Make StokesFrame use new StokesCoord from Astropy (#452)

gwcs/coordinate_frames.py

@@ -14,9 +14,10 @@
 from astropy.wcs.wcsapi.low_level_api import (validate_physical_types,
                                               VALID_UCDS)
 from astropy.wcs.wcsapi.fitswcs import CTYPE_TO_UCD1
+from astropy.coordinates import StokesCoord
 
 __all__ = ['Frame2D', 'CelestialFrame', 'SpectralFrame', 'CompositeFrame',
-           'CoordinateFrame', 'TemporalFrame']
+           'CoordinateFrame', 'TemporalFrame', 'StokesFrame']
 
 
 def _ucd1_to_ctype_name_mapping(ctype_to_ucd, allowed_ucd_duplicates):
@@ -703,68 +704,16 @@ def _world_axis_object_classes(self):
         return dict(self._wao_renamed_classes_iter)
 
 
-class StokesProfile(str):
-    # This list of profiles in Table 7 in Greisen & Calabretta (2002)
-    # modified to be 0 indexed
-    profiles = {
-        'I': 0,
-        'Q': 1,
-        'U': 2,
-        'V': 3,
-        'RR': -1,
-        'LL': -2,
-        'RL': -3,
-        'LR': -4,
-        'XX': -5,
-        'YY': -6,
-        'XY': -7,
-        'YX': -8,
-    }
-
-    @classmethod
-    def from_index(cls, indexes):
-        """
-        Construct a StokesProfile object from a numerical index.
-
-        Parameters
-        ----------
-        indexes : `int`, `numpy.ndarray`
-            An index or array of indices to construct StokesProfile objects from.
-        """
-
-        nans = np.isnan(indexes)
-        indexes = np.asarray(indexes, dtype=int)
-        out = np.empty_like(indexes, dtype=object)
-
-        for profile, index in cls.profiles.items():
-            out[indexes == index] = cls(profile)
-
-        out[nans] = np.nan
-
-        if out.size == 1 and not nans:
-            return StokesProfile(out.item())
-        elif nans.all():
-            return np.array(out, dtype=float)
-        return out
-
-    def __new__(cls, content):
-        content = str(content)
-        if content not in cls.profiles.keys():
-            raise ValueError(f"The profile name must be one of {cls.profiles.keys()} not {content}")
-        return str.__new__(cls, content)
-
-    def value(self):
-        return self.profiles[self]
-
-
 class StokesFrame(CoordinateFrame):
     """
-    A coordinate frame for representing stokes polarisation states
+    A coordinate frame for representing Stokes polarisation states.
 
     Parameters
     ----------
     name : str
         Name of this frame.
+    axes_order : tuple
+        A dimension in the data that corresponds to this axis.
     """
 
     def __init__(self, axes_order=(0,), name=None):
@@ -775,10 +724,10 @@ def __init__(self, axes_order=(0,), name=None):
     @property
     def _world_axis_object_classes(self):
         return {'stokes': (
-            StokesProfile,
+            StokesCoord,
             (),
             {},
-            StokesProfile.from_index)}
+        )}
 
     @property
     def _world_axis_object_components(self):
@@ -790,14 +739,12 @@ def coordinates(self, *args):
         else:
             arg = args[0]
 
-        return StokesProfile.from_index(arg)
+        return StokesCoord(arg)
 
     def coordinate_to_quantity(self, *coords):
-        if isinstance(coords[0], str):
-            if coords[0] in StokesProfile.profiles.keys():
-                return StokesProfile.profiles[coords[0]] * u.one
-        else:
-            return coords[0]
+        if isinstance(coords[0], StokesCoord):
+            return coords[0].value << u.one
+        return coords[0]
 
 
 class Frame2D(CoordinateFrame):

gwcs/tests/conftest.py

@@ -193,7 +193,7 @@ def gwcs_simple_imaging_units():
 
 @pytest.fixture
 def gwcs_stokes_lookup():
-    transform = models.Tabular1D([0, 1, 2, 3] * u.pix, [0, 1, 2, 3] * u.one,
+    transform = models.Tabular1D([0, 1, 2, 3] * u.pix, [1, 2, 3, 4] * u.one,
                                  method="nearest", fill_value=np.nan, bounds_error=False)
     frame = cf.StokesFrame()
 

