1 A Heterogeneous Distributed Virtual Geographic 2 Environment for Crowd Evacuation Experiments 3

Due to their strong immersion and real-time interactivity, helmet-mounted VR devices 13 are becoming increasingly popular. Based on these devices, an immersive virtual geographic 14 environment (VGE) provides a promising method for research into crowd behavior in an 15 emergency. However, the current cheaper helmet-mounted VR devices are not popular enough and 16 will continue to coexist with PC-based systems for a long time. Therefore, a heterogeneous 17 distributed virtual geographic environment (HDVGE) could be a feasible solution to solve the 18 heterogeneous problems caused by various types of clients, and support implementation of virtual 19 crowd evacuation experiments, with large numbers of concurrent participants. In this study, we 20 developed an HDVGE framework and put forward a set of design principles to define the 21 similarities between the real world and the VGE. We discussed the HDVGE architecture and 22 proposed an abstract interaction layer, a protocol-based interaction algorithm and an adjusted dead 23 reckoning algorithm to solve the heterogeneous distributed problems. We then implemented an 24 HDVGE prototype system focusing on subway fire evacuation experiments. Two types of clients 25 are considered in the system, PC and all-in-one VR. Finally, we evaluated the performances of the 26 prototype system and the key algorithms. The results showed that in a low-latency LAN 27 environment, the prototype system can smoothly support 90 concurrent users consisting of PC and 28 all-in-one VR clients. HDVGE could serve as a new means of obtaining observational data about 29 individual and group behavior in support of human geography research. 30