sensors

Article LiDAR- and AR-Based Monitoring of Evolved Building Façades upon Zoning Conflicts

Naai-Jung Shih * and Yi Chen

Department of Architecture, National Taiwan University of Science and Technology, Taipei 106, Taiwan; [email protected] * Correspondence: [email protected]; Tel.: +886-(2)-27376718



Received: 13 September 2020; Accepted: 25 September 2020; Published: 1 October 2020


Abstract: Zoning conflicts have transformed Old Street fabrics in terms of architectural style and construction material in Lukang, Taiwan. This transformation should be assessed as a contribution to digital cultural sustainability. The objective of this study was to compare the evolved façades resultant from the changes made by the development of architectural history and urban planning. A combination of 3D scan technology and a smartphone augmented reality (AR) app, Augment®, was applied to the situated comparison with direct interaction on-site. The AR application compared 20 façades in the laboratory and 18 façades in four different sites using a flexible interface. The comparisons identified the correlation of evolved façades in real sites in terms of building volumes and components, pedestrian arcades on store fronts, and previous installations. The situated comparisons were facilitated in a field study with real-time adjustments to 3D models and analyses of correlations across details and components. The application of AR was demonstrated to be effective in reinstalling scenes and differentiating diversified compositions of vocabulary in a remote site.

Keywords: markerless AR; LiDAR; old street heritage; building façade; architecture style; situated study; smartphone

1. Introduction The Old Street in Lukang is replete with historical buildings (Figure1). Lukang had originally been reconstructed from a harbor before it assumed its current fabric. Its historical identity was reshaped from a place that could hardly achieve a thorough view of the sky, to a representative icon of cultural sustainability. Its tangible pattern of development can be traced back over 300 years. The fabric, which was created from the beginning to the current setting of support, was reshaped in an evolved manner. The long-term developed urban fabric has transformed the township with the landscape of the streets being reconstructed and conserved. This evolution, which occurred within each block, dramatically impacted the construction of building style. This transformation should be assessed as a fulfillment of cultural sustainability. The assessment of heritage can benefit from rapid technological advancements in such fields as human computer interaction, information modeling, construction, situated learning, tourism, and 3D data acquisition. For example, augmented reality (AR) has been widely and successfully applied in recent years. AR enables real and virtual information in an actual environment to be combined, registered, and interacted upon in real-time [1–3]. This interaction is particularly important in tacit knowledge, which is typically challenging to articulate to others [4]. Similar to case studies of environments prior to architecture design, AR can present virtual content with the real world around the user [5]. This virtual content can be created from models originated from the physical world with a high level of realistic appearance. The integration of three different modeling methodologies (TLS, GPR, 3D modelling) were

Sensors 2020, 20, 5628; doi:10.3390/s20195628 www.mdpi.com/journal/sensors Sensors 2020, 20, 5628 2 of 26 developed to create an educational app [6]. Users can explore reality with new layers of information Sensorsusing 2020 mobile, 20, x AR FOR applications PEER REVIEW for a novel interactive and highly dynamic experience [7,8]. 2 of 26

Figure 1. StreetStreet scenes scenes of of the the Old Old Street Street in Lukang, Taiwan.

ThisAR applicationstransformation have should been be successfully assessed as a implemented fulfillment of incultural a broad sustainability. range ofdisparate The assessment fields, ofincluding heritage navigation,can benefit education,from rapid industry,technological medical advancements practice, andin such landscape fields as architecture human computer [9–13]. interaction,Technically, information huge sets of modeling, input data construction, have been situated registered learning, to reconstruct tourism, accurateand 3D data 3D cityacquisition. models Forfor ARexample, applications augmented [14]. reality Moreover, (AR) has extended been wide realityly and and successfully informative applie modelsd in have recent been years. created AR enablesfor architectural real and heritagevirtual frominformation scans toin building an actual information environment modeling to be (BIM),combined, virtual registered, reality (VR),and interactedand AR [15 upon]. Heritage in real-time building [1–3]. information This interaction modeling is particularly (HBIM) embodies important complexity in tacit knowledge, in surveying which and ispreservation typically challenging [16]. Geological to articulate view of to relics others and [4]. landscapes Similar to enhances case studies the social of environments awareness of prior culture to architectureand the protection design, of AR heritage can present [17]. virtual content with the real world around the user [5]. This virtual contentConstruction-specific can be created from studiesmodels wereoriginated made from that the focused physical on world safety with with a high the finerlevel of details realistic of VRappearance./AR environment The integration to attract of three significant different attention modeling [18 ],methodologies to simulate the(TLS, environmental GPR, 3D modelling) context wereand spatio-temporal developed to create constraints an educational of various processesapp [6]. [Users19], to can conduct explore structural reality analysiswith new to determinelayers of informationbehavior under using di ffmobileerent loadingAR applic conditionsations for of a novel interactive interactive 3D models and highly [20], todynamic setup tasks experience on a variety [7,8]. of machineAR applications tools based have on target been markers successfully [21], andimplemented to contribute in toa onlinebroad educationrange of disparate for management fields, includingand engineering navigation, [22]. Dimensional education, industry, inconsistencies medical of building practice, design and amonglandscape participants architecture in VR [9–13]. seem Technically,to be partially huge alleviated sets of throughinput data AR have by adding been regi a realstered object to thatreconstruct is accurately accurate scaled 3D [city23]. models for AR applicationsAR offers practical [14]. Moreover, advantages extended because itrealit allowsy and educators informative to use models real objects. have Education-relatedbeen created for architecturalstudies were heritage carried from out focusing scans to onbuilding STEM info [24rmation], m-learning modeling (mobile (BIM), learning), virtual reality and traditional(VR), and ARe-learning [15]. Heritage (electronic building learning) information [25], to enablemodeling students (HBIM) to locateembodies any comple object representedxity in surveying in a given and preservationspace [26], to [16]. achieve Geological a better view understanding of relics and of la culturalndscapes aspects enhances [27], tothe enhance social awareness laboratory of learning culture andenvironments the protection [28], of and heritage to develop [17]. new learning paradigms in outdoor co-space and implement a mobileConstruction-specific AR system for creative studies design were courses made that [29]. focu 3Dsed modules on safety can with be di thefficult finer to details obtain, of and VR/AR their environmentoperation should to notattract be toosignificant complicated attention in use in[18], situated to simulate learning the [30]. environmental The link between context real world and spatio-temporalobjects and digital constraints media should of various bring aprocesses new and beneficial[19], to conduct quality structural for learning analysis [31]. to determine behaviorVR andunder AR different have been loading of great conditions interest toof tourisminteractive researchers 3D models [32 [20],,33]. to Tourism setup tasks experiences on a variety can ofbe machine transformed tools bybased these on technologiestarget markers into [21], virtual and to tours contribute and augmented to online education tourism experiencesfor management [34]. andConcerning engineering tourism, [22]. ARDimensional can supply inconsistencies tourists with detailedof building and design visceral among local informationparticipants [35in– VR38]. seemIn addition, to be partially the utilities alleviated of VR through and AR AR in by communication adding a real object and engagement that is accurately can be scaled understood [23]. or improvedAR offers through practical interactions advantages with because traditional it allows 3D scenes educators or entities. to use To real achieve objects. this, Education-related the information studiesmodel shouldwere carried be extended out focusing to a direct on manipulation STEM [24], m-learning of 3D building (mobile façades learning), which possessand traditional a strong e-learningrelation to the(electronic past development learning) [25], of local to enable urban students architecture. to locate The exemplificationany object represented of components in a given can space [26], to achieve a better understanding of cultural aspects [27], to enhance laboratory learning environments [28], and to develop new learning paradigms in outdoor co-space and implement a mobile AR system for creative design courses [29]. 3D modules can be difficult to obtain, and their operation should not be too complicated in use in situated learning [30]. The link between real world objects and digital media should bring a new and beneficial quality for learning [31].

