Design and implementation of an interactive virtual library based on its physical counterpart

Though there is evidence that libraries have been to existence as early as the \(7^{th}\) century BC, as per the example of the Ashurbanipal Library (Brosius 2003), it is only recently that the physical library lost its role as the main resource of information (Aabø et al. 2010). The invention of the internet revolutionized the way to access and distribute information. Libraries are adapting and are using digital technologies in order to continue being a hub of structured information, but the lack of an actual place that users can meet, makes it challenging to keep their role as a community hub, or a place of social interaction (Massis 2015). Already, a number of immersive educational tools are available, and libraries should begin investigating Virtual Reality (VR) platforms for their services. The main objective is to develop services that are both user centered and digitally enhanced. A virtual library needs to be a community hub, a space that is persistent and dynamic where people can meet to collaborate, discuss and exchange ideas and information.

Virtual Reality is an emerging technology that allows people to experience artificial worlds with an extreme level of immersion (Bowman and McMahan 2007). Recent advancements in technology have introduced more realistic and augmented experiences; the substantial improvements of the VR headsets allow people to visualize 3D scenes with remarkable clarity and realism. VR systems have become more accessible over the last decade due to the the substantially reduced costs, the massive advances in graphics, and the exponential increase in computing power (Slater 2018). Indeed, these systems now cost less and hence have become more affordable to a wider range of entities and people, including home users as well as elementary, high school, and university students. In order to evolve in parallel with this technology, it is essential for library systems to be upgraded and hence actively participate in this virtual revolution. More and more people, especially the youngest generation, are becoming familiar with VR applications, which are already used for both educational and entertainment purposes (Hamilton et al. 2021). Libraries should therefore enhance their current services within the framework of a virtual world, so as to be in line with the current technological trends. As the Metaverse - a post-reality universe, a perpetual and persistent multi-user environment merging physical reality with digital virtuality (Mystakidis 2022) - is becoming more and more apparent, a revolutionary change is expected regarding the general understanding of education and social relationships. Developing educational tools offers tremendous learning benefits to people with with various disabilities, compared to more traditional methods. It is believed that, the design and development of a VR library in the Metaverse can be the community hub that the society needs. The first step in any virtual environment is the design and development of a virtual platform, where users can connect and interact through a Graphical User Interface (GUI) or a virtual agent. Given that many libraries are related to the architectural history of the building in which they are hosted, the use of a digital replica would help in its preservation. That could develop into a digital twin which could ultimately become a fully functional, dynamic counterpart of a physical library, with real-time data exchange.

The first formal definition about digital twins was given by Michael Grieves (Grieves 2014), that is described as a digital version of a pre-existing or planned physical object. It has been shown that digital replications of physical entities enable data to be seamlessly transmitted from physical to virtual worlds. Digital twins facilitate the means to monitor, understand and optimize the functions of all physical entities and provide people continuous feedback to improve quality of life and well-being (El Saddik 2018).

In this work, the needs and expectations of library users in the development of a virtual library, are investigated. In this case the Limassol Municipal University Library, accommodated in a Cultural Heritage Protected Building, was selected. This library is part of a public/ state University, but, originally was and still remains a Municipal library. Based on that, an immersive VR platform, was developed, in the broader perspective of digital twins within the Metaverse. In particular, a perceptual study (see Section 3) was conducted (\(n=70\)), to examine and understand the reasons why people would physically visit a library, the frequency of accessing resources in-person or online, and how satisfied they are with the available library services. This perceptual survey also explored the user’s experience in VR, and their requirements and expectations in the design and development of a virtual counterpart. The aim was to define a persona for a potential VR library user, relating to information such as background and experience in VR, with the ultimate target being to set the foundations for the design and development of future VR libraries. A number of suggested services which users believe are essential in virtual libraries, were documented and a virtual equivalent to a library, was implemented, demonstrating five case scenarios: a virtual tour of the library; book lending; seminar organizing and attendance; group study/meeting room; booking meeting with mentor. In that manner, library users can explore the emerging technology and observe its potential use as an educational and social tool.

In addition, this work paves the way for the 3D virtualization of libraries, showing the impact VR can have in the resurrection of libraries as social hubs; this has been achieved through the process of accurate digital reconstruction of the building. VR libraries can rectify the weaknesses of physical libraries, and further enhance their services through the use of VR technology. Services can be delivered in parallel 24/7, in a multi-user VR environment, which can eliminate physical queues, waiting as well as commuting time and cost. Capacity and accessibility issues can also be easily overcome, while work concentration can be improved and distractions minimized. The benefits of the latest technological trends can encourage physical library authorities to adopt the VR library concept and through that, attract the younger generation and hence preserve the traditional characteristics of a library, in the digital era. Understanding the potential users of the virtual library and identifying the scenarios in which the library could be used for, can offer substantial benefits to both the researchers in the VR domain, as well as to the library systems themselves. A library should be an organization that pioneers the use of new technology, and more specifically VR-based services, for the user experience to be impactful and of the highest quality.

This paper is an extended version of the previous work conducted by Iakovides et al. (2022). The aim was to create a proof-of-concept, of a more engaging and interactive 3D virtual environment that would provide a rich and fulfilling experience to the user. This allows the users to be largely autonomous with a high degree of agency in the navigation and use of the digital library. In order to achieve that, various essential features were incorporated into this work. More specifically, animated Non-Player Characters (NPCs) coupled with the appropriate materials, lighting, color and textures helped augment the aspect of realism and interactivity within the concept of a multi-user environment and enhanced the scene authenticity. 3D audio and the doppler effect were adopted to provide a surrounding sound experience that elevated the impact and quality of this VR experience, beyond its visual counterpart. Also, different methods and techniques providing continuous user interactivity and feedback were employed throughout, such as raycasting and GUI button highlighting, assisting the user and clearly indicating the selectable and interactive objects. At the end, a user evaluation study was conducted in order to assess the VR library’s functionality, usability and practical effectiveness as well as to evaluate the level of immersion, realism and satisfaction in the virtual environment. The analysis of the results verified that the above features have been adequately achieved and strongly endorsed by the participants. It has also been clearly indicated that the participants experience behaviors similar to physical libraries such as a sense of community or presence. Consequently, they can be considered as alternatives to physical ones in information dissemination and scholarly endeavors, thereby revitalizing the library’s status as a pivotal center for community engagement.

