# Industrial Metaverse: A Comprehensive Review, Environmental Impact, and Challenges
## 3 Industrial Metavere's Architecture, Roadmap, and Core Technologies Overview
### Cross, Virtual, Augmented, and Mixed Reality  
The term \"extended reality\" (XR) refers to a group of immersive technologies, such as electronic and digital environments with projected and represented data. XR integrates virtual reality (VR), mixed reality (MR), and augmented reality (AR) [21]. Virtual reality (VR) is a computer-generated environment that simulates real-world sights and objects, giving the users the impression that they are fully immersed in their surroundings [22]. With VR headsets or other VR devices like the Oculus Quest 2 and HP Reverb, it takes the user experience to the next level. In a realistic setting, the user uses a system to control the simulated environment, making it a self-controlled environment. Thus, sensors, displays, and other characteristics like motion and movement tracking are used in VR to improve a virtual world. VR has wide applications in areas such as military, education, healthcare, entertainment, fashion, heritage, business, engineering, sport, media, visualization, construction, film, and telecommunications. The hardware used for VR includes input devices of numerous categories [23]. Three subcategories focusing on input provision for Head-Mounted Displays (HMDs) exist. Controllers are the main input category, while the second category consists of navigation devices, which allow the user to have a more intuitive moving experience. Navigation devices function as an input source for navigating through a virtual world while giving the users the impression that they are moving through infinite spaces. Body-tracking devices fall into the third group. In this case, posture-estimation techniques take into account both the users' hand gestures and the real posture of their upper or lower body. AR is a cutting-edge technology coupled with 3D technology features, which add a contextual layer of information to the user's sensory experience of the real world. In terms of functionality, an AR-enabled gadget with a camera--such as smart glasses, tablets, or smartphones--parses a video feed in order to recognize a tangible object in the user's surroundings, like a piece of equipment or a warehouse's layout. The link between the physical and virtual worlds is created by a digital twin, which is a 3D digital version of the object stored in the cloud. After that, it gathers data from both digital and physical items. Next, data about the object are downloaded from the cloud via the augmented reality gadget. Using markers or trackers like GPS, accelerometers, orientation, and barometer sensors, it overlays digital data on the object. A hybrid digital and real-world 3D interface is generated as a result. Because products are streaming real-time data to the cloud, users may move about and utilize gestures, voice commands, or touchscreens to interact with objects and environments [24]. MR is a term referring to a live direct or indirect view of a physical, real-world environment whose elements are augmented by computer-generated sensory input, such as sound, graphics, labels, or 3D (animated) models. It creates a new habitat where physical and 3D digital things co-exist and interact in real time by fusing the real and virtual worlds. Unlike VR, MR does not take users out of their natural surroundings. With a different kind of headset (one that does not block the outside world), the generated virtual scenes adapt to the users' actual views and alter them based on where they are [25]. Digital visual superimposed on top of the real world can be altered thanks to mixed reality (MR). One project that integrates MR at the moment is Microsoft HoloLens2. By incorporating sophisticated tracking techniques, MR makes use of AR tools to continuously track the user's actual views, position, and mobility. MR offers numerous advantages in a number of fields, including engineering, healthcare, entertainment, and education.