fixed some info fields in MEG interpolation across sensor types using… (#13759)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: chsquare

doc/changes/dev/13759.bugfix.rst

@@ -0,0 +1,4 @@
+When interpolating from axial to planar gradiometers, set info fields "chs", "ch_names", and "nchan", according to the interpolated data, 
+reset info fields "device_info", "helium_info", "gantry_angle", "ctf_head_t", "dev_ctf_t", "bads", "projs", and "comps" to [] or None, and
+preserve all remaining info fields.
+by :newcontrib:`Christoph Huber-Huber`.

doc/changes/names.inc

@@ -53,6 +53,7 @@
 .. _Chris Mullins: https://crmullins.com
 .. _Christian Brodbeck: https://github.com/christianbrodbeck
 .. _Christian O'Reilly: https://github.com/christian-oreilly
+.. _Christoph Huber-Huber: https://github.com/chsquare
 .. _Christopher Dinh: https://github.com/chdinh
 .. _Chun-Hui Li: https://github.com/iamsc
 .. _Clemens Brunner: https://github.com/cbrnr

mne/channels/interpolation.py

@@ -484,13 +484,35 @@ def _interpolate_to_meg(inst, sensors, origin, mode):
     if len(picks_meg_good) == 0:
         raise ValueError("No good MEG channels available for interpolation.")
 
-    # Load target sensor configuration
-    info_to = read_meg_canonical_info(sensors)
-    info_to["dev_head_t"] = deepcopy(inst.info["dev_head_t"])
+    # Load target sensor configuration as info file
+    info_cano = read_meg_canonical_info(sensors)
 
     # Get source MEG info
     info_from = pick_info(inst.info, picks_meg_good)
 
+    # Update target info to accommodate the desired channel info
+    # and reset some channel and machine-related fields to avoid
+    # confusion later on.
+    # NOTE: We don't change the original 'dev_head_t'.
+    #       Some keys require as default an empty list.
+    info_to = deepcopy(info_from)
+    with info_to._unlock():
+        info_to.update(
+            {
+                "chs": info_cano["chs"],
+                "ch_names": info_cano["ch_names"],
+                "nchan": info_cano["nchan"],
+                "device_info": None,
+                "helium_info": None,
+                "gantry_angle": None,
+                "ctf_head_t": None,
+                "dev_ctf_t": None,
+                "bads": [],
+                "projs": [],
+                "comps": [],
+            }
+        )
+
     # Compute field interpolation mapping
     origin_val = _check_origin(origin, inst.info)
     mapping = _map_meg_or_eeg_channels(info_from, info_to, mode=mode, origin=origin_val)

mne/channels/tests/test_interpolation.py

@@ -556,8 +556,11 @@ def test_interpolate_to_meg(monkeypatch):
     monkeypatch.setattr(  # for speed
         mne.channels.channels, "_ALLOWED_INTERPOLATION_MODES", ("point",)
     )
+    evoked.resample(evoked.info["sfreq"] / 2)  # speed up even more
     kwargs = dict(mode="point", origin=(0.0, 0.0, 0.04))
     evoked_ctf = evoked.interpolate_to("ctf151", **kwargs)
+    # test whether .info["sfreq"] was preserved across interpolation
+    assert evoked_ctf.info["sfreq"] == evoked.info["sfreq"]
     evoked_ctf.pick(evoked_ctf.ch_names[::4])
     evoked_rt = evoked_ctf.interpolate_to("neuromag", **kwargs).pick(evoked.ch_names)
     corrcoef = np.corrcoef(evoked.data.ravel(), evoked_rt.data.ravel())[0, 1]