Reconstruction of Lost Cultural Heritage Sites and Landscapes: Context of Ancient Objects in Time and Space

International Journal of Geo-Information

Article Reconstruction of Lost Cultural Heritage Sites and Landscapes: Context of Ancient Objects in Time and Space

Lukáš Br ˚uha 1 , Josef Laštoviˇcka 1, Tomáš Palatý 2, Eva Štefanová 1 and PˇremyslŠtych 1,* 1 Department of Applied Geoinformatics and Cartography, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic; [email protected] (L.B.); [email protected] (J.L.); [email protected] (E.Š.) 2 Project Management Department, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic; [email protected] * Correspondence: [email protected]

Received: 5 September 2020; Accepted: 9 October 2020; Published: 14 October 2020

Abstract: Diachronic studies play a key role in the research and documentation of cultural heritage and its changes, ranging from architectural fragments to landscape. Regarding the reconstructions of lost cultural heritage sites, the determination of landscape conditions in the reconstructed era goes frequently unheeded. Often, only ruins and detached archeological artefacts remain of the built heritage. Placing them correctly within the reconstructed building complex is of similar importance as placing the lost monument in the context of the landscape at that time. The proposed method harmonizes highly heterogeneous sources to provide such a context. The solution includes the fusion of referential terrain models of diﬀerent levels of detail (LODs) as well as the fusion of diverse 3D data sources for the reconstruction of the built heritage. Although the combined modeling of large landscapes and small 3D objects of a high detail results in very large datasets, we present a feasible solution, whose data structure is suitable for Geographic Information Systems (GIS) analyses of landscapes and also provides a smooth and clear 3D visualization and inspection of detailed features. The results are demonstrated in the case study of the island monastery, the vanished medieval town of Sekanka, and the surrounding landscape, which is located in Czechia and was the subject of intensive changes over time.

Keywords: 3D modeling; diachronic reconstruction; cultural heritage; LOD; smart object; data fusion; Czechia

1. Introduction Over the course of centuries, the landscape has changed in many places to be unrecognizable. Historical places or entire monuments were significantly altered or even vanished. Virtual reconstruction has become increasingly popular since the virtual model is a valid cognitive medium through which a user can study or even interact with the object. Not only the users from the general public but also the scientists frequently employ three-dimensional (3D) models, as they provide clear understanding of objects of cultural heritage as well as changes of the landscape. Since Reilly [1], many researchers have studied the applications of virtual reconstructions to the domain of cultural heritage (and natural too) as a tool for preservation, reconstruction, analysis, and promotion [2–4]. The virtual reconstructions are used to address different issues and to target different audiences. Their point of interest ranges from very small artefacts [5,6] over the buildings [7] to whole cities (“Rome Reborn” (https://www.romereborn.org); Brno 1645 (https://www.brno1645.cz)). Accordingly, the data acquisition and the data modeling techniques vary.

ISPRS Int. J. Geo-Inf. 2020, 9, 604; doi:10.3390/ijgi9100604 www.mdpi.com/journal/ijgi ISPRS Int. J. Geo-Inf. 2020, 9, 604 2 of 25

In the literature, there are many studies regarding the techniques of digitization of 2D objects (paintings) as well as 3D monuments, sculptures, and even small objects such as pottery or jewelry. Most virtual reconstructions are based on 3D laser scanning techniques [8] or photogrammetry [9] to produce geometrically accurate as well as photorealistic products. Different techniques are used for the reconstruction of lost monuments. Such modeling is based on preserved sources from the relevant era. These sources are highly heterogeneous and include charts, engravings, testimonies, or texts in contemporary chronicles. Additionally, an inspiration can be taken from structures that remain in existence, and their design is known to have been similar. As the study elements are no longer present, the original shapes are only being known within a certain probability [10]. For the reconstruction of large environments such as the lost cities or complex monuments, the procedural modeling is frequently applied [11–13]. To avoid the drudgery related to the manual creation of virtual worlds, procedural modeling uses the so-called shape grammars, sets of formalized rules, to automatically generate complex and repetitive geometrical shapes. The most recent endeavors focus on the diachronic reconstruction of a researched site. Rodríguez-Gonzálvez et al. [10] present through the case study of the medieval wall of Avila (Spain) a 3D model that is enhanced by the time component (forming a 4D model) to represent the wall’s condition in various historical phases. The great spectrum of geomatics techniques and data sources meet in the field of cultural heritage and, clearly, the data fusion of these sources is a necessity. Many scientific works went in this direction. Especially photogrammetry and laser scanning can benefit from the integration of outputs from these methods and provide better results in a broader spectrum of measuring conditions [14–17]. Software products such as PhotoModeler (http://www.photomodeler.com), RealityCapture (Capturing Reality s.r.o., Bratislava, Slovakia), Pix4D (Pix4D S.A., Lausanne, Switzerland), CloudCompare, or Agisoft PhotoScan (http://www.agisoft.com) are examples of solutions that implemented these methods. The need for the 3D data model optimizations of reality-based models as well as their online distribution on the web was pointed out by [18] and further elaborated in [19]. A more complex approach to the optimization that goes beyond needs of visualization of the reality-based model can be found in the field of Geographic Information Systems (GIS). For example, the role of topology in the geometry simplification and model generalization process is the key element that preserves the analytical value of the spatial model; see [20]. Moreover, the data model itself and its dimensionality should be considered as a means for data volumes reduction. Often, the use of a 3D scene for the visualization of a model results in a classification of a model as 3D. However, this classification does not recognize the difference between a model that uses 2D primitives in 3D space (sometimes termed as 2.5D) and a model using 3D primitives in 3D space, forming a true volumetric 3D model [21]. The pragmatic hybrid 2.5D/3D solutions exist; for an example, see [22], which react to the structural complexity of pure 3D solutions. In order to avoid it, these approaches utilize the simpler 2D modeling as much as possible and reach for 3D only when necessary. Multiple aspects of 3D modeling, including the suitability of various modeling approaches for data management (editing, future updates) and distribution or spatial analysis, are covered in [23]. Analyses of digital terrain models can stand as an example of the functionality that GIS provides. Although the reconstructions and visualizations of lost heritage sites are an active research area, the landscape in the vicinity and the changes it underwent over the time are paid surprisingly little attention. The change of the bare Earth shape and its impact on the landscape function, land use, or the urban component is rarely discussed. Nevertheless, some works proceeded in that direction [12,13,24–28] in terms of including landscapes among cultural heritage (CH) objects, historical landscape visualization, or providing methods of relevant data processing and means for the rapid procedural modeling of landscapes. The modeling of landscapes usually comprises six ISPRS Int. J. Geo-Inf. 2020, 9, 604 3 of 25 essential elements: landform; vegetation; water; structures including architecture and infrastructure; animals and people; and atmosphere (including sun, wind, etc.) [29]. The virtual representation of a historical landscape can be used to compare present-day and historical conditions and serve as a solid foundation for rigorous spatial and temporal analyses.

1.1. Objectives of the Study With respect to the studies reviewed above, we observe a gap between solutions to 3D reconstructions of the cultural heritage sites and modeling of the landscapes. It is a context, both spatial and temporal, that current virtual reconstructions or virtual museums fail to provide for individual pieces. Our aim is to add this context to individual objects within the reconstructed monument and to add context to the monument (and even the whole lost city) within the landscape. Therefore, we propose a complete methodology to create a virtual representation that offers a combined visit to detailed objects originating from archeological findings of a lost monument, to the reconstruction of such a monument and to the ambient landscape including the neighboring vanished city in corresponding historical periods. We start with a brief introduction of the study case, namely, the lost site of Ostrovský klášter (“Island monastery”), the abandoned medieval town on the Sekanka promontory, and the surrounding landscape that has undergone intensive changes over time. Furthermore, we harmonize highly heterogeneous available data sources in Section2. The available documentation, the chronology, and the accuracy of data sources define their role in the reconstruction efforts (Sections 2.1 and 2.2). The data fusion forms the foundation of the diachronic reconstruction of the site and the environment. That includes the fusion of referential terrain models of different levels of detail (LODs) (Section 2.3), the modeling of historical landscape (Section 2.4), the fusion of a digital terrain model (DTM) with reconstructed historical objects (Section 2.5), and the fusion of 3D data sources of different LODs for the reconstruction of historical objects in the third dimension (Section 2.6). Although the combined modeling of large landscapes and 3D objects of a high detail results in very large datasets, we present a feasible technical solution that provides smooth and clear visualization. The results are given in the Section3, which is followed by the Section5.