Sensors 2020, 20, 5628 3 of 26 not only make tourists knowledgeable in rich and novel ways, but also create a pragmatic pedagogical environment through AR technology. To promote similar experiences in a wider range of settings, a representation of past virtual environments can enrich the structure of systems for more vivid involvement either on the same streets or in remote cities. Problems, however, can occur with AR under different technology limits. Marker-based AR and markerless AR constitute the two major AR types [39]. Marker-based AR in outdoor settings is usually constrained by lighting conditions of the environment, weather, or time of day. To overcome this challenge, markerless outdoor tracking was developed, which uses images created from different daylight conditions [40]. Difficulty and aesthetic concerns were involved in arranging and pasting markers on building surfaces, and markerless AR constitutes a more suitable approach for diversified scenes [41,42]. A detailed visual representation was proven to be requisite to achieve a connection to reality to increase comprehension. Light detection and ranging (LiDAR) has been applied to 3D scan technology to document as-built scenes for construction monitoring [43–45] or to retrieve geometric features from a distance with a combination of aerial images [46–51]. In contrast to creating 3D models from the beginning, 3D laser scanning is an effective tool for acquiring important geometric attributes, such as detailed trees and vegetation [52]. 3D data acquisition should be extended to provide a higher fidelity experience of the particular subject. Ground scans have been shown to be feasible for accurate street data retrieval. The combination of LiDAR and AR was proven to be both interesting and promising [53–55], and should be explored further. In order to provide an effective situated comparison experience, a smartphone should be considered as a platform through which to interact with AR. The interface should also work with Cloud support with flexibility in actual locations or laboratory settings, so that architecture tours and extended field study experiences can be applied in diverse urban environments.

2. Research Goal The objective of this study was to provide a support environment to assist situated comparisons of façades upon zoning conflict and evolution. The evolved façade needs to be assessed with direct interaction to correlate components and details in reality or in real sites. The comparison and interaction can be extended from the study conducted at Lukang Township to a remote site as a way to present and verify research findings. This study monitored and mapped the profiles of building forms upon zoning changes made within the same street block in Old Street. Urban zoning control was commonly applied to existing open spaces, such as streets, to separate commercial areas and form preservation areas. Since 1986, street blocks near Old Street have been controlled by creating separation of the two types of areas within the same block. 3D data have to be documented as needed in order to obtain an instantaneous side-by-side study of the effects of the two types of changes to the same street block. It is noted that this process can then also be beneficially applied to diverse adaptions of form in various other cities. In order to make a comparison to a real scene, a higher fidelity of appearance must be provided. LiDAR and AR-based building form mapping and monitoring are needed to achieve this. In some cases, a mesh model must also be applied to overlap with the wireframe appearance of data for clear indications of molding locations. Sensors 2020, 20, 5628 4 of 26

3. Research Methodology A situated comparison was carried out in this research. In order to verify the evolved façade, the proposed process included inspecting restructured space, applying 3D scans and supporting interaction devices, correlating both sides of the façade in AR, AR-assisted comparisons and scene reinstallations, and verification. The comparison needs an accurate assessment of configuration and a user-friendly interface with which to work. The assessment should be made by correctly reconstructed spaces or objects as a reference. In order to match with a realistic scene in an architecture site, reconstruction by 3D scans offers an effective approach to capture precise dimensions and correct relative locations in as-built form. The realistic 3D scan data will facilitate field visits and comparisons with great visual similarity and dimensional accuracy, instead of a simplified representation of vector drawings of the original design. The comparison also requires a user-friendly interface to correlate subjects in the foreground and the background in real time. Indeed, the AR setup establishes an optimal environment to interact with photorealistic subjects and backgrounds. We aim to apply a public platform to support these zoning conflict comparisons. Our former researches developed a customized AR app using ARkit 1.5® to decomposed specific spatial structures with display options [41]. Although the research purposes were fulfilled, the recycling of the original codes or design was not optimal. A platform which provides everyday Internet 3D browsing experience for the young generation would constitute a promising choice. A commercial platform, Augment® [56], which provides end-to-end AR, was selected as an approach for 3D visualization and communication in this paper. In contrast to pre-defined solutions of e-commerce, sales and marketing and platform design, we intend to utilize it as a study environment for architectural façades by comparing its development due to zoning changes and geographic differences. This environment should support façade overlay with/out the real context of background accessed either in the same site or in different cities. An easy access without a predefined structure may provide another type of flexibility in architectural interaction, with the least possible development and maintenance costs. An emphasis is given to the preparation of 3D façade models. A similar concept of scalable model can also be found in Sketchfab®, which takes the 3D point cloud for the VR display. Augment® was selected because multiple AR objects can be displayed in the same scene, to be interacted with, within a single subscriber account. Although the display of each individual object cannot be turned on or off as needed, the application paradigm can be found in interior design with multiple pieces of furniture involved in a layout process. The proposed process was made from restructuring, correlating, 3D data retrieval and conversion, scene comparison or reinstallation, and finally verification (Figure2). The flowcharts include, (1) the stepwise process of situated comparison by issues, subjects, and locations; and (2) the development of data and related conversion to support the study. Sensors 2020, 20, 5628 5 of 26 Sensors 2020, 20, x FOR PEER REVIEW 5 of 26

Figure 2.2.Flowchart Flowchart of augmentedof augmented reality reality (AR)-assisted (AR)-assis situatedted situated comparison comparison and the dataand conversion the data processconversion to support process the to support study. the study. 4. The Restructuring Background of Old Street 4. The Restructuring Background of Old Street Chenggong Road, which was the location of the former Lukang Creek (Figure3), was originally a Chenggong Road, which was the location of the former Lukang Creek (Figure 3), was originally trade distribution center. Cargo, which was unloaded and sold on the riverside, was rearranged and a trade distribution center. Cargo, which was unloaded and sold on the riverside, was rearranged repackaged after being moved indoors and sold at store fronts on the other end of buildings facing and repackaged after being moved indoors and sold at store fronts on the other end of buildings Putou Street and Yaolin Street. The entire process occurred in a house approximately 4 m wide and facing Putou Street and Yaolin Street. The entire process occurred in a house approximately 4 m as much as 40 m deep. The houses located to the west side of Old Street possessed a harbor-facing wide and as much as 40 m deep. The houses located to the west side of Old Street possessed a geographical advantage, and the houses located to the east side were generally more inconvenient for harbor-facing geographical advantage, and the houses located to the east side were generally more the commercial process. An owner had to bypass Old Street to reach Houche Lane, where the service inconvenient for the commercial process. An owner had to bypass Old Street to reach Houche Lane, entrance was located. Houche Lane is located 40 m to the east of Old Street, and faces the rear entrance where the service entrance was located. Houche Lane is located 40 m to the east of Old Street, and of buildings on Zhongshan Road. faces the rear entrance of buildings on Zhongshan Road. Lukang Old Streets have had a well-preserved Minnan architecture since the Quin Dynasty. Lukang Old Streets have had a well-preserved Minnan architecture since the Quin Dynasty. The region defined by the green boundary (Figure3, middle) is a heritage preservation area, while the The region defined by the green boundary (Figure 3, middle) is a heritage preservation area, while commercial area is in the red boundary. The famous Old Street is located at the center of the preservation the commercial area is in the red boundary. The famous Old Street is located at the center of the area. In general, the street and houses on it exist under the same zoning classification. The two areas, preservation area. In general, the street and houses on it exist under the same zoning classification. however, are now divided by a jagged form that follows the property line. The consistency of the The two areas, however, are now divided by a jagged form that follows the property line. The façade in each area stopped in the middle of a block. The lot, which was previously an undivided consistency of the façade in each area stopped in the middle of a block. The lot, which was property, was separated irrespective of the original space hierarchy at which approximately the third previously an undivided property, was separated irrespective of the original space hierarchy at or fourth hall was located (Figure4). The traditional layout between the main and rear entrance was which approximately the third or fourth hall was located (Figure 4). The traditional layout between no longer connected from the interiors. A new entrance had to be created, or the interiors had to the main and rear entrance was no longer connected from the interiors. A new entrance had to be be remodeled from a space next to the service entrance, in order to establish a feasible living space. created, or the interiors had to be remodeled from a space next to the service entrance, in order to This type of differentiation was achieved by a long-term development of urban fabric (Figure4, right). establish a feasible living space. This type of differentiation was achieved by a long-term The restructuring of living spaces has occurred since 1986. Since Houche Lane is located next to both development of urban fabric (Figure 4, right). The restructuring of living spaces has occurred since the preservation and commercial area, it is necessary to explore how the building style has developed. 1986. Since Houche Lane is located next to both the preservation and commercial area, it is necessary to explore how the building style has developed.

