GCRS¶
-
class
astropy.coordinates.
GCRS
(*args, copy=True, representation_type=None, differential_type=None, **kwargs)[source] [edit on github]¶ Bases:
astropy.coordinates.BaseRADecFrame
A coordinate or frame in the Geocentric Celestial Reference System (GCRS).
GCRS is distinct form ICRS mainly in that it is relative to the Earth’s center-of-mass rather than the solar system Barycenter. That means this frame includes the effects of aberration (unlike ICRS). For more background on the GCRS, see the references provided in the See Also section of the documentation. (Of particular note is Section 1.2 of USNO Circular 179)
This frame also includes frames that are defined relative to the Earth, but that are offset (in both position and velocity) from the Earth.
The frame attributes are listed under Other Parameters.
Parameters: - data :
BaseRepresentation
subclass instance A representation object or
None
to have no data (or use the coordinate component arguments, see below).- ra :
Angle
, optional, must be keyword The RA for this object (
dec
must also be given andrepresentation
must be None).- dec :
Angle
, optional, must be keyword The Declination for this object (
ra
must also be given andrepresentation
must be None).- distance :
Quantity
, optional, must be keyword The Distance for this object along the line-of-sight. (
representation
must be None).- pm_ra_cosdec :
Quantity
, optional, must be keyword The proper motion in Right Ascension (including the
cos(dec)
factor) for this object (pm_dec
must also be given).- pm_dec :
Quantity
, optional, must be keyword The proper motion in Declination for this object (
pm_ra_cosdec
must also be given).- radial_velocity :
Quantity
, optional, must be keyword The radial velocity of this object.
- 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 namesv_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.
Other Parameters: - obstime :
Time
The time at which the observation is taken. Used for determining the position of the Earth.
- obsgeoloc :
CartesianRepresentation
,Quantity
The position of the observer relative to the center-of-mass of the Earth, oriented the same as BCRS/ICRS. Either [0, 0, 0],
CartesianRepresentation
, or proper input for one, i.e., aQuantity
with shape (3, …) and length units. Defaults to [0, 0, 0], meaning “true” GCRS.- obsgeovel :
CartesianRepresentation
,Quantity
The velocity of the observer relative to the center-of-mass of the Earth, oriented the same as BCRS/ICRS. Either [0, 0, 0],
CartesianRepresentation
, or proper input for one, i.e., aQuantity
with shape (3, …) and velocity units. Defaults to [0, 0, 0], meaning “true” GCRS.
Attributes Summary
default_differential
default_representation
frame_attributes
frame_specific_representation_info
name
obsgeoloc
obsgeovel
obstime
Attributes Documentation
-
default_differential
¶
-
default_representation
¶
-
frame_attributes
= {'obsgeoloc': <astropy.coordinates.attributes.CartesianRepresentationAttribute object>, 'obsgeovel': <astropy.coordinates.attributes.CartesianRepresentationAttribute object>, 'obstime': <astropy.coordinates.attributes.TimeAttribute object>}¶
-
frame_specific_representation_info
¶
-
name
= 'gcrs'¶
-
obsgeoloc
= <CartesianRepresentation (x, y, z) in m (0., 0., 0.)>¶
-
obsgeovel
= <CartesianRepresentation (x, y, z) in m / s (0., 0., 0.)>¶
-
obstime
= <Time object: scale='utc' format='jyear_str' value=J2000.000>¶
- data :