1.2. The Historical Context of Study Area The area of interest includes the former Abbey of the Decollation of St John the Baptist (Figure1). The historical information about the place, including the interpretation of archeological discoveries and architectonic details can be found in [30,31]. The ruins of the monastery are located on the Vltava river island south of Prague near the confluence of the Vltava and Sázava rivers. The history of the monastery goes back to 999 when it was officially founded by Boleslaus II, the Duke of Bohemia, as the second oldest male convent in Bohemia. In addition to the missionary activity, the abbey was a key player in cultural and economic development, state politics, and diplomacy. The original wooden objects of the monastery succumbed in 1137 to an extensive fire. During the subsequent restoration, new stone buildings were built in the Romanesque style. During the 13th century, the site experienced great prosperity. A medieval settlement (Figure1) grew up above the monastery on the rocky promontory Sekanka by the river’s confluence. It existed only shortly since its foundation in 1250 until 1278, when it was plundered by Brandenburg soldiers. The town has never been restored. However, the monastery was rebuilt in the late Gothic style during the reign of the Emperor Charles IV. Later, it was pillaged multiple times during the Hussite wars. The monastery gradually fell into disrepair. In 1517, the monastic community decided to abandon the place definitely. In the west bank of the Vltava river, the Church of St. Kilián (since around 999) has been preserved (Figure1) in the re-built Baroque appearance. ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 4 of 25

However, the most prominent change refers to the rise of a water level of the Vltava river caused ISPRSby the Int. filling J. Geo-Inf. of the2020 ,reservoir9, 604 Vrané in 1936. The rise reached approximately 5 m, which caused4 of an 25 overflow of the then banks and significantly changed the shape of the island.

Figure 1. The contemporary state from an aerialaerial viewview (archeologickyatlas.cz)(archeologickyatlas.cz) with marked locations of the lost monastery (red circle), medieval town (gr (greeneen circle), and Church of St. Kilián Kilián (blue circle). Source: The ArcheologyThe atlas ofArcheology Czechia (2020; http:atlas//www.archeologickyatlas.cz of Czechia/cs/lokace /davle_pz_(2020; mestecko_sekankahttp://www.archeologickyatlas.cz/cs/lokace/davle) and Open Street Map (2020; geo:_pz_mestecko_sekanka) 49.8812, 14.3908). and Open Street Map (2020; geo: 49.8812, 14.3908). The landscape has also changed significantly over the studied periods. To pull the empty ships back2. Materials upstream, and the Methods towpath was built in the 19th century connecting both ends of the island with the westThis bank section of the river.presents These historical barriers and even geometrica caused onel data of the sources river’s armsfor the to cease3D reconstruction to exist andthe in islandmultiple to mergetime periods with the originating mainland. from Then, archeolo the drainedgical river’s research, arm early was usedmaps, for or farming modern purposes. geomatics acquisitionHowever, methods. the most The prominent method de changescribes refers the data to the assessment rise of a water and fusion level of to the obtain Vltava a model river caused of the byhistorical the filling landscape, of the reservoir 3D reconstruction Vrané in 1936. of historic The riseal reachedobjects, and approximately their integration 5 m, which within caused a single an overflowinformation of thesystem. then banks and significantly changed the shape of the island. 2. Materials and Methods 2.1. Preliminary Considerations and the High-Level Concept This section presents historical and geometrical data sources for the 3D reconstruction in The concept of the proposed method deals with four categories of data regarding the scale. The multiple time periods originating from archeological research, early maps, or modern geomatics employed classification proceeds from [25]; however, the functions of our classes differ. Each acquisition methods. The method describes the data assessment and fusion to obtain a model of category plays distinct role within the proposed solution with specific requirements on the defining the historical landscape, 3D reconstruction of historical objects, and their integration within a single data. information system. Artefact level. There are two main roles of this category in our approach. The first is the digital 2.1.preservation Preliminary of Considerationsan artefact. The and raw the High-Leveldata should Concept be archived with the highest possible detail in a detached database for possible analytical uses in the future. The conceptsecond role of theis the proposed digital methodexhibition deals of the with 3D fourmodel categories constructed of data from regarding the raw data. the scale. The TheLOD employedof the original classification data needs proceeds to be reduced from [25 fo];r this however, purpose the to functions meet the ofrequirements our classes of di webffer. Eachgraphic category libraries. plays distinct role within the proposed solution with specific requirements on the definingArchitectural data. level. This class refers to the objects of a larger extent with a dominant Z dimensionArtefact such level. as Theremonuments are two or main buildings. roles of Its this pu categoryrpose is into ourprovide approach. the most The possible first is the detailed digital preservationdepiction of ofthe an objects artefact. in various The raw periods data should of time. be archivedThat includes with thethe highestoverall possibleappearance detail of inthe a detachedinteriors databaseand exteriors. for possible Individual analytical pieces uses from in thethe future. artefact level play an important role at the architecturalThe second level, role since is the the digital preserved exhibition artefacts of the are 3D modelhelpful constructed in the reconstruction from the raw of data.lost monuments The LOD of the(position, original function, data needs context, to be reducedor relation for to this other purpose detailed to meet artefacts). the requirements of web graphic libraries. ArchitecturalUrban land. Similarly, level. This the class architectural refers to the level objects objects of a larger and extenttheir mutual with a dominantcomposition Z dimension in space suchpresent as monumentstheir development, or buildings. function, Its purpose and context is to provideat the urban the most land possible level. This detailed level depiction integrates of the objectsarchitectural in various objects, periods meaning, of time. they That are includesall referenc theed overall to its surface. appearance From of the the data interiors modeling and exteriors. point of Individual pieces from the artefact level play an important role at the architectural level, since the

ISPRS Int. J. Geo-Inf. 2020, 9, 604 5 of 25 ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 5 of 25 view,preserved the surface artefacts (2D) are is helpful a sufficient in the data reconstruction representation of lost at this monuments level, while (position, the architectural function, context,objects requireor relation the to3D other approach detailed (multiple artefacts). Z-coordinates for a single X,Y-location). The defining data of the urbanUrban land need land. toSimilarly, be at a detail the sufficient architectural for the level description objects and of man-made their mutual or natural composition changes in of space the barepresent Earth their shape development, (embankments, function, earthwork, and context landslides at the, sedimentation). urban land level. The Thisresolution level integratesof at least one the pointarchitectural per square objects, meter meaning, allows theyfor a are convincing all referenced visualization to its surface. of land From changes the data and modeling for basic point terrain of analysesview, the (slope, surface aspect, (2D) is height a suffi differences,cient data representation volumetric changes). at this level, while the architectural objects requireRural the land. 3D approach Rural land (multiple puts the Z-coordinates urban area in forthe aco singlentext of X,Y-location). a broad neighborhood. The defining Functionally, data of the iturban is supposed land need to torepresent be at a detailthe overall sufficient shape for (lowlan the descriptiond, mountainous of man-made land), orthe natural land cover/land changes of use, the andbare their Earth changes shape (embankments, over time. Moreover, earthwork, within landslides, the system, sedimentation). it has a function The resolution to navigate of at leastbetween one pointspoint perof interest square and meter support allows the for exploration a convincing simila visualizationrly to Google of Earth land changesor other digital and for Earth basic engines. terrain Fromanalyses the (slope,data modeling aspect, height point diofff view,erences, rural volumetric land is the changes). 2D surface of a lower detail than the urban land.Rural land. Rural land puts the urban area in the context of a broad neighborhood. Functionally, it is supposedConsequently, to represent the proposed the overall solution shape employs (lowland, the hybrid mountainous data model land), that the combines land cover the/land second- use, dimensionand their changes terrain surface over time. (termed Moreover, as 2.5D) withinat multip thele system,LODs with it has 3D aobjects function (varying to navigate LOD according between topoints the purpose). of interest These and support models the are exploration seamlessly similarlyjoined at toconstraints Google Earth to the or triangulation other digital Earthof the engines. terrain model.From the The data concept modeling of the point proposed of view, solution rural land is isillustrated the 2D surface in Figure of a lower 2. To detail model than the thegeometries urban land. of interiorsConsequently, and exteriors, the the proposed workflowsolution of the proced employsure uses the a hybridcombination data of model software that AutoCAD combines Civil the 3Dsecond-dimension 2018 (DEM creation terrain from surface elevation (termed points as in 2.5D)SketchUp at multiple format), LODsQGIS 3.10 with (map 3D objectspreparation (varying and surfaceLOD according creation–data to the fusion), purpose). and These SketchUp models Make are seamlessly 2017 (modeling joined and at constraints texturing). to That the triangulationincludes the fusedof the and terrain adjusted model. DTMs The with concept the offootprints the proposed (constra solutionints to TIN) is illustrated for the precise in Figure integration2. To model with thethe actualgeometries 3D geometry. of interiors GIMP and exteriors,2.8 was employed the workflow for the of theprocessing procedure and uses normalization a combination of oftextures software of interiorsAutoCAD (frescos). Civil 3D 2018 (DEM creation from elevation points in SketchUp format), QGIS 3.10 (map preparationThe final and rendering surface was creation–data carried out fusion), in software and SketchUpLumion Pro Make 10.3.2. 2017 Rendered (modeling panorama and texturing). images fromThat includesLumion were the fused employed and adjusted in Theasys DTMs online with software the footprints in which (constraints the virtual museum to TIN) forwas the designed. precise Theintegration hotspots with in the the virtual actual 3Dmuseum geometry. can GIMPbe access 2.8ed was during employed the walk for the through processing the overall and normalization model and interactivelyof textures of examined interiors (frescos). by a user in a full detail.

