def test_is_frame_attr_default():
"""
Check that the `is_frame_attr_default` machinery works as expected
"""
from astropy.time import Time
from astropy.coordinates.builtin_frames import FK5
c1 = FK5(ra=1 * u.deg, dec=1 * u.deg)
c2 = FK5(ra=1 * u.deg,
dec=1 * u.deg,
equinox=FK5.get_frame_attr_names()['equinox'])
c3 = FK5(ra=1 * u.deg, dec=1 * u.deg, equinox=Time('J2001.5'))
assert c1.equinox == c2.equinox
assert c1.equinox != c3.equinox
assert c1.is_frame_attr_default('equinox')
assert not c2.is_frame_attr_default('equinox')
assert not c3.is_frame_attr_default('equinox')
c4 = c1.realize_frame(r.UnitSphericalRepresentation(3 * u.deg, 4 * u.deg))
c5 = c2.realize_frame(r.UnitSphericalRepresentation(3 * u.deg, 4 * u.deg))
assert c4.is_frame_attr_default('equinox')
assert not c5.is_frame_attr_default('equinox')
def test_equivalent_frames():
from astropy.coordinates import SkyCoord
from astropy.coordinates.builtin_frames import ICRS, FK4, FK5, AltAz
i = ICRS()
i2 = ICRS(1 * u.deg, 2 * u.deg)
assert i.is_equivalent_frame(i)
assert i.is_equivalent_frame(i2)
with pytest.raises(TypeError):
assert i.is_equivalent_frame(10)
with pytest.raises(TypeError):
assert i2.is_equivalent_frame(SkyCoord(i2))
f0 = FK5() # this J2000 is TT
f1 = FK5(equinox='J2000')
f2 = FK5(1 * u.deg, 2 * u.deg, equinox='J2000')
f3 = FK5(equinox='J2010')
f4 = FK4(equinox='J2010')
assert f1.is_equivalent_frame(f1)
assert not i.is_equivalent_frame(f1)
assert f0.is_equivalent_frame(f1)
assert f1.is_equivalent_frame(f2)
assert not f1.is_equivalent_frame(f3)
assert not f3.is_equivalent_frame(f4)
aa1 = AltAz()
aa2 = AltAz(obstime='J2010')
assert aa2.is_equivalent_frame(aa2)
assert not aa1.is_equivalent_frame(i)
assert not aa1.is_equivalent_frame(aa2)
def test_realizing():
from astropy.coordinates.builtin_frames import ICRS, FK5
from astropy.time import Time
rep = r.SphericalRepresentation(1 * u.deg, 2 * u.deg, 3 * u.kpc)
i = ICRS()
i2 = i.realize_frame(rep)
assert not i.has_data
assert i2.has_data
f = FK5(equinox=Time('J2001'))
f2 = f.realize_frame(rep)
assert not f.has_data
assert f2.has_data
assert f2.equinox == f.equinox
assert f2.equinox != FK5.get_frame_attr_names()['equinox']
# Check that a nicer error message is returned:
with pytest.raises(TypeError) as excinfo:
f.realize_frame(f.representation_type)
assert ('Class passed as data instead of a representation'
in excinfo.value.args[0])
def test_fk5_seps():
"""
This tests if `separation` works for FK5 objects.
