# Full-Body Motion Capture-Based Virtual Reality Multi-Remote Collaboration System
## 4 Experiments and Results
### Character Scale Synchronization  
In Figure 8, A stands for User A's Height, B stands for the character height, C stands for the HMD height, and D stands for the character eye height. The value of A is calculated from the values of C, B, and D using a proportional formula. The basic eye height value D of the virtual character is divided from the height value (Localposition.y) C of the HMD worn by the user. Through this, the ratio difference between the HMD's height value and the character's eye height value is calculated. This ratio difference value is defined as the scale value (C/D). After that, the HeadEnd component is applied to the end of the character's head. If measuring the HeadEnd LocalPosition.y, the character's height B is measured. Then, by multiplying the scale value by the height value B of the character's head, the actual user's height value A can be obtained. If the size of the character is adjusted up to the defined height of A, the heights of the user and character are synchronized. There are two further issues to consider. First, it is necessary to adjust the character size to match the actual camera position of the HMD (user's eye level) and character's eye level. Second, after synchronization, the virtual camera should follow the position of the character's eyes. Figure 7: Remote collaboration system demo. Unity's basic unit is 1 m. The height of the basic character is 1.8 units, so when converted to m, it becomes 1.8 m. As shown in Figure 9, if the height of the user wearing the HMD is 1.7 m, the user's gaze rises by as much as the gaze of the character (who is 1.8 m) by the retargeting process. Because a user with a height of 1.7 m corresponds to a first-person view of a 1.8 m character, there is a difference between the real and virtual movements. Therefore, actions such as grabbing an object in the virtual environment cannot be precisely performed. After the retargeting process, the size of the character in VR should be converted to the same size as the real user. Figure 10 illustrates the task of adjusting the character to have the same height as the user's body. Figure 8: How to synchronize character scale according to user body information. Figure 9: Existing character size synchronization method. Experiments were performed with an Oculus Rift S Perception Neuron motion capture device. Eight participants experimented at the same location. The experiment first measured the actual height of the participant on the wall using a T-pose motion with an automatic extensometer. Second, the user wore motion capture equipment and went through a calibration process. Then, they put on the HMD. Next, they followed instructions to connect to the virtual system (connect to the photon server to connect to the network, and then connect through avatar selection and room selection). Subsequently, the character height was synchronized using the same T-pose as when measuring the height from the wall. The participants repeatedly performed the same motion for measurement ten times. After wearing the motion capture device, they faced the front of the measurement system and stayed in the T-pose posture for 3 s. Then, the height of the HMD was used to calculate the height of the user. The experimental participants consisted of six males and two females in their 20s and 30s (six in their 20s and two in their 30s). All participants had VR experience but no experience with wearing motion capture equipment and HMD equipment simultaneously. Table 3 shows the average error values obtained by subtracting the key value of the character as synchronized and changed when connecting 10 times in VR from the actual key. The average error of the experimenters was 0.465 cm. The experimenter with the largest difference showed a difference of 0.89 cm, whereas the experimenter with the smallest difference showed a difference of 0.15 cm. Using the proposed system, it can be confirmed that the error in the character's body size was less than 1 cm on average when the user's body scale was synchronized.