Figure 2. TheThe solution’s solution’s workflow workﬂow summary summary starting with the conceptual analysis to the employment of technology for distribution of variable thematic data layers.

2.2. ArcheologicalThe ﬁnal rendering Sources was carried out in software Lumion Pro 10.3.2. Rendered panorama images from Lumion were employed in Theasys online software in which the virtual museum was designed. Archeological sources are a key factor of the anastylosis—in this case, the digital recreation of The hotspots in the virtual museum can be accessed during the walk through the overall model and constructions that no longer exist. They provided original architectural and decorative pieces that are interactively examined by a user in a full detail. unique to our case. Within the overall model of interiors, they form certain hotspots that the user can inspect in higher detail as they can in a virtual museum.

ISPRS Int. J. Geo-Inf. 2020, 9, 604 6 of 25

2.2. Archeological Sources ArcheologicalISPRS Int. J. Geo-Inf. sources 2020, 9, x FOR are PEER a key REVIEW factor of the anastylosis—in this case, the digital 6recreation of 26 of constructionsFragments that no found longer during exist. the They archeological provided originalresearch architecturalprove the high and artistic decorative value piecesof the that are uniquemonastery to our case. decorations. Within theThe overallincorporation model of ofsuch interiors, authentic they features form into certain the virtual hotspots reconstruction that the user can inspectis in an higher intermediate detail aim as theyof this can work. in a virtual museum. FragmentsThe tiles found of Vyšehrad during thetype archeological are perhaps the research best-known prove artefact the high (see artisticFigure 3c) value that ofprobably the monastery decorations.originates The from incorporation the own production of suchof the authenticmonastery’s featuresceramics workshop. into the Researchers virtual reconstruction found floor is an and mural tiles of various shapes including the hexagonal form used for the star-shaped wall intermediate aim of this work. decorations, as can be seen in Figure 3a,c. The tilesFigure of Vyšehrad3a,b illustrate type some are of perhaps the other the fragments best-known found artefact in the (seemonastery, Figure including3c) that probablya originatesRomanesque from the pillar, own which production we have employed of the monastery’s for the modeling ceramics purposes. workshop. The abbot’s tombstone Researchers in found ﬂoor andFigure mural 3d is tiles one ofof variousseven found shapes in the including area of basilica. the hexagonal They have formbecome used a part for of the the star-shaped detailed wall decorations,modeling as of can the be interior. seen in Figure3a,c.

(a) (b)

Figure 3. Various historical sources employed: (a) Presentation of artefacts in the National Museum in Prague; (b) The Romanesque pillar of the National Museum collection; (c) The hexagonal tiles of so-called Vyšehrad type; (d) The tombstone of abbot Heˇrman.Photos: Petr Kˇríž and Tomáš Palatý (2017). ISPRS Int. J. Geo-Inf. 2020, 9, 604 7 of 25

Figure3a,b illustrate some of the other fragments found in the monastery, including a Romanesque pillar, which we have employed for the modeling purposes. The abbot’s tombstone in Figure3d is one of sevenISPRS found Int. J. Geo-Inf. in the 2020 area, 9, x of FOR basilica. PEER REVIEW They have become a part of the detailed modeling of 7 of the 25 interior.

2.3. Historicalso-called Data Vyšehrad type; (d) The tombstone of abbot Heřman. Photos: Petr Kříž and Tomáš Palatý (2017). The whole territory of the island and promontory was strongly affected throughout history, most significantly2.3. Historical Data due to the filling of the reservoir Vrané constructed between 1930 and 1936. Early mapsThe (with whole examples territory inof Figurethe island4a,b) and are promontory a valuable was source strongly for evaluationaffected throughout of theoverall history, original charactermost of significantly the landscape due to and the filling the changing of the reservoir shape Vrané of the constructed island in between historical 1930 phases. and 1936. Early Early military mappingsmaps (I,(with II Militaryexamples Mappingin Figure 4a,b) and are especially a valuable the source 3rd Militaryfor evaluation Mapping of the overall with aoriginal 1:25,000 scale, from 1874–1920),character of the the landscape Stable Cadastre and the changing (1:2880, shape from of 1840), the island Map in of historical constituency phases. andEarly judicial military districts mappings (I, II Military Mapping and especially the 3rd Military Mapping with a 1:25,000 scale, from (Mapa1874–1920), zastupitelsk the ýStablech a Cadastre soudní ch(1:2880, okres from ˚uKr. 1840), Vinohradsk Map of constituencyého a J íandlovsk judicialého, districts 1:25,000, (Mapa from 1887) and Detailedzastupitelských map of a soudních Prague okres surroundingsů Kr. Vinohradského (Podrobn a Jílovského,á mapa okol 1:25,000,í Pražsk fromé 1887)ho, 1:75,000, and Detailed from 1920) are examplesmap of Prague of such surroundings maps. Another (Podrobná source mapa ofokolí the Pražského, bygone 1:75,000, appearance from 1920) is the are Altmann examples panorama,of whichsuch displays maps. theAnother St. Kilisourceán of church the bygone on theappearan left bankce is the of Altmann the Vltava panorama, river which in its displays late Gothic the form. The panoramaSt. Kilián church portrays on boththe left banks bank of in the the Vltava year 1640.river in its late Gothic form. The panorama portrays both banks in the year 1640. Moreover, the land-surveying plans (Figure4c,d) were drawn in the 1960s during archaeological Moreover, the land-surveying plans (Figure 4c,d) were drawn in the 1960s during archaeological researchresearch led by led an by archaeologist an archaeologist Miroslav Miroslav RichterRichter [32]. [32 ].The The remnants remnants of foundations of foundations and walls and of walls of buildingsbuildings revealed revealed by excavations by excavations are are documented documented in in these these plans. plans. The Thereal appearance real appearance in 3D was in also 3D was also proposedproposed by an by archaeologist an archaeologist František František StehlStehlííkk in in 1947 1947 [33], [33 which], which were were re-drawn re-drawn by Jan byHeř Janman Heˇrmanin in 2009 (Figure2009 (Figure4e,f; https: 4e,f; https://www.hrad//www.hrady-zriceniny.czy-zriceniny.cz/s__herman_bar.htm)./s__herman_bar.htm ).

(a) (b)

Figure 4. Cont.

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(e) (f)

FigureFigure 4. 4.Examples Examples of of early early maps maps and andland-survey land-survey plans originating plans originating from archeological from archeological research: (a) research: (a) TheThe Second military military mapping; mapping; (b) (Theb) Thecadaster cadaster mapping mapping (Franziszeische (Franziszeische Kataster); Kataster);(c) The plans (c ) The plans differentiating the structures of monastery’s Romanesque and Gothic eras; (d) The plan of the lost diﬀerentiating the structures of monastery’s Romanesque and Gothic eras; (d) The plan of the lost town town Sekanka (Romanesque era); archaeological drawing of the monastery in Romanesque era (e) Sekankaand in (RomanesqueGothic era (f). Source: era); archaeological2nd Military Surv drawingey, Section of No. the 9/2, monastery Austrian State in Romanesque Archive/Military era (e) and in GothicArchive, era (Viennaf). Source: (a); State 2nd Administration Military Survey, of Land Section Surveying No. and 9/2, Cadaster Austrian (b); StateMiroslav Archive Richter/Military (1982; Archive, Vienna(c,d)); (a );František State Administration Stehlík (1947; original) of Land and Surveying Jan Heřman and (2009; Cadaster redrawn (b); Miroslavwith new Richternotes by (1982; (c,d)); Františekarcheologists; Stehlík (e (1947;,f)). original) and Jan Heˇrman(2009; redrawn with new notes by archeologists; (e,f)).