This is a regression test for github issue #891
"""
a = FK5(1. * u.deg, 1. * u.deg)
b = FK5(2. * u.deg, 2. * u.deg)
a.separation(b)
def test_transform():
"""
This test just makes sure the transform architecture works, but does *not*
actually test all the builtin transforms themselves are accurate
"""
from astropy.coordinates.builtin_frames import ICRS, FK4, FK5, Galactic
from astropy.time import Time
i = ICRS(ra=[1, 2] * u.deg, dec=[3, 4] * u.deg)
f = i.transform_to(FK5)
i2 = f.transform_to(ICRS)
assert i2.data.__class__ == r.UnitSphericalRepresentation
assert_allclose(i.ra, i2.ra)
assert_allclose(i.dec, i2.dec)
i = ICRS(ra=[1, 2] * u.deg, dec=[3, 4] * u.deg, distance=[5, 6] * u.kpc)
f = i.transform_to(FK5)
i2 = f.transform_to(ICRS)
assert i2.data.__class__ != r.UnitSphericalRepresentation
f = FK5(ra=1 * u.deg, dec=2 * u.deg, equinox=Time('J2001'))
f4 = f.transform_to(FK4)
f4_2 = f.transform_to(FK4(equinox=f.equinox))
# make sure attributes are copied over correctly
assert f4.equinox == FK4.get_frame_attr_names()['equinox']
assert f4_2.equinox == f.equinox
# make sure self-transforms also work
i = ICRS(ra=[1, 2] * u.deg, dec=[3, 4] * u.deg)
i2 = i.transform_to(ICRS)
assert_allclose(i.ra, i2.ra)
assert_allclose(i.dec, i2.dec)
f = FK5(ra=1 * u.deg, dec=2 * u.deg, equinox=Time('J2001'))
f2 = f.transform_to(FK5) # default equinox, so should be *different*
assert f2.equinox == FK5().equinox
with pytest.raises(AssertionError):
assert_allclose(f.ra, f2.ra)
with pytest.raises(AssertionError):
assert_allclose(f.dec, f2.dec)
# finally, check Galactic round-tripping
i1 = ICRS(ra=[1, 2] * u.deg, dec=[3, 4] * u.deg)
i2 = i1.transform_to(Galactic).transform_to(ICRS)
assert_allclose(i1.ra, i2.ra)
assert_allclose(i1.dec, i2.dec)
def test_create_nodata_frames():
from astropy.coordinates.builtin_frames import ICRS, FK4, FK5
i = ICRS()
assert len(i.get_frame_attr_names()) == 0
f5 = FK5()
assert f5.equinox == FK5.get_frame_attr_names()['equinox']
f4 = FK4()
assert f4.equinox == FK4.get_frame_attr_names()['equinox']
# obstime is special because it's a property that uses equinox if obstime is not set
assert f4.obstime in (FK4.get_frame_attr_names()['obstime'],
FK4.get_frame_attr_names()['equinox'])
def test_realizing():
from astropy.coordinates.builtin_frames import ICRS, FK5
from astropy.time import Time
rep = r.SphericalRepresentation(1*u.deg, 2*u.deg, 3*u.kpc)
i = ICRS()
i2 = i.realize_frame(rep)
assert not i.has_data
assert i2.has_data
f = FK5(equinox=Time('J2001'))
f2 = f.realize_frame(rep)
assert not f.has_data
assert f2.has_data
assert f2.equinox == f.equinox
assert f2.equinox != FK5.get_frame_attr_names()['equinox']
# Check that a nicer error message is returned:
with pytest.raises(TypeError) as excinfo:
f.realize_frame(f.representation_type)
assert ('Class passed as data instead of a representation' in
excinfo.value.args[0])
def test_frame_repr():
from astropy.coordinates.builtin_frames import ICRS, FK5
i = ICRS()
assert repr(i) == '<ICRS Frame>'
f5 = FK5()
assert repr(f5).startswith('<FK5 Frame (equinox=')
i2 = ICRS(ra=1 * u.deg, dec=2 * u.deg)
i3 = ICRS(ra=1 * u.deg, dec=2 * u.deg, distance=3 * u.kpc)
assert repr(i2) == ('<ICRS Coordinate: (ra, dec) in deg\n' ' (1., 2.)>')
assert repr(i3) == (
'<ICRS Coordinate: (ra, dec, distance) in (deg, deg, kpc)\n'
' (1., 2., 3.)>')
# try with arrays
i2 = ICRS(ra=[1.1, 2.1] * u.deg, dec=[2.1, 3.1] * u.deg)
i3 = ICRS(ra=[1.1, 2.1] * u.deg,
dec=[-15.6, 17.1] * u.deg,
distance=[11., 21.] * u.kpc)
assert repr(i2) == ('<ICRS Coordinate: (ra, dec) in deg\n'
' [(1.1, 2.1), (2.1, 3.1)]>')
assert repr(i3) == (
'<ICRS Coordinate: (ra, dec, distance) in (deg, deg, kpc)\n'