This section discusses the literature review, in the general scope of the reconstruction of virtual libraries as digital twins, and their educational and learning aspects that are associated with the concept of virtual museums. The related work is divided into three main sections: (a) 3D building reconstructions and the definition of digital twins; (b) educational tools and virtual museums; whereas (c), focuses on virtual libraries, which is also the topic of this work.

2.1 3D building reconstruction and digital twins

The 3D acquisition and reconstruction of any cultural heritage building (in this case, the Pilavakis Mansion in which the library is hosted) or artifact allows for the creation of virtual spaces, remotely accessible from any location at any time (Özyesil et al. 2017). Since the introduction of Virtual Reality Modeling Language (VRML) by Raggett in 1994 (Raggett et al. 1995), the number of potential applications of 3D virtual environments has been continuously increasing. One of the first internet based VR exhibition systems (VRES) was proposed by Su et al. (1998) and was based on the VRML technology. In the last decade, Vosinakis and Xenakis (2011) presented an excellent example on how a virtual and a physical environment can co-exist in the context of an art exhibition, one complementing the other. Similarly, the proposed implementation of a virtual library can have a direct association with its physical entity and hence provide all the existing benefits of a physical attendance plus the convenient features resulting from the use of VR technology. In order to achieve this goal, in this work, a 3D virtual library was created that can be used as an educational facility by the user as well as a virtual museum of the building itself.

Digital twins have only partially been investigated in the cultural heritage field. However, it has been shown that research around this area coupled with its related technologies could improve the authenticity of the virtual representation of heritage or other landmark assets (Parsinejad et al. 2021). The main purpose of a digital twin is to maintain a precise functional connection between a physical asset and its digital copy. A case study regarding the implementation of digital twin technology on an underground oil-mill in the town of Gallipoli (Puglia, Italy) (Gabellone 2020) presents an example application of how this technology could be used within the cultural heritage domain. More specifically, it enables a virtual visit to an otherwise inaccessible area of historical importance. However, in this example, the connection between the physical and digital objects is static, as it is in most cases in digital heritage and virtual archaeology, rather than being dynamic. A dynamic connection is critical for the integration of digital twins, but that is often not feasible due to external factors, such as the location of the physical assets, e.g., in restricted conflict areas (Rizvic et al. 2019), or the alteration or destruction of the original assets (Bonde et al. 2017). Regarding the virtual library implementation for this work, the building was reconstructed, along the lines of a digital twin and since the aforementioned factors do not apply in this case, a dynamic connection between the real and virtual assets has been established and hopefully will be maintained in the future.

A VR library may also be regarded as a seamless integration of physical and digital content, also known as phygital. The meaning of phygital, in the context of a VR version of a physical library, accommodated in a heritage building, as in this study, describes the combination of its physical and digital forms. This augments the presentational, functional quality, meaning and value of the library, while preserving the physical attributes of the heritage building, as also suggested by other studies related to heritage artefacts (Massimiliano and Elisabetta Caterina 2020; Kaewta and Eunice 2022).

2.2 Interactivity in virtual museums

Currently, a number of different types of virtual museums exist, either as online applications or 3D environments, exhibiting both tangible and intangible artifacts, focusing on the concept of edutainment, whilst enhancing research, promotion, and visitor’s experience (Sylaiou et al. 2009; Aristidou et al. 2021; Zotos et al. 2022). However, for the majority of online virtual museums the interaction between the user and other virtual objects is limited mainly due to the restrictions on the input devices (e.g., mouse, keyboard, touchscreen); it is therefore suggested to design VR applications that allow users to more freely interact with the environment. More recent approaches recommend developing virtual environments that are not restricted to a specific form of a predefined guide set up by the curator, but instead allow the visitors to define their own scenario and create an experience based on their interests and needs (Kyriakou and Hermon 2013). Each individual user should have their own perceptual experience based on their level of understanding. In addition, a series of projects showed that VR applications create digital involvement by active participation, and enhance learning through a cognitive dialogue with the user (Sanders 2008; Sylaiou et al. 2009). VR has indeed the potential to revolutionize education and museum/library exhibitions, while education as a whole is shifting more towards online learning. VR could be a groundbreaking addition to any form of learning, making it safe, fun, and more engaging than ever before. In that way, a VR environment was designed and developed, to enhance the overall library experience, while augmenting the user’s immersion and engagement within an enjoyable and safe setting.

2.3 3D virtual library

The library is considered to be a hub for social interaction and knowledge dissemination in a community. In a similar way, a virtual library should maintain the role of the physical library, as well as its main goals, values, and visions. Many researchers were interested in the ways VR can be used to improve the library experience (Grant and Rhind-Tutt 2019). Currently, however, only very few libraries have fully switched to a virtual counterpart. Massis (Massis 2015) in his paper shows that VR/AR provide viable additions to the tools used by libraries for engaging the users, while also discusses that through the use of VR/AR students are provided with more means to practice their information literacy skills, and learn to use every available tool to enhance their educational experience.

One of the first 3D virtual libraries was built to assess the users’ behaviors when searching for a book in VR (Das Neves and Fox 2000). The authors discussed the idea of conducting experiments in a virtual library environment with the same arrangement as its physical counterpart. The same tests were repeated in both the physical and digital worlds. Several special factors were observed with regards to the position or spatial arrangement of the library that influence the user behavior and should be taken into consideration, on the initial design. Other examples of 3D virtual libraries include the ancient library of Alexandria (Boda et al. 2014); the Oulu City Library (Holappa et al. 2018), that is operated in parallel within the physical library premises; and the National Library of the University of Debrecen (UNLUD) (Gilányi and Virágos 2013). A virtual library can also be used as an educational tool through Presense Pedagogy. In such a setting, teaching and learning are grounded in social constructivism (Bronack et al. 2008), where all users can benefit from others’ expertise. Another example closer to the digital twin concept was presented by Pouke et al. (2018), where the digital part of the library was enhanced with imaginary fantasy layers. Their qualitative user evaluation showed that this kind of a VR experience is an exciting extension to a physical library, suggesting that VR can offer unlimited experiences. Likewise, in this work, a digital replica of the Limassol Municipal University library was developed that enhances immersiveness and knowledge by means of VR technology. This work is based on the outcome of a perceptual study (see Section 3) that was conducted to define a persona for a potential VR library user, aiming to understand its expectations and challenges. Currently, some academic physical libraries are offering different, isolated XR services and training, in an effort to encourage the use of VR and its associated technologies (Megan et al. 2020). Others have introduced AR-enabled information for their physical products in the library accessed via QR codes (Indrashah 2023). There are also cases where old and rare books need to be preserved, while they continue to be accessible to everyone and hence VR versions of these books have been produced and made available within the physical library (Marzia et al. 2022).

