function [sens] = ft_datatype_sens(sens, varargin)

% FT_DATATYPE_SENS describes the FieldTrip structure that represents an MEG, EEG,

% sEEG, ECoG, or NIRS sensor array. This structure is commonly called "grad" for MEG,

% "elec" for EEG and intranial EEG, "opto" for NIRS, or in general "sens" if it could

% be any one.

%

% For all sensor types a distinction should be made between the channel (i.e. the

% output of the transducer that is A/D converted) and the sensor, which may have some

% spatial extent. For example in MEG gradiometers are comprised of multiple coils and

% with EEG you can have a bipolar channel, where the position of the channel can be

% represented as in between the position of the two electrodes.

%

% The structure for MEG gradiometers and/or magnetometers contains

% sens.label = Mx1 cell-array with channel labels

% sens.chanpos = Mx3 matrix with channel positions

% sens.chanori = Mx3 matrix with channel orientations, used for synthetic planar gradient computation

% sens.coilpos = Nx3 matrix with coil positions

% sens.coilori = Nx3 matrix with coil orientations

% sens.tra = MxN matrix to combine coils into channels

% sens.balance = structure containing info about the balancing, See FT_APPLY_MONTAGE

% and optionally

% sens.chanposold = Mx3 matrix with original channel positions (in case sens.chanpos has been updated to contain NaNs, e.g. after FT_COMPONENTANALYSIS)

% sens.chanoriold = Mx3 matrix with original channel orientations

% sens.labelold = Mx1 cell-array with original channel labels

%

% The structure for EEG, sEEG or ECoG channels contains

% sens.label = Mx1 cell-array with channel labels

% sens.chanpos = Mx3 matrix with channel positions (often the same as electrode positions)

% sens.elecpos = Nx3 matrix with electrode positions

% sens.tra = MxN matrix to combine electrodes into channels

% In case sens.tra is not present in the EEG sensor array, the channels

% are assumed to be average referenced.

%

% The structure for NIRS channels contains

% sens.label = Mx1 cell-array with channel labels

% sens.chanpos = Mx3 matrix with position of the channels (usually halfway the transmitter and receiver)

% sens.optopos = Nx3 matrix with the position of individual optodes

% sens.optotype = Nx1 cell-array with information about the type of optode (receiver or transmitter)

% sens.optolabel = Nx1 cell-array with optode labels

% sens.wavelength = 1xK vector of all wavelengths that were used

% sens.tra = MxN matrix that specifies for each of the M channels which of the N optodes transmits at which wavelength (positive integer from 1 to K), or receives (negative ingeger from 1 to K)

%

% The following fields apply to MEG, EEG, sEEG and ECoG

% sens.chantype = Mx1 cell-array with the type of the channel, see FT_CHANTYPE

% sens.chanunit = Mx1 cell-array with the units of the channel signal, e.g. 'V', 'fT' or 'T/cm', see FT_CHANUNIT

%

% Optional fields:

% type, unit, fid, chantype, chanunit, coordsys

%

% Historical fields:

% pnt, pos, ori, pnt1, pnt2, fiberpos, fibertype, fiberlabel, transceiver, transmits, laserstrength

%

% Revision history:

% (2020/latest) Updated the specification of the NIRS sensor definition.

% Dropped the laserstrength and renamed transmits into tra for consistency.

%

% (2019/latest) Updated the specification of the NIRS sensor definition.

% Use "opto" instead of "fibers", see http://bit.ly/33WaqWU for details.

%

% (2016) The chantype and chanunit have become required fields.

% Original channel details are specified with the suffix "old" rather than "org".

% All numeric values are represented in double precision.

% It is possible to convert the amplitude and distance units (e.g. from T to fT and

% from m to mm) and it is possible to express planar and axial gradiometer channels

% either in units of amplitude or in units of amplitude/distance (i.e. proper

% gradient).

%

% (2011v2) The chantype and chanunit have been added for MEG.