' [(1.1, -15.6, 11.), (2.1, 17.1, 21.)]>')
def test_faux_fk5_galactic():
from astropy.coordinates.builtin_frames.galactic_transforms import fk5_to_gal, _gal_to_fk5
class Galactic2(Galactic):
pass
dt = 1000*u.s
@frame_transform_graph.transform(FunctionTransformWithFiniteDifference,
FK5, Galactic2, finite_difference_dt=dt,
symmetric_finite_difference=True,
finite_difference_frameattr_name=None)
def fk5_to_gal2(fk5_coo, gal_frame):
trans = DynamicMatrixTransform(fk5_to_gal, FK5, Galactic2)
return trans(fk5_coo, gal_frame)
@frame_transform_graph.transform(FunctionTransformWithFiniteDifference,
Galactic2, ICRS, finite_difference_dt=dt,
symmetric_finite_difference=True,
finite_difference_frameattr_name=None)
def gal2_to_fk5(gal_coo, fk5_frame):
trans = DynamicMatrixTransform(_gal_to_fk5, Galactic2, FK5)
return trans(gal_coo, fk5_frame)
c1 = FK5(ra=150*u.deg, dec=-17*u.deg, radial_velocity=83*u.km/u.s,
pm_ra_cosdec=-41*u.mas/u.yr, pm_dec=16*u.mas/u.yr,
distance=150*u.pc)
c2 = c1.transform_to(Galactic2)
c3 = c1.transform_to(Galactic)
# compare the matrix and finite-difference calculations
assert quantity_allclose(c2.pm_l_cosb, c3.pm_l_cosb, rtol=1e-4)
assert quantity_allclose(c2.pm_b, c3.pm_b, rtol=1e-4)
def test_representation_subclass():
# Regression test for #3354
from astropy.coordinates.builtin_frames import FK5
# Normally when instantiating a frame without a distance the frame will try
# and use UnitSphericalRepresentation internally instead of
# SphericalRepresentation.
frame = FK5(representation_type=r.SphericalRepresentation,
ra=32 * u.deg,
dec=20 * u.deg)
assert type(frame._data) == r.UnitSphericalRepresentation
assert frame.representation_type == r.SphericalRepresentation
# If using a SphericalRepresentation class this used to not work, so we
# test here that this is now fixed.
class NewSphericalRepresentation(r.SphericalRepresentation):
attr_classes = r.SphericalRepresentation.attr_classes
frame = FK5(representation_type=NewSphericalRepresentation,
lon=32 * u.deg,
lat=20 * u.deg)
assert type(frame._data) == r.UnitSphericalRepresentation
assert frame.representation_type == NewSphericalRepresentation
# A similar issue then happened in __repr__ with subclasses of
# SphericalRepresentation.
assert repr(frame) == (
"<FK5 Coordinate (equinox=J2000.000): (lon, lat) in deg\n"
" (32., 20.)>")
# A more subtle issue is when specifying a custom
# UnitSphericalRepresentation subclass for the data and
# SphericalRepresentation or a subclass for the representation.
class NewUnitSphericalRepresentation(r.UnitSphericalRepresentation):
attr_classes = r.UnitSphericalRepresentation.attr_classes
def __repr__(self):
return "<NewUnitSphericalRepresentation: spam spam spam>"
frame = FK5(NewUnitSphericalRepresentation(lon=32 * u.deg, lat=20 * u.deg),
representation_type=NewSphericalRepresentation)
assert repr(
frame) == "<FK5 Coordinate (equinox=J2000.000): spam spam spam>"
def test_fk4_no_e_fk5():
lines = get_pkg_data_contents('data/fk4_no_e_fk5.csv').split('\n')
t = Table.read(lines, format='ascii', delimiter=',', guess=False)
if N_ACCURACY_TESTS >= len(t):
idxs = range(len(t))
else:
idxs = np.random.randint(len(t), size=N_ACCURACY_TESTS)
diffarcsec1 = []
diffarcsec2 = []
for i in idxs:
# Extract row
r = t[int(i)] # int here is to get around a py 3.x astropy.table bug
# FK4NoETerms to FK5
c1 = FK4NoETerms(ra=r['ra_in'] * u.deg,
dec=r['dec_in'] * u.deg,
obstime=Time(r['obstime']),
equinox=Time(r['equinox_fk4']))
c2 = c1.transform_to(FK5(equinox=Time(r['equinox_fk5'])))
# Find difference
diff = angular_separation(c2.ra.radian, c2.dec.radian,
np.radians(r['ra_fk5']),
np.radians(r['dec_fk5']))
diffarcsec1.append(np.degrees(diff) * 3600.)