As the physical library is now at a critical phase of its lifetime, with its identity and purpose being uncertain due to the digital revolution, the current use of the physical library must be clearly defined. Its limitations which discourage potential visitors, the emerging challenges and the opportunities that technology has to offer, must also be identified. Following that, a perceptual study was conducted in the form of an online questionnaire, with a sample size of 79 people, resulting in 9 incomplete and 70 valid responses.

The participants consisted of 45 males and 25 females from various educational backgrounds (6% high school graduates, 4% college graduates, 46% University graduates, 26% with a postgraduate degree, and 19% with a Doctorate) and specialization (7% Life Sciences, 21% Social Sciences & Humanities, 57% Physical Sciences & Engineering, 14% unknown) with current situation being mostly employed (61% Employed, 36% Students, 1% on maternity leave, 1% Unemployed).

The study revealed that the majority of the participants (70%), rarely visit (\(\sim\)50%) the library or not at all (\(\sim\)20%), while the remaining 30% go to the library at least once a month. It is more likely for the people from Humanity Studies to visit the library, followed by the Natural Sciences & Engineering, and finally the Social Studies. Out of the frequent library visitors, only one third of them visit the library daily (approximately 7% of the total survey population). This reveals that people no longer consider physical libraries as their main source of information and knowledge. Nevertheless, a website is an essential asset for a library, as 53% of the participants use the library’s website monthly or more frequently, which shows that people are interested in using modern technology or accessing the library’s contents online, especially from the comfort of their own home or office. Among the reasons that mostly discourage people from going to the library, is the lack of available time as well as transport and parking difficulties.

Students are the most frequent users of the library, who visit it either for reading or during breaks between classes. A commonly reported problem is the noise from conversations and printers that interrupt their focus and concentration. Also, people meet there to socialize, showing the social aspect of the library. On a multiple-choice question, where participants could vote for one or more answers, our study revealed that 69% of the physical library visitors use the library services mainly for studying, 40% for work related reasons including reading academic articles, and 13% for other reasons, such as leisure.

In the satisfaction analysis, no responses were provided from the \(\sim\)20% of the participants who never visited the library. However, feedback from the \(\sim\)50% of the participants who rarely visited the library, provided useful information regarding the reasons for doing so. In general, the participants are mostly satisfied with the provided library services: in particular, on a 5-likert scale, 70% of the library visitors reported that they are either satisfied or very satisfied with the lending services (25% neutral, 5% unsatisfied), 47% with the copying services (41% neutral, 12% unsatisfied), 68% with the access and speed of the internet and the library internet service (23% neutral, 9% unsatisfied), 68% with the information and research services (24% neutral, 8% unsatisfied), and 43% with the cultural and educational programs organized by the library (40% neutral, 17% unsatisfied).

However, it seems that not all the participants are aware of all the library services provided. For instance, 72% of the frequent visitors indeed knew that they can attend a tour within the premises of the library that briefly explains its services, while only 34% of the non-frequent visitors were aware of this service. Similarly, 76% of the frequent visitors knew that they could attend specialized lectures and seminars in the library, whereas only half of the non-frequent users were aware of this service. Other services, such as, assistance, meeting with a mentor/ subject specialist/ librarian, booking a seminar room and borrowing books from other libraries, scored low in both the frequent (56%) and non-frequent (34%) visitors. This indicates that most people who are not regular visitors are also not aware of many of the available services that they might be interested in using. This highlights the need to design a GUI menu, in the digital form of the library, that displays all the provided services, for information purposes. It is important to note that, in the question “What service could the library offer to make it better?”, a number of participants suggested having more online services, such as a booking platform, virtual environments, better printing and help desks, and more socializing spaces, such as lounge common areas and restaurants.

In this survey, another objective was to understand the technological background of the participants and to define a persona for a potential VR library user. The ultimate target was to assess the potential usability and desirability for visiting and using a virtual library. Some participants (22%) claim to regularly use or are experts in VR technology, 45% have only used it once before and 33% have never used VR. However, none of the participants actually own a VR headset, while 85% do not have direct access to one, and only 15% have access. This proves that this technology’s usability is still at an early stage for the general population. It also shows the need to modernize schools and academic institutions that should provide access to such immersive technologies. It is expected that the device prices will be further reduced, as is the case for all technological gadgets, thus headsets will be available to a wider population; such a device is expected to be an integral part of our daily lives.

Only half of the participants were either aware of or familiar with the Metaverse concept. Based on the participants’ interaction with a VR service, it is shown that there is an overall motivation in using such services as 45% of them have navigated in VR environments in the past, 66% have shown a keen interest in visiting and exploring a virtual library, plus 23% seemed to have a pure curiosity in virtual worlds (e.g. the metaverse platform). The main reasons reported in utilizing a VR library, was its convenience of use from home, quiet environment which allows for concentration, ease of access, lack of available time to visit a physical library, the motivation to try new innovative technologies as well as curiosity.

What services would be useful in a VR library?

