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[EN] Rock art documentation is a complex task that should be carried out in a complete, rigorous and exhaustive way, in order to take particular actions that allow stakeholders to preserve the archaeological sites under constant deterioration. The pigments used in prehistoric paintings present high light sensitivity and rigorous scientific color degradation mapping is not usually undertaken in overall archaeological sites. Microfading spectrometry is a suitable technique for determining the light-stability of pigments found in rock art paintings in a non-destructive way. Spectral data can be transformed into colorimetric information following the recommendations published by the Commission Internationale de l'Eclairage(CIE). The fading degree can be evaluated through the color changes produced, computing both color and chromatic differences. Microfading Tester (MFT) measurements on spot samples are time-consuming and difficult to materialize on-site. This paper presents the results of statistical Gaussian process interpolation to map the potential MFT spectral variations overtime on a scene full of prehistoric rock art paintings. In addition, a descriptive analysis of color variations that may suffer the rock art motifs overtime has been carried out. The advanced statistical methodology implemented can highlight potential changes on some rock support areas, and stable conditions on the painted red motifs over time, which can help to establish future conservation actions in the archaeological site. (C) 2020 Elsevier Masson SAS. All rights reserved., This research was partially supported by Research and Development Aid Program PAID-01-16 from the Universitat Politècnica de València [FPI-UPV2016 Sub 1 grant].

In recent years, Augmented Reality (AR) technology has experienced considerable progress and the combination of AR and 3D modeling opens up new opportunities regarding 3D data visualization and interaction. Consequently, the dissemination of cultural heritage can benefit from these technologies in order to display the cultural assets as realistically and interactively as possible. In this way, high-accuracy 3D models are integrated in the real world.Nevertheless, progress has also still been limited due to several factors. The paper presents a case study based on the recreation of the Queen Victoria sculpture in an AR application. Furthermore, the environment of the sculpture is simulated by panoramic images, inside the Library of Parliament in Ottawa, Canada. The main problems for the development of an AR smartphone application from panoramic images and photogrammetric 3D data are described in this paper. The characteristics of AR systems are explained in detail, analyzing all the steps involved and the available solutions considered.

The use of photogrammetry and terrestrial laser scanning for building information modelling (BIM) in the documentation and conservation of Cultural Heritage (CH) is now well established. By combining BIM with the latest visualization technologies, powerful, semi-immersive experiences can be developed to enhance the dissemination of CH. In semi-immersive experiences such as Augmented Reality (AR), digital content can be overlapped on to physical spaces, providing a new way to interact with both the physical space and the digital content. This paper discusses the translation of a digital object created using BIM, into a physical object and the utilisation of this physical object as a trigger for an AR experience. The case study looks at one of the neo- Gothic window frames from the House of Commons in the Centre Block of the Parliament Hill National Historic Site, in Ottawa, Canada. The window frame is one in a series that represents a Canadian province or territory with a stained glass feature that includes floral emblems and heraldic symbols from the respective provincial or territorial shield. The frame in this case study corresponds to the stained glass window of five provinces. Using the replica frame as a target, the user can select which stained glass windows they would like to view in the AR application. Through these combined technologies, we argue that CH can be revealed in a more interactive way and therefore more engaging manner – making even inaccessible architectural details readily available to the public.

[EN] Currently, marker-based tracking is the most used method to develop augmented reality (AR) applications (apps). However, this method cannot be applied in some complex and outdoor settings such as prehistoric rock art sites owing to the fact that the usage of markers is restricted on site. Thus, natural feature tracking methods have to be used. There is a wide range of libraries to develop AR apps based on natural feature tracking. In this paper, a comparative study of Vuforia and ARToolKit libraries is carried out, analysing factors such as distance, occlusion and lighting conditions that affect user experience in both indoor and outdoor environments, and eventually the app developer. Our analysis confirms that Vuforia¿s user experience indoor is better, faster and flicker-free whether the images are properly enhanced, but it does not work properly on site. Therefore, the development of AR apps for complex outdoor environments such as rock art sites should be performed with ARToolKit., The authors gratefully acknowledge the support from the Spanish Ministerio de Economia y Competitividad to the project HAR2014-59873-R. Similarly, the authors want to express their gratitude to the General Directorate of Culture and Heritage, Conselleria d'Educacio, Investigacio, Cultura i Esport, Generalitat Valenciana for letting us access and carry out research at the archaeological site.

[EN] Prehistoric rock art paintings, specifically rock-shelters exposed to environmental and anthropogenic factors, are usually faint and severely damaged, being them difficult to identify and understand by visitors. Augmented Reality (AR) supplements reality with virtual information superimposed onto the real world. This sensor-based technology in smartphones/tablets can improve the paintings experience displaying the 2D digital tracings overlapped onto the real scene (rock with faint paintings). This paper presents an AR application (app) developed in Cova dels Cavalls that shows a recreation of a possible original composition full of motifs with descriptive information to improve current guided tour user experiences. This case study aims to evaluate the rock art AR app targeting non-expert visitors as a means of improving rock art knowledge and sensibility of a fragile archaeological UNESCO Work Heritage site. To achieve this, a variety of participants with different backgrounds and interests tested the AR app on site and answered a complete questionnaire about the use of AR mobile apps. Overall, the results showed great acceptance of this AR app, mainly because in addition to adding new information interactively, it helps to identify the rock art motifs, as well as to recognise them quickly, improving their understanding., The authors gratefully acknowledge the support from the Spanish Ministerio de Economia y Competitividad to the project HAR201459873-R. The authors acknowledge the authorisation of the Conselleria d'Educacio, Investigacio, Cultura i Esports the chance to carry out research at this exceptional archaeological site.