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FigureFigure 3.3. SiteSite planplan ofofof the thethe old oldold harbor harborharbor [ 57 [57],[57],], zoning zoningzoning map, map,map, and andand di differentiatedffdifferentiatederentiated street streetstreet block blockblock (top ((toptop, from,, fromfromleft leftleftto righttoto rightright); cross);); crosscross section sectionsection of fourofof fourfour streets streetsstreets (bottom ((bottombottom). ).).

FigureFigure 4.4. TheThe sectionsection beforebefore andand afterafter zoningzoning reconfiguration reconfigurationreconfiguration ( (leftleftleft););); the the different didifferentfferent spacespace andand thethe roofroof configurationconfigurationconfiguration ofof spacesspaces ononon bothbothboth endsendsends of ofof the thethe block blockblock ( (right(rightright,,, top toptop,,, and andand bottom bottombottom).).).

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Long-termLong-term Long-term zoningzoning zoning developmentdevelopment development hadhad reconstructed hadreconstructed reconstructed twotwo twodifferentdifferent different zoneszones zones withinwithin within aa singlesingle a single streetstreet street block,block, block, andand and dramaticallydramatically dramatically reshapedreshaped reshaped thethe the urbanurban urban fabricfabric fabric inin a a 3D3D configuration.configuration.configuration. TheTheThe division divisiondivision separated separatedseparated an anan integrated integratedintegrated traditional traditionaltraditional hierarchy hierarchyhierarchy with withwith suffi sufficientsufficientcient space spacespace from fromfrom 3 to 433 fullytoto 44 fully developedfully developeddeveloped halls to hallshalls 1–2 to hallsto 1–21–2 with hallshalls insu withwithfficient insufficientinsufficient space for spacespace either forfor part eithereither of spatial partpart structure.ofof spatialspatial Moreover,structure.structure. eachMoreover,Moreover, space each typeeach space wasspace developed typetype waswas developed withdeveloped different withwith materials, diffdifferenterent vocabularies, materials,materials, vocabulavocabula styles,ries,ries, and styles,styles, spatial andand structures spatialspatial withinstructuresstructures the samewithinwithin block. thethe Insamesame fact, greatblock.block. contrast InIn fact,fact, was greatgreat established contrastcontrast by havingwaswas establishedestablished a horizontally-developed byby havinghaving aa structurehorizontally-developedhorizontally-developed of traditional architecture structurestructure ofof next traditionaltraditional to a vertically-developed archarchitectureitecture nextnext to structureto aa vertically-developedvertically-developed of street-facing buildings. structurestructure ofof street-facingstreet-facingThe zoning buildings.buildings. differentiation created problems for the truncated part of the traditional architecture. Specifically,TheThe zoningzoning the dated differentiationdifferentiation layout and dicreatedcreatedfferentiation problemsproblems of original forfor thethe functions truncatedtruncated in various partpart ofof zones thethe constrained traditionaltraditional thearchitecture.architecture. size and Specifically, flexibilitySpecifically, of thethe existing dateddated spaceslayoutlayout and fromand differentiationdifferentiation supporting many ofof originaloriginal types functionsfunctions of functions. inin variousvarious In order zoneszones to meetconstrainedconstrained commercial thethe sizesize and andand daily flexibilityflexibility needs, and ofof existingexisting simultaneously spacesspaces fromfrom maintain supportingsupporting the environment, manymany typestypes second ofof functions.functions. building InIn skinsorderorder weretoto meetmeet created commercialcommercial in an additive andand dailydaily or subtractiveneeds,needs, andand mannersisimultaneouslymultaneously (Figure 5 maintainmaintain). The skin thethe was environment,environment, accomplished secondsecond by extendingbuildingbuilding skins theskins missing werewere partcreatedcreated of an in interiorin anan additiveadditive space to theoror exteriorsubtractivesubtractive walls mannermanner or open (Figure spaces(Figure for 5).5). laundry TheThe skinskin facilities, waswas HVACaccomplishedaccomplished (heating, byby ventilation, extendingextending andthethe missingmissing air conditioning) partpart ofof anan units, ininteriorterior canopies, spacespace to posters,to thethe exteriorexterior or shop wallswalls signage, oror openopen in fixed spacesspaces or flexibleforfor laundrylaundry settings. facilities,facilities, Fixed HVACHVAC canopies, (heating,(heating, for example, ventilation,ventilation, were andand usually airair conditioning)conditioning) installed with units,units, an associated canopies,canopies, platform posters,posters, for oror boothsshopshop signage,signage, to sell merchandise. inin fixedfixed oror flexibleflexible All of thesettings.settings. commercial FixedFixed canopies, installationscanopies, forfor indicate example,example, a strong werewere usuallyusually purpose installedinstalled of interstitial withwith spaceanan associatedassociated between platformplatform the street forfor and boothsbooths indoors. toto sellsell merchandmerchandise.ise. AllAll ofof thethe commercialcommercial installationsinstallations indicateindicate aa strongstrong purposepurpose ofof interstitialinterstitial spacspacee betweenbetween thethe streetstreet andand indoors.indoors.

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FigureFigure 5. 5. ObjectsObjects added added to to the the second second skin skin between between 2019 2019 ( (toptoptop))) and andand 2011 20112011 (or (or(or 2012) 2012)2012) ( (bottombottom).).

AdditiveAdditive interstitial interstitial space space was was developed developed with with an an object-subtraction object-subtraction approach approach of of posters posters or or free-standingfree-standingfree-standing antennas.antennas.antennas. Consciousness ConsciousnConsciousnessess and andand responsibility responsibilityresponsibility were werewere also alsoalso developed developeddeveloped to rearrange toto rearrangerearrange the layout thethe layoutoflayout booths, ofof booths,booths, landscape, landscape,landscape, and personal andand personalpersonal belongings. belongings.belongings. The addition TheThe oradditionaddition subtraction oror subtractionsubtraction of installations ofof installationsinstallations represents representsanrepresents adjustment anan adjustment toadjustment the balance toto between thethe balancebalance cultural betweenbetween identity culturalcultural and facilities identityidentity for andand commercial facilitiesfacilities activitiesforfor commercialcommercial within activitiestheactivities same historicalwithinwithin thethe street samesame space. historicalhistorical Indeed, streetstreet the streetspacspace.e. space Indeed,Indeed, was thethe constructed streetstreet spacespace upon waswas a hieratical constructedconstructed structure uponupon ofaa hieraticaldemandshieratical structure andstructure supporting ofof demandsdemands facilities andand for supportingsupporting 300 years. facilitiesfacilities forfor 300300 years.years.

