function ht_plot(ti, si, xs, ys)

ti = ti/180*pi;

if ti>=0
    Y = si/cos(ti) +1;
    X = si/cos(pi/2-ti) +1;
    
    if X>1e18
      X=1e18;
    end
    if Y>1e18
      Y=1e18;
    end
    plot([1 Y],[X 1], 'r','LineWidth',3)
  elseif si>=0
    Y = si/cos( abs(ti) ) +1;
    X = (ys-Y)*tan(pi/2-abs(ti))   +1 ; 
    
    if X>1e18
      X=1e18;
    end
    if Y>1e18
      Y=1e18;
    end

    plot([ys Y],[X 1], 'r','LineWidth',3)
  else
    Y = abs(si)/cos( pi/2-abs(ti) ) +1;
    X = (ys-Y)*tan(abs(ti))   +1;  
    
    
    if X>1e18
      X=1e18;
    end
    if Y>1e18
      Y=1e18;
    end
    
    plot([X 1],[ys Y], 'r','LineWidth',3)
end