## 3 Types of Augmented Reality Applications
### Marker-Based AR  
Marker-based augmented reality applications use a specific visual trigger to overlay digital content onto the real world [32]. These markers can be anything from QR codes to specific images or symbols. When the AR device's camera detects the marker, it generates a virtual object or scene that appears to exist in the real world [33]. Please note that while marker-based AR has many uses, it also has some limitations [34]. The AR device must be able to see the marker clearly, which means that lighting conditions, angle, and distance can affect the AR experience. Also, the application can only generate AR content when a marker is present, limiting its use in environments without prepared markers [33]. Marker-based AR systems generally have two main components: the marker and the AR application. The marker is a visual cue or pattern that is recognized by the AR system. It can be a QR code, 2D bar code, or a specific image. The marker must have a high contrast and unique design for easy identification. The application uses a camera (often a smartphone or tablet camera) to capture the marker. Then, it processes the image to identify the marker and calculates its position and orientation. Once identified, the application overlays digital content (for example, 3D models, animations, or videos) onto the marker in the real world, creating an augmented experience [35]. Marker-based AR applications have gained popularity in various industries and fields, some common examples are:  
* **Museums and Exhibits:** AR can enrich the visitor experience by providing additional information or interactive experiences. For example, an exhibit sign could include a marker that, when viewed through an AR app, shows a video or 3D model related to the exhibit [17]. The Museum of London's Streetmuseum App is an excellent example of this type of technology, which overlays historical images on modern London streets. Users point their smartphone cameras at designated locations, and the app uses geolocation data as a marker to display historical photos of that location. This gives users a unique, immersive way to learn about the history of London [11]. The work of \"Interactive AR for Tangible Cultural Heritage\" [18] describes the development of a marker-based AR system used to bring museum exhibits to life. The system uses custom markers placed near each exhibit, which visitors can scan using a smartphone app. When the app recognizes a marker, it overlays a 3D animation on the exhibit, providing additional context and information.
* **Retail and Marketing:** Businesses often use AR for marketing products. For example, a furniture catalog might include markers that, when scanned with a smartphone, show what the furniture would look like in the user's own home [19]. \"Virtual Try-On Technology in Retail\" work [12] discusses the development and implementation of a marker-based AR system for a virtual dressing room. Using markers placed on clothing items, customers can use a smartphone app to see how the items would look on them.
* **Maintenance and Repair:** AR can assist in complex repair tasks. For instance, an AR application could use markers on a machine part to overlay step-by-step repair instructions [20]. Currently, there are a lot of technologies that are capable of this, it is possible to use an AR system in order to aid aircraft maintenance technicians [21]. The system uses markers placed on various parts of an aircraft. When a technician points a tablet camera at a marker, the AR application overlays instructions or diagrams that guide the technician through the maintenance process.