**1. Introduction**

A fundamental concern in the field of Cultural Heritage (CH) is the need to document historical monuments as accurately as possible. Before the advent and popularization of digital culture, it was proposed to carry out extensive suitable inventories of each site [1] with photographs and drawings used to capture the nature of these environments, and to guide conservation, restoration, or excavation activities [2,3]. Technological advances have expanded the possibilities of documenting these CH sites, using not only natural light, but also monochromatic light, ultraviolet light, and infrared rays [4]. Subsequently, photogrammetry was specifically mentioned as a standard procedure to document the properties of cultural interest in the 1987 Charter for the Conservation of Historic Towns and Urban Areas [5].

From the time atoms began to be converted into bits [6], digitization has become increasingly widespread, allowing not only for assets to be documented for their conservation, preservation [7] or restoration [8], but also for digital versions to be created. With these, which constitute the Digital Cultural Heritage (DCH), dissemination actions are promoted, play is proposed [9] and access is allowed [7] through virtual tours even in complicated circumstances such as those experienced in recent times, marked by the COVID-19 pandemic [10].

**Citation:** Benítez, A.J.; Prieto Souto, X.; Armenteros, M.; Stepanian, E.M.; Cantos, R.; García-Villaraco, M.; Solano, J.; Gómez Manzanares, Á. Multi-Camera Workflow Applied to a Cultural Heritage Building: Alhambra's Torre de la Cautiva from the Inside. *Heritage* **2022**, *5*, 21–41. https://doi.org/10.3390/ heritage5010002 4.0/). *heritage*

Academic Editors: Daniel Vázquez-Molini and Antonio Álvarez Fernández-Balbuena

Received: 28 October 2021 Accepted: 18 December 2021 Published: 22 December 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/

Some arguments have been presented against the creation of DCH models. For example, their cost, the complexity of the processes or the specialization required to obtain them [11,12]. These are arguments that have been losing strength with the simplification of software platforms, the increase in the power of hardware equipment and the lowering of the cost of both elements [9,13].

At the same time, the need for a multidisciplinary approach has been recognized (The Norms of Quito, 1967). New approaches have emerged that make it possible to produce more complete documentation and expand the possible uses of the 3D models that were obtained. An increasing number of heritage buildings have an informative model that was obtained through Historic Building Information Modeling (HBIM) procedures [9,14]. Such models are based on a complex and precise methodology [15,16] originating from architectural functionalities. These approaches encourage the construction of parametric models with the integration of many disciplines [16].

Irrespective of their origin, 3D models have been employed in the interest of the conservation and restoration of CH sites, but also for other objectives. Education [12] or entertainment in the form of video game scenarios or Virtual Reality (VR) experiences [17] are examples. Their use with the holistic intention of gathering as much knowledge as possible about a building and reaching their recipients in the form of 'edutaintment' is also remarkable [9]. Moreover, the data collected as a part of these processes can help in the restoration of irreplaceable sites after unexpected catastrophes, as recently highlighted by the fire at the Notre Dame cathedral in Paris [18].

Thus, this article is part of the exploration of the possibilities of digital modeling for historical heritage. Workflows (or pipelines) that are applicable to photogrammetry are being simplified, although they are still not fully standardized. Some of them are becoming clearer and simpler, making them accessible to the uninitiated, but they coexist with others that do require specialization. Some of the possible results can still be achieved in very different ways, sometimes by retracing routes that have already been experienced and commented on. The case that is discussed in this article has tried to avoid this as much as possible by using audiovisual procedures and using only digital photography cameras in the capture, with the aim of obtaining a useful model that works as a video game scenario as well as in a conservation and restoration environment. It was launched before some initiatives were published, several of whose elements we agree with [17], and with which we share the view that it will be necessary to continue looking for procedures that are easy to implement, effective, efficient, cheap, and that can be standardized or become universal.

In an attempt to gain a wider picture by drawing on a multidisciplinary environment, more than a few cinematography techniques are also suitable for projects of this type [19]. Minimum standards of precision and accuracy or fidelity must be achieved in the multispectral characterization of the surfaces in order to obtain the right data for HBIM [3,20]. During shooting, cinematographic photography is similarly concerned with the on-screen results, which are achieved through adequate attention to exposure and color calibration. As such, in both cases there is a need to take extreme care in the preparation procedures for shooting.

DHCs can and should be used for dissemination as they are part of a collective heritage [7,9,21]. The main goal of the audiovisual sector is that the stories engage the audience. Since the same is true for the dissemination of DCH, it would be logical to use the methods and procedures adopted by the former, i.e., defining and following a script prepared for that purpose [17]. Indeed, some of the processes that will be discussed in this text are specific to the audiovisual industry, such as: pre-production, multi-camera shooting in rigs, care in exposure, the use of RAW files, re-topology and the integration of lighting and environment.

In this case, the aim was to achieve immersion and presence, with full awareness of having discarded the real environment, in the sense attributed to it by [22]. The aim was to provide a simple viewing in VR with a level of quality that allows the user to experience photorealistic sensations [23].

There are ever more platforms available for this type of experience, although the systems still suffer from many limitations, as their manufacturers warn [17]. It is important to emphasize that at the time of starting this project, the most widespread VR devices were still unable to correctly reproduce the resolution and quality of the models that are being obtained through photogrammetry. However, given the vertiginous advances of the last few years, this team has no doubt that within a short time the performance of the systems that allow VR to be experienced will surpass that of most existing scenes and models.

The objective should be independent of the platform used. Rather, it will have to refer to the appearance of real materiality of the content, not to the predisposition to which the technology subjects the viewer. It will have more to do with contemplation, with the amazement of being in the middle of a story that leaves a feeling of photorealism. It will have to take advantage of the immersive capacity of the narrative device in order to overcome the resistance that the spectator may oppose to letting him or herself be carried away by the story, in the sense that whoever experiences it may reach a state of pathos such as that described by Sergei M. Eisenstein, whereby one is taken out of oneself and immersed in the reality presented on the screen [24]. To achieve this immersion, it was essential to work with lighting and the setting of scenarios with techniques that achieve an optimal degree of integration [12,17].

This article describes all of the processes that were carried out in order to obtain the model of the interior of the Torre de la Cautiva (The Tower of the Captive) of the Alhambra in Granada, to achieve a stereoscopic piece that can be experienced in VR 360◦ , according to a script that was set in simulations throughout different epochs. For a proper analysis of the experience, we will first present a brief approach to the selected case study and the challenges it posed. Subsequently, the methodology and workflows will be explained in greater detail. Finally, the conclusions of this study will be presented and a series of future lines of research will be proposed.
