Axial to planar gradiometer transformation

examples/preprocessing/interpolate_to.py

@@ -29,6 +29,24 @@
 print(__doc__)
 ylim = (-10, 10)
 
+# %%
+# Load the MEG data
+data_path = sample.data_path()
+fif_file_path = data_path / "MEG" / "sample" / "sample_audvis_raw.fif"
+raw_meg = mne.io.read_raw_fif(fif_file_path)
+
+raw_meg.pick("meg")
+
+# %%
+# Define the target montage
+standard_montage_meg = make_standard_montage("ctf275")
+
+# %%
+# Use interpolate_to to project MEG data to the standard montage
+raw_meg_interpolated_mne = raw_meg.copy().interpolate_to(
+    standard_montage_meg, method="MNE"
+)
+
 # %%
 # Load EEG data
 data_path = sample.data_path()

mne/channels/_standard_montage_utils.py

@@ -118,6 +118,52 @@ def _mgh_or_standard(basename, head_size, coord_frame="unknown"):
     )
 
 
+def _meg(basename, head_size):
+    fname = op.join(MONTAGE_PATH, basename)
+
+    # Create a simple class instance instead of a list
+    class CustomMontage:
+        pass
+
+    montage = CustomMontage()
+
+    # Read the file
+    with open(fname) as f:
+        # Skip header line
+        header = f.readline().strip().split()
+
+        ch_names = []
+        ch_types = []
+        pos = []
+        ori = []
+
+        for line in f:
+            parts = line.strip().split()
+            ch_names.append(parts[0])
+            ch_types.append(parts[1])
+            pos.append([float(parts[2]), float(parts[3]), float(parts[4])])
+            ori.append([float(parts[5]), float(parts[6]), float(parts[7])])
+
+    pos = np.array(pos)
+
+    montage.ch_names = ch_names
+
+    # # Create a dictionary mapping channel names to positions
+    # montage.ch_pos = dict(zip(ch_names, pos))
+    montage.ch_pos = pos
+    # # TODO - make_dig_montage():
+    #         For custom montages without fiducials, this parameter must be set
+    #         to ``'head'``. ->
+    #         "kind": FIFF.FIFFV_POINT_EEG, ->
+    #         dig names each chennel as EEG #1 ...
+
+    # These aren't standard DigMontage attributes but can be useful
+    montage.ch_types = ch_types
+    montage.ori = ori
+
+    return montage
+
+
 standard_montage_look_up_table = {
     "EGI_256": _egi_256,
     "easycap-M1": partial(_easycap, basename="easycap-M1.txt"),
@@ -165,6 +211,8 @@ def _mgh_or_standard(basename, head_size, coord_frame="unknown"):
     "brainproducts-RNP-BA-128": partial(
         _easycap, basename="brainproducts-RNP-BA-128.txt"
     ),
+    "ctf275": partial(_meg, basename="ctf275.txt"),
+    "neuromag306": partial(_meg, basename="neuromag306.txt"),
 }
 
 

mne/channels/channels.py

@@ -960,7 +960,7 @@ def interpolate_bads(
 
         return self
 
-    def interpolate_to(self, sensors, origin="auto", method="spline", reg=0.0):
+    def interpolate_to(self, sensors, origin="auto", method=None, reg=0.0):
         """Interpolate EEG data onto a new montage.
 
         .. warning::
@@ -1003,10 +1003,31 @@ def interpolate_to(self, sensors, origin="auto", method="spline", reg=0.0):
         from .montage import DigMontage
 
         # Check that the method option is valid.
-        _check_option("method", method, ["spline", "MNE"])
         _validate_type(sensors, DigMontage, "sensors")
+        # TODO: Handle the error: sensors must be an instance of DigMontage, got <class 'mne.channels._standard_montage_utils._meg.<locals>.CustomMontage'> instead.
+
+        method = _handle_default("interpolation_method", method)
+
+        # Filter method to only include 'eeg' and 'meg'
+        supported_ch_types = ["eeg", "meg"]
+        keys_to_delete = [key for key in method if key not in supported_ch_types]
+        for key in keys_to_delete:
+            del method[key]
+
+        # Force MEG to always use MNE method,
+        # otherwise when method = "spline", the _handle_default function
+        # forces all channel types to use that method
+        # TODO: Check if there is a better way to handle this
+        if "meg" in method:
+            method["meg"] = "MNE"
+        valids = {"eeg": ("spline", "MNE"), "meg": ("MNE")}
+        for key in method:
+            _check_option("method[key]", key, tuple(valids))
+            _check_option(f"method['{key}']", method[key], valids[key])
+        logger.info("Setting channel interpolation method to %s.", method)
 
         # Get target positions from the montage
+        # TODO: handle the error: AttributeError: 'CustomMontage' object has no attribute 'get_positions'
         ch_pos = sensors.get_positions().get("ch_pos", {})
         target_ch_names = list(ch_pos.keys())
         if not target_ch_names: