Source code for astropy.coordinates.builtin_frames.fk5

# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst

from astropy.utils.decorators import format_doc
from astropy.coordinates.baseframe import frame_transform_graph, base_doc
from astropy.coordinates.attributes import TimeAttribute
from astropy.coordinates.transformations import DynamicMatrixTransform
from astropy.coordinates import earth_orientation as earth

from .baseradec import BaseRADecFrame, doc_components
from .utils import EQUINOX_J2000

__all__ = ['FK5']


doc_footer = """
    Other parameters
    ----------------
    equinox : `~astropy.time.Time`
        The equinox of this frame.
"""


[docs]@format_doc(base_doc, components=doc_components, footer=doc_footer) class FK5(BaseRADecFrame): """ 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. The frame attributes are listed under **Other Parameters**. """ equinox = TimeAttribute(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)