from __future__ import annotations
import copy
import operator
import re
import warnings
from typing import TYPE_CHECKING
import erfa
import numpy as np
from astropy import units as u
from astropy.constants import c as speed_of_light
from astropy.time import Time
from astropy.utils import ShapedLikeNDArray
from astropy.utils.compat import COPY_IF_NEEDED
from astropy.utils.exceptions import AstropyUserWarning
from astropy.utils.masked import MaskableShapedLikeNDArray, combine_masks
from .angles import Angle
from .baseframe import (
BaseCoordinateFrame,
CoordinateFrameInfo,
GenericFrame,
frame_transform_graph,
)
from .distances import Distance
from .representation import (
SphericalDifferential,
SphericalRepresentation,
UnitSphericalRepresentation,
)
from .sky_coordinate_parsers import (
_get_frame_class,
_get_frame_without_data,
_parse_coordinate_data,
)
if TYPE_CHECKING:
from collections.abc import Callable
__all__ = ["SkyCoord", "SkyCoordInfo"]
[docs]
class SkyCoordInfo(CoordinateFrameInfo):
# Information for a SkyCoord is almost identical to that of a frame;
# we only need to add the name of the frame used underneath.
def _represent_as_dict(self):
sc = self._parent
out = super()._represent_as_dict()
out["frame"] = sc.frame.name
return out
[docs]
class SkyCoord(MaskableShapedLikeNDArray):
"""High-level object providing a flexible interface for celestial coordinate
representation, manipulation, and transformation between systems.
The |SkyCoord| class accepts a wide variety of inputs for initialization. At
a minimum these must provide one or more celestial coordinate values with
unambiguous units. Inputs may be scalars or lists/tuples/arrays, yielding
scalar or array coordinates (can be checked via ``SkyCoord.isscalar``).
Typically one also specifies the coordinate frame, though this is not
required. The general pattern for spherical representations is::
SkyCoord(COORD, [FRAME], keyword_args ...)
SkyCoord(LON, LAT, [FRAME], keyword_args ...)
SkyCoord(LON, LAT, [DISTANCE], frame=FRAME, unit=UNIT, keyword_args ...)
SkyCoord([FRAME], <lon_attr>=LON, <lat_attr>=LAT, keyword_args ...)
It is also possible to input coordinate values in other representations
such as cartesian or cylindrical. In this case one includes the keyword
argument ``representation_type='cartesian'`` (for example) along with data
in ``x``, ``y``, and ``z``.
See also: https://docs.astropy.org/en/stable/coordinates/
Examples
--------
The examples below illustrate common ways of initializing a |SkyCoord|
object. For a complete description of the allowed syntax see the
full coordinates documentation. First some imports::
>>> from astropy.coordinates import SkyCoord # High-level coordinates
>>> from astropy.coordinates import ICRS, Galactic, FK4, FK5 # Low-level frames
>>> from astropy.coordinates import Angle, Latitude, Longitude # Angles
>>> import astropy.units as u
The coordinate values and frame specification can now be provided using
positional and keyword arguments::
>>> c = SkyCoord(10, 20, unit="deg") # defaults to ICRS frame
>>> c = SkyCoord([1, 2, 3], [-30, 45, 8], frame="icrs", unit="deg") # 3 coords
>>> coords = ["1:12:43.2 +31:12:43", "1 12 43.2 +31 12 43"]
>>> c = SkyCoord(coords, frame=FK4, unit=(u.hourangle, u.deg), obstime="J1992.21")
>>> c = SkyCoord("1h12m43.2s +1d12m43s", frame=Galactic) # Units from string
>>> c = SkyCoord(frame="galactic", l="1h12m43.2s", b="+1d12m43s")
>>> ra = Longitude([1, 2, 3], unit=u.deg) # Could also use Angle
>>> dec = np.array([4.5, 5.2, 6.3]) * u.deg # Astropy Quantity
>>> c = SkyCoord(ra, dec, frame='icrs')
>>> c = SkyCoord(frame=ICRS, ra=ra, dec=dec, obstime='2001-01-02T12:34:56')
>>> c = FK4(1 * u.deg, 2 * u.deg) # Uses defaults for obstime, equinox
>>> c = SkyCoord(c, obstime='J2010.11', equinox='B1965') # Override defaults
>>> c = SkyCoord(w=0, u=1, v=2, unit='kpc', frame='galactic',
... representation_type='cartesian')
>>> c = SkyCoord([ICRS(ra=1*u.deg, dec=2*u.deg), ICRS(ra=3*u.deg, dec=4*u.deg)])
Velocity components (proper motions or radial velocities) can also be
provided in a similar manner::
>>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, radial_velocity=10*u.km/u.s)
>>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, pm_ra_cosdec=2*u.mas/u.yr, pm_dec=1*u.mas/u.yr)
As shown, the frame can be a `~astropy.coordinates.BaseCoordinateFrame`
class or the corresponding string alias -- lower-case versions of the
class name that allow for creating a |SkyCoord| object and transforming
frames without explicitly importing the frame classes.
Parameters
----------
frame : `~astropy.coordinates.BaseCoordinateFrame` class or string, optional
Type of coordinate frame this |SkyCoord| should represent. Defaults to
to ICRS if not given or given as None.
unit : `~astropy.units.Unit`, string, or tuple of :class:`~astropy.units.Unit` or str, optional
Units for supplied coordinate values.
If only one unit is supplied then it applies to all values.
Note that passing only one unit might lead to unit conversion errors
if the coordinate values are expected to have mixed physical meanings
(e.g., angles and distances).
obstime : time-like, optional
Time(s) of observation.
equinox : time-like, optional
Coordinate frame equinox time.
representation_type : str or Representation class
Specifies the representation, e.g. 'spherical', 'cartesian', or
'cylindrical'. This affects the positional args and other keyword args
which must correspond to the given representation.
copy : bool, optional
If `True` (default), a copy of any coordinate data is made. This
argument can only be passed in as a keyword argument.
**keyword_args
Other keyword arguments as applicable for user-defined coordinate frames.
Common options include:
ra, dec : angle-like, optional
RA and Dec for frames where ``ra`` and ``dec`` are keys in the
frame's ``representation_component_names``, including ``ICRS``,
``FK5``, ``FK4``, and ``FK4NoETerms``.
pm_ra_cosdec, pm_dec : `~astropy.units.Quantity` ['angular speed'], optional
Proper motion components, in angle per time units.
l, b : angle-like, optional
Galactic ``l`` and ``b`` for for frames where ``l`` and ``b`` are
keys in the frame's ``representation_component_names``, including
the ``Galactic`` frame.
pm_l_cosb, pm_b : `~astropy.units.Quantity` ['angular speed'], optional
Proper motion components in the `~astropy.coordinates.Galactic` frame,
in angle per time units.
x, y, z : float or `~astropy.units.Quantity` ['length'], optional
Cartesian coordinates values
u, v, w : float or `~astropy.units.Quantity` ['length'], optional
Cartesian coordinates values for the Galactic frame.
radial_velocity : `~astropy.units.Quantity` ['speed'], optional
The component of the velocity along the line-of-sight (i.e., the
radial direction), in velocity units.