# FK5 to FK4NoETerms
c1 = FK5(ra=r['ra_in'] * u.deg,
dec=r['dec_in'] * u.deg,
equinox=Time(r['equinox_fk5']))
fk4neframe = FK4NoETerms(obstime=Time(r['obstime']),
equinox=Time(r['equinox_fk4']))
c2 = c1.transform_to(fk4neframe)
# Find difference
diff = angular_separation(c2.ra.radian, c2.dec.radian,
np.radians(r['ra_fk4']),
np.radians(r['dec_fk4']))
diffarcsec2.append(np.degrees(diff) * 3600.)
np.testing.assert_array_less(diffarcsec1, TOLERANCE)
np.testing.assert_array_less(diffarcsec2, TOLERANCE)
def test_transform_to_nonscalar_nodata_frame():
# https://github.com/astropy/astropy/pull/5254#issuecomment-241592353
from astropy.coordinates.builtin_frames import ICRS, FK5
from astropy.time import Time
times = Time('2016-08-23') + np.linspace(0, 10, 12) * u.day
coo1 = ICRS(ra=[[0.], [10.], [20.]] * u.deg,
dec=[[-30.], [30.], [60.]] * u.deg)
coo2 = coo1.transform_to(FK5(equinox=times))
assert coo2.shape == (3, 12)
def test_against_pytpm_doc_example():
"""
Check that Astropy's Ecliptic systems give answers consistent with pyTPM
Currently this is only testing against the example given in the pytpm docs
"""
fk5_in = SkyCoord('12h22m54.899s', '15d49m20.57s', frame=FK5(equinox='J2000'))
pytpm_out = BarycentricMeanEcliptic(lon=178.78256462*u.deg,
lat=16.7597002513*u.deg,
equinox='J2000')
astropy_out = fk5_in.transform_to(pytpm_out)
assert pytpm_out.separation(astropy_out) < (1*u.arcsec)
def test_create_nodata_frames():
from astropy.coordinates.builtin_frames import ICRS, FK4, FK5
i = ICRS()
assert len(i.get_frame_attr_names()) == 0
f5 = FK5()
assert f5.equinox == FK5.get_frame_attr_names()['equinox']
f4 = FK4()
assert f4.equinox == FK4.get_frame_attr_names()['equinox']
# obstime is special because it's a property that uses equinox if obstime is not set
assert f4.obstime in (FK4.get_frame_attr_names()['obstime'],
FK4.get_frame_attr_names()['equinox'])
def test_fk5_galactic():
"""
Check that FK5 -> Galactic gives the same as FK5 -> FK4 -> Galactic.