2.4.2.4. Data Data Fusion—Referential Fusion—Referential Terrain Models Models WithWith the the progress progress inin thethe field field of of spatial spatial data data acquisition, acquisition, high-resolution high-resolution Light Detection Light DetectionAnd And Ranging (LiDAR)-based DTMs are often available covering the entire countries. However, for the Rangingsake of (LiDAR)-based distinct projects, DTMs local aredata often acquisition available campaigns covering provide the entire even countries.higher resolution However, DTM for the sake of distinctnecessary projects, for the localanalysis data of acquisitionsuch an area. campaigns However, for provide visualization even higherpurposes, resolution a greater DTMarea necessary for thedescribed analysis with of lower such andetail area. is required. However, If forthe visualizationextent of high-resolution purposes, DTM a greater is sufficient area described for with lowervisualization, detail is required. the parts Ifof thethe extentmodel that of high-resolution are more distant DTMfrom the is supointfficient of interest for visualization, (POI) may be the parts of the modelprogressively that are simplified more distant [34]. If it from is not thethe pointcase, the of fusion interest with (POI) a different may DTM be progressively is a solution. simplified [34]. In our case, this fusion effort is presented through an example of the Digital Terrain Model of If it is not the case, the fusion with a different DTM is a solution. the Czech Republic of the 5th generation (DMR 5G) and the Shuttle Radar Topography Mission (SRTM)In our integration. case, this fusion The first eff categoryort is presented of data employed through for an the example production of theof DTM Digital is the Terrain airborne Model of the CzechLiDAR Republic system of data the DMR 5th generation5G by CUZK (DMR(https://geopo 5G) andrtal.cuzk.cz/). the Shuttle DMR Radar 5G is Topographyan irregular network Mission (SRTM) integration.of discrete Theheight first points. category The total of mean data employederror of height for measurement the production is 0.18 of m DTM(barren) is up the to airborne 0.3 m LiDAR system(forested data DMRarea). This 5G bydataset CUZK is meant (https: for//geoportal.cuzk.cz the close vicinity of). reconstructed DMR 5G is an objects irregular of the network cultural of discrete heightheritage points. site. TheThe burden total mean of high error data ofvolumes height is measurementintroduced using is high-density 0.18 m (barren) datasets; up therefore, to 0.3 m (forested for the more distant areas, the SRTM digital elevation model (DEM) area). This dataset is meant for the close vicinity of reconstructed objects of the cultural heritage site. (https://www2.jpl.nasa.gov/srtm/) was preferred. Although there are DMR 5G data available for the Theentire burden country of high and data the volumesprogressive is simplification introduced usingwould high-densitybe possible, we datasets; decided therefore,to use freely for the more distantavailable areas, SRTM the SRTM data (DMR digital 5G elevation is a commercial model product). (DEM) ( https:Moreover,//www2.jpl.nasa.gov SRTM DTM is coherent/srtm )with was preferred. Althoughdigital Earth there systems, are DMR which 5G similar data available to Google forEart theh employs entire countryan SRTM anddata source. the progressive Therefore, this simplification wouldchoice be possible,prospectively we supports decided the to use use of freely such platforms available for SRTM presentation. data (DMR 5G is a commercial product). Moreover,The SRTM objective DTM of the is two coherent DTMs withfusion digital is to provid Earthe a systems,transition surface which in similar terms of to both Google the point Earth employs density and the height adjustment (see Figure 5). an SRTMThe data input source. to the procedure Therefore, consists this of two-point choice prospectively layers, which corresponds supports to the the usesource of data such of platforms for presentation.the two terrain models. The requirement is that both layers are aligned to an identical coordinate systemThe objective and that the of thecoverage twoDTMs of the dataset fusion with is to hi providegher resolution a transition expands surface beyond in the terms area ofthat both is the point densitystrictly and required the height to be modeled adjustment at such (see an Figure LOD. 5). The input to the procedure consists of two-point layers, which corresponds to the source data of the two terrain models. The requirement is that both layers are aligned to an identical coordinate system and that the coverage of the dataset with higher resolution expands beyond the area that is strictly required to be modeled at such an LOD. The transition surface is defined as a strip of land of a constant breadth. It is outlined on the inner side by the border with a higher resolution surface and on the outer side by the border with a lower resolution surface. ISPRS Int. J. Geo-Inf. 2020, 9, 604 9 of 25 ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 10 of 26

(a) (b)

Figure 5.Figure(a) The5. (a depiction) The depiction of the of triangulation the triangulation of two of datasetstwo datasets with with highly highly diff differenterent resolution resolution resulting in a sharpresulting divide in anda sharp unnatural divide and turn. unnatural (b) A turn. 3D view(b) A 3D on view the boundary on the bounda linery and line and triangles triangles with with too small interiortoo angles. small interior (c) An angles. illustration (c) An ofillustration the different of the DTMsdifferent geometries DTMs geometries in the in transition the transition zone—low zone— detail, high detail,low detail, andthe high transition detail, and zone the transition illustrated zone with illustrated different with colors. different (d colors.) The figure(d) The onfigure the on bottom the right bottom right depicts a 3D view on the resulting geometry of the terrain. The resulting triangulation depicts a 3D view on the resulting geometry of the terrain. The resulting triangulation consists of consists of triangles with far greater interior angles (more equilateral), which follows the objective of triangles with far greater interior angles (more equilateral), which follows the objective of the Delaunay the Delaunay triangulation and therefore adheres more closely to the actual terrain course. triangulation and therefore adheres more closely to the actual terrain course. 2.5. Modeling of Historical Landscape 2.4.1. Mesh Simplification Early maps listed in Section 2.2 served as sources for an estimate of the original shapes of the First,riverbanks, we want promontory, to avoidthe and disruptive island. The influencemost helpful that in this the aspect sharp was change the 2nd of aMilitary point densityMapping, causes to the visualizationwhich also provided and cognition the location of the of DTM,the now namely, gone me todieval avoid bridge narrow, that connected elongated the triangles. island with To the achieve a smoothleft geometrical bank until the transition 19th century. between both datasets, we progressively removed points from the finer Furthermore, the early photographs, e.g., see Figure 6, from the first two decades of the 20th resolution dataset that fell into the transition zone. century helped reconstruct the geometry of the embankments that caused the merge of the island Forwith this the sake, mainland. we have Figure assigned 6a shows a the weight connected to each island point. with the The bank weight in south. is an Figure outcome 6b shows of a the combined influenceoriginal of a point’sshape of distance the promontory from the before inner Vrané border reservoir of the filling transition and the areanorthern and part a point’s of the island. importance for the description of the surface shape. The distance component is obtained as a linear weight function, starting with a zero influence at the inner border and reaching the full influence at the outer border. For the latter component, the metric first introduced in [34] was applied, which describes the error introduced to the shape of the surface by the point’s absence. The resulting weight of a point is obtained as a weighted sum of both weights giving 85% influence to the distance component and 15% influence to the shape-description component. This ratio was determined experimentally for the researched area to achieve a visually convenient outcome. The simplification procedure stops when a threshold (the value of weight, which was also inferred experimentally) is reached, all points having the weight below the threshold removed. Consequently, the triangles of the resulting triangular irregular network (TIN) gradually grow toward the outer ISPRS Int. J. Geo-Inf. 2020, 9, 604 10 of 25 border and keep their equilateral-like shape (illustrated by the 2D view in Figure5c and 3D view in Figure5d).

2.4.2. Height Adjustment Second, to achieve a smooth transition of heights, we made use of the triangular mesh created from points of the coarser data source. For each point from the higher resolution layer within the transition surface, we have extracted its respective height from the TIN. To determine the amount of influence of the coarser DTM on the finer DTM points, we applied the linear weight function. Starting from the inner border of the transition zone, where the zero weight is given to the height derived from the coarser DTM (full weight given to the original height of finer DTM), the weight of the coarser DTM increases linearly moving to the outer border, where the coarser DTM heights gain the full influence. Weight functions different from the linear one can also be applied. For a more detailed description and an analysis of the effects the different weight functions have on the continuity of the resulting surface, refer to [35].

2.5. Modeling of Historical Landscape Early maps listed in Section 2.2 served as sources for an estimate of the original shapes of the riverbanks, promontory, and island. The most helpful in this aspect was the 2nd Military Mapping, which also provided the location of the now gone medieval bridge that connected the island with the left bank until the 19th century. Furthermore, the early photographs, e.g., see Figure6, from the ﬁrst two decades of the 20th century helped reconstruct the geometry of the embankments that caused the merge of the island with the mainland. Figure6a shows the connected island with the bank in south. Figure6b shows the ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 11 of 26 original shape of the promontory before Vrané reservoir ﬁlling and the northern part of the island.

