Use of unmanned aerial vehicle technology in the protection of Goods of Cultural Interest (GCIs): the case of the Castle of Cala (Huelva, Spain)
Abstract
Currently, the use of modern technologies, such as UAVs, allows for a detailed analysis of the protection of Sites of Cultural Interest (BICs) in Spain. Cala Castle in Huelva is selected for this study, which is one of the most important medieval fortifications in the mountainous region and was rehabilitated between 2003 and 2011. After a decade of its architectural rehabilitation, the use of this new UAV technology will allow the creation of a database of the property and its surroundings, made up of a series of 3D models and photogrammetric studies of the territory. This analysis allows us two complementary readings to the original study: on the one hand, to characterize the natural and landscape context of Cala Castle, and on the other, to identify the pre-existence of a series of historic buildings, which have historically articulated this region. The 3D models obtained provide relevant graphic information. The current state of the BIC allows this space to be considered for reactivation as a social space at the regional level. The visuals of the regional environment allow us to identify that the most recent growth has been articulated longitudinally along the N-630 highway, this infrastructure being the backbone of the nucleus. As a pilot test, the beginning of this graphic and visual database (3D) at a regional level will provide a valuable tool for the conservation and registration of built heritage, given that it seeks to incorporate other fortifications that make up Banda Gallega with the aim of defining a sustainable development strategy at county level.
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Citation: Núñez-Camarena, G.M.; Herrera-Limones, R.; López-Escamilla, Á. Use of Unmanned Aerial Vehicle Technology in the Protection of Goods of Cultural Interest (GCIs): The Case of the Castle of Cala (Huelva, Spain). Architecture 2024,4, 247–266. https://doi.org/10.3390/ architecture4020015 Academic Editors: Carlos J. Rosa Jiménez and Daniel Navas Carrillo Received: 22 February 2024 Revised: 19 April 2024 Accepted: 24 April 2024 Published: 30 April 2024 Copyright: © 2024 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/ 4.0/). Article Use of Unmanned Aerial Vehicle Technology in the Protection of Goods of Cultural Interest (GCIs): The Case of the Castle of Cala (Huelva, Spain) Gina M. Núñez-Camarena 1,2 , Rafael Herrera-Limones 1,2 and Álvaro López-Escamilla 1,2,* 1Institute of Architecture and Building Sciences, School of Architecture, University of Seville, Av. Reina Mercedes 2, 41012 Seville, Spain; [email protected] (G.M.N.-C.); herr[email protected] (R.H.-L.) 2Research Group Transhumancias HUM-965, University of Seville, 41012 Seville, Spain *Correspondence: [email protected]; Tel.: +34-954-55-65-20 Abstract: Currently, the use of modern technologies, such as UAVs, allows for a detailed analysis of the protection of Sites of Cultural Interest (BICs) in Spain. Cala Castle in Huelva is selected for this study, which is one of the most important medieval fortifications in the mountainous region and was rehabilitated between 2003 and 2011. After a decade of its architectural rehabilitation, the use of this new UAV technology will allow the creation of a database of the property and its surroundings, made up of a series of 3D models and photogrammetric studies of the territory. This analysis allows us two complementary readings to the original study: on the one hand, to characterize the natural and landscape context of Cala Castle, and on the other, to identify the pre-existence of a series of historic buildings, which have historically articulated this region. The 3D models obtained provide relevant graphic information. The current state of the BIC allows this space to be considered for reactivation as a social space at the regional level. The visuals of the regional environment allow us to identify that the most recent growth has been articulated longitudinally along the N-630 highway, this infrastructure being the backbone of the nucleus. As a pilot test, the beginning of this graphic and visual database (3D) at a regional level will provide a valuable tool for the conservation and registration of built heritage, given that it seeks to incorporate other fortifications that make up Banda Gallega with the aim of defining a sustainable development strategy at county level. Keywords: three-dimensional modeling; cultural heritage; historical building; drone; photogrammetry; digital imagen; UAV; point cloud 1. Introduction 1.1. Initiation of the Research and Intervention The archaeological and architectural research was conducted in 2001 and 2003, respectively (Proyecto de Intervención Arqueológica and Proyecto Básico, respectively), financed by the Consejería de Cultura de la Junta de Andalucía (Figure 1). The project required archaeological baselines and extensive and complex in situ data acquisition (Figure 2), which proved essential in the analysis of what was then no more than a ruin. During the whole process of documentation, data acquisition, and study, the criteria of the Krakow Charter of 2000 up to the Charter of the Restoration [ 1 ] were taken into account. Architecture 2024,4, 247–266. https://doi.org/10.3390/architecture4020015 https://www.mdpi.com/journal/architecture
Architecture 2024,4248 Architecture2024,4,FORPEERREVIEW2 Figure1.Imageofthearchaeologicalinterventionprocess. Figure2.On-sitedatacollection,2001(Ontheplan,thelettersA-Gindicatethepointswherethe surveywascarriedout). 1.2.Pre‐InterventionStatus Thefortifiedenclosurewasinastateofgeneralruin(Figure3). Thewallsandthetowerslackedboththecrowningelementandtheupperarea.The archaeologicalworksuggestedtheexistenceofcontinuousprotectionontheoutside,both onthewalkwayandonthetowers,asitwasnotpossibletodocumenttheexistenceof pinnaclesandmerlons.Therewasagreatdealofdamagetothemasonryofthewallsand towers,withlargecavitiesandmissingmaterial.Themaingatedidnotexist,asthe Figure 1. Image of the archaeological intervention process. Architecture2024,4,FORPEERREVIEW2 Figure1.Imageofthearchaeologicalinterventionprocess. Figure2.On-sitedatacollection,2001(Ontheplan,thelettersA-Gindicatethepointswherethe surveywascarriedout). 1.2.Pre‐InterventionStatus Thefortifiedenclosurewasinastateofgeneralruin(Figure3). Thewallsandthetowerslackedboththecrowningelementandtheupperarea.The archaeologicalworksuggestedtheexistenceofcontinuousprotectionontheoutside,both onthewalkwayandonthetowers,asitwasnotpossibletodocumenttheexistenceof pinnaclesandmerlons.Therewasagreatdealofdamagetothemasonryofthewallsand towers,withlargecavitiesandmissingmaterial.Themaingatedidnotexist,asthe Figure 2. On-site data collection, 2001 (On the plan, the letters A–G indicate the points where the survey was carried out). 1.2. Pre-Intervention Status The fortified enclosure was in a state of general ruin (Figure 3).
