Hidden Images in Atxurra Cave (Northern Spain) a New Proposal for Visibility Analyses of Palaeolithic Rock Art in Subterranean
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Quaternary International 566-567 (2020) 163–170 Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint Hidden images in Atxurra Cave (Northern Spain): A new proposal for visibility analyses of Palaeolithic rock art in subterranean environments T Iñaki Intxaurbea,d, Olivia Riverob,Ma Ángeles Medina-Alcaidec, Martín Arriolabengoad, Joseba Ríos-Garaizare, Sergio Salazarb, Juan Francisco Ruiz-Lópezf, Paula Ortega-Martínezg, ∗ Diego Garatea, a Instituto Internacional de Investigaciones Prehistóricas de Cantabria (IIIPC, Gobierno de Cantabria, Universidad de Cantabria, Santander). Edificio Interfacultativo, Avda. Los Castros s/n, 39005, Santander, Spain b Dpto. Prehistoria, Historia Antigua y Arqueología, Universidad de Salamanca, 37008, Salamanca, Spain c Dpto. Historia, Facultad de Letras, Universidad de Córdoba, 14071, Córdoba, Spain d Dpto. Mineralogía y Petrología. Euskal Herriko Unibertsitatea/Universidad del País Vasco, 48940, Leioa, Spain e Archaeology Program, Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Paseo Sierra de Atapuerca 3, 09002, Burgos, Spain f Dpto. de Historia. Universidad de Castilla – La Mancha, 16001, Cuenca, Spain g Independent Researcher ARTICLE INFO ABSTRACT Keywords: Visibility has been the subject of study in Palaeolithic rock art research ever since the discovery of Altamira Cave Cave art in 1879. Nevertheless, until now, the different approaches have been based on subjective assessments, due to Viewshed computational limitations for a more objective methodology. Nowadays, cutting-edge technologies such as GIS Archaeological context allow us to address spatial studies in caves and overcome their geomorphologically complex and closed char- Cave geomorphology acteristics. Here we describe an innovative methodology that uses computing tools available to any researcher to GIS study the viewsheds of the graphic units in decorated caves. We have tested its validity on the recently dis- Palaeolithic covered rock art ensemble of Atxurra Cave, in Northern Spain. We demonstrate that this technology (GIS), widely used in other fields of archaeology, especially in outdoor studies, is also useable in caverns, taking into account the complex morphologies -ceilings and diverse floor-levels, for example. These programmes have also allowed us to consider the lighting systems used by the prehistoric groups inside the cave, as well as various data previously estimated by other authors, such as the height of individuals during the European LUP. The dyna- mism of these tools −2.5D-, as well as the advancement of new 3D GIS technologies, will allow in the future remarkable progress in these types of structural studies for a better understanding of Palaeolithic cave art phenomena. 1. Introduction: research precedents and objectives by other researchers (Pastoors and Weniger, 2011). The final aim of these studies is usually to observe patterns in the The visibility (and invisibility or concealment) of Palaeolithic rock topographic distribution or organization of the rock art ensembles art images in European caves has attracted several researchers’ atten- within the cave. These patterns can then be compared between different tion since the discovery of cave art in Altamira in 1879 (Sanz de rock art sites (generally within the same geographical and chron- Sautuola, 1880), and its subsequent approval by the scientific com- ological framework). This has led to numerous interesting proposals, munity in 1902 (Cartailhac, 1902). In recent years, this aspect has been from the use of the term of sanctuaries for these caves (Leroi-Gourhan, considered by several authors, usually to compare decorated zones in 1964) to inferences about their organization (González-Sainz, 2017)or the same cave, or to illustrate Point Of Views (POVs) of each figure or even attempts to interpret their meaning in the form of sentences panel on the cave plan (González-García, 2001; Villeneuve, 2008; (Sanchidrián, 1992). Interest in spatial studies is more than justified, Garate, 2010; Ruiz-Redondo, 2014; Ochoa and García-Diez, 2018; and for that reason methods should be developed that are as objective Jouteau et al., 2019). They measure the visibility area in some cases, as possible, to validate the observations and avoid (as far as possible) all and compare it with such other spatial features as occupancy, estimated subjective interference or errors derived from personal appreciations. ∗ Corresponding author. E-mail address: [email protected] (D. Garate). https://doi.org/10.1016/j.quaint.2020.04.027 Received 13 February 2020; Received in revised form 3 April 2020; Accepted 15 April 2020 Available online 21 April 2020 