(a) (b)

Figure 6. Photographs of the former island and its merge with mainland from the beginning of the Figure 6. Photographs of the former island and its merge with mainland from the beginning of the 20th century from northeast (a) and north (b). Source: Josef Dvoˇrák (http://www.dvorak-davle.cz). 20th century from northeast (a) and north (b). Source: Josef Dvořák (http://www.dvorak-davle.cz). These raster materials were georeferenced and overlaid with the contemporary LiDAR-based These raster materials were georeferenced and overlaid with the contemporary LiDAR-based DTM. Based on these sources, the outlines of banks and the island were manually vectorized to DTM. Based on these sources, the outlines of banks and the island were manually vectorized to represent the state before the construction of the weir or the dam later. The artiﬁcial height points were represent the state before the construction of the weir or the dam later. The artificial height points generated in the area of revealed banks and their heights linearly interpolated between the original were generated in the area of revealed banks and their heights linearly interpolated between the and the new bank. The contemporary island measures 410 m in length, and the promontory measures original and the new bank. The contemporary island measures 410 m in length, and the promontory 65 m. For illustration, the length of the island inferred from the 2nd Military Mapping before water measures 65 m. For illustration, the length of the island inferred from the 2nd Military Mapping level rise amounts to 597 m, resp. 146 m of the promontory. The root-mean-square error (RMSE) of the before water level rise amounts to 597 m, resp. 146 m of the promontory. The root-mean-square error georeferencing on the x,y-coordinates reached 7.5 m. (RMSE) of the georeferencing on the x,y-coordinates reached 7.5 m. Similarly, the photographs helped delimit the outlines and area of embankments, and the adjusted artificial height points formed the terrain of the newly arisen mainland. The conventional affine transformation was employed as the rectification procedure. As matching ground control points, the changeless spots such as bedrocks exposures or the church were found. Such reference points were selected that minimized and uniformly distributed residuals across the rectified images. Moreover, the early maps, panoramas, and chronicles together with consultations with relevant experts helped obtain an idea of how the structure of the path network and the land use (including the knowledge of historical plant ecology in the wider surrounding area) looked at given historical periods. This knowledge was later used for a relevant landscape texturing of the resulting model.

2.6. Data Fusion—DTM and Reconstructed Historical Objects The land surveying plans (Figure 4c,d) originating from the archeological survey in [32] were scanned and then georeferenced using the tie points and control points acquired in situ with a Global Navigation Satellite System (GNSS) device. The outlines of cultural heritage objects as well as the outlines of their interiors were vectorized. The information of the period of construction, which was the outcome of the same archeological survey, was associated with corresponding geometries. The maximum x,y-coordinates positional error of the rectification procedure reached 0.25 m with the RMSE equal to 0.11 m. The elevation of the points that form the footprint of a reconstructed object on the bare ground was derived from the DTM (DMR 5G). The footprint acts as a constraint to the TIN; therefore, the elevation of its points was set as a mean value of DMR 5G height points directly neighboring with the footprint’s point in the TIN. These footprints stand for an exact line of contact between the 2.5D DTM and 3D models of reconstructed objects. The resulting footprint of a building’s object also serves as a mask for removal of the terrain height points that are no longer necessary in places of reconstructed 3D objects. The footprints’ line segments were densified (auxiliary vertices inserted where necessary) to provide smooth integration with TIN DTM in terms of triangles’ shape.

ISPRS Int. J. Geo-Inf. 2020, 9, 604 11 of 25

Similarly, the photographs helped delimit the outlines and area of embankments, and the adjusted artificial height points formed the terrain of the newly arisen mainland. The conventional affine transformation was employed as the rectification procedure. As matching ground control points, the changeless spots such as bedrocks exposures or the church were found. Such reference points were selected that minimized and uniformly distributed residuals across the rectified images. Moreover, the early maps, panoramas, and chronicles together with consultations with relevant experts helped obtain an idea of how the structure of the path network and the land use (including the knowledge of historical plant ecology in the wider surrounding area) looked at given historical periods. This knowledge was later used for a relevant landscape texturing of the resulting model.

2.6. Data Fusion—DTM and Reconstructed Historical Objects The land surveying plans (Figure4c,d) originating from the archeological survey in [ 32] were scanned and then georeferenced using the tie points and control points acquired in situ with a Global Navigation Satellite System (GNSS) device. The outlines of cultural heritage objects as well as the outlines of their interiors were vectorized. The information of the period of construction, which was the outcome of the same archeological survey, was associated with corresponding geometries. The maximum x,y-coordinates positional error of the rectiﬁcation procedure reached 0.25 m with the RMSE equal to 0.11 m. The elevation of the points that form the footprint of a reconstructed object on the bare ground was derived from the DTM (DMR 5G). The footprint acts as a constraint to the TIN; therefore, the elevation of its points was set as a mean value of DMR 5G height points directly neighboring with the footprint’s point in the TIN. These footprints stand for an exact line of contact between the 2.5D DTM and 3D models of reconstructed objects. The resulting footprint of a building’s object also serves as a mask for removal of the terrain height points that are no longer necessary in places of reconstructed 3D objects. The footprints’ line segments were densiﬁed (auxiliary vertices inserted where necessary) to provide smooth integration with TIN DTM in terms of triangles’ shape.

2.7. Reconstruction of Historical Objects in 3D The 3D modeling has three main stages in our workﬂow. First, it is the production of artefacts’ models, second, the reconstruction of the buildings and, lastly, their integration. Despite the limited knowledge of the vertical dimension, there are preserved architectural and functional pieces of the original construction whose location is determined with relevant accuracy. The tombstones (Figure3d) stand as an example of an artefact whose positional accuracy was estimated in the report [32] to be up to 1 m. Photogrammetric methods enable the retrieval of 3D information from 2D images. Due to the objects (archeological artefact) proportions, the close-range photogrammetry was applied. The control points were distributed around the object and marked with black-and-white targets. Imaging was gradually conducted around the object while keeping the distance and overlay ratio of the adjacent images. The parameters of the Nikon D750 camera are highlighted in Table1. Table2 sums up the processing values of the tile. The varying resolutions of the processed dense point cloud of this artefact can be seen in Figure7. ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 12 of 25

2.7. Reconstruction of Historical Objects in 3D The 3D modeling has three main stages in our workflow. First, it is the production of artefacts’ models, second, the reconstruction of the buildings and, lastly, their integration. Despite the limited knowledge of the vertical dimension, there are preserved architectural and functional pieces of the original construction whose location is determined with relevant accuracy. The tombstones (Figure 3d) stand as an example of an artefact whose positional accuracy was estimated in the report [32] to be up to 1 m. Photogrammetric methods enable the retrieval of 3D information from 2D images. Due to the objects (archeological artefact) proportions, the close-range photogrammetry was applied. The control points were distributed around the object and marked with black-and-white targets. Imaging was gradually conducted around the object while keeping the distance and overlay ratio of the adjacent images. The parameters of the Nikon D750 camera are highlighted in Table 1. Table 2 sums ISPRSup the Int. processing J. Geo-Inf. 2020 values, 9, 604 of the tile. The varying resolutions of the processed dense point cloud of 12 of 25 this artefact can be seen in Figure 7.

TableTable 1. Camera 1. Camera specification. speciﬁcation.

ParameterParameter Value Value Image resolution 6016 × 4016 px Image resolution 6016 4016 px Sensor size full frame (35.9 × 24× mm) Sensor size full frame (35.9 24 mm) Lens Nikon AF-S × Lens Nikon AF-S FocalFocal length length fixed 120 ﬁxed mm 120 mm F-stopF-stop f/8 f/8 ImageImage format format jpeg jpeg

TableTable 2.2. An overview of of the the parameters parameters of ofa model a model constructed constructed from from the highest the highest density density point cloud point cloud in in Agisoft Metashape. Agisoft Metashape. Parameter Value ParameterTie points 319,603 Value DenseTie pointscloud points 12,782,806 319,603 DenseDense cloud cloud points quality High 12,782,806 DenseDense cloud cloud processing quality time 1 day 5 Highh Dense cloud3D model processing faces time 2,332,552 1 day 5 h 3D3D model model faces vertices 1,170,947 2,332,552 3D model vertices 1,170,947 3D model processing time 22 min 11 s 3D model processing time 22 min 11 s

(a) (b) (c)

FigureFigure 7. TheThe dense dense cloud cloud representations representations of the of tile the proc tileessed processed in Agisoft in Agisoft Metashape Metashape at different at dilevelsﬀerent levels ofof detaildetail (LODs): (a ()a 12,782,806) 12,782,806 points points (b) (2,848,116b) 2,848,116 points, points, and (c and) 319,603 (c) 319,603 points. points.