"""
# Declare that SkyCoord can be used as a Table column by defining the
# info property.
info = SkyCoordInfo()
# Methods implemented by the underlying frame
position_angle: Callable[[BaseCoordinateFrame | SkyCoord], Angle]
separation: Callable[[BaseCoordinateFrame | SkyCoord], Angle]
separation_3d: Callable[[BaseCoordinateFrame | SkyCoord], Distance]
def __init__(self, *args, copy=True, **kwargs):
# these are frame attributes set on this SkyCoord but *not* a part of
# the frame object this SkyCoord contains
self._extra_frameattr_names = set()
# If all that is passed in is a frame instance that already has data,
# we should bypass all of the parsing and logic below. This is here
# to make this the fastest way to create a SkyCoord instance. Many of
# the classmethods implemented for performance enhancements will use
# this as the initialization path
if (
len(args) == 1
and len(kwargs) == 0
and isinstance(args[0], (BaseCoordinateFrame, SkyCoord))
):
coords = args[0]
if isinstance(coords, SkyCoord):
self._extra_frameattr_names = coords._extra_frameattr_names
self.info = coords.info
# Copy over any extra frame attributes
for attr_name in self._extra_frameattr_names:
# Setting it will also validate it.
setattr(self, attr_name, getattr(coords, attr_name))
coords = coords.frame
if not coords.has_data:
raise ValueError(
"Cannot initialize from a coordinate frame "
"instance without coordinate data"
)
if copy:
self._sky_coord_frame = coords.copy()
else:
self._sky_coord_frame = coords
else:
# Get the frame instance without coordinate data but with all frame
# attributes set - these could either have been passed in with the
# frame as an instance, or passed in as kwargs here
frame_cls, frame_kwargs = _get_frame_without_data(args, kwargs)
# Parse the args and kwargs to assemble a sanitized and validated
# kwargs dict for initializing attributes for this object and for
# creating the internal self._sky_coord_frame object
args = list(args) # Make it mutable
skycoord_kwargs, components, info = _parse_coordinate_data(
frame_cls(**frame_kwargs), args, kwargs
)
# In the above two parsing functions, these kwargs were identified
# as valid frame attributes for *some* frame, but not the frame that
# this SkyCoord will have. We keep these attributes as special
# skycoord frame attributes:
for attr in skycoord_kwargs:
# Setting it will also validate it.
setattr(self, attr, skycoord_kwargs[attr])
if info is not None:
self.info = info
# Finally make the internal coordinate object.
frame_kwargs.update(components)
self._sky_coord_frame = frame_cls(copy=copy, **frame_kwargs)
if not self._sky_coord_frame.has_data:
raise ValueError("Cannot create a SkyCoord without data")
@property
def frame(self):
return self._sky_coord_frame
@property
def representation_type(self):
return self.frame.representation_type
@representation_type.setter
def representation_type(self, value):
self.frame.representation_type = value
@property
def shape(self):
return self.frame.shape
# The following 3 have identical implementation as in BaseCoordinateFrame,
# but we cannot just rely on __getattr__ to get them from the frame,
# because (1) get_mask has to be able to access our own attributes, and
# (2) masked and mask are abstract properties in MaskableSharedLikeNDArray
# which thus need to be explicitly defined.
# TODO: factor out common methods and attributes in a mixin class.
@property
def masked(self):
return self.data.masked
[docs]
def get_mask(self, *attrs):
if not attrs:
# Just use the frame
return self._sky_coord_frame.get_mask()
values = operator.attrgetter(*attrs)(self)
if not isinstance(values, tuple):
values = (values,)
masks = [getattr(v, "mask", None) for v in values]
# Broadcast makes it readonly too.
return np.broadcast_to(combine_masks(masks), self.shape)
@property
def mask(self):
return self._sky_coord_frame.mask
masked.__doc__ = BaseCoordinateFrame.masked.__doc__
get_mask.__doc__ = BaseCoordinateFrame.get_mask.__doc__
mask.__doc__ = BaseCoordinateFrame.mask.__doc__
def __eq__(self, value):
"""Equality operator for SkyCoord.
This implements strict equality and requires that the frames are
equivalent, extra frame attributes are equivalent, and that the
representation data are exactly equal.
"""
if isinstance(value, BaseCoordinateFrame):
if value._data is None:
raise ValueError("Can only compare SkyCoord to Frame with data")
return self.frame == value
if not isinstance(value, SkyCoord):
return NotImplemented
# Make sure that any extra frame attribute names are equivalent.
for attr in self._extra_frameattr_names | value._extra_frameattr_names:
if not self.frame._frameattr_equiv(
getattr(self, attr), getattr(value, attr)
):
raise ValueError(
f"cannot compare: extra frame attribute '{attr}' is not equivalent"
" (perhaps compare the frames directly to avoid this exception)"
)
return self._sky_coord_frame == value._sky_coord_frame
def __ne__(self, value):
return np.logical_not(self == value)
def _apply(self, method, *args, **kwargs):
"""Create a new instance, applying a method to the underlying data.
In typical usage, the method is any of the shape-changing methods for
`~numpy.ndarray` (``reshape``, ``swapaxes``, etc.), as well as those
picking particular elements (``__getitem__``, ``take``, etc.), which
are all defined in `~astropy.utils.shapes.ShapedLikeNDArray`. It will be
applied to the underlying arrays in the representation (e.g., ``x``,
``y``, and ``z`` for `~astropy.coordinates.CartesianRepresentation`),
as well as to any frame attributes that have a shape, with the results
used to create a new instance.
Internally, it is also used to apply functions to the above parts
(in particular, `~numpy.broadcast_to`).
Parameters
----------
method : str or callable
If str, it is the name of a method that is applied to the internal
``components``. If callable, the function is applied.
*args
Any positional arguments for ``method``.
**kwargs : dict
Any keyword arguments for ``method``.
"""
def apply_method(value):
if isinstance(value, ShapedLikeNDArray):
return value._apply(method, *args, **kwargs)
else:
if callable(method):
return method(value, *args, **kwargs)
else:
return getattr(value, method)(*args, **kwargs)
# create a new but empty instance, and copy over stuff
new = super().__new__(self.__class__)
new._sky_coord_frame = self._sky_coord_frame._apply(method, *args, **kwargs)
new._extra_frameattr_names = self._extra_frameattr_names.copy()
for attr in self._extra_frameattr_names:
value = getattr(self, attr)
if getattr(value, "shape", ()):
value = apply_method(value)
elif method == "copy" or method == "flatten":
# flatten should copy also for a single element array, but
# we cannot use it directly for array scalars, since it
# always returns a one-dimensional array. So, just copy.
value = copy.copy(value)
setattr(new, "_" + attr, value)
# Copy other 'info' attr only if it has actually been defined.
# See PR #3898 for further explanation and justification, along
# with Quantity.__array_finalize__
if "info" in self.__dict__:
new.info = self.info
return new
def __setitem__(self, item, value):
"""Implement self[item] = value for SkyCoord.
The right hand ``value`` must be strictly consistent with self:
- Identical class
- Equivalent frames
- Identical representation_types
- Identical representation differentials keys
- Identical frame attributes
- Identical "extra" frame attributes (e.g. obstime for an ICRS coord)
With these caveats the setitem ends up as effectively a setitem on
the representation data.
self.frame.data[item] = value.frame.data
"""
if value is np.ma.masked or value is np.ma.nomask:
self.data.__setitem__(item, value)
self.cache.clear()
return
if self.__class__ is not value.__class__:
raise TypeError(
"can only set from object of same class: "
f"{self.__class__.__name__} vs. {value.__class__.__name__}"
)
# Make sure that any extra frame attribute names are equivalent.
for attr in self._extra_frameattr_names | value._extra_frameattr_names:
if not self.frame._frameattr_equiv(
getattr(self, attr), getattr(value, attr)
):
raise ValueError(f"attribute {attr} is not equivalent")
# Set the frame values. This checks frame equivalence and also clears
# the cache to ensure that the object is not in an inconsistent state.
self._sky_coord_frame[item] = value._sky_coord_frame
[docs]
def insert(self, obj, values, axis=0):
return self.info._insert(obj, values, axis)
insert.__doc__ = SkyCoordInfo._insert.__doc__
[docs]
def apply_space_motion(self, new_obstime=None, dt=None):
"""Compute the position to a new time using the velocities.