gwcs/tests/data/stokes.txt

@@ -0,0 +1 @@
+WCSAXES =                    4 / Number of coordinate axes                      CRPIX1  =                126.0 / Pixel coordinate of reference point            CRPIX2  =                126.0 / Pixel coordinate of reference point            CRPIX3  =                  1.0 / Pixel coordinate of reference point            CRPIX4  =                  1.0 / Pixel coordinate of reference point            CDELT1  =  -2.777777777778E-05 / [deg] Coordinate increment at reference point  CDELT2  =   2.777777777778E-05 / [deg] Coordinate increment at reference point  CDELT3  =       20000205938.09 / [Hz] Coordinate increment at reference point   CDELT4  =                  1.0 / Coordinate increment at reference point        CUNIT1  = 'deg'                / Units of coordinate increment and value        CUNIT2  = 'deg'                / Units of coordinate increment and value        CUNIT3  = 'Hz'                 / Units of coordinate increment and value        CTYPE1  = 'RA---SIN'           / Right ascension, orthographic/synthesis projectCTYPE2  = 'DEC--SIN'           / Declination, orthographic/synthesis projection CTYPE3  = 'FREQ'               / Frequency (linear)                             CTYPE4  = 'STOKES'             / Coordinate type code                           CRVAL1  =         202.78453375 / [deg] Coordinate value at reference point      CRVAL2  =       30.50915555556 / [deg] Coordinate value at reference point      CRVAL3  =       233000102969.0 / [Hz] Coordinate value at reference point       CRVAL4  =                  1.0 / Coordinate value at reference point            PV2_1   =                  0.0 / SIN projection parameter                       PV2_2   =                  0.0 / SIN projection parameter                       LONPOLE =                180.0 / [deg] Native longitude of celestial pole       LATPOLE =       30.50915555556 / [deg] Native latitude of celestial pole        RESTFRQ =       224000000000.1 / [Hz] Line rest frequency                       TIMESYS = 'UTC'                / Time scale                                     MJDREF  =                  0.0 / [d] MJD of fiducial time                       DATE-OBS= '2014-07-01T21:36:05.280000' / ISO-8601 time of observation           MJD-OBS =      56839.900061111 / [d] MJD of observation                         OBSGEO-X=       2225142.180269 / [m] observatory X-coordinate                   OBSGEO-Y=      -5440307.370349 / [m] observatory Y-coordinate                   OBSGEO-Z=      -2481029.851874 / [m] observatory Z-coordinate                   RADESYS = 'FK5'                / Equatorial coordinate system                   EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates         SPECSYS = 'TOPOCENT'           / Reference frame of spectral coordinates        END                                                                             

gwcs/tests/test_api.py

@@ -243,6 +243,9 @@ def _compare_frame_output(wc1, wc2):
     elif isinstance(wc1, str):
         assert wc1 == wc2
 
+    elif isinstance(wc1, coord.StokesCoord):
+        assert wc1 == wc2
+
     else:
         assert False, f"Can't Compare {type(wc1)}"
 
@@ -294,29 +297,30 @@ def test_stokes_wrapper(gwcs_stokes_lookup):
 
     out = hlvl.pixel_to_world(pixel_input*u.pix)
 
-    expected = np.array([['I', 'Q', 'U', 'V'],
-                         ['I', 'Q', 'U', 'V'],
-                         ['I', 'Q', 'U', 'V'],
-                         ['I', 'Q', 'U', 'V']], dtype=object)
+    expected = coord.StokesCoord([['I', 'Q', 'U', 'V'],
+                                  ['I', 'Q', 'U', 'V'],
+                                  ['I', 'Q', 'U', 'V'],
+                                  ['I', 'Q', 'U', 'V']])
 
     assert (out == expected).all()
 
     pixel_input = [-1, 4]
 
     out = hlvl.pixel_to_world(pixel_input*u.pix)
 
-    assert np.isnan(out).all()
+    assert np.isnan(out.value).all()
 
     pixel_input = [[-1, 4],
                    [1, 2]]
 
     out = hlvl.pixel_to_world(pixel_input*u.pix)
 
-    assert np.isnan(np.array(out[0], dtype=float)).all()
-    assert (out[1] == np.array(['Q', 'U'], dtype=object)).all()
+    assert np.isnan(out[0].value).all()
+    assert (out[1] == ['Q', 'U']).all()
 
     out = hlvl.pixel_to_world(1*u.pix)
 
+    assert isinstance(out, coord.StokesCoord)
     assert out == 'Q'
 
 

gwcs/tests/test_coordinate_systems.py

@@ -10,6 +10,7 @@
 from astropy.tests.helper import assert_quantity_allclose
 from astropy.modeling import models as m
 from astropy.wcs.wcsapi.fitswcs import CTYPE_TO_UCD1
+from astropy.coordinates import StokesCoord
 
 from .. import WCS
 from .. import coordinate_frames as cf
@@ -281,13 +282,10 @@ def test_coordinate_to_quantity_composite(inp):
 def test_stokes_frame():
     sf = cf.StokesFrame()
 
