Even in early human history, information from the Earth’s surface was presented in maps. In the course of technological progress, contents could be depicted with more and more geographical accuracy. Today, maps are not only needed for navigation, but also as tools to better understand spatial relationships. However, geospatial problems and questions are often 3D in nature, yet data is traditionally illustrated on 2D surfaces, like maps or computer monitors, posing cognitive challenges for users. Therefore, many tools are offered today to compensate for the lost third dimension. These include, among others, hill shading techniques that evoke the relief of a landscape through illumination effects [1
]. Another very common approach is virtual models visualized on a computer screen where the three-dimensional impression is received through rotation of the model [2
Another solution is the presentation of 3D objects and models in virtual reality (VR). In contrast to conventional visualizations of virtual 3D models, users are immersed in a computer-generated environment and information can be obtained much more intuitively and closer to reality. Head, arm, and walking movements are transferred to corresponding motions in the virtual space, letting the user immerse and decouple from reality without leaving his current position in reality.
The oxymoron virtual reality is defined as “a realistic and immersive simulation of a three-dimensional environment, created using interactive software and hardware, and experienced or controlled by movement of the body” [3
]. The term was first introduced by author Damien Broderick in his 1982 science fiction novel The Judas Mandala
. Further recent definitions are described in the literature by Dörner et al. [4
], Freina & Ott [5
], and Portman et al. [6
], which mostly describe VR in a broader sense, although some explicitly use non-interactive content.
This study examined the potential of VR for the representation of very large terrain data based on the Canadian fjord Clyde Inlet. The study proposed a workflow to represent large datasets in VR without reducing computer performance. Next to the degree of illusion and immersion, performance is a key factor for a pleasant VR experience. A low degree of performance not only frustrates the user but may also cause visually-induced motion sickness that can lead to symptoms of nausea, dizziness, headache, sweating, and, in worst cases, vomiting [7
]. As VR systems are much more demanding than any other computer visualization tool and low performances have such a negative effect, maintaining good performance is a great challenge for developers of VR applications [8
]. Many applications should also run on low or mid-end hardware to access a wide audience, thus inducing great trade-offs. The potential and user-friendliness of the application was further assessed during a user survey.
The project was carried out in 2017/2018 in cooperation between the Alfred Wegener Institute (AWI) of Helmholtz Centre for Polar and Marine Research in Bremerhaven and HafenCity University (HCU) Hamburg, Germany.
2. Related Work
Due to recent advances in hardware and software technology, virtual reality is becoming ubiquitous and accessible for the general public, as several companies have brought low-cost high-quality head-mounted systems to the market. However, technological progress and its accessibility are mainly owed to the wealthy video game industry that can effort to invest so much in pioneering industry [9
]. Therefore, many applications are designed for video games and, only recently, more and more other disciplines deploy VR. So far, VR is today successfully used for virtual surgery, virtual therapy, flight and vehicle simulations and cultural heritage [10
]. At HCU Hamburg, several VR projects have already been realized. The old town house of the city Bad Segeberg was presented as one of the first virtual museums for an immersive visit with the HTC Vive as head mounted display (HMD) [11
]. Two historical cities (including the surrounding landscape) were developed as VR applications for a virtual tour in past ages: Duisburg in 1566 [12
] and Segeberg in 1600 [13
]. Two religious cultural monuments are available as VR applications: the Selimiye Mosque in Edirne, Turkey [14
], and the wooden model of Solomon’s Temple [15
As can be seen, a variety of works about VR implementations can be found in current research works. However, with respect to terrain visualizations in VR, only a few related research papers are known. An overview on game engines and their possibilities to import and design terrains is given by Mat et al. [16
]. Further options and limitations of game engines for landscape visualizations are outlined in Reference [17
], including a representation of a small-scale landscape in Unreal Engine. Thöny et al. [18
] propose ideas for improving scientific terrain rendering with level of detail (LOD) algorithms and different rendering techniques, though none have been tested with real-world datasets. Applications of small-scale real-world terrain data using the game engine Unity have been proposed by Mat & Mahayudin [19
] and Wang et al. [20
]. While Mat & Mahayudin [19
] visualize an oil palm tree plantation to support the database management system helping decision-making processes, Wang et al. [20
] simply represent two research stations in Antarctica in their natural environment. A study about working with large-scale terrain visualizations is outlined in Reference [21
]. They propose a tile-based rendering system in combination with LOD and texture LOD algorithms to produce seamless presentations of large worlds with high rendering performance. However, this research concentrated on 3D GIS applications and was not implemented in VR. At this stage, no research work regarding large-scale terrain presentations in VR is known to the authors.
