DOC: add example showing grouped triaxial OPM topomaps

Author: PragnyaKhandelwal

examples/visualization/plot_evoked_topomap_opm_grouped.py

@@ -0,0 +1,41 @@
+"""
+=====================================
+Plot grouped triaxial OPM topomaps
+=====================================
+
+This example demonstrates grouped radial/tangential topomap rendering for
+colocated triaxial OPM sensors using a small segment of the UCL OPM auditory
+dataset. The grouped rendering places radial maps alongside tangential maps
+so orientation information is explicit.
+
+"""
+# Authors: MNE contributors
+# License: BSD-3-Clause
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+import mne
+
+# Load a small segment of the UCL OPM dataset
+subject = "sub-002"
+data_path = mne.datasets.ucl_opm_auditory.data_path()
+opm_file = (
+    data_path / subject / "ses-001" / "meg" / "sub-002_ses-001_task-aef_run-001_meg.bin"
+)
+
+# Read and crop for speed
+raw = mne.io.read_raw_fil(opm_file, verbose="error")
+raw.crop(120, 210).load_data()
+
+# Create epochs and average to get evoked
+events = mne.find_events(raw, min_duration=0.1)
+epochs = mne.Epochs(
+    raw, events, tmin=-0.1, tmax=0.4, baseline=(None, 0), verbose="error"
+)
+evoked = epochs.average()
+
+# Find a peak time and plot grouped topomap
+t_peak = evoked.times[np.argmax(np.std(evoked.copy().pick("meg").data, axis=0))]
+fig = evoked.plot_topomap(times=[float(t_peak)], ch_type="mag")
+plt.show()