# A UWB-Driven Self-Actuated Projector Platform for Interactive Augmented Reality Applications
## 2 Related Work
### Tracking Systems for Interactive Spatial Projection  
Perceiving augmented graphics in the physical world using visual feedback can be combined with the interacting ability using hand movements, leg movements, or body gestures. Different types of sensing technologies exist to afford interactions with projected screens. Camera-based detection is the most commonly used technique for tracking a user's limbs or body, thus enabling interaction with a projected screen. [PERSON] et al. [39], placed a Kinect camera in front of users to detect their hand pointing or footsteps toward or on a projected screen. In another study, a set of four projectors was placed under the floor [40], and a camera tracked the places where the user's hands and feet were in contact with the projected content. Interpersonal interactions for children with special needs were studied in [41], where a large interactive floor projection with cameras to detect the interaction was used. Using a camera-based technique guarantees a high detection accuracy, but users must stand within the camera's field of view, limiting their freedom to move. Users also must take care not to block the camera's view with their body so that cameras can keep tracking their hands [6; 25]. Such restrictions affect the intuitive interactions with the projected screen. To avoid this limitation, the camera and the projector must face different plans [39], which usually requires a particular setup and limits the interaction area.  
Another category of the tracking system is capacitive sensing, e.g., Wall++ [42], where walls can be modified to support interactions by spreading, over a wall of interest, an electrode array connected with a control circuit placed outside the wall to detect interaction coordinates. Additionally, the modified wall's electromagnetic sensing enables this system to detect the appliance's status and localize people indoors. This infrastructure requires excessive effort and cost to prepare multi-walls. Even though close interaction with the modified wall has good accuracy, it is not the same for far interactions, where accuracy decreases dramatically. The addition of different types of sensors over walls to detect interaction positions is described in [43].  
Infrared-based trackers like HTC Vive [44] supports room area tracking with high precision. Using this system requires special cautions when installing lithothouses choosing the proper height and orientation. Also, it requires removing or covering any reflective surface within the tracking envelope to achieve better tracking results. Using the HTCVive controllers has a dependency on the head-mounted display location, which must stay within the tracking area even though it is not used for interaction purposes. The optimal tracking area is placed on the center of the lightning houses' setup; therefore, tracking near the edges has relatively noisy measurements [45].  
We adapted UWB sensing technology to address the above-mentioned sensory limitations, which is considered one of the best available for indoor tracking [46]. UWB sensing supports utility tracking [47], so available tracking data are not restricted to one room. In this study, a UWB wireless network is used as a tracking system to navigate our USAP platform and enable interaction with the projected content. The ease of deploying UWB sensors supports expanding the interaction envelope systematically if needed. To our knowledge, we are the first to use a UWB positioning system in the room area to enable accurate interactions with projection-based augmented content over a dynamically changing user-defined projection screen utilizing different surfaces around. Then we propose the possibility to expand this concept to create an intuitive interactive environment.