## 5 Conclusions  
In this study, an LOS analysis technology that can be applied to 3D models was developed using ray casting technology, which can emit virtual rays and extract the point intersecting with the rays. The developed technology was applied to the Samdo mine site in Samcheok, Gangwon-do. Along with LOS analysis, we proposed the concept of SCI and were able to extract points with a relatively wide communicable area. Based on the analysis of the underground mine 3D model, ZigBee-based IoT devices were installed in areas with high SCI. After installing the first device, LOS analysis was performed at that point, and the next device was installed at a location within the communicable area and with a high SCI. A total of 29 vibration measurement devices were installed. Owing to monitoring, most devices were able to acquire and transmit data well, as the LOS between communication devices was well connected. As underground mines are dark and determining the exact location is challenging, such preliminary analysis must be performed based on 3D models. Suggesting an optimal installation point for communication devices in advance can be of great significance in the field. This not only ensures good communication between devices but also reduces unnecessary investigation time in the field. To utilize this research more universally and achieve commercialization in the future, the computing speed must be improved, a more reasonable SCI must be proposed, and the refraction and reflection of electromagnetic waves must be considered. If the technology proposed in this study is linked to existing GIS software, user convenience and visual effects can be improved further. If the propagation model or strength changes depending on various parameters are considered in the tool, more detailed location suggestions for communication devices will be possible. The number of 3D models of underground mines continues to increase, and the construction of communication networks in underground mines is of prime importance. Therefore, this study is expected to be useful to provide guidance regarding the setup of communication networks in underground mines. If this research is further improved, and its versatility improves, it can contribute to improving worker safety through the construction of smart mines.  
Conceptualization, S.-M.K.; formal analysis, W.-H.L.; methodology, S.-M.K.; software, W.-H.L. and S.-S.H.; writing--original draft, W.-H.L. and S.-M.K.; writing--review and editing, S.-S.H. All authors have read and agreed to the published version of the manuscript.  
This work was supported by (1) the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2023-00213956) and (2) Energy and MineralResources Development Association of Korea (EMRD) grant funded by the Korean government (MOTIE) (data science-based oil/gas exploration consortium).  
**Institutional Review Board Statement**: Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the information protection of the mining company that provided the data.  
**Conflicts of Interest**: The authors declare no conflict of interest.