1040-6182/ © 2020 Elsevier Ltd and INQUA. All rights reserved. I. Intxaurbe, et al. Quaternary International 566-567 (2020) 163–170 Most spatial studies involve estimating the visibility area on a cave recording method previously tested (Trimmis, 2018). plan. The use of GIS is usually avoided, adducing the limitations pro- Prior to the geolocation process, and to minimize as much as pos- duced by the three-dimensional features of caves, identified previously sible any type of magnetic distortion that could alter the measurements, in a work in La Griega Cave (Ortega, 2014), and other reasons of costs the device was calibrated within the karst system itself, and in parti- or time consumption. cular, in the main gallery of Armiña Cave (the lower part of the cave- The use of GIS in “sensorial” archaeology, and specifically in visi- system) (Fig. 2A). bility studies in rock art (Wheatley and Gillings, 2000; Gillings, 2015; Geolocating the archaeological elements with DistoX2 requires a Díaz-Andreu et al., 2017; Wernke et al., 2017; Wienhold and Robinson, process similar to the production of a conventional speleological 2017) has become very popular in recent years because of their preci- survey, in which it is necessary to draw a polygonal starting from a sion and ability to interpret the terrain, despite their strengths and point 0. To position this point 0 in space with coordinates in a specific limitations, previously identified (Gillings, 2017). These techniques are datum, it can be georeferenced on the surface, using a differential GPS, usually employed in open-air studies, but some precedents are known in for example. However, if a previously georeferenced point-cloud exists, closed and three-dimensionally complex sites (Landeschi, 2019), in- as is the case of the caves that have been scanned three-dimensionally cluding caves (Ortega, 2012, 2014). One of most successful analytical -and our case of Atxurra-, obtaining the coordinates of identifiable platforms directly uses the 3D mesh for different analyses of visibility in “reference points” (Fig. 2B and C) is easy, and the polygonal can be these types of environments (Dell’Unto et al., 2016; Landeschi et al., started from there. 2016). Once the fieldwork was carried out (Fig. 2D), the data was pro- The general objective of the present paper is the implementation of cessed in the VisualTopo® (David, 2009) program, making the pertinent “digital technologies” (like GIS or 3D models) to advance in studies on magnetic declination corrections. Finally, the data was converted to the the spatial structure of Upper Palaeolithic rock art ensembles in cave datum of our choice (ETRS 89 UTM 30). environments. As noted above, 3D GIS tools, like Lines of Sight (LOS), have been tested for visibility analyses in complex environments 3. Methodology: analysing visibility using GIS inside the cave (Landeschi et al., 2016, 2019; Landeschi, 2019). However, despite the accurate results that could be obtained in simulations and archae- 3.1. Recreation of cave geomorphology ological analyses with these 3D GIS technologies, rapid conversions to 2.5D GIS technology can offer also valid results, for example for Atxurra Cave was scanned by the company Gim-Geomatics SL using a viewshed analyses of Palaeolithic rock art ensembles in caves. The terrestrial Laser Scanner 3D Faro® Photon 120. Approximately 59.6 specific objectives of the present study are: 1) to describe the steps million points have been obtained per scan, in 538 scan stations. As for followed using certain GIS programmes to obtain precise measurements the accuracy of the operation, the estimated error is 1 mm per 25 m, of the viewshed areas of parietal figures, identifying and resolving the with 90% reflectance. After this, the point cloud was treated with main limitations; 2) to test their validity in the cave of Atxurra ArcGIS® by Gim-Geomatics SL to obtain two raster files. This work was (Northern Spain) and verify the results in situ, since its conditions are done in “strict” 3D because in 2.5D it fails both on walls and when ideal for this purpose (decorated sectors hidden from the main transit passages overlap. First a raster was defined with a cell size of about zones in the passage, archaeological remains associated with parietal 2.5 cm on which we dump the data that interests us. In this case art and related to the illumination systems used by the artists, etc.); 3) “minimum Z” is defined as the minimum value of the 3D mesh in that to explain different kinds of visibility of images in the same cave re- cell (if there are several nodes, only the minimum dimension) and garding their location, but also in relation with their iconography and “maximum Z” the maximum value. That is, search among all the nodes technique or the different illumination systems. that fall in the cell, for