def prepare_earth_position_vel(time):
"""
Get barycentric position and velocity, and heliocentric position of Earth
Parameters
-----------
time : `~astropy.time.Time`
time at which to calculate position and velocity of Earth
Returns
--------
earth_pv : `np.ndarray`
Barycentric position and velocity of Earth, in au and au/day
earth_helio : `np.ndarray`
Heliocentric position of Earth in au
"""
# this goes here to avoid circular import errors
from astropy.coordinates.solar_system import (get_body_barycentric,
get_body_barycentric_posvel)
# get barycentric position and velocity of earth
earth_p, earth_v = get_body_barycentric_posvel('earth', time)
# get heliocentric position of earth, preparing it for passing to erfa.
sun = get_body_barycentric('sun', time)
earth_heliocentric = (earth_p - sun).get_xyz(xyz_axis=-1).to_value(u.au)
# Also prepare earth_pv for passing to erfa, which wants it as
# a structured dtype.
earth_pv = erfa.pav2pv(
earth_p.get_xyz(xyz_axis=-1).to_value(u.au),
earth_v.get_xyz(xyz_axis=-1).to_value(u.au / u.d))
return earth_pv, earth_heliocentric
def prepare_earth_position_vel(time):
"""
Get barycentric position and velocity, and heliocentric position of Earth
Parameters
-----------
time : `~astropy.time.Time`
time at which to calculate position and velocity of Earth
Returns
--------
earth_pv : `np.ndarray`
Barycentric position and velocity of Earth, in au and au/day
earth_helio : `np.ndarray`
Heliocentric position of Earth in au
"""
# this goes here to avoid circular import errors
from astropy.coordinates.solar_system import (get_body_barycentric, get_body_barycentric_posvel)
# get barycentric position and velocity of earth
earth_p, earth_v = get_body_barycentric_posvel('earth', time)
# get heliocentric position of earth, preparing it for passing to erfa.
sun = get_body_barycentric('sun', time)
earth_heliocentric = (earth_p -
sun).get_xyz(xyz_axis=-1).to_value(u.au)
# Also prepare earth_pv for passing to erfa, which wants it as
# a structured dtype.
earth_pv = erfa.pav2pv(
earth_p.get_xyz(xyz_axis=-1).to_value(u.au),
earth_v.get_xyz(xyz_axis=-1).to_value(u.au/u.d))
return earth_pv, earth_heliocentric
def icrs_to_gcrs(icrs_coo, gcrs_frame):
# first set up the astrometry context for ICRS<->GCRS. There are a few steps...
# get the position and velocity arrays for the observatory. Need to
# have xyz in last dimension, and pos/vel in one-but-last.
# (Note could use np.stack once our minimum numpy version is >=1.10.)
obs_pv = erfa.pav2pv(
gcrs_frame.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_frame.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m / u.s))
# find the position and velocity of earth
jd1, jd2 = get_jd12(gcrs_frame.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(
gcrs_frame.obstime)
# get astrometry context object, astrom.
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
if icrs_coo.data.get_name(
) == 'unitspherical' or icrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just do the infinite-distance/no parallax calculation
usrepr = icrs_coo.represent_as(UnitSphericalRepresentation)
i_ra = usrepr.lon.to_value(u.radian)
i_dec = usrepr.lat.to_value(u.radian)
gcrs_ra, gcrs_dec = atciqz(i_ra, i_dec, astrom)
newrep = UnitSphericalRepresentation(lat=u.Quantity(gcrs_dec,
u.radian,
copy=False),
lon=u.Quantity(gcrs_ra,
u.radian,
copy=False),
copy=False)
else:
# When there is a distance, we first offset for parallax to get the
# BCRS coordinate direction and *then* run the ERFA transform for no
# parallax/PM. This ensures reversibility and is more sensible for
# inside solar system objects
astrom_eb = CartesianRepresentation(astrom['eb'],
unit=u.au,
xyz_axis=-1,
copy=False)
newcart = icrs_coo.cartesian - astrom_eb
srepr = newcart.represent_as(SphericalRepresentation)
i_ra = srepr.lon.to_value(u.radian)
i_dec = srepr.lat.to_value(u.radian)
gcrs_ra, gcrs_dec = atciqz(i_ra, i_dec, astrom)
newrep = SphericalRepresentation(lat=u.Quantity(gcrs_dec,
u.radian,
copy=False),
lon=u.Quantity(gcrs_ra,
u.radian,
copy=False),
distance=srepr.distance,
copy=False)
return gcrs_frame.realize_frame(newrep)
def gcrs_to_hcrs(gcrs_coo, hcrs_frame):
if np.any(gcrs_coo.obstime != hcrs_frame.obstime):
