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Journal of Archaeological Science 40 (2013) 1879e1889

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Journal of Archaeological Science

journal homepage: http : / /www.elsevier .com/locate/ jas

Latest developments in rock art recording: towards an integraldocumentation of Levantine rock art sites combining 2D and 3Drecording techniques

Inés Domingo a,*, Valentín Villaverde b, Esther López-Montalvo c, José Luis Lerma d, Miriam Cabrelles d

a ICREA at Universitat de Barcelona/SERP, Departament de Prehistòria, Història Antiga i Arqueologia, Montealegre, 6-8, 08001 Barcelona, SpainbUniversitat de València, Departament de Prehistòria i Arqueologia, Blasco Ibáñez, 28, 46010 Valencia, SpaincUniversidad de Zaragoza, Departamento de Ciencias de la Antigüedad, Área Prehistoria, Facultad de Filosofía y Letras, C/Pedro Cerbuna, 12, 50009 Zaragoza, SpaindUniversitat Politècnica de València, Dept. Cartographic Eng., Geodesy and Photogrammetry, Camino de Vera s/n, Edificio 7i, 46022 Valencia, Spain

a r t i c l e i n f o

Article history:Received 9 October 2012Received in revised form28 November 2012Accepted 29 November 2012

Keywords:Digital rock art recordingDocumentationTerrestrial laser scanningPhotogrammetry3D modelling2D tracingsLevantine rock art

* Corresponding author. Tel.: þ34 934020826; fax:E-mail addresses: ines.domingo@ub.edu (I. Domin

(V. Villaverde), emontalvo@unizar.es (E. López-M(J.L. Lerma), micablo@upvnet.upv.es (M. Cabrelles).

0305-4403/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.jas.2012.11.024

a b s t r a c t

This paper presents a further step in the integral documentation of prehistoric rock art, combining 2Dand 3D digital recording techniques. Image processing and digital enhancement techniques are aninvaluable aid to obtain high quality and accurate 2D recordings, especially when working with faintmotifs or complex superimpositions. But what constitutes a real breakthrough is the possibility ofcombining 2D digital tracings with metric 3D models, providing a whole set of metric outputs thatimprove our understanding of the motifs in their context and, at the same time, can be used to deliveraccurate metric reproductions.

The Levantine rock art at Cingle de la Mola Remigia (Ares del Maestre, Castellón, Spain) is used to testthe integral documentation performance combining 2D and 3D recording techniques to yield not merelydigital copies, but state-of-the-art documentation.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Since 1902, when the prehistoric date of Altamira rock paintingwas acknowledged, different methods of graphic documentation ofpainted and engraved motifs have been tested. The problems ofpreservation and visualization of rock art (both in situ and inphotographs) led to the extensive use of drawings and differenttracing methods as the main tools for archaeological documenta-tion. The aim was to achieve faithful and objective reproductionsthat proved the existence of rock art in a particular site. Further-more, those two-dimensional (2D) methods were used to facilitatethe study and management of the sites, to analyse and assess thestate of preservation and, finally, to make rock art accessible to thepublic. Such documentation has sometimes turned out to be ofincalculable heritage value due to either the degradation of the siteor even the disappearance of the documented motifs. In the 21st

þ34 93 403 77 33.go), valentin.villaverde@uv.esontalvo), jllerma@cgf.upv.es

All rights reserved.

century, further explorations of new indirect methods are beingcarried out in order to obtain even more faithful documentationapproaches, both from the metric and formal point of view,avoiding direct intervention both on the art and on the rock surface.

The 20th century can be considered the period of the greatestrock art discoveries worldwide. But it is also characterized byplundering and degradation of rock art sites due to human action.Many examples of this could be given worldwide. But withinLevantine rock art, which will be the focus of this paper, there areshocking examples: the figures torn away or intentionallydestroyed in Roca dels Moros and els Gascons (Barranco de Cala-patá, Teruel) (Cabré, 1915: pp. 135e136), or those in several rockshelters at Barranco de la Valltorta (Castelló) (Cabré, 1923; Viñas,1982), and the figures sawn off with a power saw in the Benir-rama rock shelter (Vall de la Gallinera, Alacant) (Hernández et al.,1998). Nowadays the existence of these motifs, which are WorldHeritage, can only be proved from early recordings produced beforesuch appalling destructive acts were perpetrated.

