function [css center]=extr_symb(cch,tstart,xc0,yc0,q1,ddy,tstop)
% if tstop==0
%     tmax=50e3;
% else
%     tmax=tstop;
% end
tmax=tstop;
t0=1000;
[vv i_end] = min(abs(cch(:,1)-tmax));
[vv i_start] = min(abs(cch(:,1)-(tstart-t0)));
%nev=size(cch,1);
nev=i_end-i_start;
css=zeros(nev,6);
%tstart=124093;
dx=15;
dy=ddy;
%q1=4; %y displacement to compensate for center in heart symbols only
%xc0=35;
%yc0=37;
yedge=120;
j0=find(cch(:,1)>=tstart-t0 & cch(:,1)<=tstart+t0 & cch(:,4)>=xc0-dx & cch(:,4)<=xc0+dx & cch(:,5)>=yc0-dy & cch(:,5)<=yc0+dy);
xc=round(mean(cch(j0,4)));
yc=round(mean(cch(j0,5)));
j1=max(j0);
j2=length(j0);
css(1:length(j0),:)=cch(j0,:);
center=zeros(length(j0),2);
center(:,1)=xc;
center(:,2)=yc;
j=j1;
a=0.0;
while yc<yedge && j<i_end %nev
    %if(cch(j,4)>=xc-dx & cch(j,4)<=xc+dx & cch(j,5)>=yc-dy & cch(j,5)<=yc+dy)
    if((cch(j,4)-xc)^2+(cch(j,5)-yc)^2 <= dy^2)
        j2=j2+1;
        css(j2,:)=cch(j,:);
        k=find(css(:,1)>=cch(j,1)-t0);
        xcnew=round(a*xc+(1-a)*mean(css(k,4)));
        ycnew=round(a*yc+(1-a)*mean(css(k,5)))+q1;
        %if xcnew>xc
            xc=xcnew;
            yc=ycnew;
        %end
        center(j2,1)=xc;
        center(j2,2)=yc;
    end
    j=j+1;
end
css=css(1:j2,:);
css(:,4)=css(:,4)-center(:,1)+16;
css(:,5)=css(:,5)-center(:,2)+16;
t1=css(1,1);
te=css(end,1);

% if te-t1>tmax
%     kk=find(css(:,1)>=t1 & css(:,1)<=t1+tmax);
%     css=css(kk,:);
% end