# if they GCRS obstime and HCRS obstime are not the same, we first
# have to move to a GCRS where they are.
frameattrs = gcrs_coo.get_frame_attr_names()
frameattrs['obstime'] = hcrs_frame.obstime
gcrs_coo = gcrs_coo.transform_to(GCRS(**frameattrs))
srepr = gcrs_coo.represent_as(SphericalRepresentation)
gcrs_ra = srepr.lon.to_value(u.radian)
gcrs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->GCRS and then convert to ICRS
# coordinate direction
obs_pv = erfa.pav2pv(
gcrs_coo.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_coo.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m / u.s))
jd1, jd2 = get_jd12(hcrs_frame.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(gcrs_coo.obstime)
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
i_ra, i_dec = aticq(gcrs_ra, gcrs_dec, astrom)
# convert to Quantity objects
i_ra = u.Quantity(i_ra, u.radian, copy=False)
i_dec = u.Quantity(i_dec, u.radian, copy=False)
if gcrs_coo.data.get_name(
) == 'unitspherical' or gcrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just use the coordinate direction to yield the
# infinite-distance/no parallax answer
newrep = UnitSphericalRepresentation(lat=i_dec, lon=i_ra, copy=False)
else:
# When there is a distance, apply the parallax/offset to the
# Heliocentre as the last step to ensure round-tripping with the
# hcrs_to_gcrs transform
# Note that the distance in intermedrep is *not* a real distance as it
# does not include the offset back to the Heliocentre
intermedrep = SphericalRepresentation(lat=i_dec,
lon=i_ra,
distance=srepr.distance,
copy=False)
# astrom['eh'] and astrom['em'] contain Sun to observer unit vector,
# and distance, respectively. Shapes are (X) and (X,3), where (X) is the
# shape resulting from broadcasting the shape of the times object
# against the shape of the pv array.
# broadcast em to eh and scale eh
eh = astrom['eh'] * astrom['em'][..., np.newaxis]
eh = CartesianRepresentation(eh, unit=u.au, xyz_axis=-1, copy=False)
newrep = intermedrep.to_cartesian() + eh
return hcrs_frame.realize_frame(newrep)
def gcrs_to_hcrs(gcrs_coo, hcrs_frame):
if np.any(gcrs_coo.obstime != hcrs_frame.obstime):
# if they GCRS obstime and HCRS obstime are not the same, we first
# have to move to a GCRS where they are.
frameattrs = gcrs_coo.get_frame_attr_names()
frameattrs['obstime'] = hcrs_frame.obstime
gcrs_coo = gcrs_coo.transform_to(GCRS(**frameattrs))
srepr = gcrs_coo.represent_as(SphericalRepresentation)
gcrs_ra = srepr.lon.to_value(u.radian)
gcrs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->GCRS and then convert to ICRS
# coordinate direction
obs_pv = erfa.pav2pv(
gcrs_coo.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_coo.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m/u.s))
jd1, jd2 = get_jd12(hcrs_frame.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(gcrs_coo.obstime)
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
i_ra, i_dec = aticq(gcrs_ra, gcrs_dec, astrom)
# convert to Quantity objects
i_ra = u.Quantity(i_ra, u.radian, copy=False)
i_dec = u.Quantity(i_dec, u.radian, copy=False)
if gcrs_coo.data.get_name() == 'unitspherical' or gcrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just use the coordinate direction to yield the
# infinite-distance/no parallax answer
newrep = UnitSphericalRepresentation(lat=i_dec, lon=i_ra, copy=False)
else:
# When there is a distance, apply the parallax/offset to the
# Heliocentre as the last step to ensure round-tripping with the
# hcrs_to_gcrs transform
# Note that the distance in intermedrep is *not* a real distance as it
# does not include the offset back to the Heliocentre
intermedrep = SphericalRepresentation(lat=i_dec, lon=i_ra,
distance=srepr.distance,
copy=False)
# astrom['eh'] and astrom['em'] contain Sun to observer unit vector,
# and distance, respectively. Shapes are (X) and (X,3), where (X) is the
# shape resulting from broadcasting the shape of the times object
# against the shape of the pv array.
# broadcast em to eh and scale eh
eh = astrom['eh'] * astrom['em'][..., np.newaxis]
eh = CartesianRepresentation(eh, unit=u.au, xyz_axis=-1, copy=False)
newrep = intermedrep.to_cartesian() + eh
return hcrs_frame.realize_frame(newrep)
def gcrs_to_icrs(gcrs_coo, icrs_frame):
srepr = gcrs_coo.represent_as(SphericalRepresentation)
gcrs_ra = srepr.lon.to_value(u.radian)
gcrs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->GCRS and then convert to BCRS
# coordinate direction
obs_pv = erfa.pav2pv(
gcrs_coo.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_coo.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m / u.s))
jd1, jd2 = get_jd12(gcrs_coo.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(gcrs_coo.obstime)
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
i_ra, i_dec = aticq(gcrs_ra, gcrs_dec, astrom)
if gcrs_coo.data.get_name(
) == 'unitspherical' or gcrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just use the coordinate direction to yield the
# infinite-distance/no parallax answer
newrep = UnitSphericalRepresentation(lat=u.Quantity(i_dec,
u.radian,
copy=False),
lon=u.Quantity(i_ra,
u.radian,
copy=False),
copy=False)
else:
# When there is a distance, apply the parallax/offset to the SSB as the
# last step - ensures round-tripping with the icrs_to_gcrs transform
# the distance in intermedrep is *not* a real distance as it does not
# include the offset back to the SSB
intermedrep = SphericalRepresentation(lat=u.Quantity(i_dec,
u.radian,
copy=False),
lon=u.Quantity(i_ra,
u.radian,
copy=False),
distance=srepr.distance,
copy=False)
astrom_eb = CartesianRepresentation(astrom['eb'],
unit=u.au,
xyz_axis=-1,
copy=False)
newrep = intermedrep + astrom_eb
return icrs_frame.realize_frame(newrep)
def icrs_to_gcrs(icrs_coo, gcrs_frame):
