# 3D User Interface Design and Usability for Immersive VR
## 1 Introduction
3D interaction involves either 3D input devices (such as hand gesture or physical walking) or 2D input devices (such as mouse) mapped into a 3D virtual location. 3D UIs as the intermediary between the human and the machine become the medium where different users directly perform the tasks within the spatial context of a 3D domain. In carrying out different tasks, users' commands, questions, intents, and goals are communicated to the system, which in turn must provide feedback with information about the status and flow for the execution of the tasks [1]. As the interaction mode is an important aspect in a 3D environment, more natural interaction modes need to be explored. One type of NUI is the gesture-based interaction. When a person uses hands, arms, face, or body to convey some information, it is deemed as a gesture. In the first place, a gesture is recognized by tracking the motion of hands, arms, face, or body. Afterward, the gesture is interpreted and mapped to a meaningful action within the context of the application. [PERSON] [3] has identified the following advantages of gestural interfaces against traditional interfaces: (1) more natural interactions; (2) less heavy or visible hardware; (3) more flexibility; and (4) more fun. Gesture recognition can be used in many areas. Some of the application domains that employ gesture interaction are VR, gaming, desktop and mobile applications, telepresence, sign language, and robotics. This work only focuses on hand gestures. The UI design and usability depend a lot on the type of input device used in a 3D UI. Additionally, the display characteristics can affect 3D interaction performance, for example, when employed for VR, Head Mounted Displays (HMDs) block out the visibility of one's hands, body, and the overall surroundings. If the user cannot see the input device then using it with good hand eye coordination is a challenging task. Therefore, it is imperative to develop a user interface that does not require the actual visibility of the hands or the body, because the user will not be comfortable moving within a physical environment with this limitation. Among the variety of applications used, the desktop is the most commonly used environment used by billions of people every day. The metaphor is used widely on desktop computers and part of it is employed in the form of the home screen design of mobile devices. As VR becomes even more ubiquitous, a successful translation of the desktop environment from the computers and mobile devices to the 3D environment is imminent. Therefore, it is important to design and analyze the usability and user experience of various user interaction paradigms in an immersive VR desktop environment. Therefore, the objective of this work is to propose an answer to the following question, what is the most suitable interaction mode for the desktop environment in immersive VR? Consequently, a new dual-layered 3D UI is proposed that allows the user to perform common desktop tasks in a VR environment. The proposed 3D UI allows the user to visualize the content on a 360-degree wide field of view, in the form of multiple curved screens. The gaze mechanism is used to switch between the screen layers and the interaction layer. The interaction layer allows the user to perform simple tasks related to a desktop environment. In order to test the new 3D UI, three user interaction modes are implemented. Finally, a comprehensive user study is performed using a mixed methods approach to validate its usability and user experience both qualitatively and quantitatively. In order to study the feasibility of the proposed new 3D UI and draw conclusions about the suitability of the three different interaction modes for a variety of tasks in an immersive VR 3D desktop environment, the main contributions of this work are:  
1. Designed a novel dual-layer 3D UI that allows the user to interact with multiple screens portrayed within a curved 360-degree effective field of view available for the user. 2.