ENH: Add Kernel helmet

Author: larsoner

mne/bem.py

@@ -1751,13 +1751,15 @@ def _add_gamma_multipliers(bem):
     FIFF.FIFFV_BEM_SURF_ID_SKULL: "outer skull",
     FIFF.FIFFV_BEM_SURF_ID_HEAD: "outer skin ",
     FIFF.FIFFV_BEM_SURF_ID_UNKNOWN: "unknown    ",
+    FIFF.FIFFV_MNE_SURF_MEG_HELMET: "MEG helmet ",
 }
 _sm_surf_name = {
     FIFF.FIFFV_BEM_SURF_ID_BRAIN: "brain",
     FIFF.FIFFV_BEM_SURF_ID_CSF: "csf",
     FIFF.FIFFV_BEM_SURF_ID_SKULL: "outer skull",
     FIFF.FIFFV_BEM_SURF_ID_HEAD: "outer skin ",
     FIFF.FIFFV_BEM_SURF_ID_UNKNOWN: "unknown    ",
+    FIFF.FIFFV_MNE_SURF_MEG_HELMET: "helmet",
 }
 
 
@@ -1850,7 +1852,8 @@ def _write_bem_surfaces_block(fid, surfs):
     """Write bem surfaces to open file handle."""
     for surf in surfs:
         start_block(fid, FIFF.FIFFB_BEM_SURF)
-        write_float(fid, FIFF.FIFF_BEM_SIGMA, surf["sigma"])
+        if "sigma" in surf:
+            write_float(fid, FIFF.FIFF_BEM_SIGMA, surf["sigma"])
         write_int(fid, FIFF.FIFF_BEM_SURF_ID, surf["id"])
         write_int(fid, FIFF.FIFF_MNE_COORD_FRAME, surf["coord_frame"])
         write_int(fid, FIFF.FIFF_BEM_SURF_NNODE, surf["np"])

mne/channels/channels.py

@@ -103,6 +103,10 @@ def _get_meg_system(info):
                 system = "ARTEMIS123"
                 have_helmet = False
                 break
+            elif coil_type == FIFF.FIFFV_COIL_KERNEL_OPM_MAG_GEN1:
+                system = "Kernel_Flux"
+                have_helmet = True
+                break
     else:
         system = "unknown"
         have_helmet = False

mne/data/helmets/Kernel_Flux.fif.gz

@@ -158,8 +158,26 @@ def _get_head_surface(subject, source, subjects_dir, on_defects, raise_error=Tru
     return surf
 
 
+# New helmets can be written for example with:
+#
+# import os.path as op
+# import mne
+# from mne.io.constants import FIFF
+# surf = mne.read_surface('kernel.obj', return_dict=True)[-1]
+# surf['rr'] *= 1000  # needs to be in mm
+# mne.surface.complete_surface_info(surf, copy=False, do_neighbor_tri=False)
+# surf['coord_frame'] = FIFF.FIFFV_COORD_DEVICE
+# surfs = mne.bem._surfaces_to_bem(
+#     [surf], ids=[FIFF.FIFFV_MNE_SURF_MEG_HELMET], sigmas=[1.],
+#     incomplete='ignore')
+# del surfs[0]['sigma']
+# bem_fname = op.join(op.dirname(mne.__file__), 'data', 'helmets',
+#                     'kernel.fif.gz')
+# mne.write_bem_surfaces(bem_fname, surfs, overwrite=True)
+
+
 @verbose
-def get_meg_helmet_surf(info, trans=None, verbose=None):
+def get_meg_helmet_surf(info, trans=None, *, verbose=None):
     """Load the MEG helmet associated with the MEG sensors.
 
     Parameters