## 2 Literature Review
### Combination of Building Information Model and Virtual Reality Technology  
In recent years, building information modeling (BIM) has been expanded to virtual reality (VR), which is an immersive environment generated from computers that can be adjusted and manipulated instantly by users. Different from the traditional BIM platform environment, VR can interact with various architectural components and provide users with a new visual space experience and project communication mode; thus, it is considered the most promising approach to the workflow quality of the overall Architecture and Engineering Construction (AEC) and Facility Management (FM) [22]. Moreover, real-time visual technology and virtual reality technology have been proven to provide an effective communication platform [1], and many experts and scholars have begun to study the integration of information model technology and virtual reality technology.  
[PERSON] et al. [12] used Autodesk Revit software to develop a plug-in capable of real-time rendering, which integrates the BIM model with virtual immersion technology through a head-mounted display, and allows design discussions at any time and place. In addition to providing detailed information about objects in the environment, it also enhances the rendering performance, navigation interface, and real-time interaction functions that BIM software lacks. Through the navigation interface, regardless of a lack of relevant background or professional knowledge, users can freely browse 3D scenes from the first-person perspective, and thus, even inexperienced users can easily interact with the model in a fast and intuitive manner when discussing design.  
[PERSON] and [PERSON] [23] proposed importing the BIM model into a collaborative visualization and simulation environment (COVISE). By integrating simulation, manipulation, and visualizations in a seamless manner, users could easily learn how to control the system, browse the virtual reality cave (VR-CAVE), and have a greater sense of presence when directly connecting the actual walking experience during browsing. With the above-mentioned increased sense of presence, users could be more integrated into the immersive environment, and the content of the space could be more clearly presented.  
While BIM software is usually run independently, the virtual environment and inter-activity capabilities that it lacks can be made up by combining it with the virtual reality technology; however, the model and underlying database must be updated constantly. In most VR environments, design changes cannot be displayed in a timely manner, as they lack an automatic and efficient data transmission method between the model and the data. By considering the time consumption and the complexity of the VR environment during the integration of simulation, reproduction, and visualization, [PERSON], [PERSON] et al. [22] developed a VR display information design that can instantly and automatically update information. In this design, the data are transmitted through cloud data based on a cross-platform cloud, where BIM data are synchronized in real-time in VR environments, and an innovative data protocol is entered.  
However, as a large number of resources and different professional backgrounds were required, the above relevant research indicated that the integration methods of virtual reality and BIM were still limited in many aspects. In order to solve the abovementioned integration problem, numerous relevant researches have been initiated to discuss the large number of information models contained in the BIM model, which could be imported into a game engine as a third-party platform to build a realistic virtual environment to achieve the best integration, and reduce the difficulties and restrictions encountered during development. In the following, this study further explores data integration for the Unity 3D game engine, as well as the cases related to developing the interactive environment functions.