5.5. CorrelatingCorrelating Both Both Sides Sides of of the the Façade Façade SinceSince zoning zoning ledled toto thethe the developmentdevelopment development ofof of differendifferen differenttt evolvingevolving evolving façadesfaçades façades andand and buildingbuilding building vocabularies,vocabularies, vocabularies, aa comparisonacomparison comparison mademade made acrossacross across zones,zones, zones, oror or eveneven even acrossacross across cities,cities, cities, shouldshould should bebe be ableable able toto confirm confirmconfirm deviations deviations and and achieveachieve a a broader broader understanding understanding of of the the architectu architecturalarchitecturalral transformation. transformation. The The first firstfirst problem problem encountered encountered waswas determining determining how how to to bring bring the the façades façades together together frfr fromomom two two opposite opposite sidessides ofof aa singlesingle streetstreet block.block. AlthoughAlthough twotwotwo photographs photographsphotographs or drawingsoror drawingsdrawings of elevations ofof elevelevationsations can be placedcancan bebe side-by-side placedplaced side-by-sideside-by-side or even overlapped oror eveneven overlappedtooverlapped highlight toto changes highlighthighlight in changes anchanges off-site inin laboratory anan off-siteoff-site laboratory setting,laboratory 2D-based setting,setting, verification2D-based2D-based verificationverification is made with isis mademade a limited withwith aunderstandinga limitedlimited understandingunderstanding of depth. ofof Otherwise, depth.depth. OtOtherwise, sectionsherwise, havesectionssections to be havehave brought toto bebe upbroughtbrought as needed upup asas in neededneeded order to inin correlate orderorder toto correlatethecorrelate differences. thethe differences.differences. ToTo solvesolvesolve the thethe problem problemproblem of ofof correlating correlatingcorrelating 3D 3D3D data datadata in di ininff erent differentdifferent locations, locations,locations, we proposed wewe proposedproposed a solution aa solutionsolution for off-site, forfor off-site,oroff-site, even on-site,oror eveneven inspection. on-site,on-site, inspecinspec Thetion.tion. approach TheThe approachapproach applies the appliesapplies AR interface thethe ARAR to interfaceinterface bring two toto3D bringbring models twotwo together3D3D modelsmodels for togetherantogether intuitive forfor inspection anan intuitiveintuitive with inspection ainspection beneficial with manipulationwith aa benefibenefi ofcialcial transition, manipulationmanipulation scale, and ofof /ortrtransition,ansition, orientation. scale,scale, In contrast and/orand/or orientation.toorientation. superimposition InIn contrastcontrast of real toto scenes superimpositionsuperimposition using a virtual ofof realreal 3D modelscenesscenes created usingusing a bya virtualvirtual software 3D3D from modelmodel the createdcreated beginning, byby softwarethesoftware fidelity fromfrom of thethethe virtualbeginning,beginning, model thethe should fidelityfidelity provide ofof thethe virtualvirtual sufficient modelmodel information shouldshould provideprovide to identify sufficientsufficient dissimilarities informationinformation in tovisualto identifyidentify and dissimilarities structuraldissimilarities details. inin visualvisual andand structuralstructural details.details. AA total total of of 40 40 buildings, buildings, i.e., i.e., 20 20 on on Old Old Street Street and and 20 20 on on Houche Houche Lane, Lane, were were selected selected according according to to fourfourfour categoriescategories basedbasedbased ononon the thethe types typetypess of ofof changes changeschanges existing existingexisting on onon both bothboth sides sisidesdes (Figure (Figure(Figure6). 6).6). Approximately ApproximatelyApproximately 63% 63%63% of ofnewof newnew constructions constructionsconstructions on onon Houche HoucheHouche Lane LaneLane are areare taller tallertaller than thanthan the thethe buildings buildingsbuildingsthat thatthat used usedused to toto be bebe locatedlocatedlocated withinwithin the the samesame property property boundary, boundary, whilewhilewhile anotheranotheranother 15%15%15% ofofof placesplacesplaces havehavehave remained remainedremained vacant. vacant.vacant.

FigureFigure 6.6. TheTheThe four fourfour volumetric volumetricvolumetric combinations combinationscombinations of of theof thethe constructions coconstructionsnstructions on Oldonon OldOld Street StreetStreet and Houcheandand HoucheHouche Lane (LaneLaneleft), (and(leftleft), the), andand new thethe constructions newnew constructionsconstructions that occurred thatthat occurreoccurre on Houchedd onon HoucheHouche Lane between LaneLane betweenbetween 2019 and 20192019 2011 andand ( right 20112011). ((rightright).).

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6. Design of the Situated Comparison in AR The application of AR was carried out based on a combination of appropriate types of 3D models and background scenes in a remote site. Since the models can be downloaded as required, the comparison becomes portable, in terms of the database, with the support of a smartphone platform. The AR application serves the following three purposes: Correlating parts at different locations: Geographically-distributed building parts were brought • together side-by-side or overlaid between different contexts to achieve a paired comparison. Applying higher fidelity of part appearance: The selected level of fidelity can be a critical factor in • the comparison. The target façades on Old Street were documented using a mid-range 3D laser scanner for visual and structural details in higher fidelity. Situated comparison using a flexible transformation interface: Transition, scaling, and/or rotation • were made possible by adjusting parts for alignment in terms of proportion, length, width, or depth.

6.1. A Reality-to-Reality Environment and a Wireframe-to-Reality Environment In order to fulfill the needs of an accurate comparison, the application facilitated an appropriate manipulation interface and versatile use environment in the following ways: A reality-to-reality environment: Two mesh models were located side-by-side to facilitate the • inspection of alignment between moldings or openings across the two models. An overlaid layout was selected to support the inspection of depth in various levels.

 A 3D mesh model over a real scene: A background context-concerned environment was applied for a meaningful study of development.  Two 3D models on a plain, simplified, or context-free background: Two 3D mesh models were applied simultaneously with or without the real scene in the background.  A number of 3D models over a real background: This is presented in a way that is similar to a set of instances to be applied for inspection. A wireframe-to-reality environment: Although vector drawings usually have lower fidelity of • details, the enhanced description of an object’s edges provides an advantage when overlaid on top of the mesh model. The wireframe constituted a set of very thin polygons that can be seen through to the 3D model behind it.

 A wireframe model over a real background.  Two 3D models on a plain, simplified, or context-free background: A 3D mesh model and a wireframe model were applied simultaneously with or without the real scene in the background. The latter was represented in a more abstract form for simplicity of comparison.  A number of wireframe models and 3D models over a real background.

6.2. Remote Comparisons Comparisons were usually carried out in “remote mode”, in which a 3D model was brought up or downloaded from the Cloud at a different location.

The opposite side of the same street block: The model was used to compare the different façade • style developed on the opposite side of the same street block. Different street block: The model was placed on a property where the original house • was demolished. Different city: The model was attached to a façade located in a different city, where the original • style evolved in a dissimilar manner. Sensors 2020, 20, x FOR PEER REVIEW 9 of 26

• In a laboratory setting: The model was downloaded in a laboratory setting without reference to any real background for a background-free context test.

