GreatCircleICRSFrame

class gala.coordinates.GreatCircleICRSFrame(*args, **kwargs)[source]

Bases: astropy.coordinates.BaseCoordinateFrame

A frame rotated into great circle coordinates with the pole and longitude

specified as frame attributes.

GreatCircleICRSFrame``s always have component names for spherical coordinates of ``phi1/phi2.

Parameters:
data : BaseRepresentation subclass instance

A representation object or None to have no data (or use the coordinate component arguments, see below).

phi1 : Quantity

Longitude component.

phi2 : Quantity

Latitude component.

distance : Quantity

Distance.

pm_phi1_cosphi2 : Quantity

Proper motion in longitude.

pm_phi2 : Quantity

Proper motion in latitude.

radial_velocity : Quantity

Line-of-sight or radial velocity.

representation_type : BaseRepresentation subclass, str, optional

A representation class or string name of a representation class. This sets the expected input representation class, thereby changing the expected keyword arguments for the data passed in. For example, passing representation_type='cartesian' will make the classes expect position data with cartesian names, i.e. x, y, z in most cases.

differential_type : BaseDifferential subclass, str, dict, optional

A differential class or dictionary of differential classes (currently only a velocity differential with key ‘s’ is supported). This sets the expected input differential class, thereby changing the expected keyword arguments of the data passed in. For example, passing differential_type='cartesian' will make the classes expect velocity data with the argument names v_x, v_y, v_z.

copy : bool, optional

If True (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument.

Attributes Summary

T Return an instance with the data transposed.
cache Cache for this frame, a dict.
cartesian Shorthand for a cartesian representation of the coordinates in this object.
data The coordinate data for this object.
default_differential
default_representation
differential_type The differential used for this frame’s data.
frame_attributes
frame_specific_representation_info
has_data True if this frame has data, False otherwise.
isscalar
name
ndim The number of dimensions of the instance and underlying arrays.
pole
proper_motion Shorthand for the two-dimensional proper motion as a Quantity object with angular velocity units.
ra0
radial_velocity Shorthand for the radial or line-of-sight velocity as a Quantity object.
representation
representation_component_names
representation_component_units
representation_info A dictionary with the information of what attribute names for this frame apply to particular representations.
representation_type The representation class used for this frame’s data.
rotation
shape The shape of the instance and underlying arrays.
size The size of the object, as calculated from its shape.
spherical Shorthand for a spherical representation of the coordinates in this object.
sphericalcoslat Shorthand for a spherical representation of the positional data and a SphericalCosLatDifferential for the velocity data in this object.
velocity Shorthand for retrieving the Cartesian space-motion as a CartesianDifferential object.

Methods Summary

copy(*args, **kwargs) Return an instance containing copies of the internal data.
diagonal(*args, **kwargs) Return an instance with the specified diagonals.
flatten(*args, **kwargs) Return a copy with the array collapsed into one dimension.
from_endpoints(coord1, coord2[, ra0, rotation]) TODO
get_frame_attr_names()
get_representation_cls([which]) The class used for part of this frame’s data.
get_representation_component_names([which])
get_representation_component_units([which])
is_equivalent_frame(other) Checks if this object is the same frame as the other object.
is_frame_attr_default(attrnm) Determine whether or not a frame attribute has its value because it’s the default value, or because this frame was created with that value explicitly requested.
is_transformable_to(new_frame) Determines if this coordinate frame can be transformed to another given frame.
ravel(*args, **kwargs) Return an instance with the array collapsed into one dimension.
realize_frame(representation_type) Generates a new frame with new data from another frame (which may or may not have data).
replicate([copy]) Return a replica of the frame, optionally with new frame attributes.
replicate_without_data([copy]) Return a replica without data, optionally with new frame attributes.
represent_as(base[, s, in_frame_units]) Generate and return a new representation of this frame’s data as a Representation object.
reshape(*args, **kwargs) Returns an instance containing the same data with a new shape.
separation(other) Computes on-sky separation between this coordinate and another.
separation_3d(other) Computes three dimensional separation between this coordinate and another.
set_representation_cls([base, s]) Set representation and/or differential class for this frame’s data.
squeeze(*args, **kwargs) Return an instance with single-dimensional shape entries removed
swapaxes(*args, **kwargs) Return an instance with the given axes interchanged.
take(indices[, axis, mode]) Return a new instance formed from the elements at the given indices.
transform_to(new_frame) Transform this object’s coordinate data to a new frame.
transpose(*args, **kwargs) Return an instance with the data transposed.

Attributes Documentation

T

Return an instance with the data transposed.

Parameters are as for T. All internal data are views of the data of the original.

cache

Cache for this frame, a dict. It stores anything that should be computed from the coordinate data (not from the frame attributes). This can be used in functions to store anything that might be expensive to compute but might be re-used by some other function. E.g.:

if 'user_data' in myframe.cache:
    data = myframe.cache['user_data']
else:
    myframe.cache['user_data'] = data = expensive_func(myframe.lat)

If in-place modifications are made to the frame data, the cache should be cleared:

myframe.cache.clear()
cartesian

Shorthand for a cartesian representation of the coordinates in this object.

data

The coordinate data for this object. If this frame has no data, an ValueError will be raised. Use has_data to check if data is present on this frame object.

default_differential
default_representation
differential_type

The differential used for this frame’s data.

