import re
import copy
import numpy as np
from astropy import _erfa as erfa
from astropy.utils.compat.misc import override__dir__
from astropy import units as u
from astropy.constants import c as speed_of_light
from astropy.wcs.utils import skycoord_to_pixel, pixel_to_skycoord
from astropy.utils.data_info import MixinInfo
from astropy.utils import ShapedLikeNDArray
from astropy.time import Time
from .distances import Distance
from .angles import Angle
from .baseframe import (BaseCoordinateFrame, frame_transform_graph,
GenericFrame)
from .builtin_frames import ICRS, SkyOffsetFrame
from .representation import (SphericalRepresentation,
UnitSphericalRepresentation, SphericalDifferential)
from .sky_coordinate_parsers import (_get_frame_class, _get_frame_without_data,
_parse_coordinate_data)
__all__ = ['SkyCoord', 'SkyCoordInfo']
class SkyCoordInfo(MixinInfo):
"""
Container for meta information like name, description, format. This is
required when the object is used as a mixin column within a table, but can
be used as a general way to store meta information.
"""
attrs_from_parent = set(['unit']) # Unit is read-only
_supports_indexing = False
@staticmethod
def default_format(val):
repr_data = val.info._repr_data
formats = ['{0.' + compname + '.value:}' for compname
in repr_data.components]
return ','.join(formats).format(repr_data)
@property
def unit(self):
repr_data = self._repr_data
unit = ','.join(str(getattr(repr_data, comp).unit) or 'None'
for comp in repr_data.components)
return unit
@property
def _repr_data(self):
if self._parent is None:
return None
sc = self._parent
if (issubclass(sc.representation_type, SphericalRepresentation)
and isinstance(sc.data, UnitSphericalRepresentation)):
repr_data = sc.represent_as(sc.data.__class__, in_frame_units=True)
else:
repr_data = sc.represent_as(sc.representation_type,
in_frame_units=True)
return repr_data
def _represent_as_dict(self):
obj = self._parent
attrs = (list(obj.representation_component_names) +
list(frame_transform_graph.frame_attributes.keys()))
# Don't output distance if it is all unitless 1.0
if 'distance' in attrs and np.all(obj.distance == 1.0):
attrs.remove('distance')
out = super()._represent_as_dict(attrs)
out['representation_type'] = obj.representation_type.get_name()
out['frame'] = obj.frame.name
# Note that obj.info.unit is a fake composite unit (e.g. 'deg,deg,None'
# or None,None,m) and is not stored. The individual attributes have
# units.
return out
class SkyCoord(ShapedLikeNDArray):
"""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: http://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 +1:12:43", "1 12 43.2 +1 12 43"]
>>> c = SkyCoord(coords, frame=FK4, unit=(u.deg, u.hourangle), 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. The frame classes that are built in
to astropy are `ICRS`, `FK5`, `FK4`, `FK4NoETerms`, and `Galactic`.
The string aliases are simply lower-case versions of the class name, and
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 ``LON`` and ``LAT`` values, respectively. If
only one unit is supplied then it applies to both ``LON`` and
``LAT``.
obstime : valid `~astropy.time.Time` initializer, optional
Time(s) of observation.
equinox : valid `~astropy.time.Time` initializer, optional
Coordinate frame equinox.
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 : valid `~astropy.coordinates.Angle` initializer, 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`, optional
Proper motion components, in angle per time units.
l, b : valid `~astropy.coordinates.Angle` initializer, 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`, optional
Proper motion components in the `Galactic` frame, in angle per time
units.
x, y, z : float or `~astropy.units.Quantity`, optional
Cartesian coordinates values
u, v, w : float or `~astropy.units.Quantity`, optional
Cartesian coordinates values for the Galactic frame.
radial_velocity : `~astropy.units.Quantity`, 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()
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
# TODO: remove these in future
@property
def representation(self):
return self.frame.representation
@representation.setter
def representation(self, value):
self.frame.representation = value
@property
def shape(self):
return self.frame.shape
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.misc.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 : tuple
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, 'size', 1) > 1:
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 transform_to(self, frame, merge_attributes=True):
"""Transform this coordinate to a new frame.
The precise frame transformed to depends on ``merge_attributes``.
If `False`, the destination frame is used exactly as passed in.