Architecture 2024,4249 Architecture2024,4,FORPEERREVIEW3 adjoiningwallhadbeendestroyed.Therewerealsoremainsofthetwostaircasesthat wouldhaveledtothecoastalwalkway,buttheywereinaruinousstate. Thecastlewasheavilyinfilledinside,withcollapsedmaterial,andtherewasalsoan accumulationofmaterialfromthedestructionofthecastle’sinternalstructures.Thebackfillundoubtedlyexertedadamagingpressureonthestructurefromthepointofviewof stability.Thewallsandtheareasadjacenttotherampartswereseverelyaffectedbywild vegetationandaccumulatedmaterials.Therewasalsoamultitudeofparasiticplant sproutsandextensivedamagetothewalls. Figure3.Initialstate,beforethearchitecturalintervention. 1.3.JustificationfortheSolutionAdoptedintheProject Althoughthegeneralstateofthecastleposednumerousproblemsregardingcertain constructiveaspects,therewassufficientdatatobeginthestudyofitscomprehensiverestoration,whichrequiredtherepairofthedamageandthevaluationofthemonumental complexbymeansoflarge-scalevolumetricrecovery,aswellastherecoveryofthosedocumentedelevations. Thisiswhy,inthe“BasicProject”of2004(Figure4),theKrakowCharterof2000[2] isapplied;inthisandwithintheenumerationofthe“principlesfortheconservationand restorationofbuiltheritage”,itisestablished(initsparagraphnº4)that: “Reconstructionin“buildingstyle”ofentirepartsofthebuildingshouldbe avoided.Thereconstructionofverylimitedpartsofarchitecturalsignificance mayexceptionallybeacceptedifitisbasedonpreciseandindisputabledocumentation.Iftheincorporationofmoreextensivespatialandfunctionalpartsis necessaryfortheproperuseofthebuilding,thelanguageofcurrentarchitecture mustbereflectedinthem.” Ontheotherhand,inthistypeofarchitecturalstudy,thereareconstructiveissues moretypicalofthescaleofthearchitecturaldetail,andothersmoretypicaloftheterritorialscale(Figure5). Thisdoublescale,macro,andmicro,showsthedifficultyofinterventionsonheritage assets.Inshort,thelinesofactionthatarespecified(alreadyinthe2008ExecutionProject) are,withrespecttothegeneralvolumetry,thefollowing: Recoveryofthethreesectionsofwalls(locatedintheN.W.,S.W.,andS.E.)facingthe population,whichconstitutethecollectivememoryofitspast:theethnographicatavismofthecitizens(Figure6).ThisoperationwillbedevelopedbymeansofaconstructivelanguagethatallowsadoublereadingoftheBIC: Figure 3. Initial state, before the architectural intervention. The walls and the towers lacked both the crowning element and the upper area. The archaeological work suggested the existence of continuous protection on the outside, both on the walkway and on the towers, as it was not possible to document the existence of pinnacles and merlons. There was a great deal of damage to the masonry of the walls and towers, with large cavities and missing material. The main gate did not exist, as the adjoining wall had been destroyed. There were also remains of the two staircases that would have led to the coastal walkway, but they were in a ruinous state. The castle was heavily infilled inside, with collapsed material, and there was also an accumulation of material from the destruction of the castle’s internal structures. The backfill undoubtedly exerted a damaging pressure on the structure from the point of view of stability. The walls and the areas adjacent to the ramparts were severely affected by wild vegetation and accumulated materials. There was also a multitude of parasitic plant sprouts and extensive damage to the walls. 1.3. Justification for the Solution Adopted in the Project Although the general state of the castle posed numerous problems regarding certain constructive aspects, there was sufficient data to begin the study of its comprehensive restoration, which required the repair of the damage and the valuation of the monumental complex by means of large-scale volumetric recovery, as well as the recovery of those documented elevations. This is why, in the “Basic Project” of 2004 (Figure 4), the Krakow Charter of 2000 [ 2 ] is applied; in this and within the enumeration of the “principles for the conservation and restoration of built heritage”, it is established (in its paragraph nº 4) that: “Reconstruction in “building style” of entire parts of the building should be avoided. The reconstruction of very limited parts of architectural significance may exceptionally be accepted if it is based on precise and indisputable documentation. If the incorporation of more extensive spatial and functional parts is necessary for the proper use of the building, the language of current architecture must be reflected in them.” On the other hand, in this type of architectural study, there are constructive issues more typical of the scale of the architectural detail, and others more typical of the territorial scale (Figure 5).
