactocentric) # doctest: +FLOAT_CMP <SkyCoord (Galactocentric: galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.122 kpc, galcen_v_sun=(12.9, 245.6, 7.78) km / s, z_sun=20.8 pc, roll=0.0 deg): (x, y, z) in kpc [( -9.43489286, -9.40062188, 6.51345359), (-21.11044918, 18.76334013, 7.83175149)]> To specify a custom set of parameters, you have to include extra keyword arguments when initializing the Galactocentric frame object:: >>> c.transform_to(coord.Galactocentric(galcen_distance=8.1*u.kpc)) # doctest: +FLOAT_CMP <SkyCoord (Galactocentric: galcen_coord=<ICRS Coordinate: (ra, dec) in deg (266.4051, -28.936175)>, galcen_distance=8.1 kpc, galcen_v_sun=(12.9, 245.6, 7.78) km / s, z_sun=20.8 pc, roll=0.0 deg): (x, y, z) in kpc [( -9.41284763, -9.40062188, 6.51346272), (-21.08839478, 18.76334013, 7.83184184)]> Similarly, transforming from the Galactocentric frame to another coordinate frame:: >>> c = coord.SkyCoord(x=[-8.3, 4.5] * u.kpc, ... y=[0., 81.52] * u.kpc, ... z=[0.027, 24.12] * u.kpc, ... frame=coord.Galactocentric) >>> c.transform_to(coord.ICRS) # doctest: +FLOAT_CMP <SkyCoord (ICRS): (ra, dec, distance) in (deg, deg, kpc) [( 88.22423301, 29.88672864, 0.17813456), (289.72864549, 49.9865043 , 85.93949064)]> Or, with custom specification of the Galactic center:: >>> c = coord.SkyCoord(x=[-8.0, 4.5] * u.kpc, ... y=[0., 81.52] * u.kpc, ... z=[21.0, 24120.0] * u.pc, ... frame=coord.Galactocentric, ... z_sun=21 * u.pc, galcen_distance=8. * u.kpc) >>> c.transform_to(coord.ICRS) # doctest: +FLOAT_CMP <SkyCoord (ICRS): (ra, dec, distance) in (deg, deg, kpc) [( 86.2585249 , 28.85773187, 2.75625475e-05), (289.77285255, 50.06290457, 8.59216010e+01)]> """
[docs] @format_doc(base_doc, components=doc_components, footer=doc_footer) class Galactocentric(BaseCoordinateFrame): r""" A coordinate or frame in the Galactocentric system. This frame allows specifying the Sun-Galactic center distance, the height of the Sun above the Galactic midplane, and the solar motion relative to the Galactic center. However, as there is no modern standard definition of a Galactocentric reference frame, it is important to pay attention to the default values used in this class if precision is important in your code. The default values of the parameters of this frame are taken from the original definition of the frame in 2014. As such, the defaults are somewhat out of date relative to recent measurements made possible by, e.g., Gaia. The defaults can, however, be changed at runtime by setting the parameter set name in `~astropy.coordinates.galactocentric_frame_defaults`. The current default parameter set is ``"pre-v4.0"``, indicating that the parameters were adopted before ``astropy`` version 4.0. A regularly-updated parameter set can instead be used by setting ``galactocentric_frame_defaults.set ('latest')``, and other parameter set names may be added in future versions. To find out the scientific papers that the current default parameters are derived from, use ``galcen.frame_attribute_references`` (where ``galcen`` is an instance of this frame), which will update even if the default parameter set is changed. The position of the Sun is assumed to be on the x axis of the final, right-handed system. That is, the x axis points from the position of the Sun projected to the Galactic midplane to the Galactic center -- roughly towards :math:`(l,b) = (0^\circ,0^\circ)`. For the default transformation (:math:`{\rm roll}=0^\circ`), the y axis points roughly towards Galactic longitude :math:`l=90^\circ`, and the z axis points roughly towards the North Galactic Pole (:math:`b=90^\circ`). For a more detailed look at the math behind this transformation, see the document :ref:`astropy:coordinates-galactocentric`. The frame attributes are listed under **Other Parameters**. """ default_representation = r.CartesianRepresentation default_differential = r.CartesianDifferential # frame attributes galcen_coord = CoordinateAttribute( frame=ICRS, doc="The coordinates of the Galactic center" ) galcen_distance = QuantityAttribute( unit=u.kpc, doc="The distance from the Sun to the