Despite all the above-mentioned sources available, the knowledge of the shape of buildings of the monastery to be reconstructed is quite limited in the third dimension since they are no longer present. Therefore, we have performed our own survey together with historians and archaeologists from the Regional Museum Jílové u Prahy to acquire an inspiration on the missing parts. This survey focused on sacral buildings in the broader region originating from the same era that are preserved to this time. Comparing the ground plans, the monastery in Milevsko was identified as the most similar preserved object to our case (two towers front facade, the Gothic basilica, and the surrounding quadrature). Other places of interest were monastic objects in Sázava, Jindˇrich˚uvHradec a Strakonice. The height and the thickness of walls of these existing objects were surveyed, and their proportions were calculated. Afterwards, the heights of objects that constitute the reconstructed monastery were inferred from the thickness of their principal walls with respect to the discovered proportions of the extant objects. Similarly, the appearance of interiors was inspired by the extant monasteries of that era. The textures for the final stage of the model design were collected at the referential sites by means of detailed photographs of frescos and architectural features. Nevertheless, the textures needed to be adjusted to fit the distinct extents of the reconstructed building as well as the geometry of incorporated shapes of the artefacts’ terrestrial laser scanning (TLS) models, which form certain hotspots in terms of trueness and higher detail. Texture processing was enabled by GIMP 2.8 software. The acquired images were transformed from central to orthographic projection and the saturation and brightness were ISPRS Int. J. Geo-Inf. 2020, 9, 604 13 of 25 adjusted. The white was balanced to restore the look of faded frescos. Subsequently, suitable filters (sepia tone, clarendon filters) were applied to normalize the color balance of individual frescoes taken from places with varying measurement conditions. The high-resolution models originating from close-range scanning required heavy simplification of the mesh to allow for effective manipulation within the modeling software packages as well as for the consequent web-based rendering and distribution. Blender 2.83.3 software was employed to decimate the numbers of edges and faces up to 1–5% of the original terrestrial laser scanning (TLS) model’s resolution. To enhance the realism of the model rendering after the coarse simplification, the edges of the model were smoothed. The AMS Soften Edges free plug-in (version 1.2.0) was applied, as it extends the capabilities of the default SketchUp Soften Edges function, and the threshold of an angle between normals is set to 4%.

3. Results Three complex reconstructions (Figures8–14 and AppendixA) were designed for di fferent periods of time forming the diachronic model of the site and its surroundings. The first two comprise all known buildingsISPRS Int. inJ. Geo-Inf. the Romanesque 2020, 9, x FOR PEER and, REVIEW respectively, the Gothic era. They are placed upon the adjusted 14 of 25 terrain and within the landscapes of the period. The third model corresponds to the first two decades In the foreground of Figures 8 and 9, there is a DMR 5G terrain model around the town Sekanka. of the 20th century with the ruins of the monastery and contemporary buildings. Three variants of The fused DMR 5G and SRTM can be seen across the rivers. In the background, there is the SRTM- landscape related to this recent era were modeled, as it was influenced by the changes of the new based model of lower resolution. The transformed DMR 5G forms the ground of the island (Figures embankment, the weir, and finally the dam. 9–12).

FigureFigure 8. 8.Visualization Visualization ofof the reconstructed middle middle age age town town Sekanka. Sekanka.

Figure 9. Illustration of the incursion of the Brandenburgers.

ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 14 of 25

In the foreground of Figures 8 and 9, there is a DMR 5G terrain model around the town Sekanka. The fused DMR 5G and SRTM can be seen across the rivers. In the background, there is the SRTM- based model of lower resolution. The transformed DMR 5G forms the ground of the island (Figures 9–12).

ISPRS Int. J. Geo-Inf. 2020, 9, 604 14 of 25 Figure 8. Visualization of the reconstructed middle age town Sekanka.

Figure 9. Illustration of the incursion of the Brandenburgers. ISPRS Int. J. Geo-Inf. 2020, 9Figure, x FOR PEER 9. Illustration REVIEW of the incursion of the Brandenburgers. 15 of 25

FigureFigure 10. 10.Visualization Visualization ofof thethe monasterymonastery in the Romanesque Romanesque era era in in the the summer summer season. season.

(a) (b)

Figure 11. Visualization of Church of St. Kilián on the left bank in the Romanesque era (a) and in the Gothic era (b).

(a) (b)

Figure 12. Visualization of the Gothic era in the winter season from southwest (a) and southeast (b).

ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 16 of 26 ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 15 of 25

Figure 10. Visualization of the monastery in the Romanesque era in the summer season. ISPRS Int. J. Geo-Inf. 2020, 9, 604 15 of 25 Figure 10. Visualization of the monastery in the Romanesque era in the summer season.

(a) (b) (a) (b) Figure 11. Visualization of Church of St. Kilián on the left bank in the Romanesque era (a) and in the FigureFigureGothic 11. 11.eraVisualization Visualization(b). ofof Church of St. Kilián Kilián on on the the left left bank bank in in the the Romanesque Romanesque era era (a) (anda) and in the in the GothicGothic era era ( b(b).).

(a) (b) (a) (b) FigureFigure 12. 12.Visualization Visualization of the Gothic era era in in the the winter winter season season from from southwest southwest (a)( anda) and southeast southeast (b).( b). Figure 12. Visualization of the Gothic era in the winter season from southwest (a) and southeast (b). The visualization and distribution of results were carried out by Lumion Pro 10.3.2 and Theasys online software. The Lumion provided all essential elements of both the landscape’s and monument’s modeling: landform; vegetation; water; structures including architecture and infrastructure; animals and people; and atmosphere. The format of the results includes high-quality images and videos. Moreover, these outputs are reused within the more interactive system providing the exploration of the CH site—the online virtual museum implemented within the Theasys application. The virtual museum’s tours offer predefined trails for a visitor, panorama images, and predefined time machine transfer between different eras with identical view frustrum for the sake of comparison. Moreover, the hotspots with higher-detail images of artefacts and descriptive texts are available as well as the 3D interactive models of artefacts, which are as a detached product linked with the museum. The figures below illustrate the results. ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 16 of 25 ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 16 of 25 The Lumion software also allows for a convincing presentation of seasonal or weather changes, The Lumion software also allows for a convincing presentation of seasonal or weather changes, the layout of shadows, and the position of the Sun, which enables a significantly more persuasive the layout of shadows, and the position of the Sun, which enables a significantly more persuasive presentation of the site in a given era, see Figures 8–12 and 14. The advanced visualization tools presentation of the site in a given era, see Figures 8–12 and 14. The advanced visualization tools helped depict historical events in a dynamic way, e.g., the devastation of the town Sekanka in Figure helped depict historical events in a dynamic way, e.g., the devastation of the town Sekanka in Figure 11. In Figures 13 and 14, the rendered images of modeled interiors can be seen. Textures and models 11. In Figures 13 and 14, the rendered images of modeled interiors can be seen. Textures and models of preserved objects were used for creating realistic scenes. Figure 13 shows stone tombs and ceramic of preserved objects were used for creating realistic scenes. Figure 13 shows stone tombs and ceramic ISPRStiles Int. created J. Geo-Inf. with2020 textures, 9, 604 (from original preserved objects) and hand-modeled window pillars (their16 of 25 tiles created with textures (from original preserved objects) and hand-modeled window pillars (their originals can be seen in Figure 3). originals can be seen in Figure 3).

Figure 13. Gothic basilica interiors including paintings of the period and tombs. Own work (2020). FigureFigure 13. 13.Gothic Gothic basilicabasilica interiors including including painting paintingss of of the the period period and and tombs. tombs. Own Own work work (2020). (2020).

Figure 14. Interiors of the Gothic quadrature nearby the cloister including paintings of the era and the Figure 14. Interiors of the Gothic quadrature nearby the cloister including paintings of the era and the Figurefloor 14.formedInteriors from of tiles. the Own Gothic work quadrature (2020). nearby the cloister including paintings of the era and the floor formed from tiles. Own work (2020). ﬂoor formed from tiles. Own work (2020).

In the foreground of Figures8 and9, there is a DMR 5G terrain model around the town Sekanka.