Compute the position of the source represented by this coordinate object
to a new time using the velocities stored in this object and assuming
linear space motion (including relativistic corrections). This is
sometimes referred to as an "epoch transformation".
The initial time before the evolution is taken from the ``obstime``
attribute of this coordinate. Note that this method currently does not
support evolving coordinates where the *frame* has an ``obstime`` frame
attribute, so the ``obstime`` is only used for storing the before and
after times, not actually as an attribute of the frame. Alternatively,
if ``dt`` is given, an ``obstime`` need not be provided at all.
Parameters
----------
new_obstime : `~astropy.time.Time`, optional
The time at which to evolve the position to. Requires that the
``obstime`` attribute be present on this frame.
dt : `~astropy.units.Quantity`, `~astropy.time.TimeDelta`, optional
An amount of time to evolve the position of the source. Cannot be
given at the same time as ``new_obstime``.
Returns
-------
new_coord : |SkyCoord|
A new coordinate object with the evolved location of this coordinate
at the new time. ``obstime`` will be set on this object to the new
time only if ``self`` also has ``obstime``.
"""
from .builtin_frames.icrs import ICRS
if (new_obstime is None) == (dt is None):
raise ValueError(
"You must specify one of `new_obstime` or `dt`, but not both."
)
# Validate that we have velocity info
if "s" not in self.frame.data.differentials:
raise ValueError("SkyCoord requires velocity data to evolve the position.")
if "obstime" in self.frame.frame_attributes:
raise NotImplementedError(
"Updating the coordinates in a frame with explicit time dependence is"
" currently not supported. If you would like this functionality, please"
" open an issue on github:\nhttps://github.com/astropy/astropy"
)
if new_obstime is not None and self.obstime is None:
# If no obstime is already on this object, raise an error if a new
# obstime is passed: we need to know the time / epoch at which the
# the position / velocity were measured initially
raise ValueError(
"This object has no associated `obstime`. apply_space_motion() must"
" receive a time difference, `dt`, and not a new obstime."
)
# Compute t1 and t2, the times used in the starpm call, which *only*
# uses them to compute a delta-time
t1 = self.obstime
if dt is None:
# self.obstime is not None and new_obstime is not None b/c of above
# checks
t2 = new_obstime
else:
# new_obstime is definitely None b/c of the above checks
if t1 is None:
# MAGIC NUMBER: if the current SkyCoord object has no obstime,
# assume J2000 to do the dt offset. This is not actually used
# for anything except a delta-t in starpm, so it's OK that it's
# not necessarily the "real" obstime
t1 = Time("J2000")
new_obstime = None # we don't actually know the initial obstime
t2 = t1 + dt
else:
t2 = t1 + dt
new_obstime = t2
# starpm wants tdb time
t1 = t1.tdb
t2 = t2.tdb
# proper motion in RA should not include the cos(dec) term, see the
# erfa function eraStarpv, comment (4). So we convert to the regular
# spherical differentials.
icrsrep = self.icrs.represent_as(SphericalRepresentation, SphericalDifferential)
icrsvel = icrsrep.differentials["s"]
parallax_zero = False
try:
plx = icrsrep.distance.to_value(u.arcsecond, u.parallax())
except u.UnitConversionError: # No distance: set to 0 by convention
plx = 0.0
parallax_zero = True
try:
rv = icrsvel.d_distance.to_value(u.km / u.s)
except u.UnitConversionError: # No RV
rv = 0.0
starpm = erfa.pmsafe(
icrsrep.lon.radian,
icrsrep.lat.radian,
icrsvel.d_lon.to_value(u.radian / u.yr),
icrsvel.d_lat.to_value(u.radian / u.yr),
plx,
rv,
t1.jd1,
t1.jd2,
t2.jd1,
t2.jd2,
)
if parallax_zero:
new_distance = None
else:
new_distance = Distance(parallax=starpm[4] << u.arcsec)
icrs2 = ICRS(
ra=u.Quantity(starpm[0], u.radian, copy=COPY_IF_NEEDED),
dec=u.Quantity(starpm[1], u.radian, copy=COPY_IF_NEEDED),
pm_ra=u.Quantity(starpm[2], u.radian / u.yr, copy=COPY_IF_NEEDED),
pm_dec=u.Quantity(starpm[3], u.radian / u.yr, copy=COPY_IF_NEEDED),
distance=new_distance,
radial_velocity=u.Quantity(starpm[5], u.km / u.s, copy=COPY_IF_NEEDED),
differential_type=SphericalDifferential,
)
# Update the obstime of the returned SkyCoord, and need to carry along
# the frame attributes
frattrs = {
attrnm: getattr(self, attrnm) for attrnm in self._extra_frameattr_names
}
frattrs["obstime"] = new_obstime
result = self.__class__(icrs2, **frattrs).transform_to(self.frame)
# Without this the output might not have the right differential type.
# Not sure if this fixes the problem or just hides it. See #11932
result.differential_type = self.differential_type
return result
def _is_name(self, string):
"""
Returns whether a string is one of the aliases for the frame.
"""
return self.frame.name == string or (
isinstance(self.frame.name, list) and string in self.frame.name
)
def __getattr__(self, attr):
"""
Overrides getattr to return coordinates that this can be transformed
to, based on the alias attr in the primary transform graph.
"""
if "_sky_coord_frame" in self.__dict__:
if self._is_name(attr):
return self # Should this be a deepcopy of self?
# Anything in the set of all possible frame_attr_names is handled
# here. If the attr is relevant for the current frame then delegate
# to self.frame otherwise get it from self._<attr>.
if attr in frame_transform_graph.frame_attributes:
if attr in self.frame.frame_attributes:
return getattr(self.frame, attr)
else:
return getattr(self, "_" + attr, None)
# Some attributes might not fall in the above category but still
# are available through self._sky_coord_frame.
if not attr.startswith("_") and hasattr(self._sky_coord_frame, attr):
return getattr(self._sky_coord_frame, attr)
# Try to interpret as a new frame for transforming.
frame_cls = frame_transform_graph.lookup_name(attr)
if frame_cls is not None and self.frame.is_transformable_to(frame_cls):
return self.transform_to(attr)
# Call __getattribute__; this will give correct exception.
return self.__getattribute__(attr)
def __setattr__(self, attr, val):
# This is to make anything available through __getattr__ immutable
if attr != "info" and not attr.startswith("_"):
if "_sky_coord_frame" in self.__dict__:
if self._is_name(attr):
raise AttributeError(f"'{attr}' is immutable")
if hasattr(self._sky_coord_frame, attr):
setattr(self._sky_coord_frame, attr, val)
return
if attr in frame_transform_graph.frame_attributes:
# All possible frame attributes can be set, but only via a private
# variable. See __getattr__ above.
super().__setattr__("_" + attr, val)
# Validate it
frame_transform_graph.frame_attributes[attr].__get__(self)
# And add to set of extra attributes
self._extra_frameattr_names |= {attr}
return
if frame_transform_graph.lookup_name(attr) is not None:
raise AttributeError(f"'{attr}' is immutable")
# Otherwise, do the standard Python attribute setting
super().__setattr__(attr, val)
def __delattr__(self, attr):
# mirror __setattr__ above
if "_sky_coord_frame" in self.__dict__:
if self._is_name(attr):
raise AttributeError(f"'{attr}' is immutable")
if not attr.startswith("_") and hasattr(self._sky_coord_frame, attr):
delattr(self._sky_coord_frame, attr)
return
frame_cls = frame_transform_graph.lookup_name(attr)
if frame_cls is not None and self.frame.is_transformable_to(frame_cls):
raise AttributeError(f"'{attr}' is immutable")
if attr in frame_transform_graph.frame_attributes:
# All possible frame attributes can be deleted, but need to remove
# the corresponding private variable. See __getattr__ above.
super().__delattr__("_" + attr)
# Also remove it from the set of extra attributes
self._extra_frameattr_names -= {attr}
else:
# Otherwise, do the standard Python attribute setting
super().__delattr__(attr)
def __dir__(self):
"""Original dir() behavior, plus frame attributes and transforms.