%

% (2011v1) To facilitate determining the position of channels (e.g. for plotting)

% in case of balanced MEG or bipolar EEG, an explicit distinction has been made

% between chanpos+chanori and coilpos+coilori (for MEG) and chanpos and elecpos

% (for EEG). The pnt and ori fields are removed.

%

% (2010) Added support for bipolar or otherwise more complex linear combinations

% of EEG electrodes using sens.tra, similar to MEG.

%

% (2009) Noise reduction has been added for MEG systems in the balance field.

%

% (2006) The optional fields sens.type and sens.unit were added.

%

% (2003) The initial version was defined, which looked like this for EEG

% sens.pnt = Mx3 matrix with electrode positions

% sens.label = Mx1 cell-array with channel labels

% and like this for MEG

% sens.pnt = Nx3 matrix with coil positions

% sens.ori = Nx3 matrix with coil orientations

% sens.tra = MxN matrix to combine coils into channels

% sens.label = Mx1 cell-array with channel labels

%

% See also FT_READ_SENS, FT_SENSTYPE, FT_CHANTYPE, FT_APPLY_MONTAGE, CTF2GRAD, FIF2GRAD,

% BTI2GRAD, YOKOGAWA2GRAD, ITAB2GRAD

% Copyright (C) 2011-2020, Robert Oostenveld & Jan-Mathijs Schoffelen

%

% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org

% for the documentation and details.

%

% FieldTrip is free software: you can redistribute it and/or modify

% it under the terms of the GNU General Public License as published by

% the Free Software Foundation, either version 3 of the License, or

% (at your option) any later version.

%

% FieldTrip is distributed in the hope that it will be useful,

% but WITHOUT ANY WARRANTY; without even the implied warranty of

% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

% GNU General Public License for more details.

%

% You should have received a copy of the GNU General Public License

% along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.

%

% $Id$

% undocumented options for the 2016 format and up

% amplitude = string, can be 'T' or 'fT'

% distance = string, can be 'm', 'cm' or 'mm'

% scaling = string, can be 'amplitude' or 'amplitude/distance'

% these are for speeding up subsequent calls with the same input arguments

persistent previous_argin previous_argout

current_argin = [{sens} varargin];

if isequal(current_argin, previous_argin)

% don't do the whole checking again, but return the previous output from cache

sens = previous_argout{1};

return

end

% get the optional input arguments, which should be specified as key-value pairs

version = ft_getopt(varargin, 'version', 'latest');

amplitude = ft_getopt(varargin, 'amplitude'); % should be 'V' 'uV' 'T' 'mT' 'uT' 'nT' 'pT' 'fT'

distance = ft_getopt(varargin, 'distance'); % should be 'm' 'dm' 'cm' 'mm'

scaling = ft_getopt(varargin, 'scaling'); % should be 'amplitude' or 'amplitude/distance', the default depends on the senstype

if ~isempty(amplitude) && ~any(strcmp(amplitude, {'V' 'uV' 'T' 'mT' 'uT' 'nT' 'pT' 'fT'}))

ft_error('unsupported unit of amplitude "%s"', amplitude);

end

if ~isempty(distance) && ~any(strcmp(distance, {'m' 'dm' 'cm' 'mm'}))

ft_error('unsupported unit of distance "%s"', distance);

end

if strcmp(version, 'latest')

version = '2020';

end

if isempty(sens)

return;

end

% this is needed further down

nchan = length(sens.label);

% these are used at multiple places, therefore we determine them only once

if isfield(sens, 'coilpos')

ismeg = true;

iseeg = true;

isnirs = false;

elseif isfield(sens, 'elecpos')

ismeg = false;

iseeg = true;

isnirs = false;

elseif isfield(sens, 'optopos')

ismeg = false;

iseeg = false;

isnirs = true;

else

% doing it this way takes a lot more CPU time

ismeg = ft_senstype(sens, 'meg');

iseeg = ft_senstype(sens, 'eeg');

isnirs = ft_senstype(sens, 'nirs');

end

switch version

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

case '2020'