"""
fk5 = FK5(ra=1*u.deg, dec=2*u.deg)
direct = fk5.transform_to(Galactic)
indirect = fk5.transform_to(FK4).transform_to(Galactic)
assert direct.separation(indirect).degree < 1.e-10
direct = fk5.transform_to(Galactic)
indirect = fk5.transform_to(FK4NoETerms).transform_to(Galactic)
assert direct.separation(indirect).degree < 1.e-10
def test_precession():
"""
Ensures that FK4 and FK5 coordinates precess their equinoxes
"""
j2000 = Time('J2000')
b1950 = Time('B1950')
j1975 = Time('J1975')
b1975 = Time('B1975')
fk4 = FK4(ra=1*u.radian, dec=0.5*u.radian)
assert fk4.equinox.byear == b1950.byear
fk4_2 = fk4.transform_to(FK4(equinox=b1975))
assert fk4_2.equinox.byear == b1975.byear
fk5 = FK5(ra=1*u.radian, dec=0.5*u.radian)
assert fk5.equinox.jyear == j2000.jyear
fk5_2 = fk5.transform_to(FK4(equinox=j1975))
assert fk5_2.equinox.jyear == j1975.jyear
def test_is_frame_attr_default():
"""
Check that the `is_frame_attr_default` machinery works as expected
"""
from astropy.time import Time
from astropy.coordinates.builtin_frames import FK5
c1 = FK5(ra=1*u.deg, dec=1*u.deg)
c2 = FK5(ra=1*u.deg, dec=1*u.deg, equinox=FK5.get_frame_attr_names()['equinox'])
c3 = FK5(ra=1*u.deg, dec=1*u.deg, equinox=Time('J2001.5'))
assert c1.equinox == c2.equinox
assert c1.equinox != c3.equinox
assert c1.is_frame_attr_default('equinox')
assert not c2.is_frame_attr_default('equinox')
assert not c3.is_frame_attr_default('equinox')
c4 = c1.realize_frame(r.UnitSphericalRepresentation(3*u.deg, 4*u.deg))
c5 = c2.realize_frame(r.UnitSphericalRepresentation(3*u.deg, 4*u.deg))
assert c4.is_frame_attr_default('equinox')
assert not c5.is_frame_attr_default('equinox')
def test_celestial_frame_to_wcs():
# Import astropy.coordinates here to avoid circular imports
from astropy.coordinates import ICRS, ITRS, FK5, FK4, FK4NoETerms, Galactic, BaseCoordinateFrame
class FakeFrame(BaseCoordinateFrame):
pass
frame = FakeFrame()
with pytest.raises(ValueError) as exc:
celestial_frame_to_wcs(frame)
assert exc.value.args[0] == ("Could not determine WCS corresponding to "
"the specified coordinate frame.")
frame = ICRS()
mywcs = celestial_frame_to_wcs(frame)
mywcs.wcs.set()
assert tuple(mywcs.wcs.ctype) == ('RA---TAN', 'DEC--TAN')
assert mywcs.wcs.radesys == 'ICRS'
assert np.isnan(mywcs.wcs.equinox)
assert mywcs.wcs.lonpole == 180
assert mywcs.wcs.latpole == 0
frame = FK5(equinox='J1987')
mywcs = celestial_frame_to_wcs(frame)
assert tuple(mywcs.wcs.ctype) == ('RA---TAN', 'DEC--TAN')
assert mywcs.wcs.radesys == 'FK5'
assert mywcs.wcs.equinox == 1987.
frame = FK4(equinox='B1982')
mywcs = celestial_frame_to_wcs(frame)
assert tuple(mywcs.wcs.ctype) == ('RA---TAN', 'DEC--TAN')
assert mywcs.wcs.radesys == 'FK4'
assert mywcs.wcs.equinox == 1982.
frame = FK4NoETerms(equinox='B1982')
mywcs = celestial_frame_to_wcs(frame)
assert tuple(mywcs.wcs.ctype) == ('RA---TAN', 'DEC--TAN')
assert mywcs.wcs.radesys == 'FK4-NO-E'
assert mywcs.wcs.equinox == 1982.
frame = Galactic()
mywcs = celestial_frame_to_wcs(frame)
assert tuple(mywcs.wcs.ctype) == ('GLON-TAN', 'GLAT-TAN')
assert mywcs.wcs.radesys == ''
assert np.isnan(mywcs.wcs.equinox)
frame = Galactic()
mywcs = celestial_frame_to_wcs(frame, projection='CAR')
assert tuple(mywcs.wcs.ctype) == ('GLON-CAR', 'GLAT-CAR')
assert mywcs.wcs.radesys == ''
assert np.isnan(mywcs.wcs.equinox)
frame = Galactic()
mywcs = celestial_frame_to_wcs(frame, projection='CAR')
mywcs.wcs.crval = [100, -30]
mywcs.wcs.set()
assert_allclose((mywcs.wcs.lonpole, mywcs.wcs.latpole), (180, 60))
frame = ITRS(obstime=Time('2017-08-17T12:41:04.43'))
mywcs = celestial_frame_to_wcs(frame, projection='CAR')
assert tuple(mywcs.wcs.ctype) == ('TLON-CAR', 'TLAT-CAR')
assert mywcs.wcs.radesys == 'ITRS'
assert mywcs.wcs.dateobs == '2017-08-17T12:41:04.430'
frame = ITRS()
mywcs = celestial_frame_to_wcs(frame, projection='CAR')
assert tuple(mywcs.wcs.ctype) == ('TLON-CAR', 'TLAT-CAR')
assert mywcs.wcs.radesys == 'ITRS'
assert mywcs.wcs.dateobs == Time('J2000').utc.fits
def test_transform_api():
from astropy.coordinates.representation import UnitSphericalRepresentation
from astropy.coordinates.builtin_frames import ICRS, FK5
from astropy.coordinates.baseframe import frame_transform_graph, BaseCoordinateFrame