Architecture 2024,4250 Architecture2024,4,FORPEERREVIEW4 (a) Fromthepointofviewoftheirintegrationintotheenvironment–territory–landscape,thematerialsused,textures,andgeneraltonesshallnotdifferfromthe pre-existingones. (b) Fromthepointofviewoftheauthenticityandintegrityofthebuilding,thedifferentlanguagescanbeclearlydifferentiatedsothatnoundesirablemimicry effectsoccur,evenovertheyears. ThesectionofwallbetweentowersAandC(facingN.E.)isconsideredtohaveits “backturned”tothetownthatprotectsthecastleand“facing”thehillsidewiththe steepestslopeandmostdistantperspectiveand,ontheotherhand,withtheaimof achievingtheoriginalityoftheexistinghistoricalremainsandthushavingaspatial recoverywithdifferentmaterialstothepre-existingonesandconservingthestateof “ruin”(obviouslyafterappropriatestructural–constructiveconsolidation)according toarchaeologicalcriteria.Thisactionisreflectedintheincorporationofafootbridge (Figure7),thusallowingcontinuityinthecoastalwalkwayatitsoriginalheights(accordingtothehypothesesofuse)andrecoveringthepre-existingvirtualvolumetry. Figure4.Projectplan. Figure 4. Project plan. Architecture2024,4,FORPEERREVIEW5 Figure5.Post-interventionphoto,2012. Havingmadethepreviouscontextualization,itisimportanttopointoutthattheuse ofrecenttechnologiesdoesnotimplytheeradicationoftraditionalstudiesintheanalysis oftheterritoryanditsassociatedhistoricalproperties.Forthisreason,thegeneralobjectiveofthisresearchworkseekstohighlighttheimportanceofincorporatingtheuseof innovativetechnologiessuchasmultirotorUAVsinthecollectionofdataassociatedwith ahistoricalandheritageasset,inthiscase,takingasacasestudytheCastleofCala (Huelva,Spain). Fromtheanalysisconducted,theaimistobuildadatabaseattheregionallevel, whichwillbecomposedofaseriesof3Dmodelsandphotogrammetricstudiesofthe territory.Inafirstphase,thistoolwillbethebasisforrecordingdatanecessaryforthe conservationandregistrationofthebuiltheritagethatispartoftheGalicianBand,togetherwithitsnaturalenvironment.Theabovewillstreamlinetheobtainingofdatafor thedevelopmentofsustainablestrategiesattheregionallevel. Figure6.Viewoftheparadeground:aftertheintervention,2012. Figure 5. Post-intervention photo, 2012. This double scale, macro, and micro, shows the difficulty of interventions on heritage assets. In short, the lines of action that are specified (already in the 2008 Execution Project) are, with respect to the general volumetry, the following: • Recovery of the three sections of walls (located in the N.W., S.W., and S.E.) facing the population, which constitute the collective memory of its past: the ethnographic
Architecture 2024,4251 atavism of the citizens (Figure 6). This operation will be developed by means of a constructive language that allows a double reading of the BIC: (a) From the point of view of their integration into the environment–territory– landscape, the materials used, textures, and general tones shall not differ from the pre-existing ones. (b) From the point of view of the authenticity and integrity of the building, the different languages can be clearly differentiated so that no undesirable mimicry effects occur, even over the years. • The section of wall between towers A and C (facing N.E.) is considered to have its “back turned” to the town that protects the castle and “facing” the hillside with the steepest slope and most distant perspective and, on the other hand, with the aim of achieving the originality of the existing historical remains and thus having a spatial recovery with different materials to the pre-existing ones and conserving the state of “ruin” (obviously after appropriate structural–constructive consolidation) according to archaeological criteria. This action is reflected in the incorporation of a footbridge (Figure 7), thus allowing continuity in the coastal walkway at its original heights (according to the hypotheses of use) and recovering the pre-existing virtual volumetry. Having made the previous contextualization, it is important to point out that the use of recent technologies does not imply the eradication of traditional studies in the analysis of the territory and its associated historical properties. For this reason, the general objective of this research work seeks to highlight the importance of incorporating the use of innovative technologies such as multirotor UAVs in the collection of data associated with a historical and heritage asset, in this case, taking as a case study the Castle of Cala (Huelva, Spain). From the analysis conducted, the aim is to build a database at the regional level, which will be composed of a series of 3D models and photogrammetric studies of the territory. In a first phase, this tool will be the basis for recording data necessary for the conservation and registration of the built heritage that is part of the Galician Band, together with its natural environment. The above will streamline the obtaining of data for the development of sustainable strategies at the regional level. Architecture2024,4,FORPEERREVIEW5 Figure5.Post-interventionphoto,2012. Havingmadethepreviouscontextualization,itisimportanttopointoutthattheuse ofrecenttechnologiesdoesnotimplytheeradicationoftraditionalstudiesintheanalysis oftheterritoryanditsassociatedhistoricalproperties.Forthisreason,thegeneralobjectiveofthisresearchworkseekstohighlighttheimportanceofincorporatingtheuseof innovativetechnologiessuchasmultirotorUAVsinthecollectionofdataassociatedwith ahistoricalandheritageasset,inthiscase,takingasacasestudytheCastleofCala (Huelva,Spain). Fromtheanalysisconducted,theaimistobuildadatabaseattheregionallevel, whichwillbecomposedofaseriesof3Dmodelsandphotogrammetricstudiesofthe territory.Inafirstphase,thistoolwillbethebasisforrecordingdatanecessaryforthe conservationandregistrationofthebuiltheritagethatispartoftheGalicianBand,togetherwithitsnaturalenvironment.Theabovewillstreamlinetheobtainingofdatafor thedevelopmentofsustainablestrategiesattheregionallevel. Figure6.Viewoftheparadeground:aftertheintervention,2012. Figure 6. View of the parade ground: after the intervention, 2012.
