elec_distance - Calculates spherical interelectrode distances (arc length).
Usage: [labels, distances] = elec_distance(elec_labels,X,Y,Z,xo,yo,zo)
Notes: Arc length method assumes a centroid at (xo,yo,zo) = (0,0,0)
and input values are in rectangular Cartesian coordinates.
Sphere radius is estimated by the average radius from
(xo,yo,zo) to any 2 pairs of electrodes. It will vary
from one pair to another, but this method works well for
small theta (eg, nearest neighbours).
Returns 2 matrices, one for paired electrode labels and
another for spherical arc length estimates.0001 function [labels, distances] = elec_distance(elec_labels,X,Y,Z,xo,yo,zo) 0002 0003 % elec_distance - Calculates spherical interelectrode distances (arc length). 0004 % 0005 % Usage: [labels, distances] = elec_distance(elec_labels,X,Y,Z,xo,yo,zo) 0006 % 0007 % Notes: Arc length method assumes a centroid at (xo,yo,zo) = (0,0,0) 0008 % and input values are in rectangular Cartesian coordinates. 0009 % 0010 % Sphere radius is estimated by the average radius from 0011 % (xo,yo,zo) to any 2 pairs of electrodes. It will vary 0012 % from one pair to another, but this method works well for 0013 % small theta (eg, nearest neighbours). 0014 % 0015 % Returns 2 matrices, one for paired electrode labels and 0016 % another for spherical arc length estimates. 0017 % 0018 0019 % $Revision: 1.1 $ $Date: 2004/11/12 01:32:33 $ 0020 0021 % Author: Darren.Weber_at_radiology.ucsf.edu 0022 % Created: 18/05/00 - linear distance 0023 % Modified: 24/06/01 - spherical arc length (should be OK for small theta 0024 % but for large theta, elliptical arc length may be 0025 % preferable). 0026 % 0027 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 0028 0029 % initialise centroid, unless input parameters defined 0030 if ~exist('xo','var') xo = 0; end 0031 if ~exist('yo','var') yo = 0; end 0032 if ~exist('zo','var') zo = 0; end 0033 0034 fprintf('%s\n', 'Calculating inter-electrode spherical arc length.'); 0035 0036 labels = cell(1); 0037 distances = []; 0038 0039 % convert numerical electrode labels to cell strings 0040 if isnumeric(elec_labels) > 0 0041 if size(elec_labels,1) > size(elec_labels,2) 0042 elec_labels = cellstr(strcat(num2str(elec_labels))); 0043 else 0044 elec_labels = cellstr(strcat(num2str(elec_labels'))); 0045 end 0046 end 0047 0048 A = [ (X-xo) (Y-yo) (Z-zo) ]; B = A; % define electrode vectors A,B, given centroid (xo,yo,zo) 0049 rows = 50; % progress indicator 0050 for a = 1:length(X) 0051 fprintf('.'); if( a == rows ) fprintf('\n'); rows = rows + 50; end % progress indicator 0052 0053 Aa = A(a,:); 0054 A_len = sqrt( sum( Aa.^2 ) ); % length of electrode vector A 0055 0056 for b = 1:length(X) 0057 0058 Bb = B(b,:); 0059 B_len = sqrt ( sum(Bb.^2) ); % length of electrode vector B 0060 0061 if( Aa == Bb ) 0062 arc_len = 0; % no distance from electrode to itself 0063 else 0064 r = (A_len + B_len)/2; % estimate sphere radius from A_len and B_len 0065 theta = acos( dot(Aa,Bb) / (A_len * B_len) ); % Angle between A & B, in radians 0066 arc_len = r * theta; % arc length = radius * theta 0067 end 0068 0069 distances(a, b) = arc_len; 0070 labels(a, b) = strcat(elec_labels(a), ', ', elec_labels(b)); 0071 end 0072 end 0073 fprintf('\n');