But this is often not quite what one wants. E.g., suppose one wants to
transform an ICRS coordinate that has an obstime attribute to FK4; in
this case, one likely would want to use this information. Thus, the
default for ``merge_attributes`` is `True`, in which the precedence is
as follows: (1) explicitly set (i.e., non-default) values in the
destination frame; (2) explicitly set values in the source; (3) default
value in the destination frame.
Note that in either case, any explicitly set attributes on the source
`SkyCoord` that are not part of the destination frame's definition are
kept (stored on the resulting `SkyCoord`), and thus one can round-trip
(e.g., from FK4 to ICRS to FK4 without loosing obstime).
Parameters
----------
frame : str, `BaseCoordinateFrame` class or instance, or `SkyCoord` instance
The frame to transform this coordinate into. If a `SkyCoord`, the
underlying frame is extracted, and all other information ignored.
merge_attributes : bool, optional
Whether the default attributes in the destination frame are allowed
to be overridden by explicitly set attributes in the source
(see note above; default: `True`).
Returns
-------
coord : `SkyCoord`
A new object with this coordinate represented in the `frame` frame.
Raises
------
ValueError
If there is no possible transformation route.
"""
from astropy.coordinates.errors import ConvertError
frame_kwargs = {}
# Frame name (string) or frame class? Coerce into an instance.
try:
frame = _get_frame_class(frame)()
except Exception:
pass
if isinstance(frame, SkyCoord):
frame = frame.frame # Change to underlying coord frame instance
if isinstance(frame, BaseCoordinateFrame):
new_frame_cls = frame.__class__
# Get frame attributes, allowing defaults to be overridden by
# explicitly set attributes of the source if ``merge_attributes``.
for attr in frame_transform_graph.frame_attributes:
self_val = getattr(self, attr, None)
frame_val = getattr(frame, attr, None)
if (frame_val is not None
and not (merge_attributes
and frame.is_frame_attr_default(attr))):
frame_kwargs[attr] = frame_val
elif (self_val is not None
and not self.is_frame_attr_default(attr)):
frame_kwargs[attr] = self_val
elif frame_val is not None:
frame_kwargs[attr] = frame_val
else:
raise ValueError('Transform `frame` must be a frame name, class, or instance')
# Get the composite transform to the new frame
trans = frame_transform_graph.get_transform(self.frame.__class__, new_frame_cls)
if trans is None:
raise ConvertError('Cannot transform from {} to {}'
.format(self.frame.__class__, new_frame_cls))
# Make a generic frame which will accept all the frame kwargs that
# are provided and allow for transforming through intermediate frames
# which may require one or more of those kwargs.
generic_frame = GenericFrame(frame_kwargs)
# Do the transformation, returning a coordinate frame of the desired
# final type (not generic).
new_coord = trans(self.frame, generic_frame)
# Finally make the new SkyCoord object from the `new_coord` and
# remaining frame_kwargs that are not frame_attributes in `new_coord`.
for attr in (set(new_coord.get_frame_attr_names()) &
set(frame_kwargs.keys())):
frame_kwargs.pop(attr)
return self.__class__(new_coord, **frame_kwargs)
def apply_space_motion(self, new_obstime=None, dt=None):
"""
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``.
"""
if (new_obstime is None and dt is None or
new_obstime is not None and dt is not 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:\n"
"https://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 inital 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']
try:
plx = icrsrep.distance.to_value(u.arcsecond, u.parallax())
except u.UnitConversionError: # No distance: set to 0 by convention
plx = 0.
try:
rv = icrsvel.d_distance.to_value(u.km/u.s)
except u.UnitConversionError: # No RV
rv = 0.
