vecvel.m

function v = vecvel(xx,SAMPLING,smoothtype)
%------------------------------------------------------------
%  FUNCTION vecvel.m
%  Calculation of eye velocity from position data
%  Please cite: Engbert, R., & Kliegl, R. (2003) Microsaccades
%  uncover the orientation of covert attention. Vision Research
%  43: 1035-1045.
%
%  (Version 1.2, 01 JUL 05)
%-------------------------------------------------------------
%
%  INPUT:
%
%  xy(1:N,1:2)     raw data, x- and y-components of the time series
%  SAMPLING        sampling rate (number of samples per second)
%  smoothtype      0: no smoothing
%                  1: 3-point smoothing 
%                  2: 5-point smoothing (default) 
%
%  OUTPUT:
%
%  v(1:N,1:2)      velocity, x- and y-components
%
%-------------------------------------------------------------
% modified by olaf.dimigen@hu-berlin.de, Oct-1-2013 for EYE-EEG toolbox

N = length(xx);             % length of the time series
v = zeros(N,2);

if nargin<3                 % default is 5-point smoothing
    smoothtype = 2;
end

switch smoothtype
    case 0 % no smoothing
        v(2:N,:)   = SAMPLING*diff(xx);
    case 1 % 3-point smoothing
        v(2:N-1,:) = SAMPLING/2*(xx(3:end,:) - xx(1:end-2,:));
    case 2 % 5-point smoothing (default)
        v(3:N-2,:) = SAMPLING/6*(xx(5:end,:) + xx(4:end-1,:) - xx(2:end-3,:) - xx(1:end-4,:));
        v(2,:)     = SAMPLING/2*(xx(3,:) - xx(1,:));
        v(N-1,:)   = SAMPLING/2*(xx(end,:) - xx(end-2,:));
end