Graphic documentation is also crucial to assess art authenticity.Recent revision of figures at the Santimamiñe Palaeolithic site(Biscay), led to the identification of addition and retouching of

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some figures (a bison, a horse and a bear) that had taken place incurrent times (González-Sainz and and Ruiz, 2010); this would nothave been detected without previous documentation of the site.

Therefore, exhaustive, integral and non-invasive documentationof rock art sites is an indispensable requirement both for their studyand to monitor degradation and alteration processes, and to guar-antee the preservation and authenticity of this heritage.

In the last decades of the 20th century, recording methods forrock art were radically transformed with the introduction of digitaltechnologies. The digital age has contributed a wide range ofequipment to archaeology, software and technologies that cancapture, retouch and digitally treat colour and geometry. Digitalimage processing and enhancement tools such as Adobe Photo-shop, GIMP, ImageJ, rdf, have been used to record painted andengravedmotifs (see: Vicent et al., 1996;Montero et al.,1998; Cachoand Gálvez, 1999; Villaverde et al., 2000; Clog et al., 2000; Domingoand López-Montalvo, 2002; López-Montalvo and Domingo, 2005,2009; Rüther, 2007; Martínez-Bea, 2009; Cassen and Robin, 2010;Ortiz et al., 2010).

Likewise, digital photogrammetry and three-dimensional (3D)scanner laser have been used to obtain extremely precise and highquality tridimensional reproductions, both for motifs and for theshape and dimension of the rock surface (Robson et al., 2001; El-Hakim et al., 2004; Díaz-Andreu et al., 2006; Lerma et al., 2010).

The results offered so far by both digital recording methods (2Dand 3D) have revolutionized graphic documentation techniques forrock art heritage: they reduce subjectivity and increase graphic andmetric precision. But both methods present deficiencies when theyare applied independently. On the one hand, 2D recording tech-niques are still producing metric distortion in the reproduction ofpanels (López-Montalvo and Domingo, 2005). On the other hand,photorealistic 3D models of sites with conservation problemsproduce volumetric reproductions where faded motifs or complexsuperimpositions cannot always be identified.

Bearing in mind these problems, our objective is to go a stepfurther in current digital rock art recording techniques bycombining both methods (2D and 3D digital recordings) in order toobtain highly precise integral reproductions. Applying thiscombinedmethod to the Levantine rock art site of Cingle de la MolaRemigia (Ares del Mestre, Castelló) (UNESCO World Heritage since1998), a new reading that surpasses previous mere digital copieshas been obtained, including an integral, metric and analyticreading of both the rock surface and the motifs.

2. Method: a new approach to the integral reproduction ofrock art. El Cingle de la Mola Remigia as a case study

Rock art reproduction or tracing, like any archaeological illus-tration, has a technical aim. Generally speaking, the aim is toproduce descriptive and analytic graphic documentation of use forarchaeological analysis that includes a metric scale to inform of thesize of figures. Scale tracings (either traditional or digital) are usefulin a number of ways. They make the visualization of themes andoverlapping motifs easier and facilitate future study and interpre-tation with both scientific and diffusion objectives. Furthermore,they can also be used for assessing alteration and degradationprocesses that have an impact both on motifs and on the rocksurface.

The heritage value of rock art recordings demands integralreconstructions of sites that should include the following fourlevels of data (Fig. 1):

1. An individual record (a digital reproduction or tracing) done toscale for each motif. In this initial record the motif must appearindependent from the rock surface, so attention can focus on

the details represented in order to facilitate comparisons withother motifs (shape, colour, size, proportions, etc.). This sort ofrecord is particularly useful for typological classification, toestablish stylistic variations and to monitor preservation.

2. A second reproduction showing the motifs in relation to eachother. This record will be useful for the study of compositionand for developing a superimposition sequence of the panel.

