# Augmented Reality: Mapping Methods and Tools for Enhancing the Human Role in Healthcare HMI
## 1 Introduction  
The human ability in controlling machines through intuitive and natural behaviors has been fostered by even more user-friendly interfaces, including gesture-based systems [1]. Innovative solutions such as Augmented Reality (AR) and Virtual Reality (VR) play a key role in this respect, adapting interfaces to individual users/scenarios through the design of virtual environments powered by biofeedback such as human posture, motion [1], and emotion [2, 3]. AR was defined as \"the concept of digitally superimposing virtual objects on physical objects in real space so that individuals can interact with both at the same time\" [4]. As perceived by humans, AR is an innovative reality in which the perception of the real world is enriched and enhanced by new virtual sensory impressions, in a way that they coexist with the real world [5]. This augmented information is provided by sensory stimuli, either visual or auditory, entirely generated by a computer and then transmitted to the user through specific tools. One of the most used is Head-Mounted Displays (HMDs), which are helmets equipped with a monitor capable of displaying holograms of a real-time video stream in the user's field of view, such as smart glasses, or showing a completely artificial 3D-generated world, such as VR headsets [6]. In this perspective, registration and tracking are essential operations to integrate virtual and real information. Registration is the possibility of overlapping the 3D model on the real surface of the acquired object, for instance, considering the medical field, a surgical tool, or even an anatomical structure;tracking refers to the possibility of anchoring and updating the 3D model position to the actual object position over time. The coexistence of virtual perceptual stimuli and the real world is the substantial difference that distinguishes AR from VR, in which, instead, desktop computers, CAVE systems, or head-mounted displays entirely generate the experience, and the individual is entirely embedded in it [7]. The term Mixed Reality (MR) was first used by [PERSON] et al. [8], who defined MR as a super set of AR and VR, in which virtual and real-world information were fused together and displayed simultaneously in a single display within the Reality-Virtuality continuum. However, with the introduction of a new class of wearable displays, its meaning has changed over time, until MR is sometimes represented as a more sophisticated iteration of AR [9]. Nowadays, AR, VR, and MR technologies, also named \"Extended Reality\" technologies [10], are becoming increasingly common and, in particular, AR is considered one of the leading advanced technologies. AR technology originated from the military field [5], where it was mostly used for training in combat situations, preparing soldiers for non-replicable conditions outside actual combat, then was extensively used commercially in gaming and entertainment [11]. The substantial interest in AR is also witnessed by the explosion in the number of scientific publications in different research fields. In fact, the possibility of creating an ideal form of HMI is getting closer thanks to the rapid growth of AR technologies [12], providing more natural and efficient ways for a user to interact with a real or virtual environment. Papers show how AR has improved its efficacy and affected a significant number of application fields, such as design and planning [13], industrial implementation, education and training [14], healthcare management [15], and emergency services [16]. In particular, there is an exponential increase in scientific studies concerning AR applications in the area of orthopedics, on which this systematic review article focuses on. Application usability has paramount importance in sensitive fields such as medicine and healthcare and is core in the development of user-centered design systems [17]. AR represents a valuable solution for improving the transfer and consideration of information during surgery [18].