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Further investigation focused on the potential services that would benefit a VR library. The following responses were obtained in order of preference; (1) content search with 86% preference; (2) seminar/ lecture attendance (82%); (3) virtual tour of library (79%); (4) using a shared study/meeting room (73%); (5) mentor/specialist assistance (70%); (6) booking a room for an exhibition/event (70%); (7) book borrowing from the library’s international network (67%); and (8) booking a personal study room (59%). As expected the content and its accessibility is the most anticipated service, followed by the educational and social services, making the VR library a hub where visitors can study and learn from books, but also meet and interact with other people. Figure 1 illustrates the responses of the participants on a 5-Likert scale in relation to the question “What services would be useful in a VR library?”. The virtual library implementation was then structured based on these observations, developing five case scenarios that users can potentially use in a VR environment. Other suggested services include: the ability to read virtual books and explore them as 3D models (with accompanying animations/ movie clips), customization (increasing font size/ making it fancier, enlarging an image from a book, etc.), social meetings, tools for disabled people, taking notes and personal dashboards, etc. Regarding the responses in question of which characteristics would make the VR library more attractive, the following were provided in order of preference; (1) visual fidelity with 86% preference; (2) VR experience with 83%; (3) gamification with 81%; and (4) social interaction with 61%. It can be seen that VR libraries will become more attractive when applications that have a direct impact on the users, such as immersion and the visual fidelity are integrated into the system, whilst leaving those with less priority to follow.

Other interesting suggestions were obtained from this, such as providing the participants with holograms of the authors explaining their work, virtual storytelling with “jumping” into the world of the book, virtual parties, combinations of virtual and augmented reality and mainly characteristics that would not be possible outside a VR environment. Arguably, an extraordinary experience of that kind would be a unique opportunity to attract more library users and retain them for longer. Nevertheless, the need of further peripheral resources make the use of such applications difficult for the time being to proceed with their implementation.

The Library of the Limassol Municipality was initially accommodated in the main hall of the Municipal Mansion and was open to the public in October 1945. Later in the early 1970 s, the library moved to the Pilavakis Mansion,^{Footnote 1} due to the limited space in the municipal hall and the needs of the citizens for a modernized library. The construction of the Pilavakis Mansion, which currently is a trademark for the city of Limassol and a point of reference for its citizens, began in 1919 and went under the ownership of the municipality in 1966. The style and decoration of this building was the vision of Antonis Pilavakis, who wanted a house resembling the architecture of a casino in Monaco (Andreou 2009). Early attempts to digitize the Municipal University Library, aiming for its digital preservation and online accessibility, have been in the form of 360 virtual tours and maps - an interactive 3D walk-through with printable floorplans, annotations and embedded media, with aerial and ground showcases.^{Footnote 2} However, these visualizations only allowed users to visit and walk-through the building, without having access or the capability to use or interact with any of the library’s services.

In this work, under the concept of digital twins, a 3D virtual counterpart of the library was created in order to allow its integration with 3D virtual platforms, such as the Metaverse. For the 3D reconstruction of the building, two different methods were used: the exterior of the building was reconstructed using the Structure From Motion (SfM) method, known as photogrammetry; this is a digitization process for the 3D data acquisition of physical objects and buildings, used widely in cultural heritage work, that also includes texture information. The 3D location of the points on an object’s digital surface are computed based on overlapping images with camera position and orientation information known as exterior orientation (Thompson et al. 1966; Yastikli 2007). On the other hand, the interior space layout of the building, has been modeled relative to its physical counterpart, but without the use of photogrammetry. It is important to note that any photogrammetry attempt for the interior was extremely difficult for three main reasons: (a) there are many objects in the library, and there was only access to limited resources, that constrained an accurate reconstruction. (b) the generally white color of the walls would make it difficult to precisely recreate the content, using photogrammetry, as it would be difficult for the software to define key-points and thus it would produce digital noise; (c) the library is an area which is constantly occupied by people, and a dynamic environment filled with numerous small and often relocated objects. Therefore, the main interior objects were correctly located within this space, based on the architectural drawings and images captured on the spot, but they are represented by standard Unity3D (package ProBuilder, progrids) parts. That was done in order to minimize time, effort, resources, and costs associated with the overall digitizing process, for the current version of our VR library, which is intended as a proof-of-concept. Those were key interior objects of the library associated with demonstrating the features and services deemed necessary from the users, based on the perceptual study.

Sparse Point Cloud of the Pilavakis Mansion

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For the reconstruction of the exterior part of the building, the process is divided into three stages. The first stage of SfM is the recording, e.g., taking the pictures. 1305 photos were taken, using a mobile phone’s camera (OnePlus 3T) for the ground level details, and a drone (DJI Mavic2 Pro) for the higher level and roof features. The photos were then processed using the “Reality Capture” software that offers high-quality results while being fast and easy to use (Kingsland 2020). The next step in the SfM workflow was the images’ alignment. The relative position of the cameras with respect to the scanned asset was computed and a sparse preview point cloud was created (see Fig. 2). Following the process of creating the sparse point clouds, the last step was the creation of a detailed mesh of the asset, and the corresponding texture map. It is strongly advised to clean up and reduce the size of the mesh resolution before creating the UV and texture map to avoid high computational cost in time and huge data files. This is more apparent when creating assets for VR where the content needs to be as efficient as possible to achieve high performance (Dhanda et al. 2019).

This work was further developed through reconstruction of the 3D model, optimization and texturing, as seen in Fig. 3. On the left side, the mesh is presented without any color information and on the right, with the texture map. More details about photogrammetry and the procedure of 3D building reconstruction can be found in Özyeşil et al. (2017).

Untextured and textured of the 3D model, as illustrated in SketchFab

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A virtual library is a digital entity that offers online services in order to complement, enhance, or augment the library experience through customization, interactivity, and rich content, in the wider concept of the Metaverse. One of the main deliverables of this work is the development of such a virtual library and its services using the actual 3D reconstructed model (digital replica) of the Pilavakis mansion. Various observations and suggestions resulting from the previously conducted user study, helped identify the five key scenarios that demonstrate a potential typical use of a virtual library. Those were thoroughly studied, adapted and implemented for this work. Several digital assets, such as plants, lamps, laptops and other decorative elements were added to the virtual environment in order to create a more representative, welcoming, and realistic atmosphere. The top image in Fig. 4, illustrates the starting scene of the user’s virtual journey.

The scope of the library’s design is to capture the interest of the visitors by creating a convenient, accessible, and interactive environment. This design requires the users to be largely autonomous with a high degree of agency in the navigation and use of the digital library. This is largely achieved by incorporating the features detailed later in this section.