Architecture 2024,4252 Architecture2024,4,FORPEERREVIEW6 Figure7.Photographofthecatwalk,2012. 1.4.UseofInnovativeToolsintheConservationandProtectionofHeritage Currently,BIMtechnologyandGISs(GeographicInformationSystems)aretoolsthat areusedinthedevelopmentofresearchinarchitecture,engineering,urbanplanning,and construction,aswellasinarchaeologyandtherehabilitationofbuildings[3,4]. BIM(BuildingInformationModeling)referstoasetofworkingmethodologiesand toolscharacterizedbytheuseofinformationinacoordinated,coherent,computable,and continuousway[5].Inthiscase,variousmethodologiesassociatedwitharchitectureand engineering,allowtheimportantdevelopmentofbigdataappliedintheconstructionof buildings,aswellasintheirrehabilitation[6,7].BIMdatabasesmayormaynotbemade upofavarietyofcomprehensiveinformationsuchasspreadsheets,photographs,cartography,imagesandraster,etc.,whichmustbeprocessedtodriveprojectmanagementas required[8]. Finally,thistechnologyprovidesamodelofthebuildinganditsenvironment,based ontheinformationextractedfromthebigdata,tomanagetheconstructionofthebuilding, itsmaintenance,orrehabilitation[9–11]. SeveralauthorsagreethataGISfacilitatesthemanagement,manipulation,andanalysisofspatiallyreferenceddata,throughwhichcomplexplanningandmanagementproblemscanbesolved[3,12]. TheGISconstitutesadatabasewithgeographicinformation,whichisassociatedwith agraphicidentifierofadigitalmap[3],resultinginthegenerationofmaps,reports, graphs,etc.[13]multiplyingtheanalyticalvariablesfocusedonterritorialanalysis[14]. Currently,researchintotheefficientoperationalizationofBIMandGISshasbeenincreasingexponentiallyduetothepossibilitiesofbothtechnologicaltools[15,16].Linkedtothe useofBIMandGIStechnologies,theapplicationofinformationobtainedfromUAVshas becomeofgreatinterest[9,17].UAVsintensivelygeneratelargeamountsofpointsand information,resultinginthegenerationofpointcloudsthatcanvaryintheirproperties, dependingonthenumberofreturnsand/orthedensityofthevegetationorurbanplan [17,18]. Itisimportanttonotethattheversatilityofthesystemallowsworkinganddefining theflightpathsoftheUAVs(Pix4DCaptureinfreeversionforprogrammingtheflight path),andtheprocedurecanalsobecarriedoutinreverse;theflightpathisdesigned withintheprogramme,andtheregionofinterestisindicated,definingthemaximumaltimetryrequiredaccordingtothetypeofflightpathinformation[17]. Figure 7. Photograph of the catwalk, 2012. 1.4. Use of Innovative Tools in the Conservation and Protection of Heritage Currently, BIM technology and GISs (Geographic Information Systems) are tools that are used in the development of research in architecture, engineering, urban planning, and construction, as well as in archaeology and the rehabilitation of buildings [3,4]. BIM (Building Information Modeling) refers to a set of working methodologies and tools characterized by the use of information in a coordinated, coherent, computable, and continuous way [ 5 ]. In this case, various methodologies associated with architecture and engineering, allow the important development of big data applied in the construction of buildings, as well as in their rehabilitation [ 6 , 7 ]. BIM databases may or may not be made up of a variety of comprehensive information such as spreadsheets, photographs, cartography, images and raster, etc., which must be processed to drive project management as required [8]. Finally, this technology provides a model of the building and its environment, based on the information extracted from the big data, to manage the construction of the building, its maintenance, or rehabilitation [9–11]. Several authors agree that a GIS facilitates the management, manipulation, and analysis of spatially referenced data, through which complex planning and management problems can be solved [3,12]. The GIS constitutes a database with geographic information, which is associated with a graphic identifier of a digital map [ 3 ], resulting in the generation of maps, reports, graphs, etc. [ 13 ] multiplying the analytical variables focused on territorial analysis [ 14 ]. Currently, research into the efficient operationalization of BIM and GISs has been increasing exponentially due to the possibilities of both technological tools [ 15 , 16 ]. Linked to the use of BIM and GIS technologies, the application of information obtained from UAVs has become of great interest [ 9 , 17 ]. UAVs intensively generate large amounts of points and information, resulting in the generation of point clouds that can vary in their properties, depending on the number of returns and/or the density of the vegetation or urban plan [17,18]. It is important to note that the versatility of the system allows working and defining the flight paths of the UAVs (Pix4D Capture in free version for programming the flight path), and the procedure can also be carried out in reverse; the flight path is designed within the programme, and the region of interest is indicated, defining the maximum altimetry required according to the type of flight path information [17].
