## 2 Related Work
### BIM Modeling and Visualization Using VR  
BIM is a \"modeling technology and associated set of processes to produce, communicate, and analyze building models\" used for the design, construction, and routine operation of buildings [24]. BIM has been used to improve product delivery, and systems based on BIM have been adopted to perform tasks such as clash detection in the design and construction industry [25], visualize and optimize schedules in four dimensions (4-D) [26], and to prepare quantity take-offs during the pre-construction phase [27]. As a BIM model can encapsulate large amounts of data and information accumulated in the design and construction phases, it is a good starting point for facility management. Many concurrent facility management systems such as ARCHIBUS use BIM to support the visualization of data and information in 3D spaces, for example, allowing users to click on a pressure gage in the model to access information such as the brand/model, installation date, purchase price, warrantee information, maintenance schedule, and other information. In this research, any information that is relevant to fire safety inspection is incorporated into the BIM model of the building and is associated with each piece of fire safety equipment. For crowdsourced inspections, it is necessary to take BIM models of commercial and public buildings to a cloud-based service that can enable visualization on mobile phones. The online visualization of BIM models is different from that employed in models running on local workstations used in the design and construction phases. An online BIM model must be significantly more lightweight (in terms of memory footprint and central processing unit usage) than a locally stored BIM model that may be more than 300 Mb in size. Until Internet service on 5G mobile phones is widely available, lightweight BIM data will be required to the model for mobile phones in order to improve the user experience. Moreover, all mobile phones do not use the same operating system (OS) and an online BIM model must be compatible with various OSs. For example, smartphones used by people in a building may use Apple iOS or Google Android, while the workstations in the fire safety management office might be running on a Microsoft Windows or Apple macOS operating system. It is imperative for the transfer of information on these platforms to be seamless. The system developed in this study uses the Forge Viewer platform to enable BIM visualization on the cloud. This platform was formerly known as Large Model View, since it allowed the handling of 3D models that were too large to run on Autodesk Design Review. Forge Viewer converts information from a simple vector format (SVF) to Web Graphic Library (WebGL) format for display on an Internet browser; this allows people with mobile devices that use any OS to view information without having to install a plug-in. WebGL is an application programming interface (API) that allows users to create 3D graphics in their device's web browser, regardless of the software package used and without having to pay royalty fees [28], and some researchers have used this API to visualize BIM models online. For example, [PERSON] et al. [29] developed a methodology for creating BIM model visualizations in three dimensions that combines the Industry Foundation Classes (IFC) data model using WebGL technology. In addition, [PERSON] et al. [30] developed a cloud-based system architecture that enables very large BIM models to be viewed, stored, and analyzed for purposes such as facility management. In order to help the building occupants to easily spot fire safety-related facilities, iInspect incorporates VR scenes along with the BIM model. Typically, VR is a simulated experience that allows users to become fully immersed in a virtual environment that could be similar to or completely different from the real world. Traditionally, a specially designed room with multiple large screens was required to create a VR environment.