3. The third reproduction should show the relation that figures,compositions and scenes have with the rock surface. Themorphology and irregularity of the rock surface can have aninfluence on the narrative discourse of scenes and on theposition and special order of figures. In some cases, the artistsintentionally modified the morphology of the rock surface inorder to adapt it to their creation.

4. Finally, a record that shows the multiplicity of planes andperspectives from where the motif recorded can be observed.

These four types of basic recording should constitute theminimum scientific documentation required in the field of rock art.Below, we apply them to Cingle de la Mola Remigia as our casestudy.

2.1. Individual reproduction or tracing

The starting point of documentation should be an individualizedunderstanding of each motif on the panel.

2D reproduction achieved bymeans of digital enhancement andprocessing of high resolution photographs currently offers the mostpractical results for this type of analysis. The possibility of workingdirectly on digital images that can be greatly magnified makesobservation of detail easier; details that are barely visible on loca-tion or during the execution of direct tracings. Besides, digitalimage processing and enhancement tools, such as Photoshop,imageJ, GIMP, offer the possibility of emphasizing differencesbetween pigments and the rock surface, they can render paintingsthat were invisible visible again. With these colour selection tools,high precision digital tracings can be produced (for a detailedexplanation of this procedure see: Domingo and López-Montalvo,2002; Domingo, 2007).

Two-dimensional reproduction of motifs painted on tridimen-sional surfaces can only take into account height and width but notthe third dimension, depth, so it involves certain metric distortion.Such deformation is further exacerbated by the use of photographsthat, due to focal distance and shooting angle, already have somedistortion. In the production of tracings, it is important that digitalphotographs are free from geometrical distortions. Therefore, it isnecessary to take into account both perspective distortion anddistortion that might be caused by the lenses used.

Perspective distortion can be minimized by keeping the opticaxel of the camera as orthogonal to the motifs as possible. Thechoice of shooting angle conditions the two-dimensional repro-duction of the tracing. A camera optic axel that is practicallyorthogonal to themotifs guarantees that the study of themotif stylewill be influenced very little by the rock surface morphology(Fig. 2).

Software for metric rectification of images (for example, rdf) canremap an image from aminimumof four coordinates. The quality ofthe results will depend on the quality of the photographs used, onthe precision and distribution of the points marked, and, above all,on the flatness of the surface. But these 2D digital post-processingsoftware that correct the effect of perspective distortion, are moresuitable to correct distortion on flat surfaces and lineal profiles thanfor the irregular surfaces characteristic of rock art (Rüther, 2007). Inthe case of rough surfaces or those with some relief, correctedimages continue to present a certain degree of distortion. The use of

Fig. 1. Documentation needed for an integral reproduction of rock art.

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calibrated digital cameras that can correct lens distorting effects isalso recommended. When this is not possible more points shouldbe measured in order to correct lens and perspective distortingeffects (Lerma, 2002: pp. 74e76 and 96e109). Fig. 3 shows howa digital image taken with a non-metric camera can distort a motifeven to the point of disfiguring it, and have an effect on the motifanalysis. For this reason, authors recommend proceeding toa previous correction of image deformation before digital tracings

or individual reproductions are made. Photographic distortion canbe corrected more easily when we work with calibrated camerasbecause then we are aware of the parameters that cause the effectsof tangential and radial distortion. When we do not have thepossibility of using a metric camera, taking a sufficient number ofphotos in order to do a photogrammetric calibration later is rec-ommended (this is usually done after the field work). The simplestsolution would be to photograph motifs with lenses that produce

Fig. 3. Correction effect of lens distortion in an image of a goat from shelter 1, Cingle de la Mola Remigia. The distortion fundamentally affects anatomic proportions.

Fig. 2. Photographs of archers 1e5/IX from Cingle de la Mola Remigia from different viewpoints. Image c, taken with the most orthogonal optic axel, has the least distortion.

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minimal distortion (aspheric type, for instance) and to limit one’sstylistic and compositional analysis to the central part of digitalimages. (Note: we assume that digital images used are taken witha digital camera. If digital images are from previous scanning ordigitalizing processes the influence of the scanner digitalizing errorwill have to be considered.)

