# Developing a BIM-Based MUVR Treadmill System for Architectural Design Review and Collaboration
## 3 System Framework  
This study proposed a BIM-based MUVR treadmill system to offer high-level immersion in design review and collaboration in the design stage. Figure 1 displays the system framework that consists of four core modules: (1) BIM model, (2) VR platform with interactive functions, (3) VR headsets and treadmills, and (4) MUVR server. It is computationally intensive if starting with a building model built by BIM software because many hidden faces and duplicating vertices are contained in BIM models. Thus, before importing a BIM model into the VR platform, the BIM model should be optimized by the computer graphic program's previsualization process. In other words, the BIM model needs to be fully optimized so that it can become computationally light-weighted with low poly-geometry, minimum overlapping faces and vertices, and minimum repetitive textures to reduce the file size and ensure smooth VR interactions without clashes. After the geometric optimization, the BIM model is imported into the VR platform to become the VR model. Several criteria must be fulfilled to establish a realistic virtual environment, including the real-world immersive experience, realistic object texture, and lighting effect. The VR model is further optimized for the lighting performance, such as prebaked lighting effects (e.g., normal map or ambient occlusion map) to produce the surrealistic rendering quality. Then, a pair of VR headsets and hand-held controllers are adopted for virtual displays and system manipulations, respectively. Regarding human locomotion, a pair of omnidirectional treadmills are integrated into the VR platform to offer users the walkthrough capability in the virtual environment without physical space constraints. All these devices are mutually supported and compatible with the VR platform. Finally, a synchronization system was developed to support multiuser interactions in the virtual environment. The system adopts the client-server model to facilitate multiuser interactions. As such, an MUVR server was provided to connect the network of other workstations (i.e., users) to access, hold, and distribute the requested information to clients over a local area network. Due to its high processing power and sufficient random-access memory in managing the massive load, the server takes a vital role in optimizing the synchronization performance between multiusers, offering users stable and reliable MUVR experiences. Four interactive functions were developed by intensive coding and programming to enhance architectural design review and collaboration effectiveness. The functions are tailor-made features that facilitate architects to review the design with their team members interactively. The first function is the primitive creation with object manipulations. This tool allows different objects with standard shapes, such as cubes, rectangles, spheres, and arrows, to be created in any dimension in the virtual environment. The objects created can be relocated anywhere or any direction by users without limitations. This tool aims to unlock user creativity during the design review process. Architects can also review different design options with their team members, making decisions efficiently and less costly. The second function is the freeform annotation tool. Annotations can be created on any object or even in the air of the virtual environment by pen-style mark-ups. Different brush sizes and pen colors can be chosen to perform better notetaking and sketching effects when discussing design detailing. These functions can be done by employing the line renderer component of the software to create lines synchronized in real-time between multiusers. The third function is the measurement tool. This tool offers quick quantity take-off in the virtual environment, and a virtual indicating line is provided so that the starting point can be more accurate. This kind of freestyle measurement (i.e., in any direction, x, y, or z) would not be possible in any 2D or 3D authoring software.