# Full-Body Motion Capture-Based Virtual Reality Multi-Remote Collaboration System
## 1 Introduction  
Because of the prolonged COVID-19 pandemic, non-face-to-face technology is rapidly developing in all industries [1]. Accordingly, the demand for non-face-to-face remote collaboration technology has increased significantly [2]. In general, remote collaboration systems use webcam-based video conferencing systems such as Google Teams and Zoom [3]. However, these video collaboration systems provide limited visual information [4]. To overcome the limitations of existing video collaboration systems, virtual reality (VR)/augmented reality (AR)-based realistic collaboration systems are emerging [5]. According to the Immersive Technologies Market Research Report published by Transparency Market Research, the revenue of the global immersive technology market in 2020 was valued at 81.82 Bn. By 2031 and is expected to exceed 2.6 Tn. Moreover, it is expected to expand at a compound annual growth rate of approximately 38% during the projected period [6]. After a VR head-mounted display (HMD) was initially developed by [PERSON] in 1968, he began to research input-processing technology to control virtual physical movements [7]. Subsequently, graphic processing and 3D stereoscopic sound technologies were developed. To expand the multi-sensory experience, various companies have developed data gloves and haptic suits [8]. When a user's illusion of body ownership occurs through a multi-sensory experience, the sense of immersion in the virtual environment increases. Body ownership is the sense of belonging to the body in the field of cognitive neuroscience [9]. A representative experiment is the \"Rubber Hands Illusion\" experiment published by [PERSON] and [PERSON] published n \"Nature\" in 1998 [10]. This experiment proved that when we transmit complex stimuli such as sight and touch stimuli to thebrain, we can mistake other objects for our own bodies. In 2008, [PERSON] and [PERSON] demonstrated through a study using a camera and VR that users can feel the body of a character in the virtual world as if it were their own [11]. When the user can see the virtual body from a first-person perspective, the sense of body ownership increases [12; 13]. To create an avatar from a first-person view, using VR technology is necessary to build a virtual environment that can be simulated. A realistic collaboration system with VR technology can enhance the effects of collaboration through information sharing, an immersive sense of presence, and natural interactions [14]. However, most VR immersive collaboration systems use the inverse kinematic (IK) method with an HMD and controller [15; 16; 17]. In this approach, the joints of the upper skeleton of the elbow or shoulder follow depending on the position of the lower skeleton, such as the hand [18]. Because the actual elbow or shoulder value is calculated and used as the median value, the user's behavior cannot be the same as that of the VR character. In this study, we propose a motion capture-based VR remote collaboration system for improving the IK method. This system implements a virtual environment that can synchronize users and characters in VR in real-time through full-body motion capture. Body motion data are obtained via a motion capture device and applied to a virtual character in the Unity development engine. An environment is created from the user's first-person perspective so that the user can observe from the character's perspective in the virtual environment. When the user accesses the virtual environment, the height of the HMD is measured to synchronize the sizes of the user and character. The accuracy of the character size synchronization system is measured by obtaining the error value between the actual user's height and a character key through an experiment. Photon Unity Network 2 (PUN2) was used to remotely collaborate between virtual characters. When three people wearing motion capture equipment collaborated remotely with a remote partner, each user was given a different network ID.