In any case it is important to remember that in prehistoric rockart, painted and engraved images are themselves two-dimensionalinterpretations (except for bas-reliefs) of real models that havebeen executed on a tridimensional rock surface. Therefore, thedistortion created in the process of two-dimensional reproductionor tracing of each motif is, in our opinion, minimal and acceptable;provided that a frontal view of the motifs is selected and that thesurfaces to be represented are small and relatively flat.

Fig. 4. Process of reproduction

Documentation generated by retouching 2D images can be veryuseful in several ways. In the first place, it helps reading andcomparison of motifs in order to analyse similarities and stylisticchanges (formal, metric and technical). But it is also fundamental inhelping to visualize motifs and themes that might be very deteri-orated or integrated in complex overlapping representations thatare hard to read at the sites or on photographs (Fig. 4) (see, forexample, Martínez and Villaverde, 2002; Domingo et al., 2007).

The equipment and lenses provided by digital photography cancurrently obtain images whose wave lengths differ from thoseobtained by traditional methods (infrared, ultraviolet, etc.). Thismeans that there are far more possibilities of recording paintedor engraved motifs that have been covered or veiled by calciteor organic matter coats. These images can be combined with

of an individual tracing.

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traditional digital photographs in order to offer synthetic tracingsthat are a great improvement on the simple treatment of imagesdone with traditional software.

It is also crucial to advance towards better control of colour bymeans of archaeometric methods and to achieve an objectivecharacterization of temperature. This is an area which has receivedscarce attention but, if documentation is to become a tool forpreservation control, it should become a priority for work andresearch.

2.2. Spatial relation among figures

The aim of the second reproduction is to facilitate the identifi-cation of potential compositions and scenes, and to analysepatterns of addition and superimposition. These are both funda-mental aspects in reconstructing the sequence of a rock art site.This reproduction should include all the motifs and remainspreserved, regardless of their grade of preservation, their entity orfigurative concept (López-Montalvo and Domingo, 2005). 2Dtechniques have so far provided acceptable results for this type ofreproductions (Fig. 5). However, its main limitation is that it inev-itably generates surface distortion because it ignores the thirddimension, depth, especially when recording irregular walls. Soevenwhen these reproductions offer good results, it is important toacknowledge that they are usually metrically inaccurate.

When we obtain a two-dimensional representation of a tridi-mensional drawing area we select a single viewpoint that willprovide a slanted image of a tridimensional reality. Selectinga conical perspective to reproduce a complete assemblage (this isthe closest perspective to real vision; the view point of an observerwith just one eye and from a fixed point) provokes deformation ofall the motifs situated on concave and convex surfaces and on thoseat angles which are different from the frontal view selected. Thatdeformation has traditionally been avoided by the construction ofcompositions from an orthogonal projection which involves rep-resenting on a frontal plane the shape of an object seen froma frontal view point. In other words, in a single 2D reproduction allthe motifs of the panel are represented from a frontal view pointthat is perpendicular to them. This solution facilitates the inter-pretation of the composition to the detriment of the distances thatseparate the motifs on the panel. The resulting distances arereduced on the projection plane. But, in our opinion, this type ofreproduction is still an essential work tool that is useful forthe diffusion of 2D reproductions, once a minimum error indistance among motifs is accepted. The advantage of this type of

Fig. 5. Partial digital tracing of rock she

reproduction is that it can achieve an optimal global reproduction(López-Montalvo and Domingo, 2005, 2009). However, orthogonalrepresentation in one direction can cause interpretation problemsin areas that are at an angle to the orthogonal projection plane(Fig. 6).

In our opinion, the solution to this problem can be found in theselection of different orthogonal projection planes. They offerbetter views of awhole assemblage, with special attention tomotifsthat are at extreme orientations (Fig. 7).

Another interesting point is that digital technology offers thepossibility of combining several reproductions in a single file, sothat panels can be separated into execution phases.

