Abstract
Due to their strong immersion and real-time interactivity, helmet-mounted virtual reality (VR) devices are becoming increasingly popular. Based on these devices, an immersive virtual geographic environment (VGE) provides a promising method for research into crowd behavior in an emergency. However, the current cheaper helmet-mounted VR devices are not popular enough, and will continue to coexist with personal computer (PC)-based systems for a long time. Therefore, a heterogeneous distributed virtual geographic environment (HDVGE) could be a feasible solution to the heterogeneous problems caused by various types of clients, and support the implementation of spatiotemporal crowd behavior experiments with large numbers of concurrent participants. In this study, we developed an HDVGE framework, and put forward a set of design principles to define the similarities between the real world and the VGE. We discussed the HDVGE architecture, and proposed an abstract interaction layer, a protocol-based interaction algorithm, and an adjusted dead reckoning algorithm to solve the heterogeneous distributed problems. We then implemented an HDVGE prototype system focusing on subway fire evacuation experiments. Two types of clients are considered in the system: PC, and all-in-one VR. Finally, we evaluated the performances of the prototype system and the key algorithms. The results showed that in a low-latency local area network (LAN) environment, the prototype system can smoothly support 90 concurrent users consisting of PC and all-in-one VR clients. HDVGE provides a feasible solution for studying not only spatiotemporal crowd behaviors in normal conditions, but also evacuation behaviors in emergency conditions such as fires and earthquakes. HDVGE could also serve as a new means of obtaining observational data about individual and group behavior in support of human geography research.
Highlights
Since virtual reality geographic information system (VRGIS) needs to process massive amounts of GIS data, and render virtual reality (VR) graphics at the same time, VRGIS applications at this time can only run on high-end workstations, and sometimes even require supercomputers
Under the conditions of 90 concurrent users and no packet lags, the personal computer (PC) client can maintain a rendering performance of approximately 300 FPS, while the all-in-one VR can only run at approximately 20 FPS, which could barely meet the requirements for a real-time user experience and interactivity
In order to solve the heterogeneous problems caused by various types of clients, and to support the implementation of virtual spatiotemporal crowd behavior experiments with large numbers of concurrent participants, the heterogeneous distributed virtual geographic environment (HDVGE) represents a feasible solution
Summary
Starting from the mid-1990s, with the advent of the virtual reality modeling language [1], the applications of the virtual reality geographic information system (VRGIS) in various fields have been rapidly developing [2]. A virtual geographic environment (VGE) is a VRGIS-based platform for multidimensional visualization, dynamic process simulation, and geocollaboration [3,4]. The second wave of VR has brought better graphics hardware and cheaper helmet-mounted displays (HMDs), greatly improving the availability and affordability of virtual reality (VR) technology. This will promote an upgrade of VRGIS, and facilitate the development of new theories and methods of geovisualization, geoanalysis, and geocollaboration
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