from astropy.coordinates.transformations import DynamicMatrixTransform
# <------------------------Transformations------------------------------------->
# Transformation functionality is the key to the whole scheme: they transform
# low-level classes from one frame to another.
# (used below but defined above in the API)
fk5 = FK5(ra=8 * u.hour, dec=5 * u.deg)
# If no data (or `None`) is given, the class acts as a specifier of a frame, but
# without any stored data.
J2001 = time.Time('J2001')
fk5_J2001_frame = FK5(equinox=J2001)
# if they do not have data, the string instead is the frame specification
assert repr(fk5_J2001_frame) == "<FK5 Frame (equinox=J2001.000)>"
# Note that, although a frame object is immutable and can't have data added, it
# can be used to create a new object that does have data by giving the
# `realize_frame` method a representation:
srep = UnitSphericalRepresentation(lon=8 * u.hour, lat=5 * u.deg)
fk5_j2001_with_data = fk5_J2001_frame.realize_frame(srep)
assert fk5_j2001_with_data.data is not None
# Now `fk5_j2001_with_data` is in the same frame as `fk5_J2001_frame`, but it
# is an actual low-level coordinate, rather than a frame without data.
# These frames are primarily useful for specifying what a coordinate should be
# transformed *into*, as they are used by the `transform_to` method
# E.g., this snippet precesses the point to the new equinox
newfk5 = fk5.transform_to(fk5_J2001_frame)
assert newfk5.equinox == J2001
# classes can also be given to `transform_to`, which then uses the defaults for
# the frame information:
samefk5 = fk5.transform_to(FK5)
# `fk5` was initialized using default `obstime` and `equinox`, so:
assert_allclose(samefk5.ra, fk5.ra, atol=1e-10 * u.deg)
assert_allclose(samefk5.dec, fk5.dec, atol=1e-10 * u.deg)
# transforming to a new frame necessarily loses framespec information if that
# information is not applicable to the new frame. This means transforms are not
# always round-trippable:
fk5_2 = FK5(ra=8 * u.hour, dec=5 * u.deg, equinox=J2001)
ic_trans = fk5_2.transform_to(ICRS)
# `ic_trans` does not have an `equinox`, so now when we transform back to FK5,
# it's a *different* RA and Dec
fk5_trans = ic_trans.transform_to(FK5)
assert not allclose(fk5_2.ra, fk5_trans.ra, rtol=0, atol=1e-10 * u.deg)
# But if you explicitly give the right equinox, all is fine
fk5_trans_2 = fk5_2.transform_to(FK5(equinox=J2001))
assert_allclose(fk5_2.ra, fk5_trans_2.ra, rtol=0, atol=1e-10 * u.deg)
# Trying to transforming a frame with no data is of course an error:
with pytest.raises(ValueError):
FK5(equinox=J2001).transform_to(ICRS)