The results comprised the VR visualization of the terrain stretching from the head of Clyde Inlet until the continental margin of Baffin Bay. All in all, five different datasets were used to create the terrain above and below the water surface, with the best possible resolution of 5 m. Furthermore, several textures, locomotion modes, and measurement tools were adopted to interact and work with the terrain (Figure 9
, Figure 10
, Figure 11
, Figure 12
and Figure 13
). Figure 11
shows the quality of the virtually generated landscape (bottom) compared to the real fjord environment illustrated in a photograph (top).
Overall, no major loss of accuracy could be detected, as the processing of the digital elevation models yielded only minor inaccuracies of several meters. The import and scaling of the terrain in UE4 was also accurate as test measurements showed deviations of only 1 to 3 m.
The performance of the real-time visualization was tested on a laptop (Intel® Core™ i7-6700HQ @2.60 GHz, a NVIDIA GeForce™ GTX 1060, and 16 GB RAM) and a personal computer (Intel® Core™ i7-6700K @4.00 GHz, a NVIDIA GeForce™ GTX 1080, and 16 GB RAM). The application was running on both computers, although the laptop had a very high central processing unit (CPU) usage and the loading of tiles was not as smooth compared to the personal computer. We therefore assumed that the application would not run on mobile devices, such as tablets or smartphones, and was thus not suitable for low-end devices.
The performance on the personal computer yielded a frame rate of 44 frames per second (FPS), while navigating slowly through the virtual world. Ideally, a VR application should run at a frame rate that complies with the refresh rate of the head-mounted display, which is 90 Hz with the HTC Vive specification [33
]. Standard recommendations from literature suggest a frame rate of at least 60 FPS [9
]. Even though the recommendations were not met, stuttering or dropping frames could not be detected while navigating slowly through the terrain. However, when the speed was increased, stuttering was noticeable each time a new level was loaded, or the world origin was shifted. No motion sickness nor any other form of discomfort was identified by various test persons. To improve the frame rate, the computational power could be simply increased by using improved CPU’s and GPU’s or by checking and enhancing performance and profiling statistics of a rendered scene in UE4. More information on two rendering techniques regarding this application is given in Reference [25
5. Usability and Utility Assessment
To discover the benefits, as well as limitations, of VR visualizations, a user survey was conducted with ten participants representing the following professional fields: hydrography, geology, geography, archaeology, civil engineering, and, lastly, the tourist industry. The interviewees (age 30–50) had a variety of functions, such as professor, Ph.D. candidates, a graduate engineer, and a general manager, and worked for different universities, institutions, and authorities. Each participant used the VR application for about 30 min, followed by a qualitative questionnaire with four questions regarding the usability and six questions considering the utility of VR. The questionnaire and its evaluation are comprehensively documented in Reference [25
All participants perceived the application as very user-friendly and easy to use. The survey also provided a good overview of all functionalities, since they could be looked up in the menu. A good orientation was provided by a compass and a mini-map. Most importantly, no participant felt uncomfortable while navigating through the virtual world nor felt any form of motion sickness. The advantages of VR visualizations are versatile and different to each specific field. Yet, all disciplines received a better impression of the terrain compared to 2D visualizations. All measuring tools were also helpful to get necessary information from the terrain and to estimate the spatial dimensions.
