# Extended Reality: Types and Applications
## 4 Hardware in Extended Reality  
### Main Types of Hardware in Extended Reality  
From the previously analyzed articles, information was obtained about the design features of the XR headsets. Extended reality includes virtual, augmented, and mixed reality technologies, but the method of visualization is different. Figure 7 graphically explains these differences. Virtual reality graphics are typically realized using head-mounted displays (HMDs), which show the simulation or game process in a virtual room/space not connected to the real world. It is possible to compare with a camera view in 3D computer games when a player moves his head. The sensors of the HMD headset detect it and send coordinates to the computer. A virtual camera sees the virtual game world or a computer simulation and rotates it by the same angle in a virtual room or space. The user sees a view that is not connected with a real world, but shown in virtual reality. Also, VR HMDs can be just a binocular display, without tracking of movement, or with tracking, that adds interactive features in visualizations. VR is widely used in computer games and simulators, for example, VR helmets with spatial controllers, Play Station VR (Sony Interactive Entertainment, Tokyo, Japan), or Oculus Rift (Oculus VR, Menlo Park, CA, USA). These helmets have the ability to track head and hand movements, allowing you to improve the game's interactivity and immerse yourself in virtual space. Nice examples of VR headset units are the Oculus Rift, Samsung Gear VR (Samsung Electronics, Suwon, Republic of Korea), and Google Cardboard (Google Inc., Mountain View, CA, USA). The main hardware components are provided below:  
* Main VR hardware: Head-mounted display (HMD). * Additional VR hardware: Motion tracking of the HMD, spatial controllers, gamepad, joystick, steering wheel, keyboard, or mouse. Augmented reality is a technology that can show more information using a real-world environment on a device with a camera and screen (smartphone, tablet) or an HMD headset with a camera and projector with a special prism, as shown in Figure 7b. A nice example of an AR headset is Google Glass. It can also be any mixed-reality headset. Also, in basic versions of AR, the camera and special markers are used to position a virtual object on the screen of the device [15]. * Main AR hardware: Head-mounted display or projector and RGB camera. * Additional AR hardware: Fiducial markers, ToF camera, or LiDAR. Mixed reality is a combination of augmented reality and a body tracking system. For visualization, it can use a projector with a prism like in AR glasses or an HMD headset  
Figure 7: Differences in methods of visualization. (**a**) VR and MR headset with HMD. (**b**) AR and MR headset with optical combiner [39]. with integrated cameras to capture the real world. Both are shown in Figure 7. The best examples of MR headsets are Microsoft HoloLens, Meta Quest, HTC Vive, and Apple Vision Pro. * Main MR hardware: Head-mounted display or projector and RGB camera. * Additional AR hardware: Fiducial markers, ToF camera or LiDAR. * Additional VR hardware: Motion tracking of HMD, spatial controllers, gamepad, joystick, steering wheel, keyboard, or mouse. Extended reality gives the operator a lot of ways to interact with virtual environments and objects. For headset tracking, it usually uses a sensor fusion from various types of sensors or their arrays. For example, the motion tracking system of the HTC Vive headset works through sensor fusion of inertial measurement units (IMU) and motion tracking using the Vive tracker system. The system defines the position using the time of arrival of the infrared (IR) signals, which are emitted as laser pulses from the base stations and detected by the photodiodes on the tracker [65]. The medium productivity and autonomy of autonomous headsets is the main disadvantage. Modern standalone XR headsets have a working time of about 2 h. It can be increased by increasing the battery, but this will negatively affect the weight and ergonomics of the device.