Furthermore, with digital technology, deteriorated panels canbe reconstructed from a combination of current and old recordings(Fig. 8). This approach to an integrated vision of assemblages bearsno relation to other current approaches of virtual “restoration-reconstruction” of motifs or panels (see, for example, Solís, 2009),that remind us of the old manual reconstruction of motifs such asCabré’s or Benitez Mellado’s (Moneva, 1993: 422e423). The inter-pretation of incomplete figures can be didactic for the generalpublic. But it involves controversy for the specialist because it canlead to mistaken interpretations that speculate beyond the motifsrepresented by the authors. Therefore, scientific recordings shouldbe faithful representations of those parts that have been preservedand must avoid idealization and figure reconstruction.

Tridimensional reconstruction of an object or a scene can beachieved in many ways, both with active sensors (e.g. laser scan-ners based on triangulation and time- of-flight) and passive scan-ners (e.g. video and photographic cameras). Remondino and ElHakim (2006) mention four alternatives: Image-based rendering,Image-based modelling, Range-based modelling and Combinationof image- and range-basedmodelling.We reject the first alternativebecause it does not offer sufficient metric quality, and accept theother three, which are those most widely used to record tridi-mensional pieces of cultural heritage.

Image-based modelling requires a passive sensor, a digitalcamera and multiple digital images with coating. The image ob-tained can be used both in traditional scientific studies and for 3Dautomatized digitalization tasks. It also requires auxiliary topo-graphic equipment to fix surveying points. The initial cost for theequipment is quite low. But photogrammetric computer visionsoftware requires specialized personnel. Now there are low-costand open source software, as well as web-based services runningon the cloud (see Remondino et al., 2012; for a critical review ofdiverse image-based solutions). Versatility is the main advantage of

lter VI, Cingle de la Mola Remigia.

Fig. 6. Partial tracing of rock shelter VI of Cingle de la Mola Remigia. The figures located on the ceiling (VI.C) are deformed and cannot be reconciled when they are reproduced fromjust one frontal orthogonal projection plane.

Fig. 7. Figures from rock shelter VI, Cingle de la Mola Remigia, with orthogonalrectification details.

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this alternative. Image-based modelling can work with any type ofphotographic image, and it adjusts any shots to the scale (precision)determined by the objective pursued.

Range-based modelling requires an active sensor; a laserscanner that can capture large amounts of information in littletime, such as 3D point clouds that reflect intensity values, or evencolour if the equipment has cameras incorporated into it. Laserequipment is a priori recommended for capturing point clouds ofscenes with complex forms, as well as large scenes, and thosewhose lighting conditions are minimal. This alternative requiresa greater expenditure, software for specific 3D treatment andspecialized training.

The third alternative combines image-based modelling andrange-based modelling. This seems to be the most suitable for rockart documentation. There are at least two clearly different varieties:firstly, the integration of high definition colour images on 3Dmodels obtained from a laser scanner (Lerma et al., 2010); secondly,a photogrammetric option based on images and the integrated useof laser, applying the concepts of multi-resolution and multi-scale(Petti et al., 2008).

The final decision regarding the most suitable alternative fordocumentation will depend on the following factors: complexityand size of the object, monument or site (English Heritage, 2007),cost, deadline, and the final product pursued (Patias, 2006).

The combination of 2D individual tracings with the possibilitiesoffered by 3D techniques is currently a rather promising option. Itspeeds up and guarantees the reconstruction process of panels(very time consuming by the traditional triangulation technique),and provides metric reproductions. High precision tridimensionalmodels, produced by means of laser scanners or photogrammetricprocedures from pair or from multiple images, when they arecombined with two-dimensional tracings obtained by means ofdigital retouch of photographic images, can provide a panel metricreproduction that has a very high degree of precision. Manyparameters are important for the precision of these techniques.However, they can be summarized in the following four points:precision when measuring points on digital images, error from thespatial orientation method, error from triangulation and meshingmethods, and processing errors (for example, smoothing, filtering

Fig. 8. In documentation from Cova dels Cavalls we combine current digital tracings, in black (Martínez and Villaverde, 2002) with older documentation in grey (Obermaier andWernet, 1919) in order to offer an integral vision of the assemblage.