This will be a subclass from BaseDifferential. For simultaneous setting of representation and differentials, see the set_represenation_cls method.

frame_attributes = {'pole': <astropy.coordinates.attributes.CoordinateAttribute object>, 'ra0': <astropy.coordinates.attributes.QuantityAttribute object>, 'rotation': <astropy.coordinates.attributes.QuantityAttribute object>}
frame_specific_representation_info
has_data

True if this frame has data, False otherwise.

isscalar
name = 'greatcircleicrsframe'
ndim

The number of dimensions of the instance and underlying arrays.

pole = None
proper_motion

Shorthand for the two-dimensional proper motion as a Quantity object with angular velocity units. In the returned Quantity, axis=0 is the longitude/latitude dimension so that .proper_motion[0] is the longitudinal proper motion and .proper_motion[1] is latitudinal. The longitudinal proper motion already includes the cos(latitude) term.

ra0 = <Quantity nan deg>
radial_velocity

Shorthand for the radial or line-of-sight velocity as a Quantity object.

representation
representation_component_names
representation_component_units
representation_info

A dictionary with the information of what attribute names for this frame apply to particular representations.

representation_type

The representation class used for this frame’s data.

This will be a subclass from BaseRepresentation. Can also be set using the string name of the representation. If you wish to set an explicit differential class (rather than have it be inferred), use the set_represenation_cls method.

rotation = <Quantity 0. deg>
shape

The shape of the instance and underlying arrays.

size

The size of the object, as calculated from its shape.

spherical

Shorthand for a spherical representation of the coordinates in this object.

sphericalcoslat

Shorthand for a spherical representation of the positional data and a SphericalCosLatDifferential for the velocity data in this object.

velocity

Shorthand for retrieving the Cartesian space-motion as a CartesianDifferential object. This is equivalent to calling self.cartesian.differentials['s'].

Methods Documentation

copy(*args, **kwargs)

Return an instance containing copies of the internal data.

Parameters are as for copy().

diagonal(*args, **kwargs)

Return an instance with the specified diagonals.

Parameters are as for diagonal(). All internal data are views of the data of the original.

flatten(*args, **kwargs)

Return a copy with the array collapsed into one dimension.

Parameters are as for flatten().

classmethod from_endpoints(coord1, coord2, ra0=None, rotation=None)[source]

TODO

classmethod get_frame_attr_names()
get_representation_cls(which='base')

The class used for part of this frame’s data.

Parameters:
which : (‘base’, ‘s’, None)

The class of which part to return. ‘base’ means the class used to represent the coordinates; ‘s’ the first derivative to time, i.e., the class representing the proper motion and/or radial velocity. If None, return a dict with both.

Returns:
representation : BaseRepresentation or BaseDifferential.
get_representation_component_names(which='base')
get_representation_component_units(which='base')
is_equivalent_frame(other)

Checks if this object is the same frame as the other object.

To be the same frame, two objects must be the same frame class and have the same frame attributes. Note that it does not matter what, if any, data either object has.

Parameters:
other : BaseCoordinateFrame

the other frame to check

Returns:
isequiv : bool

True if the frames are the same, False if not.

Raises:
TypeError

If other isn’t a BaseCoordinateFrame or subclass.

is_frame_attr_default(attrnm)

Determine whether or not a frame attribute has its value because it’s the default value, or because this frame was created with that value explicitly requested.

Parameters:
attrnm : str

The name of the attribute to check.

Returns:
isdefault : bool

True if the attribute attrnm has its value by default, False if it was specified at creation of this frame.

is_transformable_to(new_frame)

Determines if this coordinate frame can be transformed to another given frame.

Parameters:
new_frame : class or frame object

The proposed frame to transform into.

Returns:
transformable : bool or str

True if this can be transformed to new_frame, False if not, or the string ‘same’ if new_frame is the same system as this object but no transformation is defined.

Notes

A return value of ‘same’ means the transformation will work, but it will just give back a copy of this object. The intended usage is:

if coord.is_transformable_to(some_unknown_frame):
    coord2 = coord.transform_to(some_unknown_frame)

This will work even if some_unknown_frame turns out to be the same frame class as coord. This is intended for cases where the frame is the same regardless of the frame attributes (e.g. ICRS), but be aware that it might also indicate that someone forgot to define the transformation between two objects of the same frame class but with different attributes.

ravel(*args, **kwargs)

Return an instance with the array collapsed into one dimension.

Parameters are as for ravel(). Note that it is not always possible to unravel an array without copying the data. If you want an error to be raise if the data is copied, you should should assign shape (-1,) to the shape attribute.

realize_frame(representation_type)

Generates a new frame with new data from another frame (which may or may not have data). Roughly speaking, the converse of replicate_without_data.

Parameters:
representation_type : BaseRepresentation

The representation to use as the data for the new frame.