[EN] The documentation of archeological sites requires the adoption of non-destructive techniques to safeguard the unique legacy coming from prehistoric periods. This article tackles the assessment of lightfastness properties on a rock art site to deter- mine the behavior of motif's color deterioration over time in Remi¿gia Cave, Castello¿n (Spain), which is considered part of a UNESCO World Heritage Site. The measurements were performed using a microfade testing device to analyze the spectral characteristics and the aging properties of the colorant system and various substrates on site. Two scenarios have been identified depending on whether the lightness (L*) parameter of the rocky substrate changes or not in relation with the painted motifs. If the substrate remains stable without any change, red motifs con- taining iron oxide pigments will become more visible. If the substrate becomes lighter, the pigments will experience similar changes. Therefore, the contrast between paintings and support will be considerably enhanced., The authors also would like to thank the Generalitat Valenciana for providing access to the site during the measurement campaigns. Fruitful comments from the Spanish archeologists Prof. Valentín Villaverde and Dra. Esther López-Montalvo are also gratefully acknowledged. The authors acknowledge the research project HAR2014-59873-R from the Spanish Ministerio de Economía y Competitividad for providing financial support.

[EN] Augmented Reality (AR) applications have experienced extraordinary growth recently, evolving into a well-established method for the dissemination and communication of content related to cultural heritage¿including education. AR applications have been used in museums and gallery exhibitions and virtual reconstructions of historic interiors. However, the circumstances of an outdoor environment can be problematic. This paper presents a methodology to develop immersive AR applications based on the recognition of outdoor buildings. To demonstrate this methodology, a case study focused on the Parliament Buildings National Historic Site in Ottawa, Canada has been conducted. The site is currently undergoing a multiyear rehabilitation program that will make access to parts of this national monument inaccessible to the public. AR experiences, including simulated photo merging of historic and present content, are proposed as one tool that can enrich the Parliament Hill visit during the rehabilitation. Outdoor AR experiences are limited by factors, such as variable lighting (and shadows) conditions, caused by changes in the environment (objects height and orientation, obstructions, occlusions), the weather, and the time of day. This paper proposes a workflow to solve some of these issues from a multi-image tracking approach., This work has been developed under the framework of the New Paradigms/New Tools for Heritage Conservation in Canada, a project funded through the Social Sciences and Humanities Research Council of Canada (SSHRC).

[EN] Non-destructive rock art recording techniques are getting special attention in the last years, opening new research lines in order to improve the level of documentation and understanding of our rich legacy. This paper applies the principal component analysis (PCA) technique in images that include wavelengths between 400-700 nm (visible range). Our approach is focused on determining the difference provided by the image processing of the visible region through four spectral images versus an image that encompasses the entire visible spectrum. The images were taken by means of optical filters that take specific wavelengths and exclude parts of the spectrum. Simulation of rock art is prepared in laboratory. For this purpose, three different pigments were made simulating the material composition of rock art paintings. The advantages of studying the visible spectrum in separate images are analysed. In addition, PCA is applied to each of the images to reduce redundant data. Finally, PCA is applied to the image that contains the entire visible spectrum and is compared with previous results. Through the results of the four visible spectral images one can begin to draw conclusions about constituent painting materials without using decorrelation techniques., [ES] Las técnicas documentación no destructivas de arte rupestre están recibiendo especial atención en los últimos años, abriendo nuevas líneas de investigación para la mejora del nivel de documentación y comprensión de nuestro patrimonio. Este artículo aplica la técnica de análisis de componentes principales (ACP) en imágenes de longitudes de onda entre 400-700 nm (rango visible). Nuestro enfoque se centra en determinar las diferencias proporcionadas por el procesamiento de imágenes de la región del visible a través de cuatro imágenes espectrales y una imagen que abarca el espectro visible completo. Las imágenes se tomaron con filtros ópticos que recogen longitudes de onda determinadas y excluyen parte del espectro.Se preparó una simulación de pigmentos de arte ruprestre en laboratorio. Para ello se hicieron tres tipos de pigmentos diferentes simulando la composición del material de las pinturas rupestres. Se analizaron las ventajas de estudiar el espectro visible en imágenes separadas. Además, se aplicó ACP a cada una de las imágenes para reducir la información redundante. Finalmente, se realizó ACP a la imagen que abarca todo el espectro visible y se comparó con los resultados anteriores. A través de los resultados de las cuatro imágenes espectrales del visible se pueden sacar conclusiones sobre los materiales que constituyen la pintura sin aplicar técnicas de decorrelación.