7. 3D Scans and Supporting Interaction Device In contrast to drawing-based comparisons made by attaining graphics to illustrate differences, the assessment should be made by higher fidelity 3D digital data which support a real-scene-based on-site or remote inspection. Moreover, in order to support the on-site study, an accessible device Sensorsshould2020 be, 20provided, 5628 with the support of a 3D display and interaction, in addition to access to Cloud9 of 26 data. Since AR has been broadly applied in architecture for a combination of 3D models and real scenes, the assessment of differences can be achieved in an AR platform if a high level of interaction, In a laboratory setting: The model was downloaded in a laboratory setting without reference to •higher fidelity of the model, and domain-specific transformation are supported by a smartphone platformany realusing background iOS® or Android for a background-free®. context test. A street 200 m long was scanned (Figure 7). A mid-range Faro Focus 3D S120® laser scanner was 7. 3D Scans and Supporting Interaction Device applied. In total, 4.97 GB of point cloud data was retrieved and stored in PLY format. The scan of the as-builtIn contraststreet scenes to drawing-based obtained a high comparisons fidelity of street made façades. by attaining The “Poisson graphics tosurface illustrate reconstruction” differences, theof the assessment mesh modelshould was be created made from by higher the point fidelity clou 3Dd by digital selecting data whichthe “output support density a real-scene-based as SF” option on-sitein CloudCompare or remote inspection.® (Figure 8, Moreover, left). The inmesh order creation to support process the on-sitewas made study, in an Geomagic accessible Studio device® should(Figure be2). providedA “wireframe-like” with the support mesh model of a 3D (Figure display 3, andright) interaction, was also created in addition based to on access a field to survey Cloud data.using SinceAutoDesk AR has3DS been MAX broadly® (Figure applied 8, right). in architecture for a combination of 3D models and real scenes,A collection the assessment of 20 ofpaired differences façades can on beopposite achieved sides in anof ARthe platformsame street if a block high level(Figure of interaction,9, left) was highercreated fidelityby converting of the model, the 3D and scan domain-specific data to the mesh transformation models from are supportedCloudCompare by a® smartphone, Geomagic ® ® platformStudio®, usingAutoDesk iOS 3DSor Android MAX®, or. Meshlab®. The most frequent connection to the models was ® throughA street the smartphone 200 m longwas app. scanned An iPhone (Figure 10®7 with). A mid-rangeiOS 12® and Faro a Realme Focus 3D X50 S120 5G® withlaser Android scanner was10® applied.were utilized In total, as the 4.97 smartphones GB of point cloudfor field data comp wasarison retrieved with and Cloud stored links in PLY available format. from The scanAugment of the® as-built(Figure street9, right). scenes A obtainedsubscription a high Augment fidelity of® app street was façades. applied The as “Poisson a ready-made surface reconstruction” general-purpose of theplatform mesh modelto alleviate was created AR software from the developmen point cloudt byand selecting maintenance the “output effort. density It is asan SF”e-commerce option in ® ® CloudCompareplatform for sales,(Figure marketing8, left). Thesolutions, mesh creationand design process solutions. was made In in this Geomagic paper, Studio we use(Figure it as 2an). A“end-to-end “wireframe-like” AR and mesh 3D visualization model (Figure and3, communication right) was also createdplatform” based [56] onof cultural a field survey artifacts using with ® AutoDeskso-called “online 3DS MAX shopping(Figure experience”8, right). replaced by “online situated comparison experience”.

. ® Figure 7.7. 3D scans of OldOld StreetStreet shopsshops ((toptop,, bottombottom leftleft)) andand appliedapplied FaroFaro Focus Focus 3D 3D S120 S120® scanner Sensors(Faro,(Faro, 2020, Germany)Germany)20, x FOR PEER ((bottombottom REVIEW rightright ).). 10 of 26

FigureFigure 8.8. MeshMesh modelmodel creationcreation processprocess inin CloudCompareCloudCompare v2.9.1 v2.9.1®® and AutoDesk 3DS3DS MAXMAX 20152015®®..

Figure 9. A collection of paired façades on the opposite side of the same street block (left) and the model list in Augment® (right).

8. AR-Assisted Comparison and Scene Reinstallation The comparison was conducted in the following four stages: (1) selection of model pairs; (2) rough alignment; (3) detail matching; and (4) context elaboration. Two façades were selected with a similar appearance. Rough alignment was applied in order to align the two models by translation or rotation, and was usually made to the corner of the façade. Detail matching applied translation and proportional scaling to a certain dimension in order to show the difference in height or width of a specific component. Adjustments had to be made repetitively by selecting appropriate anchor nodes or edges as a reference. This is required because, for example, two windows with the same width do not necessarily have the same height. The first three stages enhanced comprehension of the aspect of focus, increased user familiarity, and achieved the desired manipulation. The final stage encouraged users to inspect any façade that they chose in the AR app by overlaying the selected model on-site with the same stages to elucidate the transformations. The stages are intuitively performed with a few taps and movements of one or two fingers. Situated comparisons in different cities were made through model adjustments, detail checks, and corresponding components (Figure 10). The initial adjustments allocated a façade model in place by referring to a number of heuristics. The reference informed the researcher of major differences in proportion. More detailed checks were made to the dimensions, partitions, or materials. Adjustments frequently occurred in switching between the reference of ground level or wall molding, as a way to elucidate the difference in composition, proportion, or missing components.

Sensors 2020, 20, 5628 10 of 26

Sensors 2020, 20, x FOR PEER REVIEW 10 of 26 A collection of 20 paired façades on opposite sides of the same street block (Figure9, left) was created by converting the 3D scan data to the mesh models from CloudCompare®, Geomagic Studio®, AutoDesk 3DS MAX®, or Meshlab®. The most frequent connection to the models was through the smartphone app. An iPhone 10® with iOS 12® and a Realme X50 5G® with Android 10® were utilized as the smartphones for field comparison with Cloud links available from Augment® (Figure9, right). A subscription Augment® app was applied as a ready-made general-purpose platform to alleviate AR software development and maintenance effort. It is an e-commerce platform for sales, marketing solutions, and design solutions. In this paper, we use it as an “end-to-end AR and 3D visualization and communication platform” [56] of cultural artifacts with so-called “online shopping experience” replaced by “online situated comparison experience”. Figure 8. Mesh model creation process in CloudCompare v2.9.1® and AutoDesk 3DS MAX 2015®.

Figure 9. AA collection collection of of paired paired façades façades on on the the opposite side side of the same street block ( left) and the ® model list in Augment® ((rightright).).

8. AR-Assisted Comparison and Scene Reinstallation The comparisoncomparison was was conducted conducted in in the the following following four four stages: stages: (1) selection (1) selection of model of model pairs; (2)pairs; rough (2) alignment;rough alignment; (3) detail (3) matching;detail matchi andng; (4) and context (4) context elaboration. elaboration. Two façades Two façades were selected were selected with a similarwith a appearance.similar appearance. Rough alignmentRough alignment was applied was inapplied order toin alignorder the to twoalign models the two by models translation by translation or rotation, andor rotation, was usually and madewas usually to the corner made ofto the the façade. corner Detail of the matching façade. Detail applied matching translation applied and proportional translation scalingand proportional to a certain scaling dimension to a in certain order todimension show the diinff ordererence to in show height the or difference width of a specificin height component. or width Adjustmentsof a specific component. had to be made Adjustments repetitively had by selectingto be ma appropriatede repetitively anchor by selecting nodes or appropriate edges as a reference. anchor Thisnodes is or required edges because,as a reference. for example, This is tworequired windows because, with thefor sameexample, width two do windows not necessarily with the have same the samewidth height.do not Thenecessarily first three have stages the same enhanced height. comprehension The first three of stages the aspect enhanced of focus, comprehension increased user of familiarity,the aspect of and focus, achieved increased the desired user familiarity, manipulation. and Theachieved final stage the desired encouraged manipulation. users to inspect The final any façadestage encouraged that they chose users in theto inspect AR app any by overlaying façade that the they selected chose model in the on-site AR app with by the overlaying same stages the to elucidateselected model the transformations. on-site with Thethe stagessame arestages intuitively to elucidate performed the withtransformations. a few taps and The movements stages are of oneintuitively or two performed fingers. with a few taps and movements of one or two fingers. Situated comparisons in different different cities were made through model adjustments, detail checks, and correspondingcorresponding componentscomponents (Figure (Figure 10 10).). The The initial initial adjustments adjustments allocated allocated a façade a façade model model in place in byplace referring by referring to a number to a ofnumber heuristics. of heuristics. The reference The informedreference the informed researcher the of researcher major diff erencesof major in proportion.differences Morein proportion. detailed checks More weredetailed made checks to the dimensions,were made partitions, to the dimensions, or materials. partitions, Adjustments or frequentlymaterials. Adjustments occurred in switching frequently between occurred the in reference switching of groundbetween level the reference or wall molding, of ground as alevel way or to elucidatewall molding, the di ffaserence a way in composition, to elucidate proportion, the difference or missing in composition, components. proportion, or missing components.

