## 2 Related Work
### Indoor Real-Time Location System  
To locate iInspect users in real time, a real-time location system (RTLS) was used. iInspect will notify the user if any fire safety-related facilities are in nearby locations, and the user can view the information on his/her mobile phone and decide whether or not to perform an inspection. Accurate indoor RTLS is needed to inspire the crowd to effectively inspect fire safety-related facilities, as people will be more apt to take on an inspection job if they are notified by the system when some facilities are nearby, instead of having to search for nearby facilities on their own. There are several  
Figure 1: (**a**) Building information modeling (BIM) model view of a corridor. (**b**) Virtual reality (VR) photograph of the same corridor from the same perspective. technologies currently used in indoor RTLSs, and these technologies are discussed in greater detail in the following paragraphs. Radio frequency identification (RFID) has been adopted in many RTLS systems because it uses an inexpensive and flexible approach to identify objects and people. RFID is commonly used in applications for indoor settings, as its range of accuracy is 1-3 m; the global positioning system (GPS) has a lower range of accuracy (5-10 m), and it is more often applied in outdoor settings. For fire evacuation management, RFID would require all occupants of a building to wear RFID tags. It might be possible for an office building in which most building occupants are regular occupants; however, the majority of occupants of a shopping mall or a hospital visit only on an occasional basis. Ultra-wide band (UWB) technology has an accuracy that ranges from 0.1 to 0.3 m, giving it greater accuracy than RFID. In addition, its short response time makes it applicable to settings that are indoor or out-of-doors. The main drawback is the high cost for implementing a UWB solution, which can make its use unfeasible for fire evacuation management [32]. While vision analysis has advantages over RFID and UWB because no tracking devices need to be affixed to the people or objects being tracked, it does have some drawbacks. Vision analysis needs access to a voluminous amount of labeled data sets to use for training prior to implementation. In addition, efficient visual analysis is difficult to achieve in an environment that is dark or dusty, which makes it problematic for evacuations during a fire, when smoke and flames may drastically reduce the accuracy of a vision-based location system. Other systems--such as Bluetooth low energy (BLE), wireless local area networks (WLAN), Wi-Fi, ultrasound, lasers, radar, infrared, and magnetic marker fields--can be used for indoor localization, and each technology has benefits and drawbacks. In previous research on RTLS technology [10], the authors compared various systems reported in the literature (Figure 2) in terms of the range of accuracy, the affordability of the technology, and how easy the technology would be to implement. In Figure 2, the size and position of each are relative, as they are not based on precise values. In this study, the proposed RTLS uses indoor localization that is based on BLE technology, which enables contextual information to be conveyed between various connected devices (such as between BLE sensors, smartphones, and computers) using a minimal amount of equipment (with regard to the size and cost of the required infrastructure) [33]. As a BLE-based system has low power requirements to operate, the tracking devices will have a long lifespan. In addition, since the BLE devices used in this system are small, they are considered to be a wearable device (it can be attached to the hardhats or safety vests of construction workers, for example). Despite its potential to be used in a wide range of areas, researchers and professionals have not considered BLE-based RTLS for very many application scenarios.