# To actually define a new transformation, the same scheme as in the
# 0.2/0.3 coordinates framework can be re-used - a graph of transform functions
# connecting various coordinate classes together. The main changes are:
# 1) The transform functions now get the frame object they are transforming the
# current data into.
# 2) Frames with additional information need to have a way to transform between
# objects of the same class, but with different framespecinfo values
# An example transform function:
class SomeNewSystem(BaseCoordinateFrame):
pass
@frame_transform_graph.transform(DynamicMatrixTransform, SomeNewSystem,
FK5)
def new_to_fk5(newobj, fk5frame):
_ = newobj.obstime
_ = fk5frame.equinox
# ... build a *cartesian* transform matrix using `eq` that transforms from
# the `newobj` frame as observed at `ot` to FK5 an equinox `eq`
matrix = np.eye(3)
return matrix
def test_frame_api():
from astropy.coordinates.representation import SphericalRepresentation, \
UnitSphericalRepresentation
from astropy.coordinates.builtin_frames import ICRS, FK5
# <--------------------Reference Frame/"Low-level" classes--------------------->
# The low-level classes have a dual role: they act as specifiers of coordinate
# frames and they *may* also contain data as one of the representation objects,
# in which case they are the actual coordinate objects themselves.
# They can always accept a representation as a first argument
icrs = ICRS(UnitSphericalRepresentation(lon=8 * u.hour, lat=5 * u.deg))
# which is stored as the `data` attribute
assert icrs.data.lat == 5 * u.deg
assert icrs.data.lon == 8 * u.hourangle
# Frames that require additional information like equinoxs or obstimes get them
# as keyword parameters to the frame constructor. Where sensible, defaults are
# used. E.g., FK5 is almost always J2000 equinox
fk5 = FK5(UnitSphericalRepresentation(lon=8 * u.hour, lat=5 * u.deg))
J2000 = time.Time('J2000')
fk5_2000 = FK5(UnitSphericalRepresentation(lon=8 * u.hour, lat=5 * u.deg),
equinox=J2000)
assert fk5.equinox == fk5_2000.equinox
# the information required to specify the frame is immutable
J2001 = time.Time('J2001')
with pytest.raises(AttributeError):
fk5.equinox = J2001
# Similar for the representation data.
with pytest.raises(AttributeError):
fk5.data = UnitSphericalRepresentation(lon=8 * u.hour, lat=5 * u.deg)
# There is also a class-level attribute that lists the attributes needed to
# identify the frame. These include attributes like `equinox` shown above.
assert all(nm in ('equinox', 'obstime')
for nm in fk5.get_frame_attr_names())
# the result of `get_frame_attr_names` is called for particularly in the
# high-level class (discussed below) to allow round-tripping between various
# frames. It is also part of the public API for other similar developer /
# advanced users' use.
# The actual position information is accessed via the representation objects
assert_allclose(icrs.represent_as(SphericalRepresentation).lat, 5 * u.deg)
# shorthand for the above
assert_allclose(icrs.spherical.lat, 5 * u.deg)
assert icrs.cartesian.z.value > 0
# Many frames have a "default" representation, the one in which they are
# conventionally described, often with a special name for some of the
# coordinates. E.g., most equatorial coordinate systems are spherical with RA and
# Dec. This works simply as a shorthand for the longer form above
assert_allclose(icrs.dec, 5 * u.deg)
assert_allclose(fk5.ra, 8 * u.hourangle)
assert icrs.representation_type == SphericalRepresentation
# low-level classes can also be initialized with names valid for that representation
# and frame:
icrs_2 = ICRS(ra=8 * u.hour, dec=5 * u.deg, distance=1 * u.kpc)
assert_allclose(icrs.ra, icrs_2.ra)
# and these are taken as the default if keywords are not given:
# icrs_nokwarg = ICRS(8*u.hour, 5*u.deg, distance=1*u.kpc)
# assert icrs_nokwarg.ra == icrs_2.ra and icrs_nokwarg.dec == icrs_2.dec
# they also are capable of computing on-sky or 3d separations from each other,
# which will be a direct port of the existing methods:
coo1 = ICRS(ra=0 * u.hour, dec=0 * u.deg)
coo2 = ICRS(ra=0 * u.hour, dec=1 * u.deg)
# `separation` is the on-sky separation
assert coo1.separation(coo2).degree == 1.0
# while `separation_3d` includes the 3D distance information
coo3 = ICRS(ra=0 * u.hour, dec=0 * u.deg, distance=1 * u.kpc)
coo4 = ICRS(ra=0 * u.hour, dec=0 * u.deg, distance=2 * u.kpc)
assert coo3.separation_3d(coo4).kpc == 1.0
# The next example fails because `coo1` and `coo2` don't have distances
with pytest.raises(ValueError):
assert coo1.separation_3d(coo2).kpc == 1.0
