Fix backwards compatibility issues with feed arrays in beamfits files

CHANGELOG.md

@@ -2,6 +2,7 @@
 All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
+
 ### Changed
 - When reading MWAX correlator files , `remove_coarse_band` now defaults to
 `False` if DERIPPLE is on. Otherwise it defaults to `True`.
@@ -13,6 +14,8 @@ raised, and no pfb shape is removed.
 fringe-stopped data.
 
 ### Fixed
+- A backwards compatibiilty issue with feed arrays in old beamfits files which
+could specify feeds as "e" or "n".
 - Compatiblity with numpy>=2.3
 
 ## [3.2.4] - 2025-09-15

src/pyuvdata/utils/pol.py

@@ -1031,7 +1031,7 @@ def get_feeds_from_x_orientation(
     if feeds is None and feed_array is None:
         warnings.warn(
             "Unknown polarization basis -- assuming linearly polarized (x/y) "
-            "feeds for Telescope.feed_array."
+            "feeds for feed_array."
         )
         feeds = ["x", "y"]
 

src/pyuvdata/uvbeam/beamfits.py

@@ -312,16 +312,25 @@ def read_beamfits(
             self.model_name = primary_header.pop("MODEL", None)
             self.model_version = primary_header.pop("MODELVER", None)
             self.mount_type = primary_header.pop("MNTSTA", mount_type)
-            x_orientation = primary_header.pop("XORIENT", "east")
+            x_orientation = primary_header.pop("XORIENT", None)
             feedlist = primary_header.pop("FEEDLIST", None)
             if feedlist is not None:
-                self.feed_array = np.array(feedlist[1:-1].split(", "))
+                feedlist = [feed.lower() for feed in feedlist[1:-1].split(", ")]
+                if "e" in feedlist and "n" in feedlist:
+                    if x_orientation is None:
+                        if feedlist.index("e") < feedlist.index("n"):
+                            x_orientation = "east"
+                        else:
+                            x_orientation = "north"
+                    feed_map = utils.pol.x_orientation_pol_map(
+                        x_orientation=x_orientation
+                    )
+                    for key, value in feed_map.items():
+                        feedlist[feedlist.index(value)] = key
+                self.feed_array = np.array(feedlist)
+
                 self.Nfeeds = len(self.feed_array)
             feedang = primary_header.pop("FEEDANG", None)
-            if feedang is not None:
-                self.feed_angle = np.array(
-                    [float(item) for item in feedang[1:-1].split(", ")]
-                )
 
             self.history = str(primary_header.get("HISTORY", ""))
             if not utils.history._check_history_version(
@@ -488,8 +497,20 @@ def read_beamfits(
                 # no bandpass information, set it to an array of ones
                 self.bandpass_array = np.ones(self.Nfreqs)
 
-        # Handle x-orientation keyword here
-        if self.feed_angle is None or self.feed_array is None:
+        # Handle missing feed orientation info here
+        if feedang is not None:
+            self.feed_angle = np.array(
+                [float(item) for item in feedang[1:-1].split(", ")]
+            )
+        else:
+            if x_orientation is None:
+                # no feed angles and no x_orientation info.
+                # Default to east x_orientation
+                warnings.warn(
+                    "This beamfits file has no information about the orientation "
+                    "of the feeds. Defaulting an East x_orientation."
+                )
+                x_orientation = "east"
             self.set_feeds_from_x_orientation(x_orientation)
 
         if run_check:

src/pyuvdata/uvbeam/uvbeam.py

@@ -645,7 +645,7 @@ def _fix_feeds(self):
             warnings.warn(
                 "Feed information now required for power beams, will default to "
                 "linear feeds with x-orientation aligned to the east (populated based "
-                "on what is preesnt in UVBeam.polarization_array). This will become an "
+                "on what is present in UVBeam.polarization_array). This will become an "
                 "error in version 3.4.",
                 DeprecationWarning,
             )

tests/uvbeam/test_beamfits.py

@@ -36,15 +36,23 @@ def cst_power_1freq_cut_healpix(cst_efield_1freq_cut_healpix_main):
 def hera_beam_casa():
     beam_in = UVBeam()
     casa_file = fetch_data("hera_casa_beam")
-    beam_in.read_beamfits(casa_file, mount_type="fixed", run_check=False)
+    with check_warnings(
+        UserWarning,
+        match=[
+            "This beamfits file has no information about the orientation of "
+            "the feeds. Defaulting an East x_orientation.",
+            "Unknown polarization basis -- assuming linearly polarized (x/y) "
+            "feeds for feed_array.",
+        ],
+    ):
+        beam_in.read_beamfits(casa_file, mount_type="fixed", run_check=False)
 