starpm = erfa.starpm(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)
icrs2 = ICRS(ra=u.Quantity(starpm[0], u.radian, copy=False),
dec=u.Quantity(starpm[1], u.radian, copy=False),
pm_ra=u.Quantity(starpm[2], u.radian/u.yr, copy=False),
pm_dec=u.Quantity(starpm[3], u.radian/u.yr, copy=False),
distance=Distance(parallax=starpm[4] * u.arcsec, copy=False),
radial_velocity=u.Quantity(starpm[5], u.km/u.s, copy=False),
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
return self.__class__(icrs2, **frattrs).transform_to(self.frame)
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 master 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.get_frame_attr_names():
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)
# Fail
raise AttributeError("'{}' object has no attribute '{}'"
.format(self.__class__.__name__, attr))
def __setattr__(self, attr, val):
# This is to make anything available through __getattr__ immutable
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):
setattr(self._sky_coord_frame, attr, val)
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 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}
else:
# 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)
@override__dir__
def __dir__(self):
"""
Override the builtin `dir` behavior to include:
- Transforms available by aliases
- Attribute / methods of the underlying self.frame object
"""
# determine the aliases that this can be transformed to.
dir_values = set()
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(set(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 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 '<{clsnm} ({coonm}{frameattrs}){data}>'.format(**locals())
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('Invalid style. Valid options are: {}'.format(",".join(styles)))
lonargs.update(kwargs)
latargs.update(kwargs)
if np.isscalar(sph_coord.lon.value):
coord_string = (sph_coord.lon.to_string(**lonargs) +
" " + sph_coord.lat.to_string(**latargs))
else:
coord_string = []
for lonangle, latangle in zip(sph_coord.lon.ravel(), sph_coord.lat.ravel()):
coord_string += [(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
def is_equivalent_frame(self, other):
"""
Checks if this object's frame as 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 `BaseCoordinateFrame` or subclass.
"""
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 np.any(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
def separation(self, other):
"""
Computes on-sky separation between this coordinate and another.
.. note::
If the ``other`` coordinate object is in a different frame, it is
first transformed to the frame of this object. This can lead to
unintuitive behavior if not accounted for. Particularly of note is
that ``self.separation(other)`` and ``other.separation(self)`` may
not give the same answer in this case.
For more on how to use this (and related) functionality, see the
examples in :doc:`/coordinates/matchsep`.
Parameters
----------
other : `~astropy.coordinates.SkyCoord` or `~astropy.coordinates.BaseCoordinateFrame`
The coordinate to get the separation to.
Returns
-------
sep : `~astropy.coordinates.Angle`
The on-sky separation between this and the ``other`` coordinate.
Notes
-----
The separation is calculated using the Vincenty formula, which
is stable at all locations, including poles and antipodes [1]_.
.. [1] https://en.wikipedia.org/wiki/Great-circle_distance
"""
from . import Angle
from .angle_utilities import angular_separation
if not self.is_equivalent_frame(other):
try:
other = other.transform_to(self, merge_attributes=False)
except TypeError:
raise TypeError('Can only get separation to another SkyCoord '
'or a coordinate frame with data')
lon1 = self.spherical.lon
lat1 = self.spherical.lat
lon2 = other.spherical.lon
lat2 = other.spherical.lat
# Get the separation as a Quantity, convert to Angle in degrees
sep = angular_separation(lon1, lat1, lon2, lat2)
return Angle(sep, unit=u.degree)
def separation_3d(self, other):
"""
Computes three dimensional separation between this coordinate
and another.
For more on how to use this (and related) functionality, see the
examples in :doc:`/coordinates/matchsep`.
Parameters
----------
other : `~astropy.coordinates.SkyCoord` or `~astropy.coordinates.BaseCoordinateFrame`
The coordinate to get the separation to.
Returns
-------
sep : `~astropy.coordinates.Distance`
The real-space distance between these two coordinates.
Raises
------
ValueError
If this or the other coordinate do not have distances.
"""
if not self.is_equivalent_frame(other):
try:
other = other.transform_to(self, merge_attributes=False)
except TypeError:
raise TypeError('Can only get separation to another SkyCoord '
'or a coordinate frame with data')
if issubclass(self.data.__class__, UnitSphericalRepresentation):
raise ValueError('This object does not have a distance; cannot '
'compute 3d separation.')
if issubclass(other.data.__class__, UnitSphericalRepresentation):
raise ValueError('The other object does not have a distance; '
'cannot compute 3d separation.')
c1 = self.cartesian.without_differentials()
c2 = other.cartesian.without_differentials()
return Distance((c1 - c2).norm())
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 (i.e., RA for
equatorial coordinates).
lat_offset : `~astropy.coordinates.Angle`
The angular offset in the latitude direction (i.e., 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 `separation`/`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
--------
separation : for the *total* angular offset (not broken out into components).