Architecture 2024,4253 The different typology of existing drones leads to the choice of a specific type as the most suitable for the recognition and observation of an asset of cultural interest. Specifically, the multirotor drone is presented as the most suitable. The possibilities offered by this type of UAV are clearly more advantageous than those of a fixed-wing UAV, for example. However, if the area to be studied is larger than one hectare or if the terrain is very uneven or requires observation from a high altitude, the fixed-wing UAV is the most suitable. Currently, most of the cultural assets to be studied are buildings or remains of small cities. In this sense, the predominant and most widely used typology is the multirotor UAV. In the field of inspection [ 19 ] and observation, the use of UAVs is becoming more common, as well as in activities related to public safety [ 20 , 21 ]; territory mapping with different applications [ 22 – 24 ], such as agriculture [ 25 ] and mining [ 26 ]; or in inspections of public works or power lines [27]. In the field of cultural property registration, photogrammetry [ 28 , 29 ], which allows 3D models to be obtained, stands out. This new application of UAVs and data processing makes the use of these new technologies possible, concluding in an application to the study of archaeological [ 30 ] and heritage properties [ 31 ]. Thus, throughout this article, the use of UAVs applied to territorial analysis is shown, focusing on the territorial analysis of a heritage property, such as the Castle of Cala. For the methodological development of the analysis of the Castle of Cala, it is convenient to specify the main characteristics, advantages, and disadvantages of the several types of UAVs (Table 1), to establish the relevance of the use of the multirotor UAV in the 3D survey of our case study. Table 1. Typology of UAVs. Features Fixed wing Aircraft It is based on the fixed-wing principle for lift. May or may not have any propulsion system such as propellers or turbines. Rotating wing Helicopter Its lift principle is based on rotating wings. The difference with multirotors is that it consists of a single sustaining rotor, which implies the existence of an anti-rotor. Multirotor Like the helicopter, the multirotor bases its lift on the principle of rotating wings. The difference is that there is more than one rotor, making the anti-rotor unnecessary. Advantages Fixed wing Aircraft Greater autonomy. They can achieve higher travel speeds. Rotating wing Helicopter It allows stationary flights. It has total freedom of movement in all three axes. Multirotor Greater stability. Greater mechanical simplicity compared to the helicopter. Disadvantages Fixed wing Aircraft It does not allow stationary flights. Slow speed on course changes. Rotating wing Helicopter Less autonomy. Increased mechanical complexity, greater likelihood of breakdowns, and higher maintenance costs. Multirotor Reduced range compared to fixed-wing aircraft. Increased mechanical complexity compared to fixed-wing aircraft The creation of a 3D digital model applied to heritage elements through the use of UAVs can have different objectives, although the main one is to provide essential information in the development of urban policies, as well as in land use planning [ 32 , 33 ]. As for the analysis of historic buildings, the creation of 3D digital models provides digital documentation [ 34 – 36 ] for the perfect conservation and reconstruction of heritage and for the support of educational programs [ 37 ], as well as for those aimed at the dissemination of heritage [38,39].
Architecture 2024,4254 Although UAVs are presented as a complement to the use of LIDAR technology [ 31 , 40 ], on occasions, as in the case of the analysis of Cala Castle, they offer better results [ 24 , 41 , 42 ] since when we analyze a heritage element associated with the territory, these elements are often located in places that are difficult to access [43]. From its landscape aspect, due to the historical importance of the territory where the Castle of Cala is located and the role of Fortaleza in the regional territory, it is mentioned that in 2000, the Council of Europe adopted the European Landscape Convention (henceforth ELC) which warned of the need to integrate the landscape and its values in urban policies, as well as in cultural, environmental, agricultural, social, and economic policies [ 44 – 48 ]. In this sense, the Government of Spain, in 2012, approved the National Plan for Cultural Landscapes (PNPC), where this concept was defined as “the result of the interaction between people and the natural environment over time, whose expression is a territory perceived and valued for its cultural qualities, the product of a process, and a corner stone of a community’s identity” [49]. 2. Case Study: The Castle of Cala 2.1. Andalusian Defensive Architecture According to the P.A.D.A. (Plan for Andalusian Defensive Architecture), belonging to the General Directorate of Cultural Heritage of the Department of Culture of the Andalusian Regional Government, the defensive architecture of the Andalusian Autonomous Community constitutes a heritage of exceptional quality, due to “its historical condition as a frontier between kingdoms and civilizations” [ 50 ]. In addition, and since a multitude of landmarks still survive in the Andalusian landscape, it can be seen how towers, castles, walls, etc., are witnesses to a jurisdictional and logical reality of implantation in the physical environment. Specifically, within the P.A.D.A., a number of objectives are prioritized, including: • Registering properties for computer processing using GIS-type applications, thus allowing databases to be associated with cartographic documentation and systematizing data processing. • To carry out conservation and restoration actions applying a methodology based on knowledge, through research processes and previous studies, and in the adaptation of projects to the characteristics and circumstances of each building. 2.2. Location and Territorial Articulation The Castle of Cala is located in the province of Huelva, at the western end of the Sierra Morena and in the low mountain ranges [ 51 , 52 ]. The heritage density of this region is notable for important constructions, including a series of fortified elements (towers and castles), which are representative of 13th century military architecture. Historically, it belongs to the Banda Gallega (part of the defensive system of the Kingdom of Seville against possible Portuguese attacks). Between the castles of Cala, Real de la Jara, and Santa Olalla de Cala, a triangular visual control was established, which was strategic, given its proximity to the territories of the Order of Santiago [ 53 ], and the crossing of the Vía de la Plata was of vital importance for its regional consolidation. The fortress stands on a 650 m. high hill, with a small plateau at its summit. The surrounding landscape corresponds to a meadow, and at its feet, the fertile plain of the river Cala stretches out. The complex is small in size and totally isolated from the town, and was probably used to house a small military garrison [52,54,55]. Cala Castle is irregular in outline but tends to be rectangular in shape. It is an enclosure enclosed by a wall of varying width, ranging from 1.93 to 2.16 m. It has a quadrangular tower at each corner and intermediate semicircular towers on three sides (Figure 8). It has a convex shape on the two longest sides, with the intermediate towers predominating, but the sides have a rectilinear layout between the towers [56,57].
