ENH: Add round-trip channel name saving (#13003)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Stefan Appelhoff <[email protected]>

doc/changes/devel/13003.newfeature.rst

@@ -0,0 +1 @@
+Added support for saving and loading channel names from FIF in :meth:`mne.channels.DigMontage.save` and :meth:`mne.channels.read_dig_fif` and added the convention that they should be saved as ``-dig.fif``, by `Eric Larson`_.

mne/_fiff/_digitization.py

@@ -11,7 +11,7 @@
 from .constants import FIFF, _coord_frame_named
 from .tag import read_tag
 from .tree import dir_tree_find
-from .write import start_and_end_file, write_dig_points
+from .write import _safe_name_list, start_and_end_file, write_dig_points
 
 _dig_kind_dict = {
     "cardinal": FIFF.FIFFV_POINT_CARDINAL,
@@ -162,10 +162,11 @@ def __eq__(self, other):  # noqa: D105
             return np.allclose(self["r"], other["r"])
 
 
-def _read_dig_fif(fid, meas_info):
+def _read_dig_fif(fid, meas_info, *, return_ch_names=False):
     """Read digitizer data from a FIFF file."""
     isotrak = dir_tree_find(meas_info, FIFF.FIFFB_ISOTRAK)
     dig = None
+    ch_names = None
     if len(isotrak) == 0:
         logger.info("Isotrak not found")
     elif len(isotrak) > 1:
@@ -183,13 +184,21 @@ def _read_dig_fif(fid, meas_info):
             elif kind == FIFF.FIFF_MNE_COORD_FRAME:
                 tag = read_tag(fid, pos)
                 coord_frame = _coord_frame_named.get(int(tag.data.item()))
+            elif kind == FIFF.FIFF_MNE_CH_NAME_LIST:
+                tag = read_tag(fid, pos)
+                ch_names = _safe_name_list(tag.data, "read", "ch_names")
         for d in dig:
             d["coord_frame"] = coord_frame
-    return _format_dig_points(dig)
+    out = _format_dig_points(dig)
+    if return_ch_names:
+        out = (out, ch_names)
+    return out
 
 
 @verbose
-def write_dig(fname, pts, coord_frame=None, *, overwrite=False, verbose=None):
+def write_dig(
+    fname, pts, coord_frame=None, *, ch_names=None, overwrite=False, verbose=None
+):
     """Write digitization data to a FIF file.
 
     Parameters
@@ -203,6 +212,10 @@ def write_dig(fname, pts, coord_frame=None, *, overwrite=False, verbose=None):
         If all the points have the same coordinate frame, specify the type
         here. Can be None (default) if the points could have varying
         coordinate frames.
+    ch_names : list of str | None
+        Channel names associated with the digitization points, if available.
+
+        .. versionadded:: 1.9
     %(overwrite)s
 
         .. versionadded:: 1.0
@@ -222,9 +235,15 @@ def write_dig(fname, pts, coord_frame=None, *, overwrite=False, verbose=None):
                 "Points have coord_frame entries that are incompatible with "
                 f"coord_frame={coord_frame}: {tuple(bad_frames)}."
             )
+    _validate_type(ch_names, (None, list, tuple), "ch_names")
+    if ch_names is not None:
+        for ci, ch_name in enumerate(ch_names):
+            _validate_type(ch_name, str, f"ch_names[{ci}]")
 
     with start_and_end_file(fname) as fid:
-        write_dig_points(fid, pts, block=True, coord_frame=coord_frame)
+        write_dig_points(
+            fid, pts, block=True, coord_frame=coord_frame, ch_names=ch_names
+        )
 
 
 _cardinal_ident_mapping = {

mne/_fiff/write.py

@@ -389,7 +389,7 @@ def write_ch_info(fid, ch):
     fid.write(b"\0" * (16 - len(ch_name)))
 
 
-def write_dig_points(fid, dig, block=False, coord_frame=None):
+def write_dig_points(fid, dig, block=False, coord_frame=None, *, ch_names=None):
     """Write a set of digitizer data points into a fif file."""
     if dig is not None:
         data_size = 5 * 4
@@ -406,6 +406,10 @@ def write_dig_points(fid, dig, block=False, coord_frame=None):
             fid.write(np.array(d["kind"], ">i4").tobytes())
             fid.write(np.array(d["ident"], ">i4").tobytes())
             fid.write(np.array(d["r"][:3], ">f4").tobytes())
+        if ch_names is not None:
+            write_name_list_sanitized(
+                fid, FIFF.FIFF_MNE_CH_NAME_LIST, ch_names, "ch_names"
+            )
         if block:
             end_block(fid, FIFF.FIFFB_ISOTRAK)
 