In this project, both the Oculus XR plug-in, which allows application building for all Oculus devices and the XR plugin Management Unity packages were employed, to enable the application to run on the Oculus Quest in a VR environment with the correct management of settings and support. The Oculus Quest settings had to be adjusted in such a way that would allow communication between the Unity program and the headset device and in order to recognize the project files and overcome any compatibility issues. This involved various features such as, point of view, field of view, head and hand tracking.

Top image shows the initial VR scene, while the bottom one displays the front desk assistance

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Existing NPC repositories (from GrabCAD^{Footnote 3} and Renderpeople^{Footnote 4}) were used, in order to increase interaction and realism. These were selected to be of high-quality and sufficiently realistic. Each character was imported along with its animations, coupled with specific materials and corresponding settings. The packages also included lighting, color, and textures, as well as the character’s limbs and joints, in order to realistically portray the characters in their true form, without being distorted, or compromising their motion flexibility. A variety of animation scenarios were used, in order to enhance scene authenticity. A number of modifications were necessary for compatibility purposes.

A 3D audio system and the doppler effect were adopted to provide a surrounding sound experience. This largely maximizes the impact and quality of a VR experience, by adding depth and hence goes beyond its visual counterpart, by perceiving sound directly from its source.

Finally, various methods and techniques providing continuous user interactivity and feedback were employed. More specifically, raycasting was used to assist the user in detecting interactive objects within their surroundings. VR haptic controllers allow the users to interact with these objects, whilst also receiving useful feedback, hence their integration within VR systems is essential. The haptic devices are correctly co-located and move with the user’s hands. Upon collision with a GUI object, the ray will change color. GUI buttons are highlighted, when raycasting is hovering over them, to give an even clearer indication of which button is selectable by the corresponding controller buttons.

In this direction, the following five case scenarios have been implemented, based on the results obtained from the user study; (a) A virtual tour of the library, (b) book lending, (c) seminar/ conference attendance, (d) meeting/ study room booking, e) mentor meeting.

Virtual library tour In this first scenario, the user can take a tour of the virtual library to get familiar with its premises and the services it provides, whilst also being briefed about the history of the library. Once the user enters the building, a GUI that demonstrates the main features and services of the library appears directly in front of them (see the bottom image in Fig. 4). This informs the user about the library’s available services. The tour takes place when requested or upon first visit, by default. An animated NPC representing the librarian welcomes and guides the user through the virtual library. Smooth transitioning and navigation between all the scenes enhances the element of realism, immersiveness, and interaction. The purpose of the tour is to answer any general questions that the user might have about the library and also its various operations such as borrowing a book, attending or organizing a virtual seminar, booking virtual meeting rooms, and obtaining mentor guidance.

Book lending In this scenario the users can browse and select electronic versions of books that they want to borrow or read. The general idea is to realistically simulate the procedure of book lending in VR; the users can read a book in either a quiet place in the virtual library, or in assigned spaces, (e.g. a virtual study room, see the top image in Fig. 5) allowing them to have social interactions similar to what they would have if they were visiting a physical library.

Top image shows the virtual study room with the library bookshelves, while the bottom one displays a seminar in operation

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For the purposes of this study, a small sample of publications are used to represent the books offered by this library. Once the user is in close proximity to the bookcase, a GUI comprising the list of available books is activated and displayed ahead of the user, providing them with easy access and selection options (see the top image in Fig. 6). This was achieved by using colliders on both the user and the bookcase and controlled through script. To open up a book, the user must simply select its GUI button via the VR haptic device. This presents the book in a reading mode, set out in front of the user at an appropriate distance.

A page curl animation package was used, enabling the user to turn the pages realistically, in a similar manner to using a physical book, but this time, using the VR controllers (see the bottom image in Fig. 6). This feature creates a more engaging reading experience for the user. Furthermore, an animated NPC walking in the background aids in the creation of an appropriate multi-user atmosphere. The NPC pauses and takes a glance at the books as it approaches the bookcase.

Top image shows the book titles GUI, while the bottom one displays the page curl animation

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Virtual Seminar organization and attendance Virtual conferences/ seminars have recently become part of our daily lives. Following this trend, users may book a seminar room specifically designed to accommodate virtual attendants or attend a pre-scheduled virtual seminar/conference. The seminar room can be used for various occasions, such as courses given by university professors, specialized lectures from companies as well as student project presentations. Virtual seminars are highly beneficial as they provide solutions to some of the limitations experienced by their live counterparts. Some of these include, larger audience capacity and attendance as people can easily join from different remote locations, hence eliminating the issue of searching/booking for an adequately large space to accommodate a specific number of people. Furthermore, there is an unobstructed view of the presenter and the screen. As shown in the bottom image in Fig. 5, a virtual seminar enables effortless social interaction and networking amongst the participants and also with the presenter, in contrast to online meetings conducted via a conference platform, such as Zoom and MS Teams.

Top image shows the virtual group study/ meeting room, while the bottom one displays the booking platform for meeting with mentor

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This scenario consists of a speaker NPC and a few others who serve as the attendees. In this, a short presentation on a given topic is conducted. Smooth animation of the projected video clip and high-quality runtime rendering augment the element of perception. Whilst the speaker is narrating the presentation, a video clip is projected on a big screen, inducing a more fulfilling seminar experience. The video presentation automatically commences soon after the user enters the room and chooses one of the available seats.

In terms of audio, a linear roll-off was deemed to be the best solution to accommodate the 3D sound of the video clip, enabling the volume to vary according to the distance from the source. Hence, as the user moves towards the presentation room, the audio becomes clearer and louder, replicating reality. Also, this eliminates any unwanted effects from occurring, such as the seminar presentation audio being heard from a different room, or even outside the library. To close the presentation, the speaker thanks the audience and is applauded.

Booking a virtual meeting room In the fourth scenario, virtual meeting rooms have been implemented which users can book upon availability. In these rooms, multiple users can join, by receiving an invitation from the organizer to work together on different group activities and projects. These common areas can also be used for virtual group study sessions, brainstorming, meetings or socializing, as in reality. The top image in Fig. 7 illustrates a meeting between three students that are using such a common room for their studies. In this work, animated NPCs are present in the background, giving the sense of a crowded study area within a multi-user environment. In this scene there is a large table with multiple seats for users to feel being within a collaborative environment. An animated player working on a laptop is also shown in this scenario.