Architecture 2024,4255 Architecture2024,4,FORPEERREVIEW9 Communityconstitutesaheritageofexceptionalquality,dueto“itshistoricalcondition asafrontierbetweenkingdomsandcivilizations”[50].Inaddition,andsinceamultitude oflandmarksstillsurviveintheAndalusianlandscape,itcanbeseenhowtowers,castles, walls,etc.,arewitnessestoajurisdictionalandlogicalrealityofimplantationinthephysicalenvironment. Specifically,withintheP.A.D.A.,anumberofobjectivesareprioritized,including: RegisteringpropertiesforcomputerprocessingusingGIS-typeapplications,thusallowingdatabasestobeassociatedwithcartographicdocumentationandsystematizingdataprocessing. Tocarryoutconservationandrestorationactionsapplyingamethodologybasedon knowledge,throughresearchprocessesandpreviousstudies,andintheadaptation ofprojectstothecharacteristicsandcircumstancesofeachbuilding. 2.2.LocationandTerritorialArticulation TheCastleofCalaislocatedintheprovinceofHuelva,atthewesternendofthe SierraMorenaandinthelowmountainranges[51,52].Theheritagedensityofthisregion isnotableforimportantconstructions,includingaseriesoffortifiedelements(towersand castles),whicharerepresentativeof13thcenturymilitaryarchitecture.Historically,itbelongstotheBandaGallega(partofthedefensivesystemoftheKingdomofSevilleagainst possiblePortugueseattacks).BetweenthecastlesofCala,RealdelaJara,andSantaOlalla deCala,atriangularvisualcontrolwasestablished,whichwasstrategic,givenitsproximitytotheterritoriesoftheOrderofSantiago[53],andthecrossingoftheVíadelaPlata wasofvitalimportanceforitsregionalconsolidation. Thefortressstandsona650m.highhill,withasmallplateauatitssummit.The surroundinglandscapecorrespondstoameadow,andatitsfeet,thefertileplainofthe riverCalastretchesout.Thecomplexissmallinsizeandtotallyisolatedfromthetown, andwasprobablyusedtohouseasmallmilitarygarrison[52,54,55]. CalaCastleisirregularinoutlinebuttendstoberectangularinshape.Itisanenclosure enclosedbyawallofvaryingwidth,rangingfrom1.93to2.16m.Ithasaquadrangular towerateachcornerandintermediatesemicirculartowersonthreesides(Figure8).Ithasa convexshapeonthetwolongestsides,withtheintermediatetowerspredominating,but thesideshavearectilinearlayoutbetweenthetowers[56,57]. Figure8.Northeastelevation,beforetherehabilitationoftheBIC,year2000. Thereisamaingatelocatedtothesouth,boundedbytwoperpendicularwallsanda probablecontinuousmachicolation,withtwoarches(semicircularandpointed)andabarrelvault;thereisalsoasecondarygate(postern)locatedtothewest,withaninternalsemicirculararchandanexternalpointedarchofgraniteashlarsframedbyarectangular slump,Betweenthearches,thereisabarrelvaultofgraniteashlars,with“levelling”of coursesofbrick. Therearetwointeriorstaircases,attachedtothewalls:onenearthemaindoorway attachedtotheSEside,whichascendsinaNEdirection,landingatthecornerformedby Figure 8. Northeast elevation, before the rehabilitation of the BIC, year 2000. There is a main gate located to the south, bounded by two perpendicular walls and a probable continuous machicolation, with two arches (semicircular and pointed) and a barrel vault; there is also a secondary gate (postern) located to the west, with an internal semicircular arch and an external pointed arch of granite ashlars framed by a rectangular slump, Between the arches, there is a barrel vault of granite ashlars, with “levelling” of courses of brick. There are two interior staircases, attached to the walls: one near the main doorway attached to the SE side, which ascends in a NE direction, landing at the corner formed by the sides and the tower, and another, next to the postern, which is attached to the NW side of the wall and ascends in a SW direction. The walls are built with two walls of faced masonry, with the intervening cavity filled with earth, clay, stones, and lime mortar. The sides of the walls are built on the rocky outcrop. In any case, the construction system is similar to that of other mountain fortresses such as Encinasola, Torres, Cortegana, Cumbres de San Bartolomé, Cumbres Mayores, and Santa Olalla. The orography, as well as the course of the water have been especially important and have marked the territory. These characteristics have defined communications throughout history, as well as the location of populations in the territory [ 54 , 58 ]. The fortifications and their location are reflected in the cartography produced during the 17th, 18th, and 19th centuries [ 59 – 61 ]. The characterization of the territory presents a clear east–west arrangement, where the topography of the Hercynian folds orders them in a northeast– southeast direction towards the eastern end (Figure 9). The Christian repopulation from the second half of the 13th century onwards had a large Galician–Leonese component; the Christian conquest assigned this territory to the land of Seville, creating from the 14th century onwards the so-called Banda Gallega [ 62 , 63 ]. Its historical definition defines it as the design of a border defence system made up of castles and fortifications [ 64 ] against Portugal in its wars with Castile [ 65 , 66 ]. The concentration of a rural population was the basis for the ruins of the current castles such as those of Cumbres Mayores, Cala, Santa Olalla de Cala, Cumbres de Enmedio, or Cumbres de San Bartolomé[57]. The fortifications are an example of defensive architecture, typical of this territory, such as the Castle of Cala. Its first traces date back to the Islamic period, during the Christian conquest; the Islamic enclosures were built at the end of the 13th century, and in the defensive programme against the kingdom of Portugal, the fortifications and towers of the so-called Banda Gallega stand out. The historical importance of this group of Andalusian fortifications is still valid; therefore, the castles of the Banda Gallega have been catalogued as an Asset of Cultural Interest (BIC).
