function C = CornerDet(X)
% CornerDet detects corners of traced outlines using the SAM04 algorithm. 
% The outline is assumed to constitute a discrete closed curve where each
% point is included just once.
% 
%
% INPUT: X (A traced outline forming a discrete closed curve)
%
% OUTPUT: C (The indices of X that consitute corner points)
%

n = length(X);

% Sets the parameters of the algorithm. Increasing D and R will give the
% same number of corners or fewer corners.
L = 80; % Controls the scale at which corners are measured.
R = 30; % Controls how close corners can appear.
D = 14; % The lower bound for the corner metric. Corner candidates with 
        % lower metric than this are rejected.

        
% Finds corner candidates        
d = zeros(1,n);
for i = 1:n
    if i+L <= n
        k = i+L;
        index = i+1:k-1;
    else
        k = i+L-n;
        index = [i+1:n,1:k-1];
    end
    
    M = X(:,k)-X(:,i);
    
    if M(1) == 0
        dCand = abs(X(1,index)-X(1,i));
    else
        m = M(2)/M(1);
        dCand = abs(X(2,index)-m*X(1,index)+m*X(1,i)-X(2,i))/sqrt(m^2+1);
    end
    
    [Y,I] = max(dCand);
    if Y > d(index(I))
        d(index(I)) = Y;
    end
end

% Rejects candidates which do not meet the lower metric bound D.
index = d < D;
d(index) = 0;
C = 1:n;
index = ~logical(index);
C = C(index);


% Rejects corners that are too close to a corner with larger metric.
l = length(C);
j = 1;
while j < l
    if abs(C(j)-C(j+1)) <= R
        if d(C(j)) > d(C(j+1))
            C = C([1:j,j+2:l]);
        else
            C = C([1:j-1,j+1:l]);
        end
        l = l-1;
    else
        j = j+1;
    end
end

if l > 1 && abs(C(1)+n-C(end)) <=R
    if d(C(end)) > d(C(1))
        C = C(2:end);
    else
        C = C(1:end-1);
    end
end


end