The fused DMR 5G and SRTM can be seen across the rivers. In the background, there is the SRTM-based model of lower resolution. The transformed DMR 5G forms the ground of the island (Figures9–12). The Lumion software also allows for a convincing presentation of seasonal or weather changes, the layout of shadows, and the position of the Sun, which enables a signiﬁcantly more persuasive presentation of the site in a given era, see Figures8–12 and 14. The advanced visualization tools helped depict historical events in a dynamic way, e.g., the devastation of the town Sekanka in Figure 11. In Figures 13 and 14, the rendered images of modeled interiors can be seen. Textures and models of preserved objects were used for creating realistic scenes. Figure 13 shows stone tombs and ceramic ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 17 of 25 ISPRS Int. J. Geo-Inf. 2020, 9, 604 17 of 25

ISPRSFigure Int. J. Geo-Inf. 15 compares 2020, 9, x FOR two PEER approaches REVIEW to interiors modeling. The first proceeds from the textures 17 of 25 acquired in extant monasteries and adjusts them to fit the geometry. The use of texture has limits due tiles created with textures (from original preserved objects) and hand-modeled window pillars (their to theFigure rectangular 15 compares shape, twowhich approaches is problematic to interior in cornerss modeling. of the room,The first and proceeds due to the from pattern, the textures which originals can be seen in Figure3). acquiredis too repetitive in extant and monasteries makes visualization and adjusts unrealistic. them to fit the geometry. The use of texture has limits due Figure 15 compares two approaches to interiors modeling. The ﬁrst proceeds from the textures to theThe rectangular second approach shape, which employs is problematic the textured in 3D corners model of of the preserved room, and floor due tiles to theand pattern, assembles which the acquired in extant monasteries and adjusts them to ﬁt the geometry. The use of texture has limits due isindividual too repetitive pieces and into makes the visualizationwhole. Although unrealistic. the model is vastly decimated, the outcome is more to the rectangular shape, which is problematic in corners of the room, and due to the pattern, which is realisticThe and second elaborate. approach It is employs at the cost the of textured increased 3D computational model of preserved demand floor (cf. tiles Tables and 3 assembles and 4). the too repetitive and makes visualization unrealistic. individual pieces into the whole. Although the model is vastly decimated, the outcome is more realistic and elaborate. It is at the cost of increased computational demand (cf. Tables 3 and 4).

(a) (b)

Figure 15. The gothic tiled ﬂoor created using adapted textures only (a) and using the processed Figure 15. The gothic(a tiled) floor created using adapted textures only (a) and(b) using the processed terrestrial laser scanning (TLS) model (b) for comparison. terrestrial laser scanning (TLS) model (b) for comparison. FigureThe second 15. The approach gothic tiled employs floor created the textured using adapted 3D model textures of preserved only (a) ﬂoorand using tiles andthe processed assembles the Finally, the rendered panorama images from the Lumion software were also used for the design individualterrestrial pieces laser into scanning the whole. (TLS) Althoughmodel (b) for the comparison. model is vastly decimated, the outcome is more realistic of the virtual museum web app (the prototype can be accessed at https://ths.li/3azGDH and and elaborate. It is at the cost of increased computational demand (cf. Tables3 and4). https://ths.li/1HOfvZ)Finally, the rendered (Supplementary panorama images Materials). from the It Lumionwas carried software out in were the alsoTheasys used software.for the design The Finally, the rendered panorama images from the Lumion software were also used for the ofresult, the whichvirtual can museum be accessed web fromapp the(the desktop prototype as we canll as be from accessed the mobile at https://ths.li/3azGDH devices over the Internet, and design of the virtual museum web app (the prototype can be accessed at https://ths.li/3azGDH https://ths.li/1HOfvZ)is illustrated by Figures (Supplementary 16 and 17, including Materials). the Itpresentation was carried of out the in digital the Theasys walk, triggeringsoftware. Thethe and https://ths.li/1HOfvZ) (Supplementary Materials). It was carried out in the Theasys software. result,hotspot, which or the can transition be accessed between from times. the desktop The virtual as we realityll as from (VR) the is alsomobile available devices using over VR the glasses Internet, or The result, which can be accessed from the desktop as well as from the mobile devices over the Internet, isthe illustrated augmented by reality Figures using 16 andgyroscope 17, including or gyrocompass the presentation in users’ ofdevices. the digital walk, triggering the is illustrated by Figures 16 and 17, including the presentation of the digital walk, triggering the hotspot, hotspot, or the transition between times. The virtual reality (VR) is also available using VR glasses or or the transition between times. The virtual reality (VR) is also available using VR glasses or the the augmented reality using gyroscope or gyrocompass in users’ devices. augmented reality using gyroscope or gyrocompass in users’ devices.

(a) (b)

Figure 16. The virtual(a museum) application with hotspots (a) that can be studied(b) in detail in its own pop-up viewer (b). Figure 16. The virtual museum application with hotspots (a) that can be studied in detail in its own Figure 16. The virtual museum application with hotspots (a) that can be studied in detail in its own pop-up viewer (b). pop-up viewer (b).

ISPRSISPRS Int. Int. J. J. Geo-Inf. Geo-Inf. 20202020,, 99,, x 604 FOR PEER REVIEW 1918 of 26 25

(a) (b)

Figure 17. TheThe navigation navigation between between historical historical periods periods ( a)) the the Romanesque Romanesque era era view view and and ( (b)) the the Gothic Gothic era view from the same spot an andd with the same view frustrum. Tables3 and4 show the quantitative summary of parameters of the designed model as they were Tables 3 and 4 show the quantitative summary of parameters of the designed model as they were natively recorded and provided by the processing software packages. For illustration, a sample of natively recorded and provided by the processing software packages. For illustration, a sample of DMR 5G data (2 2.5 km) in area of our interest consists of 805,900 points (of which a 370,819-point DMR 5G data (2 × 2.5 km) in area of our interest consists of 805,900 points (of which a 370,819-point subset was used), whereas the SRTM of this area is made up of 7283 points. The currently presented subset was used), whereas the SRTM of this area is made up of 7283 points. The currently presented model covers approximately 5 5 km. The data reduction is significant especially with a prospect for model covers approximately 5 × 5 km. The data reduction is significant especially with a prospect for future extension. future extension. Table4, which presents the statistics for models of interiors, also describes the influence of the TLS Table 4, which presents the statistics for models of interiors, also describes the influence of the models when incorporated into the overall model. The influence of different intensity of simplification, TLS models when incorporated into the overall model. The influence of different intensity of which the original tile model was subject to, is also evaluated. The floor composed of tiles of 5% of the simplification, which the original tile model was subject to, is also evaluated. The floor composed of original resolution is the component of the clearly highest numbers of faces and edges. Incorporating tiles of 5% of the original resolution is the component of the clearly highest numbers of faces and the TLS models also effects the startup times and tests the limits of software; e.g., the Lumion was not edges. Incorporating the TLS models also effects the startup times and tests the limits of software; able to contain the floor designed on the basis of tiles having either 5% or 1% of original resolution. e.g., the Lumion was not able to contain the floor designed on the basis of tiles having either 5% or For the sake of rendering, only a part of floor using tiles of 1% of the original resolution was used. 1% of original resolution. For the sake of rendering, only a part of floor using tiles of 1% of the original resolution was used. Table 3. Models of exteriors—an overview of components.

Roman Terrain and Table 3. Models of exteriors—anGothic overview Terrain of components.Romanesque Content Part/Group Type Surroundings (with Gothic Monastery and Surroundings Monastery RomanMedieval Terrain Town) and Gothic Terrain Romanesque Gothic Content Part/GroupEdges type Surroundings 1,128,516 (with 452,650and 92,110 715,102 Monastery Monastery FacesMedieval 542,375 Town) Surroundings 271,295 36,948 299,393 ComponentEdges instances 1,128,516 4653 337452,650 6592,110 715,102 165 GroupsFaces 542,375 3264 46271,295 13436,948 299,393 102 Component instances 4653 337 65 165 Component deﬁnitions 186 42 5 36 Groups 3264 46 134 102 Layers 6 3 1 1 Component definitions 186 42 5 36 MaterialsLayers 1736 1003 511 931 SizeMaterials in the SketchUp 173 100 51 93 2017—without vegetation 54.5 41.9 16.4 34.7 Size in the SketchUp (MB) 2017—without vegetation 54.5 41.9 16.4 34.7 Size in the Lumion 10—with vegetation(MB) and without 159 118 35.9 148 Sizerendering in the settingsLumion (MB) 10— withStartup vegetation time with and the 159 118 35.9 148 SketchUpwithout Makerendering 2017 (in 16.8 11.5 4.5 15.7 settingsseconds) (MB) * Startup* tested time model: with Macbook the 12” (Early 2015, Intel Core M 1.1 Ghz dual core, 8 GB 1600 Mhz DDR3, Intel HD Graphics 5300 with 1536 MB, 256 GB SSD, macOS Catalina) with background opened Mail and Safari, SkecthUp pre-opened, SketchUpFinder active;Make measured2017 (in with iPhone XR.16.8 11.5 4.5 15.7 seconds) *

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Table 4. Models of interiors—an overview of components.

