function [obzor] = topozelem20(tx, t0, elemt,  obs)
topoc=xy2sf(obs,'r2');
dt=tx-t0;
%zjednoduseni - neuvazujeme casovou zmenu elementu.
%elemt=elem(1,:)+elem(2,:)*dt;
%fir=topoc(1);
%lambdar=topoc(2);
dt*86400
Mt=mod(elemt(7)+elemt(6)*dt*86400,2*pi)
exceanom=kepler(Mt,elemt(2),8);
%v=mod(2*atan(sqrt((1+elem(2))/(1-elem(2)))*tan(exceanom/2))+2*pi,2*pi);
v=2*atan(sqrt((1+elemt(2))/(1-elemt(2)))*tan(exceanom/2));
rE=elemt(1)*(1-elemt(2)*cos(exceanom));
XSr2=rotmat(3,-elemt(4))*rotmat(1,-elemt(3))*rotmat(3,-elemt(5))*[rE*cos(v);rE*sin(v);0]
S=GST0(tx)+mod(tx,1)*2*pi*366.2422/365.2422;
XSr1gt=rotmat(3,S)*XSr2-obs;
XSr1lt=rotmat(3,topoc(2))*XSr1gt;
XSo=rotmat(2,pi/2-topoc(1))*XSr1lt;
obzor=xy2sf(XSo,'o');
end