For hydrographers, the quality of bathymetric data and its representation plays a crucial role. Since outliers in the data are very easily detectable in a three-dimensional environment, VR could act as a supportive tool for quality assessment routines. Lots of time can also be saved when outliers or hazardous material are easily identified. VR, furthermore, proved to be helpful for terrain analyses, especially considering backscatter investigations. Emitted sound signals that are backscattered from the seabed towards the hydrophone are not only investigated by their travel time but also by their intensity. Different intensities could provide information on the sediment characteristics as the intensity of the signal varies with the hardness, softness, and roughness of the seabed [34
]. However, the intensity also varies with the inclination of the terrain and the incidence angle of the signal being the strongest in nadir section and weakest in the outer sections. While the latter cannot be solved with VR, the inclination, however, can be investigated. As backscatter information is draped above the 3D terrain, correlations between sound intensity values and the slope of the terrain can be made. For geologists and geographers, VR could also serve as a helpful tool to intuitively capture measurements and information, such as the inclination of the terrain and the dimension of morphological landforms.
A VR application can also be used to support the exchange between scientists, such as biologists, geographers, geologists, etc., who work on the same project with the same dataset but at different physical locations. Within VR, everybody can work simultaneously and communicate while being physically miles apart. This feature, however, was not implemented for this project, but it was already implemented in other projects of HCU Hamburg, which are presented in Reference [12
For civil engineers, VR is also beneficial for the representation of terrain data. Since the presentation is very intuitive and self-explanatory, VR systems can be used to convince decision-makers or be displayed at civic participations showcasing new projects and reducing misconceptions. For the planning of constructions, VR could be implemented to show or hide various construction designs for decision-making processes and could be used for site selections.
Archaeologists receive a better impression for dimensions of sites, which is not possible when investigating simulations. Moreover, VR is regarded as a cost-effective tool to reconstruct places or buildings in 3D when the original site can no longer be visited. Virtual immersive reconstructions are, however, not only preferred over physical reconstructions due to financial reasons, but they also offer the possibility to investigate visual axes in a very easy way. Ancient visual axes are used to check assumptions, such as “Why would Romans construct their weir system in an Egyptian valley which is surrounded by mountains from which it is easily attackable?” Exploring the terrain in a virtual application will help understanding ancient decisions and current hypotheses. Moreover, weather conditions can be easily adjusted to observe sites with rain, sunlight, fog, snow, night, and so forth.
For tourism, VR is useful to demonstrate journeys so that potential travellers can receive a more in-depth perception of the trip. It will also be effective to showcase trips at fairs in order to attract potential customers.
Having listed numerous advantages and potential applications for different disciplines, VR applications programmed using the game engine Unreal Engine 4 still have severe disadvantages. A major disadvantage is the very limited possibility to import or export spatial datasets. Vector file formats, such as shapefile, are not supported, and raster datasets can only be imported in graphics file formats without spatial reference since no coordinate transformation algorithm is implemented.
The only way to provide a spatial link is to import raster datasets with the same extent, scale, and position as the terrain in UE4. However, currently, the greatest resolution of imported graphic formats is 8192 pixels, resulting in a very pixelated display when scaling the image over a large terrain. Individual objects can be placed onto the terrain with spatial reference, though only by taking the XY distance from the top-left corner of the terrain to the specific point (within any GIS software) and transferring the distance onto the terrain in UE4. The default coordinate origin in UE4 is the top-left corner, and the terrain must have the same extent in both the GIS software and in UE4. Using this method, coordinates within VR can be accessed, but this is by far very time-consuming and inefficient for most applications. Applying a coordinate transformation algorithm is generally possible, nevertheless it will arouse quite a challenge since the origin of the coordinate system in UE4 changes after an arbitrary distance for large terrains. To overcome this, one would have to use either small terrain sizes of less than 5 km × 5 km and disable World Origin Rebasing or initiate World Origin Rebasing manually, which is in fact very time-consuming, especially for larger terrains with lots of tiles.
Another disadvantage is the time-consuming workflow of the project, since all teleportation waypoints and normal maps must be set manually. The hardware setup can also be very tedious, as the HTC Vive Lighthouse tracking system–used for this project–with base stations has to be deployed in a room and an interaction area has to be calibrated (Figure 4