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and filling). Combining these procedures has the advantage ofobtaining tridimensional documentation that can be publishedboth in a 2D format (apt for printed distribution), and in 3D formats(with artificial and photorealistic textures or with texturescombined with tracings to facilitate the identification of motifs andthe study of superimpositions of scarce visibility). They can also beused for virtual and interactive animation, which is very apt fordigital diffusion and for making heritage accessible to the public(Lerma, 2009). Horizontal and vertical sections of a cavity that areuseful in showing the site ground and the localization of repre-sentations can also be extracted from these models (Lerma et al.,2010).

A further interesting aspect of high resolution tridimensionalmodels that are metrically correct is that they facilitate the study ofpanels, rock shelters and caves in the research department: theiruse can replace the large number of hours in the site that analysisand measurement of paintings and engravings in situ require. If wehad 3D digital models captured in different periods (4D digitalmodels) it would also be possible to monitor erosion and theevolution of the rock surface through time. This possibility couldlead to new projects for the preservation of areas in particular need.

2.3. The relation of rock art with the rock surface

It is useful to study the relation that figures and compositionshave with the rock surfaces that support them. It helps to assesswhere exactly motifs are, in relation to the surface, and to deter-mine if there are preferences for certain spaces. The use of

irregularities of the rock surface to create a space or landscaperepresentation, and any intentional modifications in the prepara-tion of the space before marking, can also be observed with thestudy of the rock surface. Last but not least, it is also useful toidentify degraded areas in order to plan preservation strategies.

Attempts to show the relation between motifs and the rocksurface go back a long time. There are examples in Levantine artreproductions, such as Benitez Mellado’s, that attempt to give anaccount of the state of the rock surface at Cueva de la Araña(Hernández-Pacheco, 1924); or the tracings done by the artistAntonio Bregante, or those done by Breuil, or Ripoll himself, thatreproduce in detail the morphology of the surface where some ofthe motifs and scenes in Cingle de la Mola Remigia were depicted(Ripoll, 1963) (Fig. 9).

This is, however, the area where the greatest limitations of 2Ddigital techniques have been found. In order to document themorphology of the rock in detail, we have resorted to photographycombined with two-dimensional tracings that, with the help ofsome graphic conventions, can present reproduction of the reliefand its alterations (López-Montalvo and Domingo, 2005, 2009). Butthis is only partly successful when it comes to showing volumetricinformation and the texture of a rock surface, and it also raisesserious difficulties in achieving tridimensional effects (Fig. 10).

It is in this area that 3D models contribute most. They canrecover the spatial and volumetric sensation characteristic of rockart, with its natural rock surface marked by pronounced changes inangle, concavity, and multiple representation planes. 3D modelscombine in the same record the tracing of each motif, the 3Dmodel

Fig. 9. War scene from rock shelter IX, Cingle de la Mola Remigia. This tracing takesinto account the morphology of the rock surface (Ripoll, 2002: 357).

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of the rock surface (with its volumetry) and the photographwith itstexture (that offers 3D photo-realistic models). Therefore, they canrecover tridimensional structures of painted spaces that bring usnear to the reality of rock art (Fig. 11).

This type of documentation opens up new possibilities for thestudy and interpretation of rock art, particularly in technical areasrelated to the use and limitations of the rock surface for theexecution of panels, compositions, scenes and even figures. Acci-dents in the rock surface can condition the application of pigment,direction and quality of the strokes, and the disposition andmorphology of some parts of the anatomy (López-Montalvo andDomingo, 2005).

Fig. 10. Two-dimensional reproduction of motifs and the rock

2.4. Multiple planes and viewpoints

One of the greatest limitations of, both traditional and digital,two-dimensional techniques is the difficulty in obtaining themultiple planes and viewpoints from where rock art representa-tions are conceived. In two-dimensional records there is usuallya dominant viewpoint that generally coincides with that of theartist (the frontal view of each motif). But they rarely show otherperspectives that are closer to that of the observer (thewhole of theassemblage). These differences are particularly important whenmotifs are located in high areas or in away that the viewpoint of theauthor is rather different from that of the observer (Video S1).

Supplementary video related to this article can be found onlineat http://dx.doi.org/10.1016/j.jas.2012.11.024.

