ft_headmodel_halfspace.m
8c8accbbb214master

ft_headmodel_halfspace.m
View Options

			function headmodel = ft_headmodel_halfspace(mesh, Pc, varargin)

			% FT_HEADMODEL_HALFSPACE creates an EEG volume conduction model that
			% is described with an infinite conductive halfspace. You can think
			% of this as a plane with on one side a infinite mass of conductive
			% material (e.g. water) and on the other side non-conductive material
			% (e.g. air).
			%
			% Use as
			% headmodel = ft_headmodel_halfspace(mesh, Pc, ...)
			% where
			% mesh.pos = Nx3 vector specifying N points through which a plane is fitted
			% Pc = 1x3 vector specifying the spatial position of a point lying in the conductive halfspace
			% (this determines the plane normal's direction)
			%
			% Additional optional arguments should be specified as key-value pairs and can include
			% 'sourcemodel' = string, 'monopole' or 'dipole' (default = 'dipole')
			% 'conductivity' = number, conductivity value of the conductive halfspace (default = 1)
			%
			% See also FT_PREPARE_VOL_SENS, FT_COMPUTE_LEADFIELD

			% Copyright (C) 2012, Donders Centre for Cognitive Neuroimaging, Nijmegen, NL
			%
			% 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/>.
			%
			% $Id$

			model = ft_getopt(varargin, 'sourcemodel', 'dipole');
			cond = ft_getopt(varargin, 'conductivity');

			if isempty(cond)
			ft_warning('Conductivity was not specified, using 1');
			cond = 1;
			end

			% the description of this volume conduction model consists of the
			% description of the plane, and a point in the void halfspace

			if isstruct(mesh) && isfield(mesh,'pos')
			pos = mesh.pos;
			elseif size(mesh,2)==3
			pos = mesh;
			else
			ft_error('incorrect specification of the geometry');
			end

			% fit a plane to the points
			[N,P] = fit_plane(pos);

			% checks if Pc is in the conductive part. If not, flip
			incond = acos(dot(N,(Pc-P)./norm(Pc-P))) > pi/2;
			if ~incond
			N = -N;
			end

			headmodel = [];
			headmodel.cond = cond;
			headmodel.pos = P(:)'; % a point that lies on the plane that separates the conductive tissue from the air
			headmodel.ori = N(:)'; % a unit vector pointing towards the air
			headmodel.ori = headmodel.ori/norm(headmodel.ori);

			if strcmpi(model,'dipole')
			headmodel.type = 'halfspace';
			elseif strcmpi(model,'monopole')
			headmodel.type = 'halfspace_monopole';
			else
			ft_error('unknow method')
			end

			function [N,P] = fit_plane(X)
			% Fits a plane through a number of points in 3D cartesian coordinates
			P = mean(X,1); % the plane is spanned by this point and by a normal vector
			X = bsxfun(@minus,X,P);
			[u, s, v] = svd(X, 0);
			N = v(:,3); % orientation of the plane, can be in either direction

iCAPs/packages/spm12/external/fieldtrip/forward/ft_headmodel_halfspace.m8c8accbbb214master

ft_headmodel_halfspace.mView Options

iCAPs/packages/spm12/external/fieldtrip/forward/ft_headmodel_halfspace.m
8c8accbbb214master

ft_headmodel_halfspace.m
View Options