function fidBase = FindFidBase(ecg, q, s, orientation)
% FindFidBase.m
% Author: Alexander Khaustov; alexander dot khaustov at gmail dot com
% Copyright (C) 2008 St.-Petersburg Institute of Cardiological Technics (Incart), www.incart.ru
% This software is released under the terms of the GNU General
% Public License (http://www.gnu.org/copyleft/gpl.html).
%
% basic fiducial point - middle of the maximum front between Q and S; to be
% improved by adjustment later
fidBase = zeros(1,length(s));
for i = 1:length(s)
[startI endI] = FindFront(ecg(q(i):s(i)), orientation);
startI = startI + q(i) - 1;
endI = endI + q(i) - 1;
% [m fidBase(i)] = max(abs(alt_series(ecg(startI:endI)))); % quite unstable, changed that
% fidBase(i) = fidBase(i) + startI - 1;
half = 0.5 * abs(ecg(endI) - ecg(startI));
for j = startI:endI
if abs(ecg(j) - ecg(startI)) > half
% closer to half between j and j - 1
if (half - abs(ecg(j - 1) - ecg(startI)) > abs(ecg(j) - ecg(startI)) - half)
fidBase(i) = j;
else
fidBase(i) = j - 1;
end;
break;
end;
end;
if (fidBase(i) == 0)
fidBase(i) = startI;
end;
end;
return;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [startI, endI] = FindFront(ecg, orientation)
% front with maximum amplitude and desired orientation
[ma maI] = max(ecg);
[mi miI] = min(ecg);
if (maI == miI)
startI = 1;
endI = length(ecg);
return;
end;
if (maI > miI) == orientation
startI = min(miI, maI);
endI = max(miI, maI);
elseif (orientation == false)
[pre preI] = max(ecg(1:miI));
[post postI] = min(ecg(maI:length(ecg)));
if (pre - mi > ma - post)
startI = preI;
endI = miI;
else
startI = maI;
endI = postI + maI - 1;
end;
else
[pre preI] = min(ecg(1:maI));
[post postI] = max(ecg(miI:length(ecg)));
if (ma - pre > post - mi)
startI = preI;
endI = maI;
else
startI = miI;
endI = postI + miI - 1;
end;
end;
if (startI == endI)
startI = min(miI, maI);
endI = max(miI, maI);
end;
return;