# first set up the astrometry context for ICRS<->GCRS. There are a few steps...
# get the position and velocity arrays for the observatory. Need to
# have xyz in last dimension, and pos/vel in one-but-last.
# (Note could use np.stack once our minimum numpy version is >=1.10.)
obs_pv = erfa.pav2pv(
gcrs_frame.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_frame.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m/u.s))
# find the position and velocity of earth
jd1, jd2 = get_jd12(gcrs_frame.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(gcrs_frame.obstime)
# get astrometry context object, astrom.
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
if icrs_coo.data.get_name() == 'unitspherical' or icrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just do the infinite-distance/no parallax calculation
usrepr = icrs_coo.represent_as(UnitSphericalRepresentation)
i_ra = usrepr.lon.to_value(u.radian)
i_dec = usrepr.lat.to_value(u.radian)
gcrs_ra, gcrs_dec = atciqz(i_ra, i_dec, astrom)
newrep = UnitSphericalRepresentation(lat=u.Quantity(gcrs_dec, u.radian, copy=False),
lon=u.Quantity(gcrs_ra, u.radian, copy=False),
copy=False)
else:
# When there is a distance, we first offset for parallax to get the
# BCRS coordinate direction and *then* run the ERFA transform for no
# parallax/PM. This ensures reversibility and is more sensible for
# inside solar system objects
astrom_eb = CartesianRepresentation(astrom['eb'], unit=u.au,
xyz_axis=-1, copy=False)
newcart = icrs_coo.cartesian - astrom_eb
srepr = newcart.represent_as(SphericalRepresentation)
i_ra = srepr.lon.to_value(u.radian)
i_dec = srepr.lat.to_value(u.radian)
gcrs_ra, gcrs_dec = atciqz(i_ra, i_dec, astrom)
newrep = SphericalRepresentation(lat=u.Quantity(gcrs_dec, u.radian, copy=False),
lon=u.Quantity(gcrs_ra, u.radian, copy=False),
distance=srepr.distance, copy=False)
return gcrs_frame.realize_frame(newrep)
def gcrs_to_icrs(gcrs_coo, icrs_frame):
srepr = gcrs_coo.represent_as(SphericalRepresentation)
gcrs_ra = srepr.lon.to_value(u.radian)
gcrs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->GCRS and then convert to BCRS
# coordinate direction
obs_pv = erfa.pav2pv(
gcrs_coo.obsgeoloc.get_xyz(xyz_axis=-1).to_value(u.m),
gcrs_coo.obsgeovel.get_xyz(xyz_axis=-1).to_value(u.m/u.s))
jd1, jd2 = get_jd12(gcrs_coo.obstime, 'tdb')
earth_pv, earth_heliocentric = prepare_earth_position_vel(gcrs_coo.obstime)
astrom = erfa.apcs(jd1, jd2, obs_pv, earth_pv, earth_heliocentric)
i_ra, i_dec = aticq(gcrs_ra, gcrs_dec, astrom)
if gcrs_coo.data.get_name() == 'unitspherical' or gcrs_coo.data.to_cartesian().x.unit == u.one:
# if no distance, just use the coordinate direction to yield the
# infinite-distance/no parallax answer
newrep = UnitSphericalRepresentation(lat=u.Quantity(i_dec, u.radian, copy=False),
lon=u.Quantity(i_ra, u.radian, copy=False),
copy=False)
else:
# When there is a distance, apply the parallax/offset to the SSB as the
# last step - ensures round-tripping with the icrs_to_gcrs transform
# the distance in intermedrep is *not* a real distance as it does not
# include the offset back to the SSB
intermedrep = SphericalRepresentation(lat=u.Quantity(i_dec, u.radian, copy=False),
lon=u.Quantity(i_ra, u.radian, copy=False),
distance=srepr.distance,
copy=False)
astrom_eb = CartesianRepresentation(astrom['eb'], unit=u.au,
xyz_axis=-1, copy=False)
newrep = intermedrep + astrom_eb
return icrs_frame.realize_frame(newrep)