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
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
--------
position_angle : inverse operation for the ``position_angle`` component
separation : inverse operation for the ``separation`` component
"""
from . import angle_utilities
slat = self.represent_as(UnitSphericalRepresentation).lat
slon = self.represent_as(UnitSphericalRepresentation).lon
newlon, newlat = angle_utilities.offset_by(
lon=slon, lat=slat,
posang=position_angle, distance=separation)
return SkyCoord(newlon, newlat, frame=self.frame)
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 :doc:`/coordinates/matchsep`.
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 : integer 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`
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 (isinstance(catalogcoord, (SkyCoord, BaseCoordinateFrame))
and catalogcoord.has_data):
self_in_catalog_frame = self.transform_to(catalogcoord)
else:
raise TypeError('Can only get separation to another SkyCoord or a '
'coordinate frame with data')
res = match_coordinates_sky(self_in_catalog_frame, catalogcoord,
nthneighbor=nthneighbor,
storekdtree='_kdtree_sky')
return res
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 :doc:`/coordinates/matchsep`.
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 : integer 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`
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 (isinstance(catalogcoord, (SkyCoord, BaseCoordinateFrame))
and catalogcoord.has_data):
self_in_catalog_frame = self.transform_to(catalogcoord)
else:
raise TypeError('Can only get separation to another SkyCoord or a '
'coordinate frame with data')
res = match_coordinates_3d(self_in_catalog_frame, catalogcoord,
nthneighbor=nthneighbor,
storekdtree='_kdtree_3d')
return res
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
`~astropy.coordinates.SkyCoord.separation`.
For more on how to use this (and related) functionality, see the
examples in :doc:`/coordinates/matchsep`.
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.
seplimit : `~astropy.units.Quantity` with angle units
The on-sky separation to search within.
Returns
-------
idxsearcharound : integer array
Indices into ``searcharoundcoords`` that match the
corresponding elements of ``idxself``. Shape matches
``idxself``.
idxself : integer 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`
The 3D distance between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ (>=0.12.0) 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')
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
`~astropy.coordinates.SkyCoord.separation_3d`.
For more on how to use this (and related) functionality, see the
examples in :doc:`/coordinates/matchsep`.
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` with distance units
The physical radius to search within.
Returns
-------
idxsearcharound : integer array
Indices into ``searcharoundcoords`` that match the
corresponding elements of ``idxself``. Shape matches
``idxself``.
idxself : integer 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`
The 3D distance between the coordinates. Shape matches
``idxsearcharound`` and ``idxself``.
Notes
-----
This method requires `SciPy <https://www.scipy.org/>`_ (>=0.12.0) 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')
def position_angle(self, other):
"""
Computes the on-sky position angle (East of North) between this
`SkyCoord` and another.
Parameters
----------
other : `SkyCoord`
The other coordinate to compute the position angle to. It is
treated as the "head" of the vector of the position angle.
Returns
-------
pa : `~astropy.coordinates.Angle`
The (positive) position angle of the vector pointing from ``self``
to ``other``. If either ``self`` or ``other`` contain arrays, this
will be an array following the appropriate `numpy` broadcasting
rules.
Examples
--------
>>> c1 = SkyCoord(0*u.deg, 0*u.deg)
>>> c2 = SkyCoord(1*u.deg, 0*u.deg)
>>> c1.position_angle(c2).degree
90.0
>>> c3 = SkyCoord(1*u.deg, 1*u.deg)
>>> c1.position_angle(c3).degree # doctest: +FLOAT_CMP
44.995636455344844
"""
from . import angle_utilities
if not self.is_equivalent_frame(other):
try:
other = other.transform_to(self, merge_attributes=False)
except TypeError:
raise TypeError('Can only get position_angle to another '
'SkyCoord or a coordinate frame with data')
slat = self.represent_as(UnitSphericalRepresentation).lat
slon = self.represent_as(UnitSphericalRepresentation).lon
olat = other.represent_as(UnitSphericalRepresentation).lat
olon = other.represent_as(UnitSphericalRepresentation).lon
return angle_utilities.position_angle(slon, slat, olon, olat)
def skyoffset_frame(self, rotation=None):
"""
Returns the sky offset frame with this `SkyCoord` at the origin.
