mne.preprocessing.compute_maxwell_basis

mne.preprocessing.compute_maxwell_basis(info, origin='auto', int_order=8, ext_order=3, calibration=None, coord_frame='head', regularize='in', ignore_ref=True, bad_condition='error', mag_scale=100.0, extended_proj=(), verbose=None)[source]

Compute the SSS basis for a given measurement info structure.

Parameters
infomne.Info

The mne.Info object with information about the sensors and methods of measurement.

originarray_like, shape (3,) | str

Origin of internal and external multipolar moment space in meters. The default is 'auto', which means (0., 0., 0.) when coord_frame='meg', and a head-digitization-based origin fit using fit_sphere_to_headshape() when coord_frame='head'. If automatic fitting fails (e.g., due to having too few digitization points), consider separately calling the fitting function with different options or specifying the origin manually.

int_orderint

Order of internal component of spherical expansion.

ext_orderint

Order of external component of spherical expansion.

calibrationstr | None

Path to the '.dat' file with fine calibration coefficients. File can have 1D or 3D gradiometer imbalance correction. This file is machine/site-specific.

coord_framestr

The coordinate frame that the origin is specified in, either 'meg' or 'head'. For empty-room recordings that do not have a head<->meg transform info['dev_head_t'], the MEG coordinate frame should be used.

regularizestr | None

Basis regularization type, must be “in” or None. “in” is the same algorithm as the “-regularize in” option in MaxFilter™.

ignore_refbool

If True, do not include reference channels in compensation. This option should be True for KIT files, since Maxwell filtering with reference channels is not currently supported.

bad_conditionstr

How to deal with ill-conditioned SSS matrices. Can be “error” (default), “warning”, “info”, or “ignore”.

mag_scalefloat | str

The magenetometer scale-factor used to bring the magnetometers to approximately the same order of magnitude as the gradiometers (default 100.), as they have different units (T vs T/m). Can be 'auto' to use the reciprocal of the physical distance between the gradiometer pickup loops (e.g., 0.0168 m yields 59.5 for VectorView).

extended_projlist

The empty-room projection vectors used to extend the external SSS basis (i.e., use eSSS).

New in version 0.21.

verbosebool | str | int | None

If not None, override default verbose level (see mne.verbose() and Logging documentation for more). If used, it should be passed as a keyword-argument only.

Returns
Sndarray, shape (n_meg, n_moments)

The basis that can be used to reconstruct the data.

pSndarray, shape (n_moments, n_good_meg)

The (stabilized) pseudoinverse of the S array.

reg_momentsndarray, shape (n_moments,)

The moments that were kept after regularization.

n_use_inint

The number of kept moments that were in the internal space.

Notes

This outputs variants of \(\mathbf{S}\) and \(\mathbf{S^\dagger}\) from equations 27 and 37 of 1 with the coil scale for magnetometers already factored in so that the resulting denoising transform of the data to obtain \(\hat{\phi}_{in}\) from equation 38 would be:

phi_in = S[:, :n_use_in] @ pS[:n_use_in] @ data_meg_good

New in version 0.23.

References

1

Samu Taulu and Matti Kajola. Presentation of electromagnetic multichannel data: the signal space separation method. Journal of Applied Physics, 97(12):124905, 2005. doi:10.1063/1.1935742.