elec_load.m

Matlab下的EEG处理程序库

function [elec,type,X,Y,Z,theta,phi,r] = elec_load(filename,coordinates,xo,yo,zo,N)
% ELEC_LOAD - Read electrode coordinate file (ascii, various coordinates).
% 
% Load an ascii electrode file and return the electrode labels, type, 
% and Cartesian (x,y,z) and/or spherical (theta,phi,r) coordinates.
%
% The ascii file format is that of NeuroScan 3Dspace export files.  Each row
% of the file comprises an electrode label, an electrode type code (see below),
% and the x,y,z coordinates (cm).  Each field is separated by spaces.
%
% Useage:   [elec,type,X,Y,Z,theta,phi,r] = elec_load(file,[coordinates],[xo],[yo],[zo],[N])
%
% where:    file = 'path\filename' with row format:
%
%           '%s %d %f %f %f' = [elec_label, type, (X,Y,Z) or (theta,phi,r)]
%
%           N is how many electrodes to load (129 default).
%           (xo,yo,zo) are the origin {(0,0,0) default}.
%
%           coordinates is a string option for input data type:
%           'Cartesian'  = cartesian in Neuroscan 3Dspace format (default);
%                          format is ['label' type X Y Z].
%           'Spherical1' = spherical, theta and phi in degrees,
%           'Spherical2' = spherical, theta and phi in radians,
%                          format is ['label' type theta phi r]
%           
%           theta is counterclockwise rotation from +x in x-y plane (azimuth),
%           phi is elevation with respect to z-axis, r is radius in cm,
%           +ve x-axis from origin through T4 (right ear)
%           +ve y-axis from origin through Nasion (theta = 90degrees = pi/2 rads)
% 
% Result:   elec is an electrode label, as cellstr array (Nx1)
%           type is an electrode type, as uint8 (unsigned integer, Nx1),
%           (X,Y,Z) & (theta,phi,r) as double floating point (Nx1), with
%           theta and phi in radians.  The origin is (0,0,0), unless forced
%           otherwise with the input arguments.
%           
% Notes: i) Type is defined as follows (from Neuroscan 3Dspace):
%
%           Electrode               Type
%           ---------               ----
%           Nasion                   110
%           Left                     108
%           Right                    114
%           electrodes 1:n            69
%           Centroid                  99    (should be <0,0,0>)
%           Ref                      120
%           Scalp Points 1:n          32
%
%           From the return values, the electrodes can be selected by:
%           index = find(type == 69);
%           X = X(index); Y = Y(index); Z = Z(index); elec = elec(index);
%
%       ii) Conversion from spherical to Cartesian coordinates is:
%           x = r .* sin(phi) .* cos(theta);
%           y = r .* sin(phi) .* sin(theta);
%           z = r .* cos(phi);
%           Phi here is elevation with respect to z-axis.  The matlab
%           function sph2cart uses elevation with respect to xy plane.
%
%      iii) Conversion from Cartesian to spherical coordinates is:
%           theta = atan2( y, x );
%           phi = atan2( sqrt( x.^2 + y.^2 ), z );
%           r = sqrt( x.^2 + y.^2 + z.^2);
%           Phi here is the elevation with respect to z-axis.  The matlab
%           function cart2sph uses elevation with respect to xy plane.
%
% Bug:      For NeuroScan 3Dspace export files, reading beyond the electrode
%           points, into the scalp points (type 32), causes all fields to
%           shift one to the left.  To avoid this error, include a short 
%           string before each '32' in the electrode file or use the N
%           option to only read the electrode points.

% $Revision: 1.2 $ $Date: 2003/03/02 03:20:44 $

% Licence:  GNU GPL, no express or implied warranties
% History:  08/1999, [e-mail]
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if ~exist('N', 'var'),  N = 129;
elseif isempty(N),      N = 129;
end
if ~exist('coordinates', 'var'),
    coordinates = 'Cartesian';
elseif isempty(coordinates),
    coordinates = 'Cartesian';
end
if ~exist('xo', 'var'), xo = 0;
elseif isempty(xo),     xo = 0;
end
if ~exist('yo', 'var'), yo = 0;
elseif isempty(xo),     yo = 0;
end
if ~exist('zo', 'var'), zo = 0;
elseif isempty(xo),     zo = 0;
end

tic;

[path,name,ext] = fileparts(filename);
file = fullfile(path,[name ext]);

fprintf('\nELEC_LOAD...\n');
fprintf('...loading ''%s'' electrodes from:\n\t%s\n', coordinates, file);

switch coordinates
    
    case 'Cartesian'
        [elec,type,X,Y,Z] = textread(file,'%s %d %f %f %f', N);
        type = uint8(type);
        
        fprintf('...converting from cm to meters.\n');
        % Convert from Neuroscan 3Dspace coordinate
        % metric (cm) to meters.
        X = X ./ 100;
        Y = Y ./ 100;
        Z = Z ./ 100;
        
        % If possible, adjust all coordinates so that origin is (0,0,0)
        index = find(type == 99);
        if ~isempty(index),
            xo = X(index);    yo = Y(index);    zo = Z(index);
        end
        fprintf('...centering origin at (0,0,0).\n');
        X = X - xo;        Y = Y - yo;       Z = Z - zo;
        xo = X(index);    yo = Y(index);    zo = Z(index);
        
        % Convert to spherical
        fprintf('...calculating spherical coordinates.\n');
        theta = atan2( (Y-yo), (X-xo) );
        phi = atan2( sqrt( (X-xo).^2 + (Y-yo).^2 ), (Z-zo) );
        r = sqrt( (X-xo).^2 + (Y-yo).^2 + (Z-zo).^2);
        
    case 'Spherical1' %degrees
        [elec,type,theta,phi,r] = textread(file,'%s %d %f %f %f', N);
        % convert theta and phi to radians
        theta = theta * (pi/180); phi = phi * (pi/180);
        [X, Y, Z] = elec_sph2cart(theta,phi,r);
        fprintf('...converting from cm to meters.\n');
        X = X ./ 100;        Y = Y ./ 100;        Z = Z ./ 100;
        
    case 'Spherical2' %radians
        [elec,type,theta,phi,r] = textread(file,'%s %d %f %f %f', N);
        [X, Y, Z] = elec_sph2cart(theta,phi,r);
        fprintf('...converting from cm to meters.\n');
        X = X ./ 100;        Y = Y ./ 100;        Z = Z ./ 100;
        
    otherwise
        msg = sprintf('...invalid coordinate type: ''%s'', see ''help elec_load''\n', coordinates);
        error(msg);
        
end

fprintf('...loaded %d electrodes\n', size(elec,1));

t = toc; fprintf('...done (%6.2f sec).\n\n',t);

return


function [X, Y, Z] = elec_sph2cart(theta,phi,r)
% SPH2CART: Convert spherical radians to Cartesian coordinates
% Phi here is elevation with respect to z-axis.  The matlab
% function sph2cart uses elevation with respect to xy plane.

    X = r .* sin(phi) .* cos(theta);
    Y = r .* sin(phi) .* sin(theta);
    Z = r .* cos(phi);
return