Sensors 2020, 20, 5628 11 of 26 Sensors 2020, 20, x FOR PEER REVIEW 11 of 26

Figure 10. The situated comparison process.

The comparisonscomparisons werewere conducted conducted at at five five sites: sites: one one laboratory laboratory site; site; one one site insite Lukang; in Lukang; and three and sitesthreein sites Taipei. in Taipei. AR made AR made a great a contributiongreat contribution in comparing in comparing the façade the façade styles styles on both on ends both of ends a block. of a Theblock. façades The façades on Lukang on Lukang Old Street Ol facilitatedd Street facilitated architectural architectural study conducted study conducted from different from viewpoints different ofviewpoints historical of culture, historical building culture, styles, building and scales. styles, A and stepwise scales. operation A stepwise and operation third-person and photographsthird-person concerningphotographs on-site concerning operations on-site are op illustratederations are in Figure illustrated 11. The in processFigure 11. was The performed process was in several performed steps fromin several scanning steps a QRfrom code, scanning pointing a QR a smartphone code, pointing camera a smartphone and moving aroundcamera toand determine moving thearound ground to plane,determine tapping the theground screen plane, to anchor tapping the 3D the model screen initially, to anchor and scalingthe 3D ormodel moving initially, the model and in scaling reference or tomoving the background. the model Eachin reference comparison to the or visit background. was followed Each by comparison discussions whichor visit were was separated followed into by threediscussions parts: (1)which the preliminarywere separated presentation into three of models;parts: (1) (2) the the prelimin on-site physicalary presentation adjustments; of models; and (3) the(2) post-visitingthe on-site physical group-discussion adjustments; of findingsand (3) the with post-v screenisiting shots group-discussion for verification. The of findings last part waswithhelpful screen toshots recall for ignored verification. components The last orpart missed was helpful mentions to ofrecall adjustments. ignored components While most or of missed the field mentions work was of conductedadjustments. by While an individual most of researcher,the field work some was of the cond fielducted work by was an individual also performed researcher, by two some researchers, of the whichfield work enabled was themalso performed to compare by their two findings. researchers, which enabled them to compare their findings.

Sensors 2020, 20, 5628 12 of 26 Sensors 2020, 20, x FOR PEER REVIEW 12 of 26

Figure 11. TheThe screen screen shot shot ( (toptop),), third-person third-person photographs photographs ( (middlemiddle),), and and the stepwise operation process: launch launch app, app, scan scan QR QR code code of of a a selected selected 3D 3D model, model, detect detect plane, plane, tap tap to to allocate allocate the the model, model, and adjust the model’s scale, lo location,cation, or rotation angles (bottom).

8.1. Laboratory Laboratory Site Site The firstfirst set set of comparisons,of comparisons, which which included included the original the 40original models 40 with models two sets with of heterogeneous two sets of heterogeneousfaçades, were madefaçades, to thewere set ofmade wireframe-like to the set of models wireframe-like (20 models) models and mesh (20 modelsmodels) (20and models) mesh modelson a plain (20 background models) on ina theplain interiors. background Findings in the were interiors. obtained Findings during thewere interaction obtained betweenduring the interactiontwo types of between models. the Even two without types of the models. real context Even ofwithout a scene the presented real context in the of background, a scene presented different in theforms background, and layout compositionsdifferent forms were and identified layout compos in the twoitions sets. were The laboratoryidentified sitein the was two used sets. to make The laboratorya comparison siteirrespective was used to of make background a comparison (Figure irrespective 12) or prior of to background the field application. (Figure 12) Using or prior a mesh to themodel field and application. a wireframe-like Using a mesh mesh model model highlighted and a wireframe-like each one’s geometricmesh model characteristics. highlighted each one’s geometric characteristics.

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Figure 12. AR comparisons of the booth, material, and composition of façades on the two streets in a laboratory setting, using a mesh model andand aa wireframe-likewireframe-like meshmesh model.model. TheThe toptop,, middle, and two bottom images represent four cases ofof comparisons.comparisons.

8.2. Lukang Lukang Site Site The second setset ofof comparisonscomparisons was was made made in in Lukang Lukang by by the the same same researcher researcher with with mesh mesh models models on onreal real scenes scenes under under a homogeneous a homogeneous appearance. appearance. The The former former indoor indoor and oandff-site off-site comparison comparison results results were wereverified verified in real in sites real with sites further with emphasesfurther emphases on coherence on ofcoherence neighborhood of neighborhood heritage relics, heritage continuity relics, of continuityalley fabrics, of reinstallationalley fabrics, of reinstallation facades in demolished of facades sites, in demolished and the evolved sites, formand ofthe pedestrian evolved form arcades. of pedestrianThe four locations arcades. in The Lukang four werelocations selected in Lukang according were to condition,selected according if it was (1)to empty;condition, (2) demolished;if it was (1) (3)empty; in current (2) demolished; form; or (4) (3) located in current next to form; a historical or (4) artifact. located The next issues to a involved historical consistency artifact. The of style issues or involvedcontinuity consistency in terms of buildingof style componentsor continuity and in constructionterms of building methods. components An urban conversationand construction was methods.restored to An the urban past conditions.conversation was restored to the past conditions. The façadefaçade on on Yaolin Yaolin Street Street was relocatedwas relocated to Houche to Houche Lane for Lane a more for straightforward a more straightforward side-by-side side-by-sidecomparison (Figurecomparison 13, from (Figure top to13, bottom, from top left to to bottom, right): left to right): • The first first comparison was was conducted conducted on on buildings buildings with with a asimilar similar scale. scale. For For example, example, its itseave eave is • islocated located at atapproximately approximately the the same same height height as that as that of the of thenext next building. building. The TheAR simulation AR simulation of a ofcoherent a coherent building building component component created created a scene a of scene continuity of continuity which was which rarely was found rarely in found Houche in HoucheLane. Lane. • The second comparison was carried out next to the Lukang Gate, which is conspicuous among • the modernized constructions. The The inconsistency inconsistency in in style style was was alleviated with the traditional façade installedinstalled next next to to it init frontin front of an of empty an em site.pty ARsite. was AR used was to used reconstruct to reconstruct a similar a historical similar streethistorical scene. street scene. • The thirdthird comparisoncomparison was was performed performed to compareto compare diff erentdifferent building building styles. styles. The side-by-side The side-by-side layout • clearlylayout revealedclearly revealed the diff erencethe difference in construction in construction materials, materials, opening partitions,opening partitions, and mass and volume. mass Thevolume. fourth comparison was conducted at an empty site where a former red brick building was • • demolished.The fourth comparison The site was was left conducted unused and at unconstructed.an empty site where The same a former model red was brick inserted building in order was todemolished. restore continuity The site of was the originalleft unused street and scene. unconstructed. The same model was inserted in order to restore continuity of the original street scene.