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)
rotation : `~astropy.coordinates.Angle` or `~astropy.units.Quantity` with angle units
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.
"""
return SkyOffsetFrame(origin=self, rotation=rotation)
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 <http://cdsarc.u-strasbg.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 infromation 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
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
"""
return skycoord_to_pixel(self, wcs=wcs, origin=origin, mode=mode)
@classmethod
def from_pixel(cls, xp, yp, wcs, origin=0, mode='all'):
"""
Create a new `SkyCoord` from pixel coordinates using an
`~astropy.wcs.WCS` object.
Parameters
----------
xp, yp : float or `numpy.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 : an instance of this class
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
"""
return pixel_to_skycoord(xp, yp, wcs=wcs, origin=origin, mode=mode, cls=cls)
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 cooordinate
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)
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` with velocity units
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. Strictly speaking, the barycentric correction is
multiplicative and should be applied as::
sc = SkyCoord(1*u.deg, 2*u.deg)
vcorr = sc.rv_correction(kind='barycentric', obstime=t, location=loc)
rv = rv + vcorr + rv * vcorr / consts.c
If your target is nearby and/or has finite proper motion you may need to account
for terms arising from this. See Wright & Eastmann (2014) for details.
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::
sc = SkyCoord(1*u.deg, 2*u.deg)
with coord.solar_system_ephemeris.set('jpl'):
rv += sc.rv_correction(obstime=t, location=loc)
"""
# 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
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:
raise ValueError('Cannot compute radial velocity correction if '
'`obstime` argument is passed in and it is '
'inconsistent with the `obstime` frame '
'attribute on the SkyCoord')
pos_earth, v_earth = get_body_barycentric_posvel('earth', obstime)
if kind == 'barycentric':
v_origin_to_earth = v_earth
elif kind == 'heliocentric':
v_sun = get_body_barycentric_posvel('sun', obstime)[1]
v_origin_to_earth = v_earth - v_sun
else:
raise ValueError("`kind` argument to radial_velocity_correction must "
"be 'barycentric' or 'heliocentric', but got "
"'{}'".format(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
if self.data.__class__ is UnitSphericalRepresentation:
targcart = self.icrs.cartesian
else:
# skycoord has distances so apply parallax
obs_icrs_cart = pos_earth + gcrs_p
icrs_cart = self.icrs.cartesian
targcart = icrs_cart - obs_icrs_cart
targcart /= targcart.norm()
if kind == 'barycentric':
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 + targcart.dot(beta_obs)) / (1 + gr/speed_of_light) - 1
return zb * speed_of_light
else:
# do a simpler correction 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)
# Table interactions
@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 the components of the requested frames, 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 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
The table to load data from.
coord_kwargs
Any additional keyword arguments are passed directly to this class's
constructor.
Returns
-------
newsc : same as this class
The new `SkyCoord` (or subclass) object.
"""
_frame_cls, _frame_kwargs = _get_frame_without_data([], coord_kwargs)
frame = _frame_cls(**_frame_kwargs)
coord_kwargs['frame'] = coord_kwargs.get('frame', frame)
comp_kwargs = {}
for comp_name in frame.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('(' + starts_with_comp + ')|(' + ends_with_comp + ')',
re.IGNORECASE | re.UNICODE)
for col_name in table.colnames:
if rex.match(col_name):
if comp_name in comp_kwargs:
oldname = comp_kwargs[comp_name].name
msg = ('Found at least two matches for component "{0}"'
': "{1}" and "{2}". Cannot continue with this '
'ambiguity.')
raise ValueError(msg.format(comp_name, oldname, col_name))
comp_kwargs[comp_name] = table[col_name]
for k, v in comp_kwargs.items():
if k in coord_kwargs:
raise ValueError('Found column "{}" in table, but it was '
'already provided as "{}" keyword to '
'guess_from_table function.'.format(v.name, k))
else:
coord_kwargs[k] = v
return cls(**coord_kwargs)
# Name resolve
@classmethod
def from_name(cls, name, frame='icrs', parse=False):
"""
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 eg:
'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.
Returns
-------
coord : SkyCoord
Instance of the SkyCoord class.
"""
from .name_resolve import get_icrs_coordinates
icrs_coord = get_icrs_coordinates(name, parse)
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)