function lmk = landid(x,t,p)

%function lmk = landid(x,t,p)
%
%Graphical landmark identification
%
%INPUT
%   x: data matrix (n x m)
%   t: time grid (1 x m)
%   p: number of landmarks per curve (scalar)
%
%OUTPUT
%   lmk: landmark matrix (n x p)
%
%NOTE: This routine draws each curve on X so you can manually identify the
%       landmarks by clicking on the plot. Note that X is not necessarily
%       the data matrix to be registered: in many cases it's easier to spot
%       landmarks using first or second derivatives.
%      More specifically, this routine assumes that your landmarks are
%       zero crossings, so it draws a horizontal line at y=0 for better
%       visualization.
%
%No external routines are called.

%Checking input consistency
[n,m] = size(x);
if length(t)~=m
    disp('Dimensions of T and X are inconsistent')
    lmk = [];
    return
elseif size(t,1)==m
    t = t';
end

lmk = zeros(n,p);
for i = 1:n
    plot(t,x(i,:),t,zeros(size(t)))
    hold on
    for j = 1:p
        title(['Curve ' num2str(i) ': click on graph to identify landmark ' num2str(j) ...
               ' of ' num2str(p)])
        [lmk(i,j),y] = ginput(1);
        plot(lmk(i,j),0,'ro')
    end
    hold off
end