Towards Preserving Transylvanian Fortified Churches in Virtual Reality
A fortified church is a building which has a religious meaning, but also played a defensive role in times of war. Many fortified churches from countries such as Romania, Slovenia, Switzerland, Poland, France, Denmark, Portugal, Germany or Belarus featured thick walls and high battlements and embrasures. However, Middle Age fortified churches are different from castles and fortresses because they were designed to protect small communities. Transylvania hosts the highest number of fortified churches from Europe. In the medieval ages, more than 300 churches were built by the inhabitants of this area. This was the direct result of the constant invasions from the Ottomans and other nomad populations such as Tatars. Many of these edifices date since the 13th century, but some are in an advanced state of degradation, caused mainly by poor preservation measures and lack of interest from the local authorities.
This paper introduces a system which aims to increase the awareness about the fortified churches from a small area of Transylvania called “Țara Bârsei”. Our focus is on the visual preservation of several of these monuments through the technique of photogrammetry, as well as the implementation of a stand which would attract the potential tourists. The key idea of our study is to influence them to visit several churches by placing next to each other in Virtual Reality both mainstream and low-profile objectives. We assess users’ opinion about a holographic stand commanded by a mobile application which includes the 3D models, pictures and a short description of the fortified churches based on a modified HARUS questionnaire. Results show increased interest, directly resulted from the visualization technology.
KeywordsTransylvanian fortified churches Cultural heritage Preservation
A study from 2011 shows that although some of the UNESCO churches listed above are well-known, there are others which are also popular among the local population. These are Cisnădie, Cisnădioara, Agnita and Slimnic. However, not being listed in UNESCO index makes them virtually invisible to the foreign tourists, according to .
Several researchers tried to find the possibilities of development of these areas, considering their rich cultural heritage. E.g. in , authors propose a set of long-term actions which they think it will act towards the preservation and the development of these settlements. However, some of these activities have been undergone in the past by local authorities and decisional factors, with little or no success. It is showed in  that the problems are more severe than what authorities initially thought. The Saxons, the population which maintained the fortified churches and the old village centers, have left Romania in the exodus which occurred right after the revolution from 1989. Many of the buildings are either uninhabited or were bought by new owners, which modernized them without considering the idea of preserving the past looks (materials, shapes and colors). Although this region is important on multiple levels (i.e. it hosts a unique habit ), the poor road infrastructure and the nonexistent regional strategy for tourism have contributed to the decay.
One idea which seem to catch was ecotourism . However, ecotourism needs to be naturally sustained by an organic growth of visitors, resulted directly from a constant activity and a reasonable long-term preservation strategy, engaging enough to catch the interest of the newer generations of tourists, travelers and other stakeholders. Another idea which seemed to multiply the awareness effects was to ease the return of the Saxons, which are occasionally traveling to Romania to visit their homeland . However, the amplitude of this phenomena is low, compared to the average numbers of tourists from the region. Even the most well-known fortified church from Transylvania, Viscri, is still struggling to implement a Western model of heritage management which will eventually allow better engagement with visitors, higher touristic rating and in the end, larger audience .
1.1 Types of Fortified Churches
Churches with fortified walls - the church itself is not a defensive structure, but it is surrounded by walls which fulfill this function. One good example is Prejmer Fortified Church (see Fig. 2).
Fortified churches - the church’s body is a defensive construction, and the outside fortifications are not present or if they are, they are not actually playing a defensive role. Large churches with thick walls such as Feldioara can be included here.
- Fortress churches - the fortified walls are provided with fortified storerooms for supplies and fortified with towers, bastions and warehouses, often being surrounded by a water channel. Fortress churches are related to notion of “citadel”, but they differ because they were not permanently inhabited, but only in case of war and siege (see Fig. 4).
Transylvanian fortified churches are fairly different from the ones built in the Western Europe, as their purpose was different. While Western Europe fortified churches belong to religious cults such as the Templars, or to the Catholic Church, and hosted only sacred relics and books, the Transylvanian fortified churches were supposed to offer protection against invaders for the tens of families for each of the villages which had them. Very often, each family had their own cellar in which they could store separately their belongings.
