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# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
from __future__ import (absolute_import, unicode_literals, division,
print_function)
from ..representation import SphericalRepresentation
from ..baseframe import (BaseCoordinateFrame, frame_transform_graph,
TimeFrameAttribute, RepresentationMapping)
from ..transformations import DynamicMatrixTransform
from .. import earth_orientation as earth
from .utils import EQUINOX_J2000
class FK5(BaseCoordinateFrame):
"""
A coordinate or frame in the FK5 system.
Note that this is a barycentric version of FK5 - that is, the origin for
this frame is the Solar System Barycenter, *not* the Earth geocenter.
Parameters
----------
representation : `BaseRepresentation` or None
A representation object or None to have no data (or use the other keywords)
ra : `Angle`, optional, must be keyword
The RA for this object (``dec`` must also be given and ``representation``
must be None).
dec : `Angle`, optional, must be keyword
The Declination for this object (``ra`` must also be given and
``representation`` must be None).
distance : `~astropy.units.Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
(``representation`` must be None).
equinox : `~astropy.time.Time`, optional, must be keyword
The equinox of this frame.
copy : bool, optional
If `True` (default), make copies of the input coordinate arrays.
Can only be passed in as a keyword argument.
"""
frame_specific_representation_info = {
'spherical': [RepresentationMapping('lon', 'ra'),
RepresentationMapping('lat', 'dec')]
}
frame_specific_representation_info['unitspherical'] = \
frame_specific_representation_info['spherical']
default_representation = SphericalRepresentation
equinox = TimeFrameAttribute(default=EQUINOX_J2000)
@staticmethod
def _precession_matrix(oldequinox, newequinox):
"""
Compute and return the precession matrix for FK5 based on Capitaine et
al. 2003/IAU2006. Used inside some of the transformation functions.
Parameters
----------
oldequinox : `~astropy.time.Time`
The equinox to precess from.
newequinox : `~astropy.time.Time`
The equinox to precess to.
Returns
-------
newcoord : array
The precession matrix to transform to the new equinox
"""
return earth.precession_matrix_Capitaine(oldequinox, newequinox)
# This is the "self-transform". Defined at module level because the decorator
# needs a reference to the FK5 class
@frame_transform_graph.transform(DynamicMatrixTransform, FK5, FK5)
def fk5_to_fk5(fk5coord1, fk5frame2):
return fk5coord1._precession_matrix(fk5coord1.equinox, fk5frame2.equinox)
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