This dir includes:
- All attributes of the SkyCoord class
- Coordinate transforms available by aliases
- Attribute / methods of the underlying self.frame objects
"""
dir_values = set(super().__dir__())
# determine the aliases that this can be transformed to.
for name in frame_transform_graph.get_names():
frame_cls = frame_transform_graph.lookup_name(name)
if self.frame.is_transformable_to(frame_cls):
dir_values.add(name)
# Add public attributes of self.frame
dir_values.update(
{attr for attr in dir(self.frame) if not attr.startswith("_")}
)
# Add all possible frame attributes
dir_values.update(frame_transform_graph.frame_attributes.keys())
return sorted(dir_values)
def __repr__(self):
clsnm = self.__class__.__name__
coonm = self.frame.__class__.__name__
frameattrs = self.frame._frame_attrs_repr()
if frameattrs:
frameattrs = ": " + frameattrs
data = self.frame._data_repr()
if data:
data = ": " + data
return f"<{clsnm} ({coonm}{frameattrs}){data}>"
[docs]
def to_string(self, style="decimal", **kwargs):
"""
A string representation of the coordinates.
The default styles definitions are::
'decimal': 'lat': {'decimal': True, 'unit': "deg"}
'lon': {'decimal': True, 'unit': "deg"}
'dms': 'lat': {'unit': "deg"}
'lon': {'unit': "deg"}
'hmsdms': 'lat': {'alwayssign': True, 'pad': True, 'unit': "deg"}
'lon': {'pad': True, 'unit': "hour"}
See :meth:`~astropy.coordinates.Angle.to_string` for details and
keyword arguments (the two angles forming the coordinates are are
both :class:`~astropy.coordinates.Angle` instances). Keyword
arguments have precedence over the style defaults and are passed
to :meth:`~astropy.coordinates.Angle.to_string`.
Parameters
----------
style : {'hmsdms', 'dms', 'decimal'}
The formatting specification to use. These encode the three most
common ways to represent coordinates. The default is `decimal`.
**kwargs
Keyword args passed to :meth:`~astropy.coordinates.Angle.to_string`.
"""
sph_coord = self.frame.represent_as(SphericalRepresentation)
styles = {
"hmsdms": {
"lonargs": {"unit": u.hour, "pad": True},
"latargs": {"unit": u.degree, "pad": True, "alwayssign": True},
},
"dms": {"lonargs": {"unit": u.degree}, "latargs": {"unit": u.degree}},
"decimal": {
"lonargs": {"unit": u.degree, "decimal": True},
"latargs": {"unit": u.degree, "decimal": True},
},
}
lonargs = {}
latargs = {}
if style in styles:
lonargs.update(styles[style]["lonargs"])
latargs.update(styles[style]["latargs"])
else:
raise ValueError(f"Invalid style. Valid options are: {','.join(styles)}")
lonargs.update(kwargs)
latargs.update(kwargs)
if np.isscalar(sph_coord.lon.value):
coord_string = (
f"{sph_coord.lon.to_string(**lonargs)}"
f" {sph_coord.lat.to_string(**latargs)}"
)
else:
coord_string = []
for lonangle, latangle in zip(sph_coord.lon.ravel(), sph_coord.lat.ravel()):
coord_string += [
f"{lonangle.to_string(**lonargs)} {latangle.to_string(**latargs)}"
]
if len(sph_coord.shape) > 1:
coord_string = np.array(coord_string).reshape(sph_coord.shape)
return coord_string
[docs]
def to_table(self):
"""
Convert this |SkyCoord| to a |QTable|.
Any attributes that have the same length as the |SkyCoord| will be
converted to columns of the |QTable|. All other attributes will be
recorded as metadata.
Returns
-------
`~astropy.table.QTable`
A |QTable| containing the data of this |SkyCoord|.
Examples
--------
>>> sc = SkyCoord(ra=[40, 70]*u.deg, dec=[0, -20]*u.deg,
... obstime=Time([2000, 2010], format='jyear'))
>>> t = sc.to_table()
>>> t
<QTable length=2>
ra dec obstime
deg deg
float64 float64 Time
------- ------- -------
40.0 0.0 2000.0
70.0 -20.0 2010.0
>>> t.meta
{'representation_type': 'spherical', 'frame': 'icrs'}
"""
table = self.frame.to_table()
# Record extra attributes not on the frame that have the same length as self as
# columns in the table, and the other attributes as table metadata.
# This matches table.serialize._represent_mixin_as_column().
table.meta["frame"] = self.frame.name
for key in self._extra_frameattr_names:
value = getattr(self, key)
if getattr(value, "shape", ())[:1] == (len(self),):
table[key] = value
else:
table.meta[key] = value
return table
[docs]
def is_equivalent_frame(self, other):
"""
Checks if this object's frame is the same as that of the ``other``
object.
To be the same frame, two objects must be the same frame class and have
the same frame attributes. For two |SkyCoord| objects, *all* of the
frame attributes have to match, not just those relevant for the object's
frame.
Parameters
----------
other : SkyCoord or BaseCoordinateFrame
The other object to check.
Returns
-------
isequiv : bool
True if the frames are the same, False if not.
Raises
------
TypeError
If ``other`` isn't a |SkyCoord| or a subclass of
`~astropy.coordinates.BaseCoordinateFrame`.
"""
if isinstance(other, BaseCoordinateFrame):
return self.frame.is_equivalent_frame(other)
elif isinstance(other, SkyCoord):
if other.frame.name != self.frame.name:
return False
for fattrnm in frame_transform_graph.frame_attributes:
if not BaseCoordinateFrame._frameattr_equiv(
getattr(self, fattrnm), getattr(other, fattrnm)
):
return False
return True
else:
# not a BaseCoordinateFrame nor a SkyCoord object
raise TypeError(
"Tried to do is_equivalent_frame on something that isn't frame-like"
)
# High-level convenience methods
[docs]
def spherical_offsets_to(self, tocoord):
r"""
Computes angular offsets to go *from* this coordinate *to* another.
Parameters
----------
tocoord : `~astropy.coordinates.BaseCoordinateFrame`
The coordinate to find the offset to.
Returns
-------
lon_offset : `~astropy.coordinates.Angle`
The angular offset in the longitude direction. The definition of
"longitude" depends on this coordinate's frame (e.g., RA for
equatorial coordinates).
lat_offset : `~astropy.coordinates.Angle`
The angular offset in the latitude direction. The definition of
"latitude" depends on this coordinate's frame (e.g., Dec for
equatorial coordinates).