1.2 Study Objectives
Our final aims are to discover which the best means of digitally conserving these monuments, to implement a system which will enhance the visibility of less-known fortified churches from Transylvania and to assess the perception of the proposed implementation by the general public and by experts in the field of cultural heritage. On a side note, we wanted to build accurate 3D models for all the fortified churches from this region and to offer these for free to the cultural heritage enthusiasts, within an online repository. In order to accomplish these goals, we needed to interact with the representatives of the fortified churches, to ask permission to photograph and inspect the landmarks. Deriving from discussions with the curators, one idea which we hope to put in practice is to offer the developed system, the holostand presented in Fig. 5, to be displayed in the most visited churches from the regions, Prejmer and Harman, and perhaps, in the Bran castle. The purpose of this endeavor would be that tourists which are passing by would learn about the other churches and would want to also visit these, since all are very close one to the other. Although our study doesn’t address the idea of a tour creation, the system proposed in this paper leaves tourists aware of the close proximity of similar landmarks, a piece of information which will help them decide on their next objective.
2 Methods and Materials
Photogrammetry is a technique which allows users to create 3D models from photos. We have used photogrammetry to build the 3D models presented in the holographic stand. The photogrammetry software used in most of the cases was Agisoft PhotoScan and Reality Capture. These programs allow users to import any kind of photo for the reconstruction phase. Thus, we have used several cameras, among which we can list Canon EOS 1300, Nikon D5300 and Samsung S8. In full compliance with this technique we notice that the higher resolution was used, the better were the results. Besides the photos taken from the surface level, use have used a drone (DJI Phantom 4 Pro) with 4K lenses to catch the looks of the roofs and of the crannies and nooks of the architectural elements from upper body of the monuments. Agisoft produces weaker results in terms of resemblance, but can accept a higher number of images, whereas Reality Capture is limited to 2500 (for a standard license).
Other software used in our study was Blender and Meshlab (for trimming the models to an acceptable number of polygons) and Unity (for constructing the 3D slow-revolving setup for the glass pyramid).
Doing the field work, we’ve discovered that a typical church needs at least 2000-3000 photos in order to get a good 3D model. There are cases where, because of the large dimensions of the monument, we’ve used approximately 10000 photos to build the 3D model.
The process of taking photos for photogrammetry is not trivial. The photos need to be focused well. Any defocused/blurry image can ruin the model. Cameras were adjusted to get the best exposure (the best ratio between ISO, aperture, shutter speed and zoom). After the photo shooting sessions, the pictures need to be sorted for eliminating all the ill-focused ones. Finally, using the .raw format may require more space, but also proves to be the best choice, especially in the preprocessing phase.
On a side note, the best time to take the pictures is when it is cloudy, because the sun light influences the resulted textures. Thus, posing a wall directly illuminated by the sun light outputs overexposed colors and diminishes the details of the surface.
Finally, computing the 3D model for medium quality may take even a week of continuous processing, using several connected servers.
In the post-processing phase, the surroundings which are not connected to the fortified church were cropped and the models were optimized to a smaller amount of polygons, in order to be ready for import in Unity.
2.2 3D Models
Our team computed 3D models for the following fortified churches: Prejmer, Harman, Vulcan, Sanpetru, Maierus and Feldioara. Additionally, Rotbav, the church which collapsed in 2016, was modelled in CAD and showcased on the stand. There are several other fortified churches for which we are in the process of obtaining the authorizations to photograph them. Our final aim is to offer these models for free on the portal of the eHeritage Project, in the repository section .
2.3 Holographic Stand
The holographic stand uses the classic principle of holography: the image emitted from a highly luminous 4K TV screen is reflected by a single-side reflexive glass mounted at an angle of 45°. Inside the glass construction, a white base lighten by a weak light source breaks the reflection sensation and creates the feeling of having the image reflected being inside the pyramid, instead of being on the surface of the glass. Thanks to the 3 reflections offered by the 3 sides of the pyramid, users can experience a greater sense of immersion.