Sensors 2020, 20, x FOR PEER REVIEW 14 of 26 SensorsSensors2020 2020,,20 20,, 5628 x FOR PEER REVIEW 1414 ofof 2626

Figure 13. AR screenshots of relocating façades on alternative sites in Houche Lane, Lukang. FigureFigure 13.13. ARAR screenshotsscreenshots ofof relocatingrelocating façadesfaçades onon alternativealternative sitessites inin HoucheHouche Lane,Lane, Lukang.Lukang. 8.3.8.3. Taipei Taipei Site Site 8.3. Taipei Site Another comparison was carried out for three sites in Taipei, based on the development of Another comparison was carried out for three sites in Taipei, based on the development of pedestrianAnother arcades comparison (Figure was 14). Onecarried comparison out for threewas made sites toin oneTaipei, of the based earliest on street the development buildings, the of pedestrian arcades (Figure 14). One comparison was made to one of the earliest street buildings, pedestrianLinwuhu House,arcades constructed(Figure 14). inOne 1851. comparison The most was significant made to difference one of the is earliest whether street it is buildings, a recessed the the Linwuhu House, constructed in 1851. The most significant difference is whether it is a recessed Linwuhupedestrian House, arcade constructed from the façade in 1851. or extruded The most as an si gnificantadditional difference canopy outside is whether of the façade.it is a recessed pedestrian arcade from the façade or extruded as an additional canopy outside of the façade. pedestrianThe third arcade set fromof comparisons the façade wasor extruded conducted as anbased additional on the results canopy of outside the second of the set façade. by selecting The third set of comparisons was conducted based on the results of the second set by selecting fiveThe unique third types set ofof comparisonsfacades with differentwas conducted variations based of second on the skins,results booth of the settings second on set shop by selecting fronts, five unique types of facades with different variations of second skins, booth settings on shop fronts, fiveand unique relative types dimensions, of facades for with a more different detailed variations inspection of second through skins, adjustments booth settings and assessments on shop fronts, of and relative dimensions, for a more detailed inspection through adjustments and assessments of andnon-matching relative dimensions, components. for aMost more of detailed the previo inspusection findings through were adjustments reconfirmed and and assessments elaborated of non-matching components. Most of the previous findings were reconfirmed and elaborated through non-matchingthrough the evolved components. design ofMost certain of components,the previous such findings as the werearcades reconfirmed or the transitions and elaboratedbetween the evolved design of certain components, such as the arcades or the transitions between indoors and throughindoors theand evolved outdoors design with/out of certain the articulated components, level suchdifference as the ofarcades steps. orThe the homogeneous-based transitions between outdoors with/out the articulated level difference of steps. The homogeneous-based comparison was indoorscomparison and outdoorswas successful with/out because the articulatedthe context levelwas ridifferencecher than thatof steps. of the The second homogeneous-based set. The urban successful because the context was richer than that of the second set. The urban fabric was replete with comparisonfabric was repletewas successful with diverse because objects the and context activi wasties, whichricher werethan thatevaluated of the according second set. to theThe types urban diverse objects and activities, which were evaluated according to the types involved and confirmed by fabricinvolved was andreplete confirmed with diverse by the objectsfrequency and of activi adjustments.ties, which Four were facades evaluated were comparedaccording twice, to the each types the frequency of adjustments. Four facades were compared twice, each with daytime and night scenes. involvedwith daytime and confirmed and night scenes.by the frequency of adjustments. Four facades were compared twice, each The major difference in the situated comparisons between the second and third sets was the with daytimeThe major and difference night scenes. in the situated comparisons between the second and third sets was the richness of context that informed the researcher’s comprehension of the evolved façade in today’s richnessThe majorof context difference that informed in the situated the researcher’s comparisons comprehension between the of thesecond evolved and façadethird sets in today’s was the fabricfabric setting. setting. Many Many third-person third-person photographsphotographs and screenshots were were taken taken to to elucidate elucidate the the so-called so-called richness of context that informed the researcher’s comprehension of the evolved façade in today’s interferenceinterference as as part part of of everyday everyday lifelife oror thethe causecause of evolvement, without without ob objectsjects hidden hidden deliberately. deliberately. fabric setting. Many third-person photographs and screenshots were taken to elucidate the so-called TheThe unselected unselected photos photos revealed revealed the the accidental accidental involvement involvement of of pedestrians pedestrians or or tourists tourists in in the the period period of interference as part of everyday life or the cause of evolvement, without objects hidden deliberately. theof Covid-19the Covid-19 pandemic. pandemic. The unselected photos revealed the accidental involvement of pedestrians or tourists in the period of the Covid-19 pandemic.

Figure 14. Cont.

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FigureFigure 14. 14.AR-based AR-based simulation simulation and and comparison comparison of façades of façades in Dihua in Dihua Street, Street, Chifeng Chifeng Street, andStreet, Bopiliao and , TaipeiBopiliao, (from Taipeitop to (frombottom top ).to bottom).

8.4.8.4. Reviewing Reviewing of of SituatedSituated ComparisonComparison AA matrix matrix was was created created afterwardsafterwards toto review each comparison according according to to the the adjustments adjustments made made duringduring each each field field trip trip (Table(Table1 ).1). A A table table was was constructed constructed basedbased onon thethe researcher’sresearcher’s description description and and screenshots.screenshots. The The evaluation evaluation process process was basedwas based on items on defineditems indefined the flowchart. in the flowchart. Similar adjustments, Similar whichadjustments, were shared which by were almost shared all comparisons,by almost all comparisons, were related were to the related transformation to the transformation of the entire of model the andentire the model alignment and the to groundalignment level. to ground A more level. detailed A more assessment, detailed assessment, including theincluding width the and width height ofand openings, height of was openings, not performed, was not sinceperformed, the 3D since models the were3D models opaque were to theopaque background. to the background. Alternative operationsAlternative were operations carried were out by carried moving out the by model moving sideways the model or verticallysideways toor revealvertically the detailsto reveal hidden the behind.details Thishidden problem behind. was This subsequently problem solvedwas subseque by providingntly solved semi-transparent by providing models semi-transparent to elucidate the missedmodels details to elucidate in the the background missed details during in thethe ARbackground simulation. during the AR simulation.

Sensors 2020, 20, 5628 16 of 26

Table 1. The reviewing record of situated comparisons.

Adjustments & Correlations Adjust 3D Model Transformation Alignment

Locations Address Transition Rotation Scaling Ground Corner Wall Column Roof Ceiling 1 44, Houche Ln. (A) v v v v 2 47-1, Houche Ln. (B) v v v v v Lukang 3 49, Houche Ln. (C) v v v v v 4 65, Houche Ln. (D) v v v v v 5 24. Sect. 1, Dihua St. (A) v v v v v v v

Dihua St. 6 26. Sect. 1, Dihua St. (B) v v v v v v v v Taipei 7 28. Sect. 1, Dihua St. (C) v v v v v v v v 8 156. Sect. 1, Dihua St. (D) v v v v v v v v 9 A v v v v v v v 10 B v v v v v v v Bopiliao 11 C v v v v v v v Taipei 12 D v v v v v 13 E v v v v v v 14 7, 47 Ln., Chifeng St. (A) v v v v v v v v 15 9, 47 Ln., Chifeng St. (B) v v v v v v Chifeng St. 16 16, 47 Ln., Chifeng St. (C) v v v v v v v v Taipei 17 18, 47 Ln., Chifeng St. (D) v v v v v v v 18 24, 47 Ln., Chifeng St. (E) v v v v v v v Sensors 2020, 20, 5628 17 of 26

Table 1. Cont.

Adjustments & Correlations Correlate Details Dimensions Partitions Materials Door Window V/H Width Floor Height Bay No. Moldings Wood Brick Concrete Locations Address W/H W/H Orientation 1 44, Houche Ln. (A) v v 3 v v v v 2 47-1, Houche Ln. (B) v v 3 v v v Lukang 3 49, Houche Ln. (C) v v v 3 v v v 4 65, Houche Ln. (D) v v 3 v v v 5 24. Sect. 1, Dihua St. (A) v v 3 v v v

Dihua St. 6 26. Sect. 1, Dihua St. (B) v v 3 v v Taipei 7 28. Sect. 1, Dihua St. (C) v v 3 v 8 156. Sect. 1, Dihua St. (D) v v 3 v 9 A v v 3 v v 10 B v 3 v v Bopiliao 11 C v 3 v v Taipei 12 D v v 3 v v 13 E v v 3 v v 14 7, 47 Ln., Chifeng St. (A) v v 3 v 15 9, 47 Ln., Chifeng St. (B) v 3 v Chifeng St. 16 16, 47 Ln., Chifeng St. (C) v v 3 v v Taipei 17 18, 47 Ln., Chifeng St. (D) v v 3 v v 18 24, 47 Ln., Chifeng St. (E) v v 3 v v v v Sensors 2020, 20, 5628 18 of 26

Table 1. Cont.