% update it to the previous standard version

new_argin = ft_setopt(varargin, 'version', '2019');

sens = ft_datatype_sens(sens, new_argin{:});

if isfield(sens, 'coordsys')

sens = fixcoordsys(sens);

end

if isnirs

sens = renamefields(sens, 'transmits', 'tra'); % this makes it more consistent with EEG and MEG

sens = removefields(sens, {'laserstrength'});

if isfield(sens, 'optotype') && isfield(sens, 'tra')

% the read_artinis_oxy3 file returns the wrong sign for the receivers and transmitters

% but since it is p-code, it cannot be fixed

tmp = sens.tra(:, strcmp(sens.optotype, 'transmitter')); correctT = all(tmp(:)>=0);

tmp = sens.tra(:, strcmp(sens.optotype, 'receiver' )); correctR = all(tmp(:)<=0);

if ~correctT

ft_warning('flipping sign for transmitters');

sens.tra(:, strcmp(sens.optotype, 'transmitter')) = -sens.tra(:, strcmp(sens.optotype, 'transmitter'));

end

if ~correctR

ft_warning('flipping sign for receivers');

sens.tra(:, strcmp(sens.optotype, 'receiver')) = -sens.tra(:, strcmp(sens.optotype, 'receiver'));

end

end

end % ifnirs

% ensure internal consistency

nchan = numel(sens.label);

if isfield(sens, 'chanpos')

assert(size(sens.chanpos, 1)==nchan, 'sensor structure is inconsistent');

end

if isfield(sens, 'chanori')

assert(size(sens.chanori, 1)==nchan, 'sensor structure is inconsistent');

end

if isfield(sens, 'tra')

assert(size(sens.tra, 1)==nchan);

if isfield(sens, 'elecpos')

assert(size(sens.tra,2)==size(sens.elecpos,1), 'sensor structure is inconsistent')

elseif isfield(sens, 'optopos')

assert(size(sens.tra,2)==size(sens.optopos,1), 'sensor structure is inconsistent')

elseif isfield(sens, 'coilpos')

assert(size(sens.tra,2)==size(sens.coilpos,1), 'sensor structure is inconsistent')

end

end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

case '2019'

% update it to the previous standard version

new_argin = ft_setopt(varargin, 'version', '2016');

sens = ft_datatype_sens(sens, new_argin{:});

if isnirs

% rename some NIRS field names

sens = renamefields(sens, 'fiberpos', 'optopos');

sens = renamefields(sens, 'fibertype', 'optotype');

sens = renamefields(sens, 'fiberlabel', 'optolabel');

sens = renamefields(sens, 'transceiver', 'transmits');

% these might be present due to the reading functions but are not part of the user/technical documentation yet, so better not include them for now

% especially the chanunit field needs some careful thought when converting between optical densities and chromophore concentrations.

sens = removefields(sens, {'chantype', 'chanunit'});

end

% ensure all positions are represented as 3D, not 2D

fn = {'chanpos', 'optopos', 'elecpos', 'coilpos'};

for i=1:numel(fn)

if isfield(sens, fn{i}) && size(sens.(fn{i}),2)==2

ft_notice('converting %s from 2D to 3D', fn{i});

sens.(fn{i})(:,3) = 0;

end

end % for

if isfield(sens, 'optolabel')

if length(sens.optolabel)~=length(unique(sens.optolabel))

ft_warning('non-unique optode labels detected');

end

end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

case '2016'

% update it to the previous standard version

new_argin = ft_setopt(varargin, 'version', '2011v2');

sens = ft_datatype_sens(sens, new_argin{:});

% rename from org to old (reverse = false)

sens = fixoldorg(sens, false);

% ensure that all numbers are represented in double precision

% this only affects the top-level fields and does not recurse

sens = ft_struct2double(sens, 1);

