JP-3686: Allow tweakreg to parse skycoord objects in absolute refcat

changes/333.bugfix.rst

@@ -0,0 +1 @@
+Allow tweakreg to parse absolute reference catalogs with skycoord objects in them

src/stcal/tweakreg/tweakreg.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import numpy as np
 import math
 import warnings
 from pathlib import Path
@@ -253,14 +254,43 @@ def _parse_refcat(abs_refcat: str | Path,
         )
 
     if Path(abs_refcat).is_file():
-        return Table.read(abs_refcat)
+        return _parse_sky_centroid(Table.read(abs_refcat))
 
     msg = (f"Invalid 'abs_refcat' value: {abs_refcat}. 'abs_refcat' must be "
            "a path to an existing file name or one of the supported "
            f"reference catalogs: {_SINGLE_GROUP_REFCAT_STR}.")
     raise ValueError(msg)
 
 
+def _parse_sky_centroid(catalog: Table) -> Table:
+    """Turn SkyCoord object into simple RA/DEC columns.
+
+    The inclusion of SkyCoord objects via sky_centroid.ra and sky_centroid.dec
+    permits the use of catalogs directly from the jwst source_catalog step.
+    No action is taken if the catalog already contains RA and DEC columns.
+    """
+    cols = [name.lower() for name in catalog.colnames]
+    if ("ra" in cols) and ("dec" in cols):
+        if "sky_centroid" in cols:
+            msg = ("Catalog contains both (RA, DEC) and sky_centroid. "
+                   "Ignoring sky_centroid.")
+            warnings.warn(msg, stacklevel=2)
+            catalog.remove_column("sky_centroid")
+        return catalog
+    if "sky_centroid" not in cols:
+        msg = ("Absolute reference catalog contains neither RA, DEC "
+               "nor sky_centroid.ra, sky_centroid.dec.")
+        raise KeyError(msg)
+
+    skycoord = catalog["sky_centroid"].to_table()
+
+    catalog["ra"] = skycoord["ra"]
+    catalog["dec"] = skycoord["dec"]
+    catalog.remove_column("sky_centroid")
+
+    return catalog
+
+
 def _is_wcs_correction_small(correctors,
                              use2dhist=True,
                              searchrad=2.0,

tests/test_tweakreg.py

@@ -11,12 +11,14 @@
 from astropy.modeling.models import Shift
 from astropy.table import Table
 from astropy.time import Time
+from astropy.coordinates import SkyCoord
 
 from stcal.tweakreg import astrometric_utils as amutils
 from stcal.tweakreg.tweakreg import (
     TweakregError,
     _is_wcs_correction_small,
     _parse_refcat,
+    _parse_sky_centroid,
     _wcs_to_skycoord,
     absolute_align,
     construct_wcs_corrector,
@@ -203,17 +205,19 @@ def datamodel(wcsobj2, group_id=None):
     return MinimalDataWithWCS(wcsobj2, group_id=group_id)
 
 
-def test_parse_refcat(datamodel, tmp_path):
+@pytest.fixture(scope="module")
+def abs_refcat(datamodel):
 
     wcsobj = datamodel.meta.wcs
-    correctors = fake_correctors(0.0)
-
-    # Get radius and fiducial
     radius, fiducial = amutils.compute_radius(wcsobj)
+    return amutils.get_catalog(fiducial[0], fiducial[1], search_radius=radius,
+                            catalog=TEST_CATALOG)
 
-    # Get the catalog
-    cat = amutils.get_catalog(fiducial[0], fiducial[1], search_radius=radius,
-                              catalog=TEST_CATALOG)
+
+def test_parse_refcat(datamodel, abs_refcat, tmp_path):
+
+    correctors = fake_correctors(0.0)
+    cat = abs_refcat
 
     # save refcat to file
     cat.write(tmp_path / CATALOG_FNAME, format="ascii.ecsv", overwrite=True)
@@ -232,6 +236,36 @@ def test_parse_refcat(datamodel, tmp_path):
     assert isinstance(refcat, Table)
 
 
+def test_parse_sky_centroid(abs_refcat):
+
+    # make a SkyCoord object out of the RA and DEC columns
+    cat = abs_refcat.copy()
+    sky_centroid = SkyCoord(cat["ra"], cat["dec"], unit="deg")
+    cat["sky_centroid"] = sky_centroid
+
+    # test case where ra, dec, and sky_centroid are all present
+    with pytest.warns(UserWarning):
+        cat_out = _parse_sky_centroid(cat)
+    cat_out = _parse_sky_centroid(cat)
+    assert isinstance(cat_out, Table)
+    assert np.all(cat["ra"] == cat_out["ra"])
+    assert np.all(cat["dec"] == cat_out["dec"])
+    assert "sky_centroid" not in cat_out.columns
+
+    # test case where ra, dec are no longer present
+    cat["sky_centroid"] = sky_centroid
+    cat.remove_columns(["ra", "dec"])
+    cat_out = _parse_sky_centroid(cat)
+    assert isinstance(cat_out, Table)
+    assert np.all(cat["ra"] == cat_out["ra"])
+    assert np.all(cat["dec"] == cat_out["dec"])
+
+    # test case where neither present
+    cat.remove_columns(["ra", "dec"])
+    with pytest.raises(KeyError):
+        _parse_sky_centroid(cat)
+
+
 @pytest.fixture(scope="module")
 def input_catalog(datamodel):
     """Get catalog from gaia, transform it to x,y in the image frame,