# CAR-Tourist: An Integrity-Preserved Collaborative Augmented Reality Framework-Tourism as a Use-Case
## 3 Methodology and Proposed Architecture
### Marker-Less Collaborative AR  
The main objective of the CAR-Tourist app is to give AR experiences to tourists. Whenever the tourist needs assessment they can use the camera to receive guidance from the guide remotely. The guide receives the live video transmission from the user and the guide can add virtual objects and annotations to describe the landmarks. If the tourist needs guidance to reach a particular spot within the boundary of the visited landmark, the guide can add annotations to help the tourist reach the exact location. After the addition of different virtual objects and annotations. The final view is visible to the tourist through the CAR-Tourist app. The app consists of camera tracking, annotation editing, and the rendering of virtual objects in the real environment. Google ARCore is used to track the position of objects with the help of smartphones. This study used Unity SDK to render the virtual objects in the real environment. After rendering these virtual objects, the guide can modify their position and orientation. The guide can also add annotations in the real-virtual video transmission between the guide and the user. These annotations help the user to better understand and identify the landmarks. The guide can also add other virtual objects or remove them from the screen. As the CAR-Tourist app is a location-based AR application, it uses a camera sensor, gyroscope, and magnetometer to create a local map of the landmark and locate the tourist on that map. This map becomes global when shared with the guide for editing and modifying. If multiple tourists are present at one place, then one guide can assist multiple tourists at once by making a group of tourists visit together. All of them will receive the same information and details by using their own mobile devices, as depicted in Figure 3. This helps the guide to facilitate multiple tourists, saving more time.  
CAR-Tourist app based on markerless collaborative AR in other words location-based collaborative AR. In this AR system, the magnetometer is used to detect the orientation of the mobile device. The camera of the device is used to capture the live feed on which the virtual elements are imposed. Magnetometer enables the mobile to always know which direction is north. It is the key element of the proposed framework i.e., location-based AR app CAR-Tourist. GPS (Global Positioning System) is used to provide the correct Geolocation concerning time. The proposed framework's tracking technique is Inside-Out tracking, in which the camera and other important sensors are built into a device like a smartphone. The most important reason to use Google ARCore in our app is to provide motion tracking with the help of SLAM (Simultaneous Location and Mapping). SLAM gathers the data from the camera and other sensors like magnetometer, gyroscope, and light sensor to understand the real environment and correctly render the virtual objects in the real world [45].  
The general idea of SLAM is to build a map of an unknown real environment. This technique is widely used in robots and other AR-based systems. The building of a map and locating itself in it is the purpose of using SLAM. In our CAR-Tourist app, SLAM is used to build a map of the visited landmark so that the AR experiences are rendered accurately. Tourists' accurate location is dependent on two inputs. The first one is the data on the previous location of the user and the recent movements that occurred. The second dependency is on readings from the camera sensors of the mobile device. SLAM combines these data and readings through general probability distribution as presented below:  
\[P(Sx,L|A0-x,H0-x,S0) \tag{1}\]  
\[S0=Startingpointoftheuser \tag{2}\]  
\[A0-x=Setallobservationsofthelandmarks \tag{3}\]  
\[H0-x=Historyoftheradingsofchanginglocationonthemap \tag{4}\]  
\[L=Alllandmarklocations \tag{5}\]