% in version 2011v2 this was optional, now it is required

if ~isfield(sens, 'chantype') || all(strcmp(sens.chantype, 'unknown'))

sens.chantype = ft_chantype(sens);

end

% in version 2011v2 this was optional, now it is required

if ~isfield(sens, 'chanunit') || all(strcmp(sens.chanunit, 'unknown'))

sens.chanunit = ft_chanunit(sens);

end

if ~isempty(distance)

% update the units of distance, this also updates the tra matrix

sens = ft_convert_units(sens, distance);

else

% determine the default, this may be needed to set the scaling

distance = sens.unit;

end

if ~isempty(amplitude) && isfield(sens, 'tra')

% update the tra matrix for the units of amplitude, this ensures that

% the leadfield values remain consistent with the units

for i=1:nchan

if ~isempty(regexp(sens.chanunit{i}, 'm$', 'once'))

% this channel is expressed as amplitude per distance

sens.tra(i,:) = sens.tra(i,:) * ft_scalingfactor(sens.chanunit{i}, [amplitude '/' distance]);

sens.chanunit{i} = [amplitude '/' distance];

elseif ~isempty(regexp(sens.chanunit{i}, '[T|V]$', 'once'))

% this channel is expressed as amplitude

sens.tra(i,:) = sens.tra(i,:) * ft_scalingfactor(sens.chanunit{i}, amplitude);

sens.chanunit{i} = amplitude;

else

ft_error('unexpected channel unit "%s" in channel %d', sens.chanunit{i}, i);

end

end

else

% determine the default amplityde, this may be needed to set the scaling

if any(~cellfun(@isempty, regexp(sens.chanunit, '^T')))

% one of the channel units starts with T

amplitude = 'T';

elseif any(~cellfun(@isempty, regexp(sens.chanunit, '^fT')))

% one of the channel units starts with fT

amplitude = 'fT';

elseif any(~cellfun(@isempty, regexp(sens.chanunit, '^V')))

% one of the channel units starts with V

amplitude = 'V';

elseif any(~cellfun(@isempty, regexp(sens.chanunit, '^uV')))

% one of the channel units starts with uV

amplitude = 'uV';

else

% this unknown amplitude will cause a problem if the scaling needs to be changed between amplitude and amplitude/distance

amplitude = 'unknown';

end

end

% perform some sanity checks

if ismeg

sel_m = ~cellfun(@isempty, regexp(sens.chanunit, '/m$'));

sel_dm = ~cellfun(@isempty, regexp(sens.chanunit, '/dm$'));

sel_cm = ~cellfun(@isempty, regexp(sens.chanunit, '/cm$'));

sel_mm = ~cellfun(@isempty, regexp(sens.chanunit, '/mm$'));

if strcmp(sens.unit, 'm') && (any(sel_dm) || any(sel_cm) || any(sel_mm))

ft_error('inconsistent units in input gradiometer');

elseif strcmp(sens.unit, 'dm') && (any(sel_m) || any(sel_cm) || any(sel_mm))

ft_error('inconsistent units in input gradiometer');

elseif strcmp(sens.unit, 'cm') && (any(sel_m) || any(sel_dm) || any(sel_mm))

ft_error('inconsistent units in input gradiometer');

elseif strcmp(sens.unit, 'mm') && (any(sel_m) || any(sel_dm) || any(sel_cm))

ft_error('inconsistent units in input gradiometer');

end

if ~strcmp(amplitude, 'unknown') && ~strcmp(distance, 'unknown')

% the default should be "amplitude/distance" for neuromag and "amplitude" for all others

if isempty(scaling)

if ft_senstype(sens, 'neuromag') && ~any(contains(sens.chanunit, '/'))

ft_warning('assuming that the default scaling should be amplitude/distance rather than amplitude');

scaling = 'amplitude/distance';

elseif ft_senstype(sens, 'yokogawa440') && any(contains(sens.chanunit, '/'))

ft_warning('assuming that the default scaling should be amplitude rather than amplitude/distance');

scaling = 'amplitude';

end

end

% update the gradiometer scaling

if strcmp(scaling, 'amplitude') && isfield(sens, 'tra')

for i=1:nchan

if strcmp(sens.chanunit{i}, [amplitude '/' distance])

