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ea_calc_distance.m
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ea_calc_distance.m
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function varargout=ea_calc_distance(varargin)
% Example:
% [normfactor,dist_mm,dist_vox]=calc_distance(priordist,trajectory,mat,img)
% priordist is the distance in real-life in mm
% trajectory is the vector on which the electrodes lie
% mat is the transformation matrix that has been used to change the
% distances.
% __________________________________________________________________________________
% Copyright (C) 2014 Charite University Medicine Berlin, Movement Disorders Unit
% Andreas Horn
priordist=varargin{1};
trajvector=varargin{2};
mat=varargin{3};
newtrajvector=trajvector*mat; % i.e. the vector between 0,0,0 and some point in direction of trajvector.
% stretch factor in trajectory as found by mat.
normfactor=norm(newtrajvector)/norm(trajvector); % scalar value denoting the relationship between distances defined by trajvector in native and mni space.
% distance in millimeters
dist_mm=priordist*normfactor;
varargout{2}=dist_mm;
varargout{1}=normfactor;
% calculate voxel distances if nargin > 3.
if nargin>3
img=varargin{4};
V=spm_vol(img);
XYZ_mm=[0,0,0,1;trajvector,1]';
XYZ_vx= V.mat \ XYZ_mm;
XYZ_vx=XYZ_vx(1:3,:);
trajvox=diff(XYZ_vx')';
worldtovoxfactor=norm(trajvox)/norm(trajvector);
dist_vox=priordist*worldtovoxfactor*normfactor;
varargout{3}=dist_vox;
end