Returns:
frameobj : same as this frame

A new object with the same frame attributes as this one, but with the representation as the data.

replicate(copy=False, **kwargs)

Return a replica of the frame, optionally with new frame attributes.

The replica is a new frame object that has the same data as this frame object and with frame attributes overriden if they are provided as extra keyword arguments to this method. If copy is set to True then a copy of the internal arrays will be made. Otherwise the replica will use a reference to the original arrays when possible to save memory. The internal arrays are normally not changeable by the user so in most cases it should not be necessary to set copy to True.

Parameters:
copy : bool, optional

If True, the resulting object is a copy of the data. When False, references are used where possible. This rule also applies to the frame attributes.

Any additional keywords are treated as frame attributes to be set on the
new frame object.
Returns:
frameobj : same as this frame

Replica of this object, but possibly with new frame attributes.

replicate_without_data(copy=False, **kwargs)

Return a replica without data, optionally with new frame attributes.

The replica is a new frame object without data but with the same frame attributes as this object, except where overriden by extra keyword arguments to this method. The copy keyword determines if the frame attributes are truly copied vs being references (which saves memory for cases where frame attributes are large).

This method is essentially the converse of realize_frame.

Parameters:
copy : bool, optional

If True, the resulting object has copies of the frame attributes. When False, references are used where possible.

Any additional keywords are treated as frame attributes to be set on the
new frame object.
Returns:
frameobj : same as this frame

Replica of this object, but without data and possibly with new frame attributes.

represent_as(base, s='base', in_frame_units=False)

Generate and return a new representation of this frame’s data as a Representation object.

Note: In order to make an in-place change of the representation of a Frame or SkyCoord object, set the representation attribute of that object to the desired new representation, or use the set_representation_cls method to also set the differential.

Parameters:
base : subclass of BaseRepresentation or string

The type of representation to generate. Must be a class (not an instance), or the string name of the representation class.

s : subclass of BaseDifferential, str, optional

Class in which any velocities should be represented. Must be a class (not an instance), or the string name of the differential class. If equal to ‘base’ (default), inferred from the base class. If None, all velocity information is dropped.

in_frame_units : bool, keyword only

Force the representation units to match the specified units particular to this frame

Returns:
newrep : BaseRepresentation-derived object

A new representation object of this frame’s data.

Raises:
AttributeError

If this object had no data

Examples

>>> from astropy import units as u
>>> from astropy.coordinates import SkyCoord, CartesianRepresentation
>>> coord = SkyCoord(0*u.deg, 0*u.deg)
>>> coord.represent_as(CartesianRepresentation)  # doctest: +FLOAT_CMP
<CartesianRepresentation (x, y, z) [dimensionless]
        (1., 0., 0.)>
>>> coord.representation = CartesianRepresentation
>>> coord  # doctest: +FLOAT_CMP
<SkyCoord (ICRS): (x, y, z) [dimensionless]
    (1., 0., 0.)>
reshape(*args, **kwargs)

Returns an instance containing the same data with a new shape.

Parameters are as for reshape(). Note that it is not always possible to change the shape of an array without copying the data (see reshape() documentation). If you want an error to be raise if the data is copied, you should assign the new shape to the shape attribute (note: this may not be implemented for all classes using ShapedLikeNDArray).

separation(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 unintutive 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.

Parameters:
other : BaseCoordinateFrame

The coordinate to get the separation to.

Returns:
sep : 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
separation_3d(other)

Computes three dimensional separation between this coordinate and another.

Parameters:
other : BaseCoordinateFrame

The coordinate system to get the distance to.

Returns:
sep : Distance

The real-space distance between these two coordinates.

Raises:
ValueError

If this or the other coordinate do not have distances.

set_representation_cls(base=None, s='base')

Set representation and/or differential class for this frame’s data.

Parameters:
base : str, BaseRepresentation subclass, optional

The name or subclass to use to represent the coordinate data.

s : BaseDifferential subclass, optional

The differential subclass to use to represent any velocities, such as proper motion and radial velocity. If equal to ‘base’, which is the default, it will be inferred from the representation. If None, the representation will drop any differentials.

squeeze(*args, **kwargs)

Return an instance with single-dimensional shape entries removed

Parameters are as for squeeze(). All internal data are views of the data of the original.

swapaxes(*args, **kwargs)

Return an instance with the given axes interchanged.

Parameters are as for swapaxes(): axis1, axis2. All internal data are views of the data of the original.

take(indices, axis=None, mode='raise')

Return a new instance formed from the elements at the given indices.

Parameters are as for take(), except that, obviously, no output array can be given.

transform_to(new_frame)

Transform this object’s coordinate data to a new frame.

Parameters:
new_frame : class or frame object or SkyCoord object

The frame to transform this coordinate frame into.

Returns:
transframe

A new object with the coordinate data represented in the newframe system.

Raises:
ValueError

If there is no possible transformation route.

transpose(*args, **kwargs)

Return an instance with the data transposed.

Parameters are as for transpose(). All internal data are views of the data of the original.