# A UWB-Driven Self-Actuated Projector Platform for Interactive Augmented Reality Applications
## 2 Related Work
### Mobility Levels of Projection-Based AR  
Researchers in [23] summarized the mobility levels of projection-based AR and divided them into four main categories: Environmental projectors, moveable projectors, hand-held and body-worn projectors, and self-actuated projectors. Environmental projectors are confined to one location with or without the ability to steer them to augment graphics over one or multiple surfaces indoors. [PERSON] et al. [24], presented an example of a fixed projector installed to support manual component assembly; this technique reduces worker error in assembly, especially when training a new worker or assembling a new board model. A steerable type effectively augments multi-surfaces; in [25; 26], the researchers proposed a technique for registering suitable projection surfaces, making it easier for the user to display the graphical content. These environmental projectors suffer from a limited projection area, which is usually not more extensive than a room, which has moved researchers to examine more portable solutions. Moveable projectors are commercially available through different manufacturers. One example is from the Hachi company [27], whose latest interactive projector allows the user to interact with the displayed augmented screen on a floor or wall, depending on how the projector is set up. Users could carry it and place it at any location. Even though the mobility increases, the user still needs to place the projector in different locations. For more flexibility, hand-held and body-worn projectors are explored in [28; 29]. Combining a pan-tilt actuated projector with the Hololens AR headset enlarges the display field of view [30], where the local augmented display is projected onto the physical world, then various levels of content's manipulation and sharing are possible. For these projectors, the user must have the projector attached to their body when augmenting a surface is a simple task by directing the projector over that surface; however, hand-held and body-worn projectors cause a burden on the human body that could exhaust the user, mainly if used for a long time. A self-actuated projector (SAP) can navigate on its own. Usually, a robotics platform is used to provide the required mobility. Tripon [31] is a commercially available projection robot that can project an 80-inch screen from 3 m, and the user can control its movement and change the projection parameters via mobile application. Researchers propose using SAP to scan for the best projection walls [32], allowing humans to better perceive the augmented content. Other studies propose SAP's usage to guide users reaching their destination by providing visual clues over different surfaces [33; 34]. Following the same concept, human aware path planning has been proposed for a ground robot that can navigate to a target position and avoid harming users if they stand in the projector's throw field [35]. Besides, the authors propose SAP using image-based tracking for museum-related applications. However, several ambiguities emerge: How can users perceive interactions with such a platform? Where are interactions performed? How can users optimize the interaction location? The same study considered the robot as an initiator that provides augmented information for preplanned places and neglecting the fact that humans may need to ask for supplementary information. Designing an SAP platform in a dynamic environment, such as a museum, requires a focused understanding of human needs and detailed interaction practicality testing. Like ground robots, flying robots can work as hosts for the projector unit [36]. Drones were used to support indoor and outdoor interactive displays [37; 38]. In [37], the user stood under a fling robot and interacted with projected content around them using hand gestures. Using drones has its safety concerns, especially when flying indoors with static and dynamic obstacles. It is obvious how an SAP platform moves projection-based AR beyond room boundaries.