Mentoring In this last scenario, a virtual mentor booking platform has been developed, where the users can book slots with experts who can provide knowledge and information in relation to their domain, as part of their collaboration with the library (see the bottom image in Fig. 7). The purpose of this service is to assist the users in their work or projects, by providing them with possible solutions to any questions that they might have. To book a meeting, the users first select their area of interest from the given list and based on that, time slots showing the availability of each mentor are presented. In this project, the following subject fields are covered by the mentors; Life Sciences, Social Sciences and Humanities, Physical Sciences and Engineering, Medicine, Gymnastics, and HealthCare. Free time slots indicating mentor availability appear highlighted in white and those already booked in red. At this stage, only one mentor is used, appearing as an animated NPC, in an office.

6.1 Methodology

6.1.1 Aims and procedure

In this user study, VR technology was employed to explore the use of a virtual twin of the Limassol Municipal University Library and its main services. Conducting a user evaluation study and analyzing its results is of great importance for this work. The purpose was to test and assess the VR library’s functionality, usability, and practical effectiveness, as well as to evaluate the level of immersion, realism, and satisfaction in the virtual environment. Each participant was asked to wear a Head-Mounted Display (HMD), more specifically, the Oculus Quest and navigate through the VR library space. Initially, they were shown a guided library tour video as an introduction, prior to the test. Then, they entered the VR Library, where they had the opportunity to explore and interact with its environment, facilities, and main services, and experience both the visual and audio features.

Throughout the duration of the experiment, the participants remained in a stationary, standing position, whilst movement and rotation was enabled via connected haptic controllers and head rotation, respectively. The walking speed was also regulated by the users, via the haptic-integrated joystick. The users’ motion and actions were closely tracked and monitored through a computer screen. This helped to confirm that everything was functioning correctly, while allowing intervention whenever deemed necessary. Also, that allowed observation of their individual behavior and response, when encountering different situations.

Minimal risks were associated with the participation in this study, including the possibility of some individuals experiencing minor discomfort or motion sickness, while using the VR equipment. However, the benefits included the immersive experience of attending a remote library and enjoying its environment and extended services without incurring any additional time and financial costs. Also, users were provided with the opportunity to contribute to the advancement of knowledge in the field of VR library research, by providing their valuable feedback, through the various questionnaires and interviews conducted.

The overall duration of each test was, on average, 27.5 min, with a minimum and maximum of 18 and 50 min, respectively. More specifically that included, preparation and pre-experiment questionnaires, the VR test and finally post-experiment questionnaires and interviews.

6.1.2 Participants demographics

A total of 28 users participated in this user evaluation. The number of participants, with reference to several similar VR projects was deemed adequate and practical (Ponton et al. 2023; Marshall et al. 2023). Furthermore, the participants were carefully selected so that they would largely represent a wide majority of interested parties. This kind of VR in-person experiments face several challenges and constraints associated with the time and cost required for hardware setup and limited availability, continuous and close monitoring, pre and post processing of questionnaires, health and safety measures and space availability as well as the need for breaks in-between sessions.

The participants consisted of, 50.0% females and 50.0% males. The majority of the participants were aged between 25 and 34 years, and they specialized in Humanity studies (17.9%), Natural Sciences and Engineering (57.1%), and Social studies (25.0%). Most of the participants were Cypriots (85.7%) and the rest were Greek (7.1%), Iranian (3.6%) and Pakistani (3.6%). All the participants, however, were resident in Cyprus, hence that allowed the experiments to be conducted in-person. It is noted that one participant did not fully complete the experiment, due to cybersickness and as a result was excluded from the post experiment statistics.

6.1.3 Data collection

Prior to the study, each participant was asked to read through an informed consent form which comprised a brief summary of the experiment, its structure, the risks and benefits of the experiment as well as the user’s acceptance signature, as to be in line with all the needs and regulations, to ensure the participants’ safety and comfort. The users were also requested to complete two online google form questionnaires, related to demographic and cybersickness information, in preparation and readiness for the test. To evaluate and compare the VR Induced Symptoms and Effects (VRISE), a well-established tool, named the CyberSickness in Virtual Reality Questionnaire (CSQ-VR) (Kourtesis et al. 2023), was utilized both before and after the experiment, in order to follow-up on the user’s condition.

Two additional essential questionnaires were conducted after the study. The first, enabled the collection of useful user feedback related to measuring the overall feeling of presence within the VR experience (Witmer and Singer 1998; Witmer et al. 2005). The second, involved interview questions specific to the participant’s VR library experience, where the user responded to mainly seven-point scale questions, and a couple of open-ended ones. The latter facilitated the provision of detailed responses and remarks about their experiences. This questionnaire was specifically designed for the purposes of this study. In-depth analysis of both of the above questionnaires is provided in the following sections.

6.1.4 Data post-processing

For this study, it was essential to take into account each participant’s prior user-experience in VR as well as experience with physical and online libraries (website services), in order for a correct assessment to be made and conclusions to be drawn. To that end, participants were carefully selected from approximately equal groups, representing experienced and non-experienced users, in the above areas.

To indicate how often the participants visit the physical library, a scale from one to seven was adopted, corresponding to, daily, weekly, monthly, tri-monthly, bi-annually, annually, never, respectively. The collected data were then divided into two groups and analyzed. The first three scale points (1,2,3) form the first group, representing frequent visitors, who specifically are library staff members, and the remaining points (4-7) form the other group. Similarly, for the VR and online library experience, a seven-point scale was also used, with score 1 indicating no experience and 7 corresponding to plenty, while 4 is considered as average.

Cybersickness and in particular motion sickness has an impact on how users perceive the VR experience and interaction. For this reason, six associated symptoms were evaluated via the questionnaire, both before and after the experiment. Each of those was assessed based on a seven-point response scale, in order to better understand the presence and intensity of symptoms, starting from an absent (1) to an extreme feeling (7).

