## 3 System Design and Development
### Field Operator System  
As shown in Table 2, FOS consists of three modules: (1) Mixed Reality (MR) Simulation module, (2) Office Manager Information Management module, and (3) FOS Communication module. First, the MR Simulation module spatially aligns the virtual BIM elements on the real-world image in MR. This module also assists the user in moving the BIM object through the user's finger-pointing cue. The Office Manager Information Management module tracks the IDs of FOS and OMS devices and controls the dynamic IP address of OMS devices to connect them directly. Finally, the FOS Communication module creates \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Unit System** & & **Software** & **Hardware** \\ \hline \multirow{4}{*}{Field Operator System} & - & Window 10 (OS) & \\  & - & Unity 2020.3.25 (Simulation Development Tool) & HoloLens 2 \\  & - & Visual Studio 2019 (Integrated Development Environment) & Desktop computer \\  & - & Mixed Reality Toolkit Foundation v2.8.0 (HoloLens 2 Development Library) & \\ \hline \multirow{4}{*}{Communication Server} & - & Ubuntu 18.04 (OS) & \\  & - & Node.js 14 (Communication Server) & \\ \cline{1-1}  & - & WebRTC (Relay Server Development Library) & Workstation \\ \cline{1-1}  & - & Maria-DB 14 (Database) & \\ \hline \multirow{2}{*}{Office Manager System} & - & Window 10 (OS) & \\ \cline{1-1}  & - & Node.js 14 (Relay Server Development Library) & Desktop computer \\ \hline \hline \end{tabular}
\end{table} 
Table 1: System Development Environment. Figure 1: Overall System Architecture. MRC, the combined image of the real-world image of the field and the BIM virtual image, and sends it to the OMS. Furthermore, this module supports voice communication. To use FOS, BIM objects first need to be superimposed into the MR environment. For this, we used the spatial alignment method using QR codes. Virtual BIM objects are spatially aligned by matching the QR code images obtained from the real world by the HMD camera and retrieved from the database in the Communication Server, as shown in Figure 2.  
FOS is designed for users to manipulate virtual BIM objects with finger-pointing cues. This function uses the right-hand model of Mixed Reality Toolkit Foundation v2.8.0 provided by Microsoft (Figure 3a). This model identifies the 'Grab' gesture by tracking the thumb tip and index fingertip (Figure 3b). The user can move the BIM object from the grab state to the desired position. The grabbed object is released and positioned there when the user gestures to release the thumb and index finger, as shown in Figure 3c. However, when a user moves the BIM object, it is difficult to position it to the desired location. Thus, a function was created to move the virtual object along the surface to solve this problem. For example, a window on a wall moves along the wall surface. Figure 4 shows relationships between the Office Manager Information Management module, Communication Server, and Field Operator Information Management module. The Office Manager Information Management module is developed to prevent disconnection even if the IP address of the OMS device is changed. For this purpose, the Application Server and Relay Server of the Communication Server have been designed to manage FOS and OMS device IDs and the dynamic IP address of the OMS device. Usually, this communication device works only in the Wi-Fi zone; Thus, it has a spatial limitation because the IP address varies depending on the connection location. This study overcomes this limitation by applying WebRTC technology. WebRTC is a technology to find dynamic IP addresses.