Raises
------
ValueError
If the ``tocoord`` is not in the same frame as this one. This is
different from the behavior of the
:meth:`~astropy.coordinates.BaseCoordinateFrame.separation`/:meth:`~astropy.coordinates.BaseCoordinateFrame.separation_3d`
methods because the offset components depend critically on the
specific choice of frame.
Notes
-----
This uses the sky offset frame machinery, and hence will produce a new
sky offset frame if one does not already exist for this object's frame
class.
See Also
--------
:meth:`~astropy.coordinates.BaseCoordinateFrame.separation` :
for the *total* angular offset (not broken out into components).
:meth:`~astropy.coordinates.BaseCoordinateFrame.position_angle` :
for the direction of the offset.
"""
if not self.is_equivalent_frame(tocoord):
raise ValueError(
"Tried to use spherical_offsets_to with two non-matching frames!"
)
aframe = self.skyoffset_frame()
acoord = tocoord.transform_to(aframe)
dlon = acoord.spherical.lon.view(Angle)
dlat = acoord.spherical.lat.view(Angle)
return dlon, dlat
[docs]
def spherical_offsets_by(self, d_lon, d_lat):
"""
Computes the coordinate that is a specified pair of angular offsets away
from this coordinate.
Parameters
----------
d_lon : angle-like
The angular offset in the longitude direction. The definition of
"longitude" depends on this coordinate's frame (e.g., RA for
equatorial coordinates).
d_lat : angle-like
The angular offset in the latitude direction. The definition of
"latitude" depends on this coordinate's frame (e.g., Dec for
equatorial coordinates).
Returns
-------
newcoord : `~astropy.coordinates.SkyCoord`
The coordinates for the location that corresponds to offsetting by
``d_lat`` in the latitude direction and ``d_lon`` in the longitude
direction.
Notes
-----
This internally uses `~astropy.coordinates.SkyOffsetFrame` to do the
transformation. For a more complete set of transform offsets, use
`~astropy.coordinates.SkyOffsetFrame` or `~astropy.wcs.WCS` manually.
This specific method can be reproduced by doing
``SkyCoord(SkyOffsetFrame(d_lon, d_lat, origin=self.frame).transform_to(self))``.
See Also
--------
spherical_offsets_to : compute the angular offsets to another coordinate
directional_offset_by : offset a coordinate by an angle in a direction
"""
from .builtin_frames.skyoffset import SkyOffsetFrame
return self.__class__(
SkyOffsetFrame(d_lon, d_lat, origin=self.frame).transform_to(self)
)
[docs]
def directional_offset_by(self, position_angle, separation):
"""
Computes coordinates at the given offset from this coordinate.
Parameters
----------
position_angle : `~astropy.coordinates.Angle`
position_angle of offset
separation : `~astropy.coordinates.Angle`
offset angular separation
Returns
-------
newpoints : `~astropy.coordinates.SkyCoord`
The coordinates for the location that corresponds to offsetting by
the given ``position_angle`` and ``separation``.
Notes
-----
Returned SkyCoord frame retains only the frame attributes that are for
the resulting frame type. (e.g. if the input frame is
`~astropy.coordinates.ICRS`, an ``equinox`` value will be retained, but
an ``obstime`` will not.)
For a more complete set of transform offsets, use `~astropy.wcs.WCS`.
`~astropy.coordinates.SkyCoord.skyoffset_frame()` can also be used to
create a spherical frame with (lat=0, lon=0) at a reference point,
approximating an xy cartesian system for small offsets. This method
is distinct in that it is accurate on the sphere.
See Also
--------
:meth:`~astropy.coordinates.BaseCoordinateFrame.position_angle` :
inverse operation for the ``position_angle`` component
:meth:`~astropy.coordinates.BaseCoordinateFrame.separation` :
inverse operation for the ``separation`` component
"""
from .angles import offset_by
slat = self.represent_as(UnitSphericalRepresentation).lat
slon = self.represent_as(UnitSphericalRepresentation).lon
newlon, newlat = offset_by(
lon=slon, lat=slat, posang=position_angle, distance=separation
)
return SkyCoord(newlon, newlat, frame=self.frame)
[docs]
def match_to_catalog_sky(self, catalogcoord, nthneighbor=1):
"""
Finds the nearest on-sky matches of this coordinate in a set of
catalog coordinates.
For more on how to use this (and related) functionality, see the
examples in :ref:`astropy-coordinates-separations-matching`.
Parameters
----------
catalogcoord : `~astropy.coordinates.SkyCoord` or `~astropy.coordinates.BaseCoordinateFrame`
The base catalog in which to search for matches. Typically this
will be a coordinate object that is an array (i.e.,
``catalogcoord.isscalar == False``)
nthneighbor : int, optional
Which closest neighbor to search for. Typically ``1`` is
desired here, as that is correct for matching one set of
coordinates to another. The next likely use case is ``2``,
for matching a coordinate catalog against *itself* (``1``
is inappropriate because each point will find itself as the
closest match).
Returns
-------
idx : int array
Indices into ``catalogcoord`` to get the matched points for
each of this object's coordinates. Shape matches this
object.
sep2d : `~astropy.coordinates.Angle`
The on-sky separation between the closest match for each
element in this object in ``catalogcoord``. Shape matches
this object.
dist3d : `~astropy.units.Quantity` ['length']
The 3D distance between the closest match for each element
in this object in ``catalogcoord``. Shape matches this
object. Unless both this and ``catalogcoord`` have associated
distances, this quantity assumes that all sources are at a
distance of 1 (dimensionless).
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ to be
installed or it will fail.
See Also
--------
astropy.coordinates.match_coordinates_sky
SkyCoord.match_to_catalog_3d
"""
from .matching import match_coordinates_sky
if not (
isinstance(catalogcoord, (SkyCoord, BaseCoordinateFrame))
and catalogcoord.has_data
):
raise TypeError(
"Can only get separation to another SkyCoord or a "
"coordinate frame with data"
)
res = match_coordinates_sky(
self, catalogcoord, nthneighbor=nthneighbor, storekdtree="_kdtree_sky"
)
return res
[docs]
def match_to_catalog_3d(self, catalogcoord, nthneighbor=1):
"""
Finds the nearest 3-dimensional matches of this coordinate to a set
of catalog coordinates.
This finds the 3-dimensional closest neighbor, which is only different
from the on-sky distance if ``distance`` is set in this object or the
``catalogcoord`` object.
For more on how to use this (and related) functionality, see the
examples in :ref:`astropy-coordinates-separations-matching`.
Parameters
----------
catalogcoord : `~astropy.coordinates.SkyCoord` or `~astropy.coordinates.BaseCoordinateFrame`
The base catalog in which to search for matches. Typically this
will be a coordinate object that is an array (i.e.,
``catalogcoord.isscalar == False``)
nthneighbor : int, optional
Which closest neighbor to search for. Typically ``1`` is
desired here, as that is correct for matching one set of
coordinates to another. The next likely use case is
``2``, for matching a coordinate catalog against *itself*
(``1`` is inappropriate because each point will find
itself as the closest match).
Returns
-------
idx : int array
Indices into ``catalogcoord`` to get the matched points for
each of this object's coordinates. Shape matches this
object.
sep2d : `~astropy.coordinates.Angle`
The on-sky separation between the closest match for each
element in this object in ``catalogcoord``. Shape matches
this object.
dist3d : `~astropy.units.Quantity` ['length']
The 3D distance between the closest match for each element
in this object in ``catalogcoord``. Shape matches this
object.