The introduction of tridimensional recording techniques forrock art has made up for this deficiency and opens new possibilitiesof interpretation. With the help of 3D viewfinders, tridimensionalmodels can be scaled and rotated in order to perceive figures fromdifferent viewpoints. In that way we can obtain multiple perspec-tives and angles as we move in the cavity.

With the help of tridimensional recording techniques, therelation between the physical reality of the shelter and composi-tions with a large number of figures that occupy particular areascan be assessed with more precision. With tridimensional modelswe can choose to visualize a composition fromwhere the observer,in theory, stands (taking into account the topography, the limita-tions of the area where one can stand, the height in relation to thelevel from where the observation takes place, etc.), and we wouldobtain a view similar to that seen at the actual shelter. We can evenresort to alternative views in cases where selecting just one view-point is not easy or advisable because it hinders a view of particularmotifs, or provokes deformation.

surface (Mas d’en Josep, Castelló, Domingo et al., 2003).

Fig. 11. The combination of 2D tracings and 3D models offers multiple readings of a panel.

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3. Results and conclusions

Digital recording is a useful technique for the study, preserva-tion and dissemination of rock art that has introduced greatimprovements in the graphic and metric quality of documentation.Since it consists of non-invasive techniques, it has also reduced theimpact of the process of recording on motifs and on the rocksurface.

Graphic documentation produced by means of conventionaltechniques constitutes mere static records which are difficult torevise. In contrast, digital documentation allows the overlapping ofmany records or readings of a panel, constant revision and updat-ing, and the possibility of breaking down a composition in order toadapt it to different aims, such as research, preservation anddissemination.

As described above, digital 2D documentation techniques(photography and tracing) and 3D techniques are complementary.Using a combination of both, we can increase the number ofreadings of a record and we can also offer more exhaustive andintegral readings. 3D models provide more detailed information of

the shape and dimensions of a site, the location of motifs and theirrelation to the rock surface (they register the tridimensional natureof the sites). But 2D tracings are still necessary in order to facilitatethe interpretation of motifs, compositions and scenes, especiallywhen figures are very deteriorated (or faded) or there are complexsuperimpositions.

Currently, the choice of one of these techniques, or the combi-nation of both, is still clearly connected to the resources available.3D techniques require greater expenditure and specializedpersonnel. Today, it is possible to create 3D models out of inex-pensive 3D still and video cameras instead of laser scanning. Thereis a wide range of web-based computer vision software that makesavailable 3D point clouds or even 3D models. Examples of both areARC3D Webservice (http://www.arc3d.be/) and Autodesk 123Catch (http://www.123dapp.com/catch). They are an alternative forfast visualization for projects with limited funding. However,documentation of cultural heritage requires comprehensive pro-cessing to get reliable models and reconstructions, anticipatingtheir potential degradation caused by weathering, natural disastersor human activities. Limitation when uploading large imagery is

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still there as well as lack of reliability. In addition, the chance to getsuccessful and accurate documentation reports is not realistic yet.

The adaptation of 2D and 3D documents to scientific commu-nication and general dissemination varies considerably because 3Dformats are not very common yet. Furthermore, both the possibil-ities of storing 3D models and their use in the comparison of rockart assemblages for research are still limited.

Two-dimensional documents are still necessary for printeddistribution, whether obtained from a 3D model or directlyproduced in 2D format. The analysis of motifs, compositions andscenes is also simplified in 2D formats, and thus they are especiallyuseful for studies involving detailed stylistic description of motifsand motif comparisons. 3D formats are, currently, the best type offormat for virtual dissemination (publications on digital format,web pages, museums, etc.). New software tools that admit 3Dformats incorporated into a file (as PDF3D format) will encouragethe demand for 3D models and their use in everyday tasks in theanalysis of prehistoric paintings and engravings.

Acknowledgements

This paper was written within the context of the Prometeo/2008/165 project, directed by Professor Valentín Villaverde andfunded by the Generalitat Valenciana and the HAR2011-25445project, directed by Research Professor Ines Domingo and fundedby MECC (Ministry of Economy and Competitiveness).

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