Upon successful completion of the VR library navigation, the users were asked to rate their overall feeling of presence within the VR experience, through a set of targeted questions. In order to quantitatively measure that, a widely used tool, named the Presence Questionnaire (PQ) (Witmer and Singer 1998; Witmer et al. 2005), was utilized, with a seven-point scale response, starting from an absent (1) to an extreme feeling (7). The most relevant questions in relation to this study were selected from the PQ, as illustrated in Table 1. This tool allowed the evaluation of the collected responses. In order to assess any differences in the responses to the above questions in general, due to the level of experience of the participants, in VR, the results were divided into two groups. Furthermore, that was done, to effectively draw conclusions on a larger scale. The first group represents those with lower familiarity (score less than 4) and the second, the more experienced ones (score higher or equal to 4).

Following the experiment, the users were requested to complete a structured interview questionnaire, with the aim of gaining a deeper insight on the overall practical effectiveness, functionality, desirability, and realism of this VR library implementation. The questionnaire comprised 24 questions, the majority of which were seven-point scale response type, starting from a negative (1) to a positive opinion (7), except from two open-ended ones. Each question was based on and assigned to one of four hypotheses, defined as follows:

• \({\varvec{H}}_1\): People can attend the library remotely, through a virtual environment, with the highest possible degree of realism.

• \({\varvec{H}}_2\): People can be provided with the same services and in certain cases go well beyond that of its physical counterpart.

• \({\varvec{H}}_3\): People desire VR libraries which are easy and intuitive to use.

• \({\varvec{H}}_4\): People need VR libraries that can serve as community as well as knowledge hubs.

All the questions and corresponding hypotheses are listed in Table 2.

The seven-point scale responses to the interview questions, exclude the VR experience and open-ended questions (Q12,13,14 & Q7,11). In order to assess any differences in the responses to the above questions and on the hypotheses, in general, due to the level of experience of the participants, with physical libraries and their services, the results were divided into two groups. The first represents those with lower familiarity (score higher or equal to 4) and the second, the more experienced ones (score less than 4).

6.2 Results

6.2.1 Statistics

According to the results, in relation to the participants’ prior user-experience in VR, the frequent library visitors group account for 50.0% and the other group, for the remaining 50.0%. For the VR and online library experience, the analysis yielded results corresponding to 57.1% of the participants having an average or higher experience in VR and 42.9%, considered less than average. In relation to the online library services, the user experience levels resulted in 78.6%, having an average or higher rating and 21.4%, having less than average.

6.2.2 Cybersickness

According to the results and with reference to the pre-experiment cybersickness average values, the following ratings have been estimated; nausea (Q1) and dizziness (Q2), increased by 2, disorientation (Q3) by 1.5, postural instability (Q4) and visually induced discomfort (Q6) by 1, but, visually induced fatigue (Q5) showed a decrease of 0.5. These results are visually displayed in Fig. 8, together with their mean values and standard deviation error bars. Furthermore, the users with higher familiarity in VR, experienced less cybersickness after the experiment, resulting in an average value of 2.18, in comparison to those with less VR user experience, which yielded a value of 3.23. This indicates that the participants with none or little experience in VR, were more prone to motion sickness, as expected.

Cybersickness Comparison; nausea (Q1), dizziness (Q2), disorientation (Q3), postural instability (Q4), visually induced fatigue (Q5) and visually induced discomfort (Q6)

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6.2.3 VR experience

Overall, the average score obtained from the participants for the presence questionnaire was 4.89, which is sufficiently above the mean point of the response scales, thus verifying a good level of satisfaction. The PQ results are shown in Fig. 9, together with the mean values and standard deviation error bars. The responses were analyzed and demonstrated that for more than 68% of the questions, the experienced VR users provided a higher score, indicating a stronger presence feeling.

VR Presence Questionnaire (Q1-Q22 presented in Table 1) in relation to the User Experience score level* in VR

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6.2.4 VR library user survey interviews

The collected responses from the interview questionnaire, provided reliable evidence for the validity of each of the above hypotheses, which together with the questions were both specifically formulated for this study, in such a way as to gather and group the necessary information, that would support the aforementioned aim. Collectively, the average score for each hypothesis was calculated as, 5.41, 5.02, 5.19 and 4.38, respectively, clearly validating that they are all strongly supported.

The interview questionnaire results are shown in Fig. 10, together with their mean values and standard deviation error bars. The responses were analyzed in a similar manner, with reference to the corresponding hypotheses, as done previously. For the less experienced users, the average hypotheses (\(H_1\)-\(H_4\)) scores were found to be 5.23, 4.67, 5.00 and 4.17, respectively, whereas for the more experienced, the corresponding scores were 5.60, 5.41, 5.38 and 4.49, respectively. Overall, those with experience endorsed the validity of the hypotheses, with clearly higher scores, thus providing stronger support of the VR library concept. This is also proved by the responses to Q21, with the majority of users confirming that they would be definitely happy (score higher than 4) to make use of this VR Library platform in the future. More specifically, the experienced users scored an average of 5.15, in comparison to the inexperienced ones, with 4.64.

Interview Questionnaire (Q1-Q24 presented in Table 2) in relation to the score level* of Experience with Physical Libraries

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Regarding Q7 and Q11, the responses were designed to be open-ended, in order to capture some opinions and remarks, which could not be otherwise included in the point-scale questions, but they could potentially provide useful feedback. For Q11, in particular, 53.6% of the participants indicated that they would like to have more services/ facilities added to this VR library. Some would like to see the addition of internet browsing, seminar timetable and booking system, as well as a screen zooming capability for seminar presentations.

The second open-ended question Q7 was intended to seek the users’ opinion on possible, desired features to be added, in the overall VR library experience. Those included a fully categorized publication catalog with search capability and flip-through book cover images for selection. The ability to grab and open a book, to have more people in the study room with more natural NPC body motion and facial expressions, real-time verbal chat with library staff and the option to be seated in the group study or seminar area. The users also highlighted the need for more bookshelves and furniture, higher resolution interior environment graphics, for more realism, short context help videos as well as a library map and door signs with the facility to be directly transferred to all library areas via GUIs and selection raycast lines to be visible only on-demand.