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ to be
installed or it will fail.
See Also
--------
astropy.coordinates.match_coordinates_3d
SkyCoord.match_to_catalog_sky
"""
from .matching import match_coordinates_3d
if not (
isinstance(catalogcoord, (SkyCoord, BaseCoordinateFrame))
and catalogcoord.has_data
):
raise TypeError(
"Can only get separation to another SkyCoord or a "
"coordinate frame with data"
)
res = match_coordinates_3d(
self, catalogcoord, nthneighbor=nthneighbor, storekdtree="_kdtree_3d"
)
return res
[docs]
def search_around_sky(self, searcharoundcoords, seplimit):
"""
Searches for all coordinates in this object around a supplied set of
points within a given on-sky separation.
This is intended for use on `~astropy.coordinates.SkyCoord` objects
with coordinate arrays, rather than a scalar coordinate. For a scalar
coordinate, it is better to use
:meth:`~astropy.coordinates.BaseCoordinateFrame.separation`.
For more on how to use this (and related) functionality, see the
examples in :ref:`astropy-coordinates-separations-matching`.
Parameters
----------
searcharoundcoords : coordinate-like
The coordinates to search around to try to find matching points in
this |SkyCoord|. This should be an object with array coordinates,
not a scalar coordinate object.
seplimit : `~astropy.units.Quantity` ['angle']
The on-sky separation to search within.
Returns
-------
idxsearcharound : int array
Indices into ``searcharoundcoords`` that match the
corresponding elements of ``idxself``. Shape matches
``idxself``.
idxself : int array
Indices into ``self`` that match the
corresponding elements of ``idxsearcharound``. Shape matches
``idxsearcharound``.
sep2d : `~astropy.coordinates.Angle`
The on-sky separation between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
dist3d : `~astropy.units.Quantity` ['length']
The 3D distance between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ to be
installed or it will fail.
In the current implementation, the return values are always sorted in
the same order as the ``searcharoundcoords`` (so ``idxsearcharound`` is
in ascending order). This is considered an implementation detail,
though, so it could change in a future release.
See Also
--------
astropy.coordinates.search_around_sky
SkyCoord.search_around_3d
"""
from .matching import search_around_sky
return search_around_sky(
searcharoundcoords, self, seplimit, storekdtree="_kdtree_sky"
)
[docs]
def search_around_3d(self, searcharoundcoords, distlimit):
"""
Searches for all coordinates in this object around a supplied set of
points within a given 3D radius.
This is intended for use on `~astropy.coordinates.SkyCoord` objects
with coordinate arrays, rather than a scalar coordinate. For a scalar
coordinate, it is better to use
:meth:`~astropy.coordinates.BaseCoordinateFrame.separation_3d`.
For more on how to use this (and related) functionality, see the
examples in :ref:`astropy-coordinates-separations-matching`.
Parameters
----------
searcharoundcoords : `~astropy.coordinates.SkyCoord` or `~astropy.coordinates.BaseCoordinateFrame`
The coordinates to search around to try to find matching points in
this |SkyCoord|. This should be an object with array coordinates,
not a scalar coordinate object.
distlimit : `~astropy.units.Quantity` ['length']
The physical radius to search within.
Returns
-------
idxsearcharound : int array
Indices into ``searcharoundcoords`` that match the
corresponding elements of ``idxself``. Shape matches
``idxself``.
idxself : int array
Indices into ``self`` that match the
corresponding elements of ``idxsearcharound``. Shape matches
``idxsearcharound``.
sep2d : `~astropy.coordinates.Angle`
The on-sky separation between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
dist3d : `~astropy.units.Quantity` ['length']
The 3D distance between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ to be
installed or it will fail.
In the current implementation, the return values are always sorted in
the same order as the ``searcharoundcoords`` (so ``idxsearcharound`` is
in ascending order). This is considered an implementation detail,
though, so it could change in a future release.
See Also
--------
astropy.coordinates.search_around_3d
SkyCoord.search_around_sky
"""
from .matching import search_around_3d
return search_around_3d(
searcharoundcoords, self, distlimit, storekdtree="_kdtree_3d"
)
[docs]
def skyoffset_frame(self, rotation=None):
"""
Returns the sky offset frame with this SkyCoord at the origin.
Parameters
----------
rotation : angle-like
The final rotation of the frame about the ``origin``. The sign of
the rotation is the left-hand rule. That is, an object at a
particular position angle in the un-rotated system will be sent to
the positive latitude (z) direction in the final frame.
Returns
-------
astrframe : `~astropy.coordinates.SkyOffsetFrame`
A sky offset frame of the same type as this |SkyCoord| (e.g., if
this object has an ICRS coordinate, the resulting frame is
SkyOffsetICRS, with the origin set to this object)
"""
from .builtin_frames.skyoffset import SkyOffsetFrame
return SkyOffsetFrame(origin=self, rotation=rotation)
[docs]
def get_constellation(self, short_name=False, constellation_list="iau"):
"""
Determines the constellation(s) of the coordinates this SkyCoord contains.
Parameters
----------
short_name : bool
If True, the returned names are the IAU-sanctioned abbreviated
names. Otherwise, full names for the constellations are used.
constellation_list : str
The set of constellations to use. Currently only ``'iau'`` is
supported, meaning the 88 "modern" constellations endorsed by the IAU.
Returns
-------
constellation : str or string array
If this is a scalar coordinate, returns the name of the
constellation. If it is an array |SkyCoord|, it returns an array of
names.
Notes
-----
To determine which constellation a point on the sky is in, this first
precesses to B1875, and then uses the Delporte boundaries of the 88
modern constellations, as tabulated by
`Roman 1987 <https://cdsarc.cds.unistra.fr/viz-bin/Cat?VI/42>`_.
See Also
--------
astropy.coordinates.get_constellation
"""
from .funcs import get_constellation
# because of issue #7028, the conversion to a PrecessedGeocentric
# system fails in some cases. Work around is to drop the velocities.
# they are not needed here since only position information is used
extra_frameattrs = {nm: getattr(self, nm) for nm in self._extra_frameattr_names}
novel = SkyCoord(
self.realize_frame(self.data.without_differentials()), **extra_frameattrs
)
return get_constellation(novel, short_name, constellation_list)
# the simpler version below can be used when gh-issue #7028 is resolved
# return get_constellation(self, short_name, constellation_list)
# WCS pixel to/from sky conversions
[docs]
def to_pixel(self, wcs, origin=0, mode="all"):
"""
Convert this coordinate to pixel coordinates using a `~astropy.wcs.WCS`
object.
Parameters
----------
wcs : `~astropy.wcs.WCS`
The WCS to use for convert
origin : int
Whether to return 0 or 1-based pixel coordinates.
mode : 'all' or 'wcs'
Whether to do the transformation including distortions (``'all'``) or
only including only the core WCS transformation (``'wcs'``).
Returns
-------
xp, yp : `numpy.ndarray`
The pixel coordinates
See Also
--------
astropy.wcs.utils.skycoord_to_pixel : the implementation of this method
"""
from astropy.wcs.utils import skycoord_to_pixel
return skycoord_to_pixel(self, wcs=wcs, origin=origin, mode=mode)
[docs]
@classmethod
def from_pixel(cls, xp, yp, wcs, origin=0, mode="all"):
"""
Create a new SkyCoord from pixel coordinates using a World Coordinate System.
