# Application of Three-Dimensional Vision Technology in Dance
## 2 Three-Dimensional Vision Technology
### Virtual Reality and Augmented Reality Based on 3D Vision Technology  
VR and AR, as promising next-generation display technologies, offer an attractive new way to perceive the world [37; 38; 39; 40; 41]. They are closely related to 3D vision technology (Figure 8) [42].  
VR technology is based on a 3D virtual scene simulated by a computer. The scene's content is usually modeled or recreated based on reality and is widely applied in the dance, entertainment, industrial manufacturing, military and aerospace, and teaching fields. While using it, the user obtains an immersive and realistic virtual world experience based on auditory, visual, and tactile sensations utilizing free observation from multiple viewpoints and human-computer interaction. VR technology combines many advanced technologies, such as digital image processing, artificial intelligence, sensing, and 3D vision technology. Among them, 3D vision technology is one of the critical technologies for users to feel immersive and is also one of the necessary conditions for VR system construction [43; 44]. During the external information acquisition, 80-90% of the information is from vision. The objects generally observed by human eyes are 3D, so the information acquisition in VR is mainly based on 3D information such as the object's shape, size, and proximity. To make the virtual world more spatial, it is important to construct high-quality scene models based on 3D vision technology [45].  
AR technology, also known as mixed reality and extended reality, applies virtual elements to the real world through computers to make the two interact more realistically and fittingly  
Figure 7: Holographic technology (Reprinted from Ref. [31] with permission from Elsevier 2024).  
in real time. AR is used in dance, entertainment, digital cities, medical care, military, and other fields [46]. Unlike the immersive experience of the virtual world in VR, AR not only displays computer-generated virtual objects but also requires it to be well integrated with various elements in the real world, realizing the superposition of information in the real scene and enhancing visual enjoyment. AR technology mainly relies on 3D vision technology, real-time tracking and localization technology, etc., and 3D vision technology is an essential platform for integrating virtual elements and real scenes [47]. In AR, stereoscopic visual simulation and computation based on the scene and the virtual model begin after identifying and scanning the real scene. The parallax map generated by the calculation is input to both eyes through glasses and other devices, and the final view is the stereoscopic visual effect of the real-time superposition between the virtual object and the real scene.  
Most 3D vision technologies in VR and AR are realized through head-mounted displays (HMDs) [48, 49, 50]. As shown in Figure 8c, the HMD is equipped with two small displays, which are directly connected to the video signal output of the computer to provide two images with parallax to the left and right eyes, respectively, and ultimately form stereoscopic vision under the combination of the brain [51]. The tracking sensing equipment in the helmet can capture information such as head movement and position in real time and transmit it to the computer to adjust the image screen in the display based on the real-time situation. However, helmet displays have many limitations. For example, only helmet wearers can obtain stereoscopic vision, and wearing the device for a long period can easily lead to fatigue.