Basilica’s Floor Using Basilica’s Floor Using Cloister’s Floor Using Content Part/Group Type Basilica Cloister Tiles of 1% of Tiles of 5% of Tiles of 1% of Original Resolution Original Resolution Original Resolution Edges 860,048 893,553 66,049,248 425,160,789 66,942,801 Faces 374,231 390,417 41,115,014 278,209,820 41,505,431 Component instances 334 143 1862 2416 2005 Groups 618 337 33 31 370 Component deﬁnitions 100 36 1 1 37 Layers 3 1 1 1 1 Materials 106 77 3 5 80 Size in the SketchUp 2017—without vegetation 76.1 65.7 4.4 30 70.4 (MB) Size in the Lumion 10—with vegetation (in case of exteriors 207 213 - - - and cloister) and without rendering settings (MB) Startup time with the SketchUp Make 2017 15.5 10.1 16.5 170 23.7 (in seconds) * * tested model: Macbook 12” (Early 2015, Intel Core M 1.1 Ghz dual core, 8 GB 1600 Mhz DDR3, Intel HD Graphics 5300 with 1536 MB, 256 GB SSD, macOS Catalina) with background opened Mail and Safari, SkecthUp pre-opened, Finder active; measured with iPhone XR.

4. Discussion The contributions of the presented work inhere in two main aspects. First, the proposed methodology facilitates a smooth integration of geometry originating from heterogeneous sources ranging from the small archeological artefacts up to the large areas of landscape. As a result, it puts the available knowledge of a researched site in the spatial context. Second, the models of the studied place were designed following this methodology and covering several historical eras. The derived diachronic reconstruction served both the professionals and the general public as a basis for presentation purposes, comparative analysis, and CH maintenance policies during numerous opportunities, which provided valuable feedback. Beyond the technological aspects of 3D reconstruction of the CH site, the experiment dealt with harmonization of the LOD of the source data. Despite the recent hardware developments, using the finest detail of all data that enter the final reconstruction would just produce extremely big data. Such data volumes prevent smooth responses when processing and analyzing the geometry of data in GIS desktop software or when rendering the final visualization. The distribution of the model and therefore the web compatibility is an even greater further challenge because of the limitations of web graphics libraries. That was already observed in [19], where the TLS and close-range photogrammetry models needed to be decimated up to 0.07% of the original size to meet such limitations, which leads to the loss of potentially important details. The hybrid solution proposed here combines geometries of different dimensions and LODs. This approach allows preserving the detail only where needed and intensifies the simplification in less important regions, where only an outline is required. Therefore, the method allows the preservation of selected important details. The practical outcome of our work indicates it is a promising solution for systems that combine features of virtual museums, digital Earth, GIS, or even BIM. Although the BIM concept is apparently more meaningful for CH sites that are significantly more preserved than our case, the vision of intelligent objects demonstrating their function and relation to other features in the information system is enabled by contemporary BIM technologies. The intersection of CH, GIS, and BIM wins increasing interest within the scientific community [36–38]. Another interdisciplinary prospect emerges from the utilization of game engines (Unity, Unreal Engine). Especially in terms of increased navigation capabilities and interaction with 3D objects [39,40], their use would enhance the ISPRS Int. J. Geo-Inf. 2020, 9, 604 20 of 25

CH virtual museum based on Lumion and Theasys with its predeﬁned visitor’s trails. The aspect of navigation between various POIs is a core of digital Earth technologies although at a far smaller scale (greater spatial extent). The integration of these systems is a future challenge.

5. Conclusions We proposed a novel solution that combines the approach of a virtual museum with a reconstruction of the cultural heritage site and the landscape. We provided the most comprehensive diachronic reconstruction possible considering a complete range of available data sources. By those means, the known story of the site was reconstructed from existing fragments, interpreted, and visually conveyed. As a result, a user can experience a detailed representation of objects coming from archeological findings in the context of the whole monument and the monument within the landscape in selected periods of time. Our approach integrates multiple data sources resulting in a hybrid data model. Regarding the dimensionality, the referential terrain model remains in the second dimension (2.5D) and consists of two different LODs with the smooth LOD change in between. The constraints to the TIN-based DTM act as an interface at which the DTM is joined with the true 3D models of reconstructed monuments. The archeological pieces scanned with very high resolution were incorporated into the reconstructed missing parts of the monument. Moreover, they were also modeled as a detached product, the hotspot, which a user can interactively discover in a high resolution. The presented solution combines different dimensionalities and consists of multiple LODs of reality with a higher detail applied only where needed. This hybrid approach has proven to be effective when dealing with increasing data volumes and the current limitations of web graphics libraries such as the polygon count or textures. On multiple occasions, the presented system, which combines the inspection of detailed features with the building or even landscape level, promoted the site and attracted the attention of both the general and the professional public to the case. Such popularization events include the national-level television news, popular science media, lectures, or a part of the permanent exposition in a regional museum.

Supplementary Materials: The virtual museum application with hotspots: https://ths.li/1HOfvZ and https: //ths.li/3azGDH. The ceramic tile from Ostrovký klášter: https://skfb.ly/6RHZ8. Author Contributions: Conceptualization, Lukáš Br ˚uha,PˇremyslŠtych, Josef Laštoviˇckaand Tomáš Palatý; Methodology, Josef Laštoviˇcka,Lukáš Br ˚uha,PˇremyslŠtych, and Eva Štefanová; Software, Josef Laštoviˇcka, Lukáš Br ˚uhaand Eva Štefanová; Validation, Lukáš Br ˚uha,Josef Laštoviˇcka;Formal Analysis, Josef Laštoviˇcka and Lukáš Br ˚uha; Investigation, Josef Laštoviˇcka, Tomáš Palatý, Pˇremysl Štych and Lukáš Br ˚uha; Resources, Tomáš Palatý; Data Curation, Tomáš Palatý; Writing—Original Draft Preparation, Lukáš Br ˚uha and Josef Laštoviˇcka;Writing—Review and Editing, Lukáš Br ˚uha,Tomáš Palatý and PˇremyslŠtych; Visualization, Josef Laštoviˇcka and Lukáš Br ˚uha; Supervision, Pˇremysl Štych; Project Administration, Tomáš Palatý, PˇremyslŠtych; Funding Acquisition, Josef Laštoviˇcka,PˇremyslŠtych, Lukáš Br ˚uhaand Tomáš Palatý; Senior Author, PˇremyslŠtych. All authors have read and agreed to the published version of the manuscript. Funding: This study was supported by the Ministry of Culture of the Czech Republic, programme NAKI II, DG18P02OVV065: “Live map: Topography of History of Natural Sciences in the Czech Lands”. Acknowledgments: We would like to thank the Ministry of Culture of the Czech Republic and the Faculty of Science, Charles University for the NAKI II project. We would also like to thank Pavlo Kryshenyk (co-author of the model) and the Regional Museum Jílové u Prahy for their cooperation, especially Šárka Juˇrinová and Jan Vizner, and to our sponsor Mitsubishi. We would like to thank LUMION CZ (https://www.lumion3d.cz) for support, especially OndˇrejValach and JindˇrichWoytela. Conﬂicts of Interest: The authors declare no conﬂict of interest. ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 21 of 25 ISPRS Int. J. Geo-Inf. 2020, 9, x FOR PEER REVIEW 21 of 25 the model) and the Regional Museum Jílové u Prahy for their cooperation, especially Šárka Juřinová and Jan the model) and the Regional Museum Jílové u Prahy for their cooperation, especially Šárka Juřinová and Jan Vizner, and to our sponsor Mitsubishi. We would like to thank LUMION CZ/lumiartsoft s.r.o. Vizner, and to our sponsor Mitsubishi. We would like to thank LUMION CZ/lumiartsoft s.r.o. (https://www.lumion3d.cz)ISPRS Int. J. Geo-Inf. 2020, 9, 604 for support, especially Ondřej Valach and Jindřich Woytela. 21 of 25 (https://www.lumion3d.cz) for support, especially Ondřej Valach and Jindřich Woytela. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest. Appendix A Appendix A Appendix A

Figure A1. Illustration of the incursion of the Brandenburgers (the Romanesque era). Figure A1. IllustrationIllustration of of the the incursion incursion of of the Brandenburgers (the Romanesque era).

Figure A2. Visualization of Church of St. Kilián and the monastery in the Romanesque era. Figure A2. VisualizationVisualization of Church of St. Kilián Kilián and the monastery in the Romanesque era.

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Figure A3. Visualization of Church of St. Kilián and the monastery in the Gothic era. Figure A3. VisualizationVisualization of Church of St. Kilián Kilián and the monastery in the Gothic era.

Figure A4. Visualization of the monastery in the Gothic era. Figure A4. VisualizationVisualization of the monastery in the Gothic era.

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Figure A5. Visualization of Church of St. Kilián and the monastery in the Gothic era. Figure A5. Visualization of Church of St. Kilián and the monastery in the Gothic era.

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