Parameters
----------
xp, yp : float or ndarray
The coordinates to convert.
wcs : `~astropy.wcs.WCS`
The WCS to use for convert
origin : int
Whether to return 0 or 1-based pixel coordinates.
mode : 'all' or 'wcs'
Whether to do the transformation including distortions (``'all'``) or
only including only the core WCS transformation (``'wcs'``).
Returns
-------
coord : `~astropy.coordinates.SkyCoord`
A new object with sky coordinates corresponding to the input ``xp``
and ``yp``.
See Also
--------
to_pixel : to do the inverse operation
astropy.wcs.utils.pixel_to_skycoord : the implementation of this method
"""
from astropy.wcs.utils import pixel_to_skycoord
return pixel_to_skycoord(xp, yp, wcs=wcs, origin=origin, mode=mode, cls=cls)
[docs]
def contained_by(self, wcs, image=None, **kwargs):
"""
Determines if the SkyCoord is contained in the given wcs footprint.
Parameters
----------
wcs : `~astropy.wcs.WCS`
The coordinate to check if it is within the wcs coordinate.
image : array
Optional. The image associated with the wcs object that the coordinate
is being checked against. If not given the naxis keywords will be used
to determine if the coordinate falls within the wcs footprint.
**kwargs
Additional arguments to pass to `~astropy.coordinates.SkyCoord.to_pixel`
Returns
-------
response : bool
True means the WCS footprint contains the coordinate, False means it does not.
"""
if image is not None:
ymax, xmax = image.shape
else:
xmax, ymax = wcs._naxis
import warnings
with warnings.catch_warnings():
# Suppress warnings since they just mean we didn't find the coordinate
warnings.simplefilter("ignore")
try:
x, y = self.to_pixel(wcs, **kwargs)
except Exception:
return False
return (x < xmax) & (x > 0) & (y < ymax) & (y > 0)
[docs]
def radial_velocity_correction(
self, kind="barycentric", obstime=None, location=None
):
"""
Compute the correction required to convert a radial velocity at a given
time and place on the Earth's Surface to a barycentric or heliocentric
velocity.
Parameters
----------
kind : str
The kind of velocity correction. Must be 'barycentric' or
'heliocentric'.
obstime : `~astropy.time.Time` or None, optional
The time at which to compute the correction. If `None`, the
``obstime`` frame attribute on the |SkyCoord| will be used.
location : `~astropy.coordinates.EarthLocation` or None, optional
The observer location at which to compute the correction. If
`None`, the ``location`` frame attribute on the passed-in
``obstime`` will be used, and if that is None, the ``location``
frame attribute on the |SkyCoord| will be used.
Raises
------
ValueError
If either ``obstime`` or ``location`` are passed in (not ``None``)
when the frame attribute is already set on this |SkyCoord|.
TypeError
If ``obstime`` or ``location`` aren't provided, either as arguments
or as frame attributes.
Returns
-------
vcorr : `~astropy.units.Quantity` ['speed']
The correction with a positive sign. I.e., *add* this
to an observed radial velocity to get the barycentric (or
heliocentric) velocity. If m/s precision or better is needed,
see the notes below.
Notes
-----
The barycentric correction is calculated to higher precision than the
heliocentric correction and includes additional physics (e.g time dilation).
Use barycentric corrections if m/s precision is required.
The algorithm here is sufficient to perform corrections at the mm/s level, but
care is needed in application. The barycentric correction returned uses the optical
approximation v = z * c. Strictly speaking, the barycentric correction is
multiplicative and should be applied as::
>>> from astropy.time import Time
>>> from astropy.coordinates import SkyCoord, EarthLocation
>>> from astropy.constants import c
>>> t = Time(56370.5, format='mjd', scale='utc')
>>> loc = EarthLocation('149d33m00.5s','-30d18m46.385s',236.87*u.m)
>>> sc = SkyCoord(1*u.deg, 2*u.deg)
>>> vcorr = sc.radial_velocity_correction(kind='barycentric', obstime=t, location=loc) # doctest: +REMOTE_DATA
>>> rv = rv + vcorr + rv * vcorr / c # doctest: +SKIP
Also note that this method returns the correction velocity in the so-called
*optical convention*::
>>> vcorr = zb * c # doctest: +SKIP
where ``zb`` is the barycentric correction redshift as defined in section 3
of Wright & Eastman (2014). The application formula given above follows from their
equation (11) under assumption that the radial velocity ``rv`` has also been defined
using the same optical convention. Note, this can be regarded as a matter of
velocity definition and does not by itself imply any loss of accuracy, provided
sufficient care has been taken during interpretation of the results. If you need
the barycentric correction expressed as the full relativistic velocity (e.g., to provide
it as the input to another software which performs the application), the
following recipe can be used::
>>> zb = vcorr / c # doctest: +REMOTE_DATA
>>> zb_plus_one_squared = (zb + 1) ** 2 # doctest: +REMOTE_DATA
>>> vcorr_rel = c * (zb_plus_one_squared - 1) / (zb_plus_one_squared + 1) # doctest: +REMOTE_DATA
or alternatively using just equivalencies::
>>> vcorr_rel = vcorr.to(u.Hz, u.doppler_optical(1*u.Hz)).to(vcorr.unit, u.doppler_relativistic(1*u.Hz)) # doctest: +REMOTE_DATA
See also `~astropy.units.doppler_optical`,
`~astropy.units.doppler_radio`, and
`~astropy.units.doppler_relativistic` for more information on
the velocity conventions.
The default is for this method to use the builtin ephemeris for
computing the sun and earth location. Other ephemerides can be chosen
by setting the `~astropy.coordinates.solar_system_ephemeris` variable,
either directly or via ``with`` statement. For example, to use the JPL
ephemeris, do::
>>> from astropy.coordinates import solar_system_ephemeris
>>> sc = SkyCoord(1*u.deg, 2*u.deg)
>>> with solar_system_ephemeris.set('jpl'): # doctest: +REMOTE_DATA
... rv += sc.radial_velocity_correction(obstime=t, location=loc) # doctest: +SKIP
"""
# has to be here to prevent circular imports
from .solar_system import get_body_barycentric_posvel
# location validation
timeloc = getattr(obstime, "location", None)
if location is None:
if self.location is not None:
location = self.location
if timeloc is not None:
raise ValueError(
"`location` cannot be in both the passed-in `obstime` and this"
" `SkyCoord` because it is ambiguous which is meant for the"
" radial_velocity_correction."
)
elif timeloc is not None:
location = timeloc
else:
raise TypeError(
"Must provide a `location` to radial_velocity_correction, either as"
" a SkyCoord frame attribute, as an attribute on the passed in"
" `obstime`, or in the method call."
)
elif self.location is not None or timeloc is not None:
raise ValueError(
"Cannot compute radial velocity correction if `location` argument is"
" passed in and there is also a `location` attribute on this SkyCoord"
" or the passed-in `obstime`."
)
# obstime validation
coo_at_rv_obstime = self # assume we need no space motion for now
if obstime is None:
obstime = self.obstime
if obstime is None:
raise TypeError(
"Must provide an `obstime` to radial_velocity_correction, either as"
" a SkyCoord frame attribute or in the method call."
