  Waves in excitable media can be treated by a simple geometric theory. The
propagation velocity is assumed known and evolution of wave fronts is
determined by elementary physical principles (Fermat's principle, Huygens'
principle). Based on this geometric theory a fast computational method is
developed. By this method the distorting effect of the spatial grid is avoided.
The method is applied to the cases when a circular obstacle is surrounded by a
homogeneous and heterogeneous medium, respectively. The numerical simulations
show that the method is convenient, fast and reliable.