Galactic center" ) galcen_v_sun = DifferentialAttribute( allowed_classes=[r.CartesianDifferential], doc="The velocity of the Sun in the Galactocentric frame", ) z_sun = QuantityAttribute( unit=u.pc, doc="The distance from the Sun to the Galactic midplane" ) roll = QuantityAttribute( unit=u.deg, doc="The rotation angle relative to the orientation for Galactic" ) def __init__(self, *args, **kwargs): # Set default frame attribute values based on the ScienceState instance # for the solar parameters defined above default_params = galactocentric_frame_defaults.get() self.frame_attribute_references = ( galactocentric_frame_defaults.references.copy() ) for k in default_params: if k in kwargs: # If a frame attribute is set by the user, remove its reference self.frame_attribute_references.pop(k, None) # Keep the frame attribute if it is set by the user, otherwise use # the default value kwargs[k] = kwargs.get(k, default_params[k]) super().__init__(*args, **kwargs)
[docs] @classmethod def get_roll0(cls): """The additional roll angle (about the final x axis) necessary to align the final z axis to match the Galactic yz-plane. Setting the ``roll`` frame attribute to -this method's return value removes this rotation, allowing the use of the `~astropy.coordinates.Galactocentric` frame in more general contexts. """ # note that the actual value is defined at the module level. We make at # a property here because this module isn't actually part of the public # API, so it's better for it to be accessible from Galactocentric return _ROLL0
# ICRS to/from Galactocentric -----------------------> def get_matrix_vectors(galactocentric_frame, inverse=False): """ Use the ``inverse`` argument to get the inverse transformation, matrix and offsets to go from Galactocentric to ICRS. """ # shorthand gcf = galactocentric_frame # rotation matrix to align x(ICRS) with the vector to the Galactic center mat1 = rotation_matrix(-gcf.galcen_coord.dec, "y") mat2 = rotation_matrix(gcf.galcen_coord.ra, "z") # extra roll away from the Galactic x-z plane mat0 = rotation_matrix(gcf.get_roll0() - gcf.roll, "x") # construct transformation matrix and use it R = mat0 @ mat1 @ mat2 # Now need to translate by Sun-Galactic center distance around x' and # rotate about y' to account for tilt due to Sun's height above the plane translation = r.CartesianRepresentation(gcf.galcen_distance * [1.0, 0.0, 0.0]) z_d = gcf.z_sun / gcf.galcen_distance H = rotation_matrix(-np.arcsin(z_d), "y") # compute total matrices A = H @ R # Now we re-align the translation vector to account for the Sun's height # above the midplane offset = -translation.transform(H) if inverse: # the inverse of a rotation matrix is a transpose, which is much faster # and more stable to compute A = matrix_transpose(A) offset = (-offset).transform(A) offset_v = r.CartesianDifferential.from_cartesian( (-gcf.galcen_v_sun).to_cartesian().transform(A) ) offset = offset.with_differentials(offset_v) else: offset = offset.with_differentials(gcf.galcen_v_sun) return A, offset def _check_coord_repr_diff_types(c): if isinstance(, r.UnitSphericalRepresentation): raise ConvertError( "Transforming to/from a Galactocentric frame requires a 3D coordinate, e.g." " (angle, angle, distance) or (x, y, z)." ) if "s" in and isinstance(["s"], ( r.UnitSphericalDifferential, r.UnitSphericalCosLatDifferential, r.RadialDifferential, ), ): raise ConvertError( "Transforming to/from a Galactocentric frame requires a 3D velocity, e.g.," " proper motion components and radial velocity." ) @frame_transform_graph.transform(AffineTransform, ICRS, Galactocentric) def icrs_to_galactocentric(icrs_coord, galactocentric_frame): _check_coord_repr_diff_types(icrs_coord) return get_matrix_vectors(galactocentric_frame) @frame_transform_graph.transform(AffineTransform, Galactocentric, ICRS) def galactocentric_to_icrs(galactocentric_coord, icrs_frame): _check_coord_repr_diff_types(galactocentric_coord) return get_matrix_vectors(galactocentric_coord, inverse=True) # Create loopback transformation frame_transform_graph._add_merged_transform(Galactocentric, ICRS, Galactocentric)