)
elif self.obstime is not None and self.frame.data.differentials:
# we do need space motion after all
coo_at_rv_obstime = self.apply_space_motion(obstime)
elif self.obstime is None and "s" in self.data.differentials:
warnings.warn(
"SkyCoord has space motion, and therefore the specified "
"position of the SkyCoord may not be the same as "
"the `obstime` for the radial velocity measurement. "
"This may affect the rv correction at the order of km/s"
"for very high proper motions sources. If you wish to "
"apply space motion of the SkyCoord to correct for this"
"the `obstime` attribute of the SkyCoord must be set",
AstropyUserWarning,
)
pos_earth, v_origin_to_earth = get_body_barycentric_posvel("earth", obstime)
if kind == "heliocentric":
v_origin_to_earth -= get_body_barycentric_posvel("sun", obstime)[1]
elif kind != "barycentric":
raise ValueError(
"`kind` argument to radial_velocity_correction must "
f"be 'barycentric' or 'heliocentric', but got '{kind}'"
)
gcrs_p, gcrs_v = location.get_gcrs_posvel(obstime)
# transforming to GCRS is not the correct thing to do here, since we don't want to
# include aberration (or light deflection)? Instead, only apply parallax if necessary
icrs_cart = coo_at_rv_obstime.icrs.cartesian
targcart = icrs_cart.without_differentials()
if self.data.__class__ is not UnitSphericalRepresentation:
# SkyCoord has distances, so apply parallax by calculating
# the direction of the target as seen by the observer.
targcart -= pos_earth + gcrs_p
targcart /= targcart.norm()
if kind == "heliocentric":
# Do a simpler correction than for barycentric ignoring time dilation and
# gravitational redshift. This is adequate since heliocentric corrections
# shouldn't be used if cm/s precision is required.
return targcart.dot(v_origin_to_earth + gcrs_v)
beta_obs = (v_origin_to_earth + gcrs_v) / speed_of_light
gamma_obs = 1 / np.sqrt(1 - beta_obs.norm() ** 2)
gr = location.gravitational_redshift(obstime)
# barycentric redshift according to eq 28 in Wright & Eastmann (2014),
# neglecting Shapiro delay and effects of the star's own motion
zb = gamma_obs * (1 + beta_obs.dot(targcart)) / (1 + gr / speed_of_light)
# try and get terms corresponding to stellar motion.
if icrs_cart.differentials:
try:
ro = self.icrs.cartesian
beta_star = ro.differentials["s"].to_cartesian() / speed_of_light
# ICRS unit vector at coordinate epoch
ro = ro.without_differentials()
ro /= ro.norm()
zb *= (1 + beta_star.dot(ro)) / (1 + beta_star.dot(targcart))
except u.UnitConversionError:
warnings.warn(
"SkyCoord contains some velocity information, but not enough to"
" calculate the full space motion of the source, and so this"
" has been ignored for the purposes of calculating the radial"
" velocity correction. This can lead to errors on the order of"
" metres/second.",
AstropyUserWarning,
)
return (zb - 1) * speed_of_light
# Table interactions
[docs]
@classmethod
def guess_from_table(cls, table, **coord_kwargs):
r"""
A convenience method to create and return a new SkyCoord from the data
in an astropy Table.
This method matches table columns that start with the case-insensitive
names of the components of the requested frames (including
differentials), if they are also followed by a non-alphanumeric
character. It will also match columns that *end* with the component name
if a non-alphanumeric character is *before* it.
For example, the first rule means columns with names like
``'RA[J2000]'`` or ``'ra'`` will be interpreted as ``ra`` attributes for
`~astropy.coordinates.ICRS` frames, but ``'RAJ2000'`` or ``'radius'``
are *not*. Similarly, the second rule applied to the
`~astropy.coordinates.Galactic` frame means that a column named
``'gal_l'`` will be used as the ``l`` component, but ``gall`` or
``'fill'`` will not.
The definition of alphanumeric here is based on Unicode's definition
of alphanumeric, except without ``_`` (which is normally considered
alphanumeric). So for ASCII, this means the non-alphanumeric characters
are ``<space>_!"#$%&'()*+,-./\:;<=>?@[]^`{|}~``).
Parameters
----------
table : `~astropy.table.Table` or subclass
The table to load data from.
**coord_kwargs
Any additional keyword arguments are passed directly to this class's
constructor.
Returns
-------
newsc : `~astropy.coordinates.SkyCoord` or subclass
The new instance.
Raises
------
ValueError
If more than one match is found in the table for a component,
unless the additional matches are also valid frame component names.
If a "coord_kwargs" is provided for a value also found in the table.
"""
_frame_cls, _frame_kwargs = _get_frame_without_data([], coord_kwargs)
frame = _frame_cls(**_frame_kwargs)
coord_kwargs["frame"] = coord_kwargs.get("frame", frame)
representation_component_names = set(
frame.get_representation_component_names()
).union(set(frame.get_representation_component_names("s")))
comp_kwargs = {}
for comp_name in representation_component_names:
# this matches things like 'ra[...]'' but *not* 'rad'.
# note that the "_" must be in there explicitly, because
# "alphanumeric" usually includes underscores.
starts_with_comp = comp_name + r"(\W|\b|_)"
# this part matches stuff like 'center_ra', but *not*
# 'aura'
ends_with_comp = r".*(\W|\b|_)" + comp_name + r"\b"
# the final regex ORs together the two patterns
rex = re.compile(
rf"({starts_with_comp})|({ends_with_comp})", re.IGNORECASE | re.UNICODE
)
# find all matches
matches = {col_name for col_name in table.colnames if rex.match(col_name)}
# now need to select among matches, also making sure we don't have
# an exact match with another component
if len(matches) == 0: # no matches
continue
elif len(matches) == 1: # only one match
col_name = matches.pop()
else: # more than 1 match
# try to sieve out other components
matches -= representation_component_names - {comp_name}
# if there's only one remaining match, it worked.
if len(matches) == 1:
col_name = matches.pop()
else:
raise ValueError(
f'Found at least two matches for component "{comp_name}":'
f' "{matches}". Cannot guess coordinates from a table with this'
" ambiguity."
)
comp_kwargs[comp_name] = table[col_name]
for k, v in comp_kwargs.items():
if k in coord_kwargs:
raise ValueError(
f'Found column "{v.name}" in table, but it was already provided as'
' "{k}" keyword to guess_from_table function.'
)
coord_kwargs[k] = v
return cls(**coord_kwargs)
# Name resolve
[docs]
@classmethod
def from_name(cls, name, frame="icrs", parse=False, cache=True):
"""
Given a name, query the CDS name resolver to attempt to retrieve
coordinate information for that object. The search database, sesame
url, and query timeout can be set through configuration items in
``astropy.coordinates.name_resolve`` -- see docstring for
`~astropy.coordinates.get_icrs_coordinates` for more
information.
Parameters
----------
name : str
The name of the object to get coordinates for, e.g. ``'M42'``.
frame : str or `BaseCoordinateFrame` class or instance
The frame to transform the object to.
parse : bool
Whether to attempt extracting the coordinates from the name by
parsing with a regex. For objects catalog names that have
J-coordinates embedded in their names, e.g.,
'CRTS SSS100805 J194428-420209', this may be much faster than a
Sesame query for the same object name. The coordinates extracted
in this way may differ from the database coordinates by a few
deci-arcseconds, so only use this option if you do not need
sub-arcsecond accuracy for coordinates.
cache : bool, optional
Determines whether to cache the results or not. To update or
overwrite an existing value, pass ``cache='update'``.
Returns
-------
coord : SkyCoord
Instance of the SkyCoord class.
"""
from .name_resolve import get_icrs_coordinates
icrs_coord = get_icrs_coordinates(name, parse, cache=cache)
icrs_sky_coord = cls(icrs_coord)
if frame in ("icrs", icrs_coord.__class__):
return icrs_sky_coord
else:
return icrs_sky_coord.transform_to(frame)