## 2 Research Background  
### AR Application Cases for Construction Site Management  
Virtual Reality (VR) and Augmented Reality (AR) are types of Mixed Reality (MR) technologies that allow interactions of digital artifacts in conjunction with the real world through 3D digital projections [17]. In VR, users acquire 3D digital projection and related information in a fully immersed virtual environment. VR allows users to experience prearranged scenarios within which they can interact separately from the real world [18]. Conversely, AR superimposes 3D artifacts into the real world without setting up a separate virtual environment, allowing physical and digital objects to coexist and interact in real-time [19]. This superimposition between digital objects and the real world promotes intuitive information delivery [20]. In the construction industry, VR has been primarily used for educating personnel about safety hazards, quality checking, and installation procedures before their actual site deployment [21]. AR has been used to directly provide relevant information in the field by superimposing 3D models and relevant field data. Existing studies have shown that AR approaches can reduce times for information searches by as much as 50% compared to conventional management methods [10]. AR has also been shown to improve the effectiveness of progress monitoring, equipment maintenance, as well as safety and quality inspections [22]. The following provides summaries of existent AR systems in these areas:  
1. Progress monitoring Holobuilder (Holobuilder, Inc., Lake Mary, FL, USA) developed a construction monitoring service that enables collaborations between headquarters and field workers by providing images and videos of the site as an AR-based 360-degree visualization. To support the work efficiency of construction managers, [23] utilized an AR-based simulation system to provide information on design, construction, and maintenance processes. Furthermore, [24] developed a real-time 4D AR system that can provide AR-based 4D BIM information to construction managers to identify issues and address them before construction. In addition, [25] developed a machine learning-based object detection system to enable the monitoring of construction progress using an AR device. Equipment inspection and maintenance  
VIRNECT (VIRNECT, Co., Ltd., Seoul, Korea) developed an AR device to project the operations, maintenance, and assembly procedures of equipment at a construction site; an example of the use of this technology for quality and maintenance. SK Telecom (SK Telecom, Co., LTD., Seoul, Korea) developed a technology that uses a smartphone embedded with Trimble's Site Vision to provide on-site construction information and 3D blueprints. Additionally, Deutsche Bahn (Deutsch Bahn AG, Berlin, Germany) provided AR-based step-by-step repair processes to improve the efficiency of maintenance work at railway facilities. AR has also been explored for safety management. [PERSON] et al. [26] developed an AR system that provides visualization of step-by-step tasks and safety guidelines to enable safe work processes and procedural execution at construction sites. [PERSON] et al. [27] developed an AR-based system for the automatic evaluation of structural safety by examining displacements between tunnel constructions. [PERSON] et al. [28] developed an AR-based system that projects risk information onto smart glasses so that workers are aware of risk factors to avoid before accidents occur. In addition, XYZ Reality (XYZ Reality Ltd., London, UK) developed an AR-based remote sensing system to improve worker safety and ensure increased productivity by 40% compared to conventional productivity management methods. Furthermore, DEEP.FINE (DEEP.FINE Co., Ltd., Seoul, Korea) has been demonstrated to reduce inspection time and cost by up to 60% through a remote safety inspection service. These studies show that AR has been explored for its potential to improve construction-related tasks.