     # fill in missing parameters
     beam_in.data_normalization = "peak"
     beam_in.feed_name = "casa_ideal"
     beam_in.feed_version = "v0"
     beam_in.model_name = "casa_airy"
     beam_in.model_version = "v0"
-    beam_in.mount_type = "fixed"
 
     # this file is actually in an orthoslant projection RA/DEC at zenith at a
     # particular time.
@@ -205,6 +213,49 @@ def test_read_cst_write_read_fits_change_freq_units(cst_power_1freq, tmp_path):
     return
 
 
+@pytest.mark.parametrize(
+    ("feedlist", "feedang"),
+    [("[E, N]", [np.pi / 2, 0]), ("[E, N]", None), ("[N, E]", [0, np.pi / 2])],
+)
+def test_e_n_feeds(cst_efield_1freq_cut, feedlist, feedang, tmp_path):
+    # this test was inspired by an error reading in an old beamfits file that
+    # Ruby made for the LWA. It had a feed array of [E, N], which errored.
+    beam_in = cst_efield_1freq_cut
+    beam_out = UVBeam()
+
+    write_file = str(tmp_path / "outtest_beam.fits")
+    write_file2 = str(tmp_path / "outtest_beam2.fits")
+    beam_in.write_beamfits(write_file, clobber=True)
+
+    # now change frequency units
+    with fits.open(write_file) as fname:
+        data = fname[0].data
+        primary_hdr = fname[0].header
+        primary_hdr["FEEDLIST"] = feedlist
+        if feedang is None:
+            del primary_hdr["FEEDANG"]
+        else:
+            primary_hdr["FEEDANG"] = (
+                "[" + ", ".join(str(item) for item in feedang) + "]"
+            )
+        hdunames = fits_utils._indexhdus(fname)
+        bandpass_hdu = fname[hdunames["BANDPARM"]]
+        basisvec_hdu = fname[hdunames["BASISVEC"]]
+
+        prihdu = fits.PrimaryHDU(data=data, header=primary_hdr)
+        hdulist = fits.HDUList([prihdu, basisvec_hdu, bandpass_hdu])
+
+        hdulist.writeto(write_file2, overwrite=True)
+        hdulist.close()
+
+    beam_out.read_beamfits(write_file2)
+
+    if np.flip(beam_in.feed_angle).tolist() == feedang:
+        beam_in.feed_angle = np.flip(beam_in.feed_angle)
+
+    assert beam_in == beam_out
+
+
 def test_writeread_healpix(cst_efield_1freq_cut_healpix, tmp_path):
     beam_in = cst_efield_1freq_cut_healpix.copy()
     beam_out = UVBeam()

tests/uvbeam/test_uvbeam.py

@@ -3023,6 +3023,7 @@ def test_generic_read_cst():
 
 
 @pytest.mark.filterwarnings("ignore:Unknown polarization basis")
+@pytest.mark.filterwarnings("ignore:This beamfits file has no information about")
 @pytest.mark.filterwarnings("ignore:The mount_type keyword is set")
 @pytest.mark.parametrize(
     "dname", ["hera_fagnoni_dipole_yaml", "mwa_full_EE", "hera_casa_beam"]
@@ -3147,6 +3148,7 @@ def test_generic_read_all_bad_files(tmp_path):
 
 
 @pytest.mark.filterwarnings("ignore:Unknown polarization basis")
+@pytest.mark.filterwarnings("ignore:This beamfits file has no information about")
 @pytest.mark.filterwarnings("ignore:The mount_type keyword is set")
 @pytest.mark.parametrize(
     "dname", ["hera_fagnoni_dipole_yaml", "mwa_full_EE", "hera_casa_beam"]
@@ -3184,6 +3186,7 @@ def test_from_file(dname):
 
 @pytest.mark.filterwarnings("ignore:The mount_type keyword is set")
 @pytest.mark.filterwarnings("ignore:Unknown polarization basis")
+@pytest.mark.filterwarnings("ignore:This beamfits file has no information about")
 @pytest.mark.parametrize(
     ["dname", "path_var", "relative_path", "file_list"],
     [