Source code for astropy.coordinates.sky_coordinate


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']


[docs]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
[docs]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
[docs] 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)
[docs] 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())
[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('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
[docs] 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
[docs] 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)
[docs] 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())
[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 (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
[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 -------- 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)
[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 :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
[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 :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
[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 `~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')
[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 `~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')
[docs] 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)
[docs] 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)
[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 <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
[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 """ 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 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)
[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 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)
[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` 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
[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 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>_!"#$%&'()*+,-./\:;<=>[email protected][]^`{|}~``). 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
[docs] @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)