The system (in various versions) was presented at various events such the EU Open Day 2018 from Brussels, Belgium, AFCO 2018 from Brasov, Romania, Researchers Night from Brasov, Romania, Internet Festival 2017 from Pisa, Italy and the Lubec 2017 from Lucca, Italy.
Q1: Have you used VR technologies before?
Q2: Have you ever seen a hologram before?
Q3: Are you familiar with the principles of holography?
Q4: I thought that using the system requires a lot of mental effort
Q5: I thought the amount of information displayed on the screen of the tablet was appropriate
Q6: I thought that the information displayed on screen of the tablet was difficult to read
Q7: I felt that the system was responding fast enough
Q8: I thought that the information displayed on screen of the tablet was confusing
Q9: I thought the words and symbols on screen of the tablet were easy to read
Q10: I felt that the quality of the 3D models was good
Q11: I thought that the information displayed on screen was consistent
Q12: I enjoyed using the system
Q13: I found the system unpleasant
Q14: I found the system exciting
Q15: I found the system boring
Q16: By using the holographic stand, I was able understand the location of the fortified churches
Q17: By using the holographic stand, I was more interested in visiting the fortified churches
Q18: By using the holographic stand, I was able understand more about the history of “Tara Barsei”
Q19: By using the holographic stand, I am more likely to visit fortified churches in the future
Q20: Which 3D model was the most appealing?
Q21: Which 3D model was the most unpleasant?
Q22: Which fortified church would you be interesting in visiting the most in the near future?
Each participant was asked to fill in a modified version of the Handheld Augmented Reality Usability Scale questionnaire . The HARUS questionnaire was developed to evaluate the comprehensibility and manipulability of AR applications for handheld devices. Since the system developed is not really an AR application, we have tweaked the questionnaire to cover the subject of our study, while preserving the statistical computation process behind it.
Thus, the first section, Personal Skills (Q1–Q3), was intended to create a baseline, derived from the degree of familiarity of the subjects with virtual reality and more particularly, with holography. The second section (Q4–Q11) aims to assess the usability of the holographic stand. Enjoyment (Q12–Q15) and Usefulness (Q16–Q19) derive directly from the HARUS design. Last but not least, the Empirical section tries to infer some common knowledge about the study itself, about the quality of the 3D models presented to the public and about their intentions in the near future. All of the questions from sections Comprehensibility, Enjoyment and Usefulness use a 7-point Likert scale, ranging from 1 – “strongly disagree”, to 7 – “strongly agree”. As a side note, in some cases, the 22 questions were perceived as too many by some of the respondents.
The empirical questions were used to tweak features such as the luminosity of the light source inside the pyramid, or the luminosity and the position of the light source inside the scenario built in Unity. The 3D models were calibrated to cover all the screen allowed by the dimensions of the glass. All the answers from sections 2, 3 and 4 were aggregated in order to obtain values for each of the 3 constructs: Comprehensibility, Enjoyment and Usefulness.
4 Conclusions and Future Developments
As we initially thought, the system was very well received by all the participants of this study. Many praised the idea and the content, and even promised they will visit some of the fortified churches presented in the holographic stand, in the near future. However, there are still improvements to be made.
There are still 4 churches which need to be “photo-scanned” in order to obtain their 3D models and to put them in the application, not to mention the old city of Brasov, which we will most likely be represent by the fortress of Brasov. This means that additional 3D content needs to be developed.
Another way to develop the system is to add more interaction. Users like to interact with systems in a natural way. Using a mix between Leap Motion and the Andoird application installed on the tablet could prove worthy of investigating. Speaking of the application, one development which may have a greater impact would be to create an app which could be available to download for free on Google Play and IOS Marketplace, presenting the 3D models and historical facts about each of the monuments.
Other improvements related to the physical features of the holographic stand. We can improve the interior lighting of the glass pyramid, by investigating which light source is the best for holography (warm or cold) and which is the best light intensity. Last but not least, one of our future aims is to seal tight the stand and display it at several fortified churches from the area “Tara Barsei”.
This paper is supported by European Union’s Horizon 2020 research and innovation programme under grant agreement No 692103, project eHERITAGE (Expanding the Research and Innovation Capacity in Cultural Heritage Virtual Reality Applications).
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