def cirs_to_icrs(cirs_coo, icrs_frame):
srepr = cirs_coo.represent_as(SphericalRepresentation)
cirs_ra = srepr.lon.to_value(u.radian)
cirs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->cirs and then convert to
# astrometric coordinate direction
jd1, jd2 = get_jd12(cirs_coo.obstime, 'tdb')
x, y, s = get_cip(jd1, jd2)
earth_pv, earth_heliocentric = prepare_earth_position_vel(cirs_coo.obstime)
astrom = erfa.apci(jd1, jd2, earth_pv, earth_heliocentric, x, y, s)
i_ra, i_dec = aticq(cirs_ra, cirs_dec, astrom)
if cirs_coo.data.get_name() == 'unitspherical' or cirs_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_cirs 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_cirs(icrs_coo, cirs_frame):
# first set up the astrometry context for ICRS<->CIRS
jd1, jd2 = get_jd12(cirs_frame.obstime, 'tt')
x, y, s = get_cip(jd1, jd2)
earth_pv, earth_heliocentric = prepare_earth_position_vel(
cirs_frame.obstime)
# erfa.apci requests TDB but TT can be used instead of TDB without any significant impact on accuracy
astrom = erfa.apci(jd1, jd2, earth_pv, earth_heliocentric, x, y, s)
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)
cirs_ra, cirs_dec = atciqz(i_ra, i_dec, astrom)
newrep = UnitSphericalRepresentation(lat=u.Quantity(cirs_dec,
u.radian,
copy=False),
lon=u.Quantity(cirs_ra,
u.radian,
copy=False),
copy=False)
else:
# When there is a distance, we first offset for parallax to get the
# astrometric 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)
cirs_ra, cirs_dec = atciqz(i_ra, i_dec, astrom)
newrep = SphericalRepresentation(lat=u.Quantity(cirs_dec,
u.radian,
copy=False),
lon=u.Quantity(cirs_ra,
u.radian,
copy=False),
distance=srepr.distance,
copy=False)
return cirs_frame.realize_frame(newrep)
def cirs_to_icrs(cirs_coo, icrs_frame):
srepr = cirs_coo.represent_as(SphericalRepresentation)
cirs_ra = srepr.lon.to_value(u.radian)
cirs_dec = srepr.lat.to_value(u.radian)
# set up the astrometry context for ICRS<->cirs and then convert to
# astrometric coordinate direction
jd1, jd2 = get_jd12(cirs_coo.obstime, 'tt')
x, y, s = get_cip(jd1, jd2)
earth_pv, earth_heliocentric = prepare_earth_position_vel(cirs_coo.obstime)
# erfa.apci requests TDB but TT can be used instead of TDB without any significant impact on accuracy
astrom = erfa.apci(jd1, jd2, earth_pv, earth_heliocentric, x, y, s)
i_ra, i_dec = aticq(cirs_ra, cirs_dec, astrom)
if cirs_coo.data.get_name(
) == 'unitspherical' or cirs_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_cirs 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_cirs(icrs_coo, cirs_frame):
# first set up the astrometry context for ICRS<->CIRS
jd1, jd2 = get_jd12(cirs_frame.obstime, 'tdb')
x, y, s = get_cip(jd1, jd2)
earth_pv, earth_heliocentric = prepare_earth_position_vel(cirs_frame.obstime)
astrom = erfa.apci(jd1, jd2, earth_pv, earth_heliocentric, x, y, s)
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)
cirs_ra, cirs_dec = atciqz(i_ra, i_dec, astrom)
newrep = UnitSphericalRepresentation(lat=u.Quantity(cirs_dec, u.radian, copy=False),
lon=u.Quantity(cirs_ra, u.radian, copy=False),
copy=False)
else:
# When there is a distance, we first offset for parallax to get the
# astrometric 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)
cirs_ra, cirs_dec = atciqz(i_ra, i_dec, astrom)
newrep = SphericalRepresentation(lat=u.Quantity(cirs_dec, u.radian, copy=False),
lon=u.Quantity(cirs_ra, u.radian, copy=False),
distance=srepr.distance, copy=False)
return cirs_frame.realize_frame(newrep)