# Augmented Reality and the Digital Twin: State-of-the-Art and Perspectives for Cybersecurity
## 3 Literature Review and State-of-the-Art
### Qualitative Results
#### 3.3.2 Where?--Main Application Areas
AR can make learning processes more involving, as well as increases training improvements with digital technology trends, such as the DT concept [50]. Combining DT and AR allows the visualization of digital data in a physical context that uses remote teaching concepts [33]. These teaching concepts are highly inclusive for students, even if they are not physically on-site. In a more business-oriented context, AR and DT are applied to enhance training and workplace learning. AR enables participants to perceive data provided by the DT that would otherwise not be available directly. The DT makes it possible to trace quality issues or predicting future stresses. All this information can be displayed via AR. For example, augmenting the real manufacturing environment with this additional information and process steps supports inexperienced operators in their learning process with step-by-step guidance throughout various scenarios. This setting enables an efficient, guided, learning-by-doing approach for workplace learning [51]. This idea is also picked up by applying AR to train staff members with visual manuals. For example, AR presents a machine's status data based on its DT and shows technicians how to maintain the machine [52]. [PERSON] and [PERSON] also use DT and AR for training [53]. The authors apply AR in combination with a DT to provide training and situational awareness in physical security systems, such as military installations or security command posts. The DT is a model of the site under consideration connected to sensors. AR is used to make suggestions determined by the DT (e.g., best maneuver routes, courses of action with minimal damage) easily accessible to security forces. **Cities, Transportation, and Energy:** For cities, one potential application area is construction. AR-DT technology is supporting the interaction with construction machinery, improving operation precision, as well as safety [35, 54]. In the transportation, or more specifically, in the aerospace sector, AR is a commonly applied technology [13, 57]. With the DT, AR becomes a vital tool to facilitate (predictive) maintenance of aircrafts [55]. An aircraft's DT collects data used for the analysis over a timeframe of the vehicle's lifetime or even its complete lifespan. Markers attached to the physical components allow synchronizing AR with the DT and displaying relevant information based on the DT's analyses. Thus, maintenance tasks become more efficient, and the optimal point in time to perform these tasks gets predictable. In the energy sector, combining AR with DT technology is used to monitor and analyze critical processes. [PERSON] et al. implement a DT of a wind farm, allowing users to analyze the complete farm within an AR environment [56]. The AR displays the wind farm landscape with all data required to plan necessary (predicted) maintenance work or coordinate contracts and customers. **General:** Besides the mentioned application areas, other application areas do not seem to have adopted the AR-DT combination, although many other areas could benefit from applying this combination. However, first, more general approaches [4, 34] and surveys [6] are fundamental to make the concept of using AR to visualize DT data more accessible for other application areas, as well. For example, [PERSON] et al. are using the combination for a real-time interaction with a 3D Printer [59].