# The VIRTUALDiver Project. Making Greece's Underwater Cultural Heritage Accessible to the Public
## 3 Results and Discussion
### Santorini Case Study  
The platform is piloted for the submarine area of the Santorini caldera, but also for the Mediterranean underwater volcano, Kolumbo (Figure 10), and enables users to navigate virtually in environments accessible only by underwater vehicles and in cost-intensive research and scientific missions. Santorini is strategically targeted as one of the most touristic destinations in the world. The uniqueness and importance of the island are due to the active volcano, which has a history of 2.5  million years. Throughout its geologic record, several volcanic events sculptured Santorini, with the last major eruption, the Minoan eruption, having formed the current caldera 3600 years ago. The unique geomorphological scenery of the inner slopes of the caldera, which continues on the seabed (Figure 11), the particular settlement development, as well as the geological history and evolution of the volcano are the main themes of the created interactive narrative. Figure 8: Overall system architecture. Figure 9: The Interaction Component Library: List of Interaction Components created for the VIRTUALDiver platform accompanied by their respective icons. Specific user scenarios were created, highlighting the cultural heritage of the island using the Interaction Components that were developed for the platform. The scenarios include specific routes with stops where the user is able to receive multimedia material in various ways. The experience consists of three navigation modes: (a) Fly, (b) Walk, and (c) Diver Mode. In each mode, the user can navigate differently. Fly Mode acts as a way for the user to navigate over Santorini and aims to give  
Figure 11: Underwater photo, case in point of the marvelous underwater volcanic character of Santorini region, showing the “Atlantis steps” at the submarine area near Thirasia island (credits to [PERSON]). Figure 10: Map showing the exact location of the Santorini volcanic field within the Aegean Sea. Modified by [PERSON] et al., 2017 and [PERSON] et al., 2013 [50,51]. him/her the freedom to choose the POI he/she would like to interact with. For the development of the navigation system in Fly Mode, a system was developed that combines the sensors of the Oculus Rift S with the controls and tools provided by VRTK. The user targets the controllers in the direction he/she wants to move and activates the push of the virtual avatar towards it [52]. The speed for this movement is regulated in order not to provoke discomfort and dizziness to the user [53]. The user interacts with the POI using the VR controls combined with a pointer. Walk Mode allows the user to browse the Interaction Components and the multimedia content in the POI and move through the stages of each scenario. Finally, Diver Mode is a special case of navigation in an underwater environment, where the user can navigate and interact with. There, he/she can be informed about the flora and fauna of the seabed, examine shipwcks, and geological phenomena, as well as obtain relevant multimedia content (see Supplementary Materials). Initializing the application, the user has the option to navigate between different scenes, routes, and guided tours that are available by the platform (Figures 12 and 13). This option is added in order to ease the user's navigation through different POIs and is accessible at any time during the experience. In the example of the Oia-Kolumbo scenario, the user starts in Fly Mode (Figures 14 and 15), where he/she flies over Santorini. For the representation of the terrain, a special three-dimensional model is used, which is the result of research and standard data processing. To improve realism and, consequently, the user's immersion, water, volumetric clouds, high-resolution Skybox as well as the necessary soundscapes were added. Using the controls of the VR glasses, the user has the ability to fly over the island. Each POI is represented by a 3D Symbol accompanied by its interaction components for the user to identify and interact with.