mne/channels/montage.py

@@ -46,6 +46,7 @@
     _on_missing,
     _pl,
     _validate_type,
+    check_fname,
     copy_function_doc_to_method_doc,
     fill_doc,
     verbose,
@@ -409,9 +410,22 @@ def save(self, fname, *, overwrite=False, verbose=None):
             The filename to use. Should end in .fif or .fif.gz.
         %(overwrite)s
         %(verbose)s
+
+        See Also
+        --------
+        mne.channels.read_dig_fif
+
+        Notes
+        -----
+        .. versionchanged:: 1.9
+           Added support for saving the associated channel names.
         """
+        fname = _check_fname(fname, overwrite=overwrite)
+        check_fname(fname, "montage", ("-dig.fif", "-dig.fif.gz"))
         coord_frame = _check_get_coord_frame(self.dig)
-        write_dig(fname, self.dig, coord_frame, overwrite=overwrite)
+        write_dig(
+            fname, self.dig, coord_frame, overwrite=overwrite, ch_names=self.ch_names
+        )
 
     def __iadd__(self, other):
         """Add two DigMontages in place.
@@ -808,17 +822,15 @@ def read_dig_dat(fname):
     return make_dig_montage(electrodes, nasion, lpa, rpa)
 
 
-def read_dig_fif(fname):
+@verbose
+def read_dig_fif(fname, *, verbose=None):
     r"""Read digitized points from a .fif file.
 
-    Note that electrode names are not present in the .fif file so
-    they are here defined with the convention from VectorView
-    systems (EEG001, EEG002, etc.)
-
     Parameters
     ----------
     fname : path-like
         FIF file from which to read digitization locations.
+    %(verbose)s
 
     Returns
     -------
@@ -835,17 +847,28 @@ def read_dig_fif(fname):
     read_dig_hpts
     read_dig_localite
     make_dig_montage
+
+    Notes
+    -----
+    .. versionchanged:: 1.9
+       Added support for reading the associated channel names, if present.
+
+    In some files, electrode names are not present (e.g., in older files).
+    For those files, the channel names are defined with the convention from
+    VectorView systems (EEG001, EEG002, etc.).
     """
-    fname = _check_fname(fname, overwrite="read", must_exist=True)
+    check_fname(fname, "montage", ("-dig.fif", "-dig.fif.gz"))
+    fname = _check_fname(fname=fname, must_exist=True, overwrite="read")
     # Load the dig data
     f, tree = fiff_open(fname)[:2]
     with f as fid:
-        dig = _read_dig_fif(fid, tree)
+        dig, ch_names = _read_dig_fif(fid, tree, return_ch_names=True)
 
-    ch_names = []
-    for d in dig:
-        if d["kind"] == FIFF.FIFFV_POINT_EEG:
-            ch_names.append(f"EEG{d['ident']:03d}")
+    if ch_names is None:  # backward compat from when we didn't save the names
+        ch_names = []
+        for d in dig:
+            if d["kind"] == FIFF.FIFFV_POINT_EEG:
+                ch_names.append(f"EEG{d['ident']:03d}")
 
     montage = DigMontage(dig=dig, ch_names=ch_names)
     return montage
@@ -1572,6 +1595,7 @@ def read_custom_montage(
     --------
     make_dig_montage
     make_standard_montage
+    read_dig_fif
 
     Notes
     -----

mne/channels/tests/test_montage.py

@@ -19,6 +19,7 @@
     assert_equal,
 )
 
+import mne.channels.montage
 from mne import (
     __file__ as _mne_file,
 )
@@ -56,6 +57,7 @@
     _BUILTIN_STANDARD_MONTAGES,
     _check_get_coord_frame,
     transform_to_head,
+    write_dig,
 )
 from mne.coreg import get_mni_fiducials
 from mne.datasets import testing
@@ -138,7 +140,8 @@ def test_dig_montage_trans(tmp_path):
     _ensure_trans(trans)
     # ensure that we can save and load it, too
     fname = tmp_path / "temp-mon.fif"
-    _check_roundtrip(montage, fname, "mri")
+    with pytest.warns(RuntimeWarning, match="MNE naming conventions"):
+        _check_roundtrip(montage, fname, "mri")
     # test applying a trans
     position1 = montage.get_positions()
     montage.apply_trans(trans)
@@ -1074,12 +1077,12 @@ def _ensure_fid_not_nan(info, ch_pos):
 
 
 @testing.requires_testing_data
-def test_fif_dig_montage(tmp_path):
+def test_fif_dig_montage(tmp_path, monkeypatch):
     """Test FIF dig montage support."""
-    dig_montage = read_dig_fif(fif_dig_montage_fname)
+    dig_montage = read_dig_fif(fif_dig_montage_fname, verbose="error")
 
     # test round-trip IO
-    fname_temp = tmp_path / "test.fif"
+    fname_temp = tmp_path / "test-dig.fif"
     _check_roundtrip(dig_montage, fname_temp)
 