% this channel is expressed as amplitude per distance

coil = find(abs(sens.tra(i,:))~=0);

if length(coil)~=2

ft_error('unexpected number of coils contributing to channel %d', i);

end

baseline = norm(sens.coilpos(coil(1),:) - sens.coilpos(coil(2),:));

sens.tra(i,:) = sens.tra(i,:)*baseline; % scale with the baseline distance

sens.chanunit{i} = amplitude;

elseif strcmp(sens.chanunit{i}, amplitude)

% no conversion needed

elseif isfield(sens, 'balance') && strcmp(sens.balance.current, 'comp')

% no conversion needed

elseif isfield(sens, 'balance') && strcmp(sens.balance.current, 'planar')

% no conversion needed

else

% see http://bugzilla.fieldtriptoolbox.org/show_bug.cgi?id=3144

ft_warning('unexpected channel unit "%s" in channel %d', sens.chanunit{i}, i);

end % if

end % for nchan

elseif strcmp(scaling, 'amplitude/distance') && isfield(sens, 'tra')

for i=1:nchan

if strcmp(sens.chanunit{i}, amplitude)

% this channel is expressed as amplitude

coil = find(abs(sens.tra(i,:))~=0);

if length(coil)==1 || strcmp(sens.chantype{i}, 'megmag')

% this is a magnetometer channel, no conversion needed

continue

elseif length(coil)~=2

ft_error('unexpected number of coils (%d) contributing to channel %s (%d)', length(coil), sens.label{i}, i);

end

baseline = norm(sens.coilpos(coil(1),:) - sens.coilpos(coil(2),:));

sens.tra(i,:) = sens.tra(i,:)/baseline; % scale with the baseline distance

sens.chanunit{i} = [amplitude '/' distance];

elseif strcmp(sens.chanunit{i}, [amplitude '/' distance])

% no conversion needed

else

% see http://bugzilla.fieldtriptoolbox.org/show_bug.cgi?id=3144

ft_warning('unexpected channel unit "%s" in channel %d', sens.chanunit{i}, i);

end % if

end % for nchan

end % if strcmp scaling

end % if amplitude and scaling are not unknown

else

sel_m = ~cellfun(@isempty, regexp(sens.chanunit, '/m$'));

sel_dm = ~cellfun(@isempty, regexp(sens.chanunit, '/dm$'));

sel_cm = ~cellfun(@isempty, regexp(sens.chanunit, '/cm$'));

sel_mm = ~cellfun(@isempty, regexp(sens.chanunit, '/mm$'));

if any(sel_m | sel_dm | sel_cm | sel_mm)

ft_error('scaling of amplitude/distance has not been considered yet for EEG');

end

end % if iseeg or ismeg

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

case '2011v2'

% rename from old to org (reverse = true)

sens = fixoldorg(sens, true);

if ~isempty(amplitude) || ~isempty(distance) || ~isempty(scaling)

ft_warning('amplitude, distance and scaling are not supported for version "%s"', version);

end

% This speeds up subsequent calls to ft_senstype and channelposition.

% However, if it is not more precise than MEG or EEG, don't keep it in

% the output (see further down).