Architecture 2024,4262 Architecture2024,4,FORPEERREVIEW16 Figure15.Southelevation;imageobtainedfromthephotogrammetricprocess,2020. Figure16.Westelevation;imageobtainedfromthephotogrammetricprocess,2020. Figure17.Southwestelevation;imageobtainedfromthephotogrammetricprocess,2020. Figure18.Eastelevation;obtainedfromthephotogrammetricprocess,2020. Today,theuseofUAVsinthefieldofheritageanalysisallowsthegenerationof3D modelsandcomplementsthecollectionofinformationonhistoricalandheritage Figure 18. East elevation; obtained from the photogrammetric process, 2020. Today, the use of UAVs in the field of heritage analysis allows the generation of 3D models and complements the collection of information on historical and heritage properties, with the aim of establishing strategies focused on the maintenance, conservation, and enhancement of the fortresses of the defensive strip of Galicia (Figure 19). Architecture2024,4,FORPEERREVIEW17 properties,withtheaimofestablishingstrategiesfocusedonthemaintenance,conservation,andenhancementofthefortressesofthedefensivestripofGalicia(Figure19). IntheresearchworkcarriedoutforCalaCastle,thecreationofthe3Dmodelallowed ustostudythecurrentsituationofboththebuildingandtheterritorywhereitislocated. Forthisreason,theworkcarriedoutconstitutesapartofthedatabaseofheritageinterest, whichwilllaterbecontinuedwiththecastleofCumbresMayores(rehabilitatedandin use)andthecastleofCumbresdeSanBartolomé,studyingitsimportancefromthepoint ofviewofsustainability,whichwillagainconstitutefutureresearchworkthroughthe applicationofUAVtechnologies. Forthisreason,itisconsideredthatforthisdatabasetohaveauseandapplication, notonlyintheacademic,scientific,andgovernmentalsphere,thelocalsocietymustbe involvedandconsideritaspartofthegenerationofinformationabouttheproperty,so thatthecollaborativestrategiesaroundtheheritagepropertiesare“localbottomup”, whichcanlaterbetransferredtothecountylevel. Figure19.Northwestelevation;imageobtainedfromthephotogrammetricprocess,2020. 5.Conclusions Theresearchworkconductedsupportsthehypothesesonthesuitabilityofmodifyingwhatalreadyexists,asopposedtotheproductionofnewbuiltelements.Asaresult ofthe3Dsurveyofthebuilding,itispossibletoappreciatethesituationinwhichthe refurbishmentwasconductedmorethanadecadeago.Atthesametime,thewalkways areinperfectcondition.Inaddition,themembersoftheteammadeaphysicaltour.Due tothelackofmaintenance,andbecauseoftheirlocationoutside,theboxescontainingthe electricalinstallationsmustbecheckedbyatechnician. Toconstructthereliefunderwhichthisassetofculturalinterestislocated,theuseof photogrammetrywasnecessarytoobtainthe3Dmodels.Regardingthesurveyofthesurroundingsofthecastle,itcanberecognizedthattheviewthatdominatestheregionisstill preserved,ahistoricalvaluethatgaveahierarchytotheCastleofCalawithrespecttothe restofthebuildingsintheregion.Whilethephotogrammetricsurveyallowsustorecognizethattheterritorystillpreservesremainsandtracesofthecontinuityoftraditional activitiessuchasagriculture,thiscanbeidentifiedthroughthenaturalexploitationofthe pasturesforpigs,sheep,andgoats,withoutforgettingthatthecorkindustryisadeterminingfactorinlocaleconomicdevelopment. Firstly,itshouldbenotedthat,comparedtotheuseoftraditionalsurveys,thedata collectiontimewasreduced.ForthedimensionsoftheCastleofCala,itisshownthatthe useofUAVsismorepracticalthantheuseofLIDARtechnology,astheuseofUAVsallowedaccesstothesurroundingsoftheCastleofCalainamoreagileway.Asthereisno maintenance,naturehasonceagaincoveredthemarkedpathstoaccessthecastleandthe surroundingarea. Figure 19. Northwest elevation; image obtained from the photogrammetric process, 2020. In the research work carried out for Cala Castle, the creation of the 3D model allowed us to study the current situation of both the building and the territory where it is located. For this reason, the work carried out constitutes a part of the database of heritage interest, which will later be continued with the castle of Cumbres Mayores (rehabilitated and in use) and the castle of Cumbres de San Bartolomé, studying its importance from the point of view of sustainability, which will again constitute future research work through the application of UAV technologies. For this reason, it is considered that for this database to have a use and application, not only in the academic, scientific, and governmental sphere, the local society must be involved and consider it as part of the generation of information about the property, so that the collaborative strategies around the heritage properties are “local bottom up”, which can later be transferred to the county level. 5. Conclusions The research work conducted supports the hypotheses on the suitability of modifying what already exists, as opposed to the production of new built elements. As a result