     # Make a BrainVision file like the one the user would have had
@@ -1119,16 +1122,32 @@ def test_fif_dig_montage(tmp_path):
     # Roundtrip of non-FIF start
     montage = make_dig_montage(hsp=read_polhemus_fastscan(hsp), hpi=read_mrk(hpi))
     elp_points = read_polhemus_fastscan(elp)
-    ch_pos = {f"EEG{k:03d}": pos for k, pos in enumerate(elp_points[8:], 1)}
-    montage += make_dig_montage(
+    ch_pos = {f"ECoG{k:03d}": pos for k, pos in enumerate(elp_points[3:], 1)}
+    assert len(elp_points) == 8  # there are only 8 but pretend the last are ECoG
+    other = make_dig_montage(
         nasion=elp_points[0], lpa=elp_points[1], rpa=elp_points[2], ch_pos=ch_pos
     )
+    assert other.ch_names[0].startswith("ECoG")
+    montage += other
+    assert montage.ch_names[0].startswith("ECoG")
     _check_roundtrip(montage, fname_temp, "unknown")
     montage = transform_to_head(montage)
     _check_roundtrip(montage, fname_temp)
     montage.dig[0]["coord_frame"] = FIFF.FIFFV_COORD_UNKNOWN
     with pytest.raises(RuntimeError, match="Only a single coordinate"):
-        montage.save(fname_temp)
+        montage.save(fname_temp, overwrite=True)
+    montage.dig[0]["coord_frame"] = FIFF.FIFFV_COORD_HEAD
+
+    # Check that old-style files can be read, too, using EEG001 etc.
+    def write_dig_no_ch_names(*args, **kwargs):
+        kwargs["ch_names"] = None
+        return write_dig(*args, **kwargs)
+
+    monkeypatch.setattr(mne.channels.montage, "write_dig", write_dig_no_ch_names)
+    montage.save(fname_temp, overwrite=True)
+    montage_read = read_dig_fif(fname_temp)
+    default_ch_names = [f"EEG{ii:03d}" for ii in range(1, 6)]
+    assert montage_read.ch_names == default_ch_names
 
 
 @testing.requires_testing_data
@@ -1175,8 +1194,8 @@ def test_egi_dig_montage(tmp_path):
         atol=1e-4,
     )
 
-    # test round-trip IO
-    fname_temp = tmp_path / "egi_test.fif"
+    # test round-trip IO (with GZ)
+    fname_temp = tmp_path / "egi_test-dig.fif.gz"
     _check_roundtrip(dig_montage, fname_temp, "unknown")
     _check_roundtrip(dig_montage_in_head, fname_temp)
 
@@ -1330,7 +1349,7 @@ def test_read_dig_captrak(tmp_path):
     )
 
     montage = transform_to_head(montage)  # transform_to_head has to be tested
-    _check_roundtrip(montage=montage, fname=str(tmp_path / "bvct_test.fif"))
+    _check_roundtrip(montage=montage, fname=tmp_path / "bvct_test-dig.fif")
 
     fid, _ = _get_fid_coords(montage.dig)
     assert_allclose(
@@ -1495,15 +1514,15 @@ def test_montage_positions_similar(fname, montage, n_eeg, n_good, bads):
     assert_array_less(0, ang)  # but not equal
 
 
-# XXX: this does not check ch_names + it cannot work because of write_dig
 def _check_roundtrip(montage, fname, coord_frame="head"):
     """Check roundtrip writing."""
     montage.save(fname, overwrite=True)
     montage_read = read_dig_fif(fname=fname)
 
-    assert_equal(repr(montage), repr(montage_read))
-    assert_equal(_check_get_coord_frame(montage_read.dig), coord_frame)
+    assert repr(montage) == repr(montage_read)
+    assert _check_get_coord_frame(montage_read.dig) == coord_frame
     assert_dig_allclose(montage, montage_read)
+    assert montage.ch_names == montage_read.ch_names
 
 
 def test_digmontage_constructor_errors():
@@ -1910,7 +1929,7 @@ def test_get_montage():
 
     # 4. read in BV test dataset and make sure montage
     # fulfills roundtrip on non-standard montage
-    dig_montage = read_dig_fif(fif_dig_montage_fname)
+    dig_montage = read_dig_fif(fif_dig_montage_fname, verbose="error")
 
     # Make a BrainVision file like the one the user would have had
     # with testing dataset 'test.vhdr'

mne/viz/tests/test_montage.py

@@ -48,7 +48,7 @@ def test_plot_montage():
     assert "0 channels" in repr(montage)
     with pytest.raises(RuntimeError, match="No valid channel positions"):
         montage.plot()
-    d = read_dig_fif(fname=fif_fname)
+    d = read_dig_fif(fname=fif_fname, verbose="error")
     assert "61 channels" in repr(d)
     # XXX this is broken; dm.point_names is used. Sometimes we say this should
     # Just contain the HPI coils, other times that it's all channels (e.g.,

tutorials/forward/35_eeg_no_mri.py

@@ -105,7 +105,7 @@
 # in the MRI coordinate frame, which can be used to compute the
 # MRI<->head transform ``trans``:
 fname_1020 = subjects_dir / subject / "montages" / "10-20-montage.fif"
-mon = mne.channels.read_dig_fif(fname_1020)
+mon = mne.channels.read_dig_fif(fname_1020, verbose="error")  # should be named -dig.fif
 mon.rename_channels({f"EEG{ii:03d}": ch_name for ii, ch_name in enumerate(ch_names, 1)})
 trans = mne.channels.compute_native_head_t(mon)
 raw.set_montage(mon)