if ~isfield(sens, 'type')

sens.type = ft_senstype(sens);

end

if isfield(sens, 'pnt')

if ismeg

% sensor description is a MEG sensor-array, containing oriented coils

sens.coilpos = sens.pnt; sens = rmfield(sens, 'pnt');

sens.coilori = sens.ori; sens = rmfield(sens, 'ori');

else

% sensor description is something else, EEG/ECoG/sEEG, etc

sens.elecpos = sens.pnt; sens = rmfield(sens, 'pnt');

end

end

if isfield(sens, 'pos')

if ismeg

% sensor description is a MEG sensor-array, containing oriented coils

sens.coilpos = sens.pos; sens = rmfield(sens, 'pos');

sens.coilori = sens.ori; sens = rmfield(sens, 'ori');

else

% sensor description is something else, EEG/ECoG/sEEG, etc

sens.elecpos = sens.pos; sens = rmfield(sens, 'pos');

end

end

if ~isfield(sens, 'chanpos')

if ismeg

% sensor description is a MEG sensor-array, containing oriented coils

[chanpos, chanori, lab] = channelposition(sens);

% the channel order can be different in the two representations

[selsens, selpos] = match_str(sens.label, lab);

sens.chanpos = nan(length(sens.label), 3);

sens.chanori = nan(length(sens.label), 3);

% insert the determined position/orientation on the appropriate rows

sens.chanpos(selsens,:) = chanpos(selpos,:);

sens.chanori(selsens,:) = chanori(selpos,:);

if length(selsens)~=length(sens.label)

ft_warning('cannot determine the position and orientation for all channels');

end

else

% sensor description is something else, EEG/ECoG etc

% note that chanori will be all NaNs

[chanpos, chanori, lab] = channelposition(sens);

% the channel order can be different in the two representations

[selsens, selpos] = match_str(sens.label, lab);

sens.chanpos = nan(length(sens.label), 3);

% insert the determined position/orientation on the appropriate rows

sens.chanpos(selsens,:) = chanpos(selpos,:);

if length(selsens)~=length(sens.label)

ft_warning('cannot determine the position and orientation for all channels');

end

end

end

if ~isfield(sens, 'chantype') || all(strcmp(sens.chantype, 'unknown'))

if ismeg

sens.chantype = ft_chantype(sens);

else

% for EEG it is not required

end

end

if ~isfield(sens, 'unit')

% this should be done prior to calling ft_chanunit, since ft_chanunit uses this for planar neuromag channels

sens = ft_determine_units(sens);

end

if ~isfield(sens, 'chanunit') || all(strcmp(sens.chanunit, 'unknown'))

if ismeg

sens.chanunit = ft_chanunit(sens);

else

% for EEG it is not required

end

end

if any(strcmp(sens.type, {'meg', 'eeg', 'magnetometer', 'electrode', 'unknown'}))

% this is not sufficiently informative, so better remove it

% see also http://bugzilla.fieldtriptoolbox.org/show_bug.cgi?id=1806

sens = rmfield(sens, 'type');

end

if size(sens.chanpos,1)~=length(sens.label) || ...

isfield(sens, 'tra') && size(sens.tra,1)~=length(sens.label) || ...

isfield(sens, 'tra') && isfield(sens, 'elecpos') && size(sens.tra,2)~=size(sens.elecpos,1) || ...

isfield(sens, 'tra') && isfield(sens, 'coilpos') && size(sens.tra,2)~=size(sens.coilpos,1) || ...

isfield(sens, 'tra') && isfield(sens, 'coilori') && size(sens.tra,2)~=size(sens.coilori,1) || ...

isfield(sens, 'chanpos') && size(sens.chanpos,1)~=length(sens.label) || ...

isfield(sens, 'chanori') && size(sens.chanori,1)~=length(sens.label)

ft_error('inconsistent number of channels in sensor description');

end

if ismeg

% ensure that the magnetometer/gradiometer balancing is specified

if ~isfield(sens, 'balance') || ~isfield(sens.balance, 'current')

sens.balance.current = 'none';

end

% try to add the chantype and chanunit to the CTF G1BR montage

if isfield(sens, 'balance') && isfield(sens.balance, 'G1BR') && ~isfield(sens.balance.G1BR, 'chantype')

sens.balance.G1BR.chantypeorg = repmat({'unknown'}, size(sens.balance.G1BR.labelorg));

sens.balance.G1BR.chanunitorg = repmat({'unknown'}, size(sens.balance.G1BR.labelorg));

sens.balance.G1BR.chantypenew = repmat({'unknown'}, size(sens.balance.G1BR.labelnew));

sens.balance.G1BR.chanunitnew = repmat({'unknown'}, size(sens.balance.G1BR.labelnew));

