BUG: Fix dev_head_t for EEG data

doc/changes/devel/13112.bugfix.rst

@@ -0,0 +1 @@
+Fix bug with :func:`mne.io.read_raw_egi` where ``info["dev_head_t"]`` was an identity matrix instead of ``None``, by `Eric Larson`_.

mne/_fiff/meas_info.py

@@ -3315,7 +3315,7 @@ def create_info(ch_names, sfreq, ch_types="misc", verbose=None):
 )
 
 
-def _empty_info(sfreq):
+def _empty_info(sfreq, *, dev_head_t=True):
     """Create an empty info dictionary."""
     from ..transforms import Transform
 
@@ -3364,7 +3364,11 @@ def _empty_info(sfreq):
     info["highpass"] = 0.0
     info["sfreq"] = float(sfreq)
     info["lowpass"] = info["sfreq"] / 2.0
-    info["dev_head_t"] = Transform("meg", "head")
+    if dev_head_t is True:
+        dev_head_t = Transform("meg", "head")
+    elif dev_head_t is False:
+        dev_head_t = None
+    info["dev_head_t"] = dev_head_t
     info._update_redundant()
     info._check_consistency()
     return info

mne/io/egi/egimff.py

@@ -440,7 +440,7 @@ def __init__(
         assert egi_events.shape[1] == egi_info["last_samps"][-1]
 
         meas_dt_utc = egi_info["meas_dt_local"].astimezone(datetime.timezone.utc)
-        info = _empty_info(egi_info["sfreq"])
+        info = _empty_info(egi_info["sfreq"], dev_head_t=False)
         info["meas_date"] = _ensure_meas_date_none_or_dt(meas_dt_utc)
         info["utc_offset"] = egi_info["utc_offset"]
         info["device_info"] = dict(type=egi_info["device"])

mne/io/egi/tests/test_egi.py

@@ -83,6 +83,7 @@ def test_egi_mff_pause(fname, skip_times, event_times):
                 events_as_annotations=False,
             )
     assert raw.info["sfreq"] == 250.0  # true for all of these files
+    assert raw.info["dev_head_t"] is None  # no MEG data
     assert len(raw.annotations) == len(skip_times)
 
     # assert event onsets match expected times