ITRS#
- class astropy.coordinates.ITRS(*args, copy=True, representation_type=None, differential_type=None, **kwargs)[source]#
Bases:
BaseCoordinateFrame
A coordinate or frame in the International Terrestrial Reference System (ITRS). This is approximately a geocentric system, although strictly it is defined by a series of reference locations near the surface of the Earth (the ITRF). For more background on the ITRS, see the references provided in the See Also section of the documentation.
This frame also includes frames that are defined relative to the center of the Earth, but that are offset (in both position and velocity) from the center of the Earth. You may see such non-geocentric coordinates referred to as “topocentric”.
Topocentric ITRS frames are convenient for observations of near Earth objects where stellar aberration is not included. One can merely subtract the observing site’s EarthLocation geocentric ITRS coordinates from the object’s geocentric ITRS coordinates, put the resulting vector into a topocentric ITRS frame and then transform to
AltAz
orHADec
. The other way around is to transform an observedAltAz
orHADec
position to a topocentric ITRS frame and add the observing site’s EarthLocation geocentric ITRS coordinates to yield the object’s geocentric ITRS coordinates.On the other hand, using
transform_to
to transform geocentric ITRS coordinates to topocentric ITRS, observedAltAz
, or observedHADec
coordinates includes the difference between stellar aberration from the point of view of an observer at the geocenter and stellar aberration from the point of view of an observer on the surface of the Earth. If the geocentric ITRS coordinates of the object include stellar aberration at the geocenter (e.g. certain ILRS ephemerides), then this is the way to go.Note to ILRS ephemeris users: Astropy does not currently consider relativistic effects of the Earth’s gravatational field. Nor do the
AltAz
orHADec
refraction corrections compute the change in the range due to the curved path of light through the atmosphere, so Astropy is no substitute for the ILRS software in these respects.- Parameters:
- data
BaseRepresentation
subclass instance A representation object or
None
to have no data (or use the coordinate component arguments, see below).- 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 unless overridden viaframe_specific_representation_info
. To see this frame’s names, check out<this frame>().representation_info
.- 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
unless overridden viaframe_specific_representation_info
. To see this frame’s names, check out<this frame>().representation_info
.- copybool, optional
If
True
(default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument.
- data
- Other Parameters:
- obstime
Time
The time at which the observation is taken. Used for determining the position of the Earth and its precession.
- location
EarthLocation
The location on the Earth. This can be specified either as an
EarthLocation
object or as anything that can be transformed to anITRS
frame. The default is the centre of the Earth.
- obstime
Attributes Summary
Default representation for differential data (e.g., velocity)
Default representation for position data
The data in this frame as an
EarthLocation
class.Mapping for frame-specific component names
The location on Earth of the observer
The reference time (e.g., time of observation)
Attributes Documentation
- default_differential#
Default representation for differential data (e.g., velocity)
- default_representation#
Default representation for position data
- earth_location#
The data in this frame as an
EarthLocation
class.
- frame_attributes = {'location': <astropy.coordinates.attributes.EarthLocationAttribute object>, 'obstime': <astropy.coordinates.attributes.TimeAttribute object>}#
- frame_specific_representation_info#
Mapping for frame-specific component names
- location#
The location on Earth of the observer
Default: (0.0, 0.0, 0.0) km
- name = 'itrs'#
- obstime#
The reference time (e.g., time of observation)
Default: J2000.000