% the synthetic gradient montage does not fundamentally change the chantype or chanunit

[sel1, sel2] = match_str(sens.balance.G1BR.labelorg, sens.label);

sens.balance.G1BR.chantypeorg(sel1) = sens.chantype(sel2);

sens.balance.G1BR.chanunitorg(sel1) = sens.chanunit(sel2);

[sel1, sel2] = match_str(sens.balance.G1BR.labelnew, sens.label);

sens.balance.G1BR.chantypenew(sel1) = sens.chantype(sel2);

sens.balance.G1BR.chanunitnew(sel1) = sens.chanunit(sel2);

end

% idem for G2BR

if isfield(sens, 'balance') && isfield(sens.balance, 'G2BR') && ~isfield(sens.balance.G2BR, 'chantype')

sens.balance.G2BR.chantypeorg = repmat({'unknown'}, size(sens.balance.G2BR.labelorg));

sens.balance.G2BR.chanunitorg = repmat({'unknown'}, size(sens.balance.G2BR.labelorg));

sens.balance.G2BR.chantypenew = repmat({'unknown'}, size(sens.balance.G2BR.labelnew));

sens.balance.G2BR.chanunitnew = repmat({'unknown'}, size(sens.balance.G2BR.labelnew));

% the synthetic gradient montage does not fundamentally change the chantype or chanunit

[sel1, sel2] = match_str(sens.balance.G2BR.labelorg, sens.label);

sens.balance.G2BR.chantypeorg(sel1) = sens.chantype(sel2);

sens.balance.G2BR.chanunitorg(sel1) = sens.chanunit(sel2);

[sel1, sel2] = match_str(sens.balance.G2BR.labelnew, sens.label);

sens.balance.G2BR.chantypenew(sel1) = sens.chantype(sel2);

sens.balance.G2BR.chanunitnew(sel1) = sens.chanunit(sel2);

end

% idem for G3BR

if isfield(sens, 'balance') && isfield(sens.balance, 'G3BR') && ~isfield(sens.balance.G3BR, 'chantype')

sens.balance.G3BR.chantypeorg = repmat({'unknown'}, size(sens.balance.G3BR.labelorg));

sens.balance.G3BR.chanunitorg = repmat({'unknown'}, size(sens.balance.G3BR.labelorg));

sens.balance.G3BR.chantypenew = repmat({'unknown'}, size(sens.balance.G3BR.labelnew));

sens.balance.G3BR.chanunitnew = repmat({'unknown'}, size(sens.balance.G3BR.labelnew));

% the synthetic gradient montage does not fundamentally change the chantype or chanunit

[sel1, sel2] = match_str(sens.balance.G3BR.labelorg, sens.label);

sens.balance.G3BR.chantypeorg(sel1) = sens.chantype(sel2);

sens.balance.G3BR.chanunitorg(sel1) = sens.chanunit(sel2);

[sel1, sel2] = match_str(sens.balance.G3BR.labelnew, sens.label);

sens.balance.G3BR.chantypenew(sel1) = sens.chantype(sel2);

sens.balance.G3BR.chanunitnew(sel1) = sens.chanunit(sel2);

end

end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

otherwise

ft_error('converting to version %s is not supported', version);

end % switch

% this makes the display with the "disp" command look better

sens = sortfieldnames(sens);

% remember the current input and output arguments, so that they can be

% reused on a subsequent call in case the same input argument is given

current_argout = {sens};

previous_argin = current_argin;

previous_argout = current_argout;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% SUBFUNCTION

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

function b = sortfieldnames(a)

fn = sort(fieldnames(a));

for i=1:numel(fn)

b.(fn{i}) = a.(fn{i});

end