Architecture 2024,4263 of the 3D survey of the building, it is possible to appreciate the situation in which the refurbishment was conducted more than a decade ago. At the same time, the walkways are in perfect condition. In addition, the members of the team made a physical tour. Due to the lack of maintenance, and because of their location outside, the boxes containing the electrical installations must be checked by a technician. To construct the relief under which this asset of cultural interest is located, the use of photogrammetry was necessary to obtain the 3D models. Regarding the survey of the surroundings of the castle, it can be recognized that the view that dominates the region is still preserved, a historical value that gave a hierarchy to the Castle of Cala with respect to the rest of the buildings in the region. While the photogrammetric survey allows us to recognize that the territory still preserves remains and traces of the continuity of traditional activities such as agriculture, this can be identified through the natural exploitation of the pastures for pigs, sheep, and goats, without forgetting that the cork industry is a determining factor in local economic development. Firstly, it should be noted that, compared to the use of traditional surveys, the data collection time was reduced. For the dimensions of the Castle of Cala, it is shown that the use of UAVs is more practical than the use of LIDAR technology, as the use of UAVs allowed access to the surroundings of the Castle of Cala in a more agile way. As there is no maintenance, nature has once again covered the marked paths to access the castle and the surrounding area. As a result of the work conducted, it can be affirmed that the use of innovative technologies such as UAVs is contributing to the recovery of built properties that form part of Spain’s heritage. With this first phase as a pilot experience conducted in the Castle of Cala, it is identified that the construction of a database at a regional level represents an opportunity to record specific data for each property analyzed. Author Contributions: Conceptualization, G.M.N.-C., R.H.-L. and Á.L.-E.; Data curation, G.M.N.-C., R.H.-L. and Á.L.-E.; Writing—original draft, G.M.N.-C., R.H.-L. and Á.L.-E. The handling of the drone was the responsibility of Á.L.-E. All authors participated in data collection and analysis. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Data are contained within the article. Conflicts of Interest: The authors declare no conflict of interest. References 1. Instituto Juan de Herrera. Documentos Internacionales: Carta de Atenas, Carta de Venecia, Carta Del Restauro, Carta de París, Carta de Amsterdam, Carta de Nairobi, Carta de Toledo y Carta de Ravello. In Cuadernos del Instituto Juan de Herrera de la Escuela de Arquitectura de Madrid; 28.01; Instituto Juan de Herrera: Madrid, Spain, 1998. 2. ICOMOS. Carta De Cracovia 2000 Principios Para La Conservación Y Restauración Del Patrimonio Construido; ICOMOS: Paris, France, 2000. 3. Hidalgo Sánchez, F.M. Interoperatividad Entre SIG y BIM Aplicada Al Patrimonio Arquitectónico, Exploración de Posibilidades Mediante La Realización de Un Modelo Digitalizado de La Antigua Iglesia de Santa Lucía y Posterior Análisis; Universidad de Sevilla: Seville, Spain, 2018. 4. Pepe, M.; Alfio, V.S.; Costantino, D. UAV Platforms and the SfM-MVS Approach in the 3D Surveys and Modelling: A Review in the Cultural Heritage Field. Appl. Sci. 2022,12, 12886. [CrossRef] 5. Coloma Picó, E. Tecnologia BIM per Al Disseny Arquitectònic; Universitat Politècnica de Catalunya: Barcelona, Spain, 2011. 6. Raguseo, E. Big Data Technologies: An Empirical Investigation on Their Adoption, Benefits and Risks for Companies. Int. J. Inf. Manag. 2018,38, 187–195. [CrossRef] 7. Pinto Puerto, F.S. La Tutela Sostenible Del Patrimonio Cultural a Través de Modelos Digitales BIM y SIG Como Contribución Al Conocimiento e Innovación Social. PH Boletín Del Inst. Andal. Del Patrim. Histórico 2018,26, 27–29. [CrossRef] 8. Tibaut, A.; Zazula, D. Sustainable Management of Construction Site Big Visual Data. Sustain. Sci. 2018,13, 1311–1322. [CrossRef] 9. Rebolj, D.; Tibaut, A.; ˇ Cuš-Babiˇc, N.; Magdiˇc, A.; Podbreznik, P. Development and Application of a Road Product Model. Autom. Constr. 2008,17, 719–728. [CrossRef]
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