Furthermore, the participants made some additional remarks, not as a result of the questionnaire, but were considered useful to note. In general, participants with previous VR user experience felt that this application did not induce any more cybersickness than other applications they had tried. Overall, an enjoyable and interesting experience for the majority of the users, very useful with good functionality and future prospects. The quality of the library’s exterior model was praised. The seminar room’s doppler effect, added to the realism. It is worth mentioning that several users highlighted that the book reading, seminar attendance, and mentor platform features were very appealing. In addition, the users expressed some concerns on certain aspects of the VR library’s future acceptance, associated with fatigue and cybersickness tendencies exhibited by a proportion of the population. For example, the prolonged wearing of the headset and the need for standing, posture, movement restrictions, and screen size. This is in line with previous studies, that have shown that there is a slight discomfort associated with reading in VR (Monika et al. 2012).

6.3 Discussion

The user evaluation study was carefully planned and conducted with appropriately selected and balanced groups of participants, representing different levels of experience in the use of physical libraries, online services and VR. That ensured the collection of robust and reliable views and opinions on key aspects regarding the overall success and effectiveness of this VR library implementation. It also provided a platform to assess the incorporated features and services and receive valuable feedback on potential desirable future additions or improvements. The VR experiment was designed to exhibit the essential elements of the intended application and to provide a basis for accurate analysis and results, unbiased by the user experience and physical condition. That was attained via appropriately formulated pre and post experiment questionnaires.

Cybersickness has normally a negative impact on how the VR experience is perceived and that was verified in the experiment, with the more experienced users being less affected. In this context, the analysis of results proved that all symptoms increased in intensity during the experiment, with the exception of visually induced fatigue, which interestingly enough, decreased. Perhaps that is attributed to the users’ deep immersion and associated alertness. This also shows that the VR experience stimulates and maintains the users’ interest, throughout the session. Hence, it does not lead to fatigue and its continuous use can be comfortably extended over longer periods.

Regarding the feeling of presence in VR, this study indicates a good level of satisfaction and a much better result for the VR experienced users, positively confirming a strong presence feeling. This indicates that the developed VR library is a realistic and immersive environment, in which the users feel part of it and act naturally and thus subconsciously interact as they would do in physical surroundings. Finally, the assessment of the practical effectiveness, functionality, desirability, and realism of this application yields relatively high scores, confirming that the hypotheses in question, are strongly supported. In particular, this study confirms that the VR library counterpart reinvigorates the library’s role as a central hub for community engagement, information dissemination, and scholarly pursuits. Further analysis provided even higher ratings for the physical library-experienced users, endorsing the validity of the set hypotheses and hence their support for the VR library concept. This is further affirmed by the library staff participants, who know exactly what is desired and essential in the operations of a physical library with its services and facilities. All the above, as well as the desire to make use of VR libraries in the future, were clearly indicated by the overall participant responses.

In this work, a 3D virtual library has been designed and developed. That set the foundations for the technological advances required for integration in libraries within the general concept of a virtual environment/Metaverse. In relation to that, a perceptual study was conducted, which helped to understand the current use of a library, and highlighted the limitations that physical libraries present. Various reasons have been identified as to why libraries are currently not the most preferable meeting places for studying and academic socializing, and also why the number of visitors is reducing over time. In addition, personas were created that portrayed the potential users of a virtual library and led to understanding their needs and expectations. The Limassol Municipal University Library was reconstructed within the Digital Twin concept, using photogrammetry and 3D modeling. This work also revealed the apparent need of modernization of libraries, in order to maintain their importance throughout the new virtual era. Based on the outcomes of the conducted survey, five main case scenarios that users could encounter in the real world were identified and implemented; a virtual tour, book/proceedings borrowing, seminar/conference organizing and attendance, group study/meeting room booking, and meeting with a mentor. The user evaluation study that followed the completion of the final implementation, provided firm statistical results which fully endorse the attainment of the overall goals, set for this work. It also confirmed, the user satisfaction and desirability for its future deployment and use.

Limitations In contrast to the exterior design of the building, the interior has been modeled instead of being scanned. This led to a reduced level of realism of the interior, and more specifically when it comes to the illustrated detail of books and other small objects within it. Nevertheless, 3D reconstruction using photogrammetry requires increased resources in order to capture and incorporate the details into the models of numerous small objects as well as an enormous amount of post-processing time. In addition, Virtual Reality and Metaverse are relatively new concepts, and as verified by this study, access to VR headsets is normally very limited and only a minority of users have any experience in using them, especially within social sciences. Hence, this raises the question whether virtual libraries can continue to be a community hub for all researchers and scholars and a place for their social interaction. The success of the social virtual library concept is highly reliant on user numbers. As the virtual library still needs to encompass the social aspect of physical libraries, a low number of users would therefore result in a library with minimal social interactions, which is contrary to the concept of being a social hub. Finally, due to copyright issues, books could not be included for use in this virtual library. Alternatively 10 selected academic publications were used, for demonstration purposes. However, this could be easily amended in the future provided the required permissions are obtained.

Future Work Based on the experience from this work, some observations and suggestions for future improvement are made. These could facilitate, expedite and optimize the smooth transitioning and operation of virtual libraries, with an ultimate goal to develop them and their services in line with the digital twin concept. Many libraries are not up to date, in terms of technology, and it is expected that their services must be continuously updated to meet new user needs. Libraries, along with academic institutions, should offer seminars on how to make use of emerging technologies and have sufficient available headsets at their premises, to facilitate the use of immersive technology in their settings. Additionally, there is inadequate staff with VR skills, hence training them on this technology is essential. Currently, a lot of libraries do not have enough VR or even IT-experienced staff, especially those that are located in remote areas or are small in size and inadequately funded.

Another key area of future improvement would be further developing the mentor scenario into a meeting platform, where the mentor will be interacting in real-time with the user via an audio link, while his movements, eye gaze and lips are tracked and synced by a camera. Creating a multi-user environment where everyone can connect to a VR library from any place at any time, whilst having full access to all the available services is another future key requirement. It is important to know that the rapidly developing HMD technology as well as the associated software and methodologies now allow the integration of multimodality in user interaction, such as hand tracking and speech recognition. It also provides improved resolution, refresh rate and other processing capabilities. Those would further enhance interactivity within this virtual library environment and should be integrated in future implementations of the VR library. Visual aid tools such as could additionally enhance the book reading scenario with pop-up explanations and animations, making it more interesting and engaging. Various elements of this work could also constitute the baseline for further individual work and future publications.