Online simulation is a relatively new control strategy for short term decision making for the control and management of processes in existing systems. In contrast to traditional "nonterminating" simulation, online simulation cannot use a transient phase to tune the models because the simulation models need to run very quickly and also need to deliver results right from the start. In this context, the initialization of such online simulation models represents a special problem. It requires mapping between the system-describing variables in the model and the available data in the real system. This paper examines two different methods of initialization. Special emphasis is placed on explaining the approach of parent model synchronization. Both initialization approaches are transferred to the context of analyzing and forecasting pedestrian flows in a public building. A first prototypical implementation in SLX is also briefly presented.