**4. Conclusions**

The Torre de la Cautiva is located in one of the walls of the Alhambra in Granada, a complex named a World Heritage Site in 1984, and is one of its enclaves to which the general public does not usually have access.

Bearing in mind its historic value and the fact that it can rarely be enjoyed in person, the challenge of creating a photorealistic 3D model of its interior was posed. This initiative was intended to serve both conservators and restorers, and as a DCH site for public dissemination and entertainment. Throughout this article we have explained the workflow that achieves this.

Regarding the execution of the project, it should be noted that the data collection was carried out with important restrictions: only ten hours to shoot, using only natural light, and with no cables or control points. The model was built with low-cost photogrammetry techniques, using conventional DSLR cameras as passive sensors. The display was planned on 360◦ Stereoscopic VR platforms with interactivity and 3DoF on the scale of freedom of action.

The script contemplated several scenes that predominantly focused on the past, although one of them was set in the present day. The others recreated a night storm, a typical scene of the period in which the interior of the tower was decorated, and a third evoking the routine atmosphere of the captive princess's lodging. In addition, three lines of work were defined for the script: that of the stage, which should be given maximum prominence, that of the characters with a narrative sense and that of the assets, fulfilling the function of ambience and decoration. A specific procedure was used to obtain data for each of these lines.

Without reaching the demands that HBIM informative models may have, a certain historical and traditional coherence with the period scenes was attempted, as well as a certain level of detail and fidelity to the original decoration.

Although in agreement with the academic literature in many points and starting from a script and a desire for photorealism, this project also adopted some procedures commonly employed in the audiovisual industry, which is accustomed to this type of complexity. The pre-production process is therefore analyzed in more detail within its workflow.

Since it is difficult to reach an agreement on the meaning of photorealism, especially if the past is to be shown, it was established as a principle of the project that it could be perceived naturally and coherently by the viewer. In this case, moreover, being accurate with geometry and color characterization was assumed as being of the utmost importance.

Another common process in the audiovisual industry that was an important part of the project workflow was the multi-camera work, which was carried out with vertical rigs and careful planning.

In the post-shooting processes, the importance of re-topology to obtain simpler meshes and of UDIM textures to retain great definition of detail was clear, as was the importance of the script to be able to work separately on the integration of the elements in the scenes, their lighting, environmental effects, and animation.

Two key ideas for future work stem from the experience of this project: the convenience of using robotic devices coupled to AI algorithms to optimize decisions during the data acquisition process, and the adaptation of rendering engines, not only for final viewing or creation of VR environments, but also for previsualization and tests, since they radically reduce the time required to perform different procedures.

**Author Contributions:** Conceptualization, A.J.B., X.P.S., M.A.; methodology, A.J.B., X.P.S., M.A.; validation, A.J.B., X.P.S., M.A., E.M.S., J.S., Á.G.M.; investigation, A.J.B., X.P.S., M.A., Á.G.M.; resources, M.A., M.G.-V.; data curation, M.G.-V., J.S., R.C.; writing—original draft preparation, A.J.B.; writing—review and editing, A.J.B., X.P.S., E.M.S.; visualization, A.J.B., M.A., M.G.-V., R.C.; supervision, A.J.B., X.P.S., M.A., E.M.S., J.S., Á.G.M.; funding acquisition, Á.G.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by of the Ministry of Science and Innovation of Spain, project number RTI2018-097633-A-I00, 'Photonic restoration applied to cultural heritage: Application to Dali's painting: Two Figures'.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** The authors wish to thank Miopía FX, GVAM SL, Voxel School of Digital Arts and its students, as well as the Patronato de la Alhambra y El Generalife de Granada (Alhambra and Generalife Trust).

**Conflicts of Interest:** The authors have no conflict of interest to declare. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