-    assert sf.coordinates(0) == 'I'
-    assert sf.coordinates(0 * u.pix) == 'I'
-    assert sf.coordinate_to_quantity('I') == 0 * u.one
-    assert sf.coordinate_to_quantity(0) == 0
-
-def test_stokes_profile():
-    assert (cf.StokesProfile.from_index(np.arange(-8, 4) * u.one) == np.array(['YX', 'XY', 'YY,', 'XX', 'LR', 'RL', 'LL', 'RR', 'I', 'Q', 'U', 'V'], dtype="U2")).all()
+    assert sf.coordinates(1) == 'I'
+    assert sf.coordinates(1 * u.pix) == 'I'
+    assert sf.coordinate_to_quantity(StokesCoord('I')) == 1 * u.one
+    assert sf.coordinate_to_quantity(1) == 1
 
 
 @pytest.mark.parametrize('inp', [

gwcs/tests/test_wcs.py

@@ -32,6 +32,7 @@
 focal = cf.Frame2D(name='focal', axes_order=(0, 1), unit=(u.m, u.m))
 spec = cf.SpectralFrame(name='wave', unit=[u.m, ], axes_order=(2, ), axes_names=('lambda', ))
 time = cf.TemporalFrame(name='time', unit=[u.s, ], axes_order=(3, ), axes_names=('time', ), reference_frame=Time("2020-01-01"))
+stokes = cf.StokesFrame(axes_order=(2,))
 
 pipe = [wcs.Step(detector, m1),
         wcs.Step(focal, m2),
@@ -223,6 +224,15 @@ def test_return_coordinates():
     output_quant = w.output_frame.coordinate_to_quantity(*num_plus_output)
     assert_allclose(utils.get_values(w.unit, *output_quant), numerical_result)
 
+    # CompositeFrame - [celestial, Stokes]
+    output_frame = cf.CompositeFrame(frames=[icrs, stokes])
+    transform = m1 & models.Identity(1)
+    w = wcs.WCS(forward_transform=transform, output_frame=output_frame)
+    numerical_result = transform(x, y, y)
+    num_plus_output = w(x, y, y, with_units=True)
+    output_quant = w.output_frame.coordinate_to_quantity(*num_plus_output)
+    assert_allclose(utils.get_values(w.unit, *output_quant), numerical_result)
+
 
 def test_from_fiducial_sky():
     sky = coord.SkyCoord(1.63 * u.radian, -72.4 * u.deg, frame='fk5')
@@ -1270,3 +1280,39 @@ def test_sip_roundtrip():
                         atol=0.0,
                         rtol=1.0e-8 * 10**(i + j)
                     )
+
+
+def test_spatial_spectral_stokes():
+    """ Converts a FITS WCS to GWCS and compares results."""
+    hdr = fits.Header.fromfile(get_pkg_data_filename("data/stokes.txt"))
+    aw = astwcs.WCS(hdr)
+    crpix = aw.wcs.crpix
+    crval = aw.wcs.crval
+    cdelt = aw.wcs.cdelt
+
+    fk5 = cf.CelestialFrame(reference_frame=coord.FK5(), name='FK5')
+    detector = cf.Frame2D(name='detector', axes_order=(0, 1))
+    spec = cf.SpectralFrame(name='FREQ', unit=[u.Hz, ], axes_order=(2, ), axes_names=('freq', ))
+    stokes = cf.StokesFrame(axes_order=(3,))
+    world = cf.CompositeFrame(frames=[fk5, spec, stokes])
+
+    det2sky = (models.Shift(-crpix[0]) & models.Shift(-crpix[1]) |
+               models.Scale(cdelt[0]) & models.Scale(cdelt[1]) |
+               models.Pix2Sky_SIN() | models.RotateNative2Celestial(crval[0], crval[1], 180))
+    det2freq = models.Shift(-crpix[2]) | models.Scale(cdelt[2]) | models.Shift(crval[2])
+    det2stokes = models.Shift(-crpix[3]) | models.Scale(cdelt[3]) | models.Shift(crval[3])
+
+    gw = wcs.WCS([wcs.Step(detector, det2sky & det2freq & det2stokes),
+                  wcs.Step(world, None)]
+                )
+
+    x1 = np.array([0, 0, 0, 0, 0])
+    x2 = np.array([0, 1, 2, 3, 4])
+
+    gw_sky, gw_spec, gw_stokes = gw.pixel_to_world(x1+1, x1+1, x1+1, x2+1)
+    aw_sky, aw_spec, aw_stokes = aw.pixel_to_world(x1, x1, x1, x2)
+
+    assert_allclose(gw_sky.data.lon, aw_sky.data.lon)
+    assert_allclose(gw_sky.data.lat, aw_sky.data.lat)
+    assert_allclose(gw_spec.value, aw_spec.value)
+    assert_allclose(gw_stokes.value, aw_stokes.value)

pyproject.toml

@@ -7,7 +7,7 @@ authors = [
 ]
 dependencies = [
     "asdf >= 2.8.1",
-    "astropy >= 5.1",
+    "astropy >= 5.3",
     "numpy",
     "scipy",
     "asdf_wcs_schemas",