Adjustments & Correlations Correlate Components Pedestrian Eaves Cantilevels Canopies Front Steps Spring Couplets Openings Locations Address Arcades 1 44, Houche Ln. (A) v v v v 2 47-1, Houche Ln. (B) v Lukang 3 49, Houche Ln. (C) v v 4 65, Houche Ln. (D) v 5 24. Sect. 1, Dihua St. (A) v v v

Dihua St. 6 26. Sect. 1, Dihua St. (B) v v Taipei 7 28. Sect. 1, Dihua St. (C) v v 8 156. Sect. 1, Dihua St. (D) v v v v 9 A v v v v v 10 B v v v v Bopiliao 11 C v v v Taipei 12 D v v 13 E v v v 14 7, 47 Ln., Chifeng St. (A) v v v v v 15 9, 47 Ln., Chifeng St. (B) v Chifeng St. 16 16, 47 Ln., Chifeng St. (C) v v v v Taipei 17 18, 47 Ln., Chifeng St. (D) v v v v 18 24, 47 Ln., Chifeng St. (E) v v v v Sensors 2020, 20, 5628 19 of 26

9. Research Findings The application of AR assisted the differentiation of diversified vocabulary composition or the reinstallation of scene in a remote site.

9.1. Volumes and Building Components 3D models were created for comparison. As shown on the top of Figure 12, the 3D polygon model is a typical Minnan street house on Old Street. The wireframe represents a new concrete building on Houche Lane after the previous house was demolished. The latter, which is located in the middle of Old Street and Zhongshan Road, was influenced by the vocabularies of the two streets alternately for the past 300 years. For example, a concrete guard railing on the second floor can be found on Zhongshan Road. However, new wood door panels and vintage components also emerged on Old Street. The zoning development in the middle of the block had razed the old courtyard. The former, which adopted an old symmetric layout of openings, also ended up with a very limited area of windows. In contrast, the irregular opening layout of new concrete buildings had interior lighting that was far superior to that of the previous houses. The zoning policy had changed the living and environmental quality on either side, and simultaneously gradually adopted vocabularies from either street as a connection to, or recognition of, the local cultural identity. The overlapped AR models on the bottom right of Figure 12 show that part of the wireframe model is obscured by the extruded canopy at approximately the height of the second floor. This means that the height of the ground floor on the Old Street side is approximately one half of a story higher, and is the altitude at which a canopy was installed. The evolved space on Old Street, which is located in a conservation area, has most of the building façade covered by commercial facilities. Merchandise booths also appear on the shop fronts. In contrast, the situation is different on Houche Lane, which is located in the commercial area. While there was a former restriction of bay width of approximately 4–5 m, a rearrangement of property occurred on Houche Lane, as three lots were merged into one large apartment property.

9.2. Pedestrian Arcades on Store Front The Minnan style street houses in Lukang and Dihua Street, Taipei, exhibit noticeably dissimilar pedestrian arcade designs (Figure 15, top). The arcade, which is a covered passage corridor at the front of a building, can also offer utility as a weather shelter. The arcade on Dihua Street was designed to be set back from the projected property boundary, in contrast to the canopy-like shelter outside of the property boundary in Lukang, as the street does not open to the sky. Although the latter was reconstructed into an environmentally-friendly open-air design, resemblance was expressed by the vocabulary and component composition applied to the façade (Figure 15, bottom). In addition to the physical layout, the arrangement and the words of spring couplets for Chinese New Year, located on the top and both sides of the main entrance, present the business identity of the owner. A similar connection between the architectural components and tradition custom was also established by where the couplets were posted. Approximately 85% of the Lukang population came from Quanzhou, China, during the period of Japanese occupation [58]. The recessed design of the arcade, which was not applied in Quanzhou, was also not initially implemented by early immigrants in Lukang. The interstitial space, defined by the arcade or canopy, significantly improved convenience for both owners and customers. Although the mechanically-retractable rolling canopies reshaped the appearance of Old Street, the components were installed without violating the original layout. Cultural sustainability was maintained to a certain extent, and living demands were met by using a flexible extension to the second skin. Sensors 2020, 20, 5628 20 of 26 Sensors 2020, 20, x FOR PEER REVIEW 20 of 26

Figure 15.15. The pedestrian arcade withwith/out/out a recessed setting (top), three façadesfaçades appliedapplied toto recessedrecessed setting inin DihuaDihua StreetStreet ((upperupper middlemiddle),), comparisoncomparison ofof thethe didifferentfferent openingopening compositioncomposition onon anan oldold ground floorfloor on on Lukang Lukang Old Old Street Street and and a new a new three-story three-story high high construction construction on Dihua on Dihua Street atStreet a remote at a siteremote (lower site middle(lower ),middle and the), and original the original 3D façades 3D faça modeldes of model Dihua of Street Dihua (bottom Street ().bottom).

9.3. Differentiation Differentiation of Street Façade inin EarlyEarly DaysDays byby ReinstallationsReinstallations Due to the geographic advantage of Lukang as a harbor in its early days, both the Minnan style and the Baroque (or Western) stylestyle ofof streetstreet houseshouses werewere preserved.preserved. The reconstructionreconstruction made in the periodperiod ofof JapaneseJapanese occupation occupation also also reshaped reshaped the the street street style style on on Dihua Dihua Street, Street Taipei., Taipei. Specifically, Specifically, the oldthe façadeold façade in Lukang in Lukang was was superimposed superimpos oned thaton that of Dihua of Dihua Street Street in AR in AR to reinstall to reinstall the streetthe street style style to the to formthe form of its of early its early days indays virtual in virtual space, space, with the with reality the createdreality bycreated referring by referring to the remote to the site. remote Figure site. 14 illustratesFigure 14 theillustrates different the opening different compositions opening compositions on the old ground on the floor old and ground a new floor construction and a new of a three-storyconstruction high of a structure. three-story high structure. This AR-basedAR-based study study facilitated facilitated the illustrationthe illustration of differences of differences in façade vocabularyin façade andvocabulary composition, and materialcomposition, composition, material reconstruction composition, due reconstructi to propertyon transfer,due to andproperty coherence transfer, in construction and coherence materials. in Dueconstruction to the open materials. design Due of the to the pedestrian open design arcade of onthe the pedestrian ground floorarcade and on thethe verticalground organizationfloor and the ofvertical spaces, organization the façade onof Dihuaspaces, Street the façade presents on a Dihua dissimilar Street vocabulary presents anda dissimilar composition. vocabulary Symmetry, and however,composition. remained Symmetry, on both however, sites. In remained addition, on the both façade sites. was In primarilyaddition, madethe façade of wood was in primarily Lukang, comparedmade of wood to the in red Lukang, brick andcompared cement to stucco the red found brick on and Dihua cement Street. stucco The found former on has Dihua openings Street. made The offormer wood, has while openings the latter made features of wood, openings while the comprised latter features of metal openings frame comprised and glass. of The metal old frame and small and houses,glass. The which old wereand small allocated houses, in individual which were lots, alloca wereted reconstructed in individual into lots, apartments were reconstructed with a volume into apartments with a volume that significantly transformed the local fabric. Materials similar to the

Sensors 2020, 20, 5628 21 of 26 that significantly transformed the local fabric. Materials similar to the selections of Old Street were also applied for coherence of historical appearance. Wood openings or bricks were used even in cases in which the new buildings possessed a concrete structure.

10. Discussion

10.1. Contributions A more direct connection to architectural study was achieved by integrating façades, 3D data, and application environments. Correlations were made to the evolved design or style of pedestrian arcades on store fronts to fulfill functional needs under geographic variances. The differences between old façades and new ones were verified by the components and their compositions. Differentiation of street façades in early days was achieved by reinstallations of façades in front of a demolished site with an emphasis on coherence and continuity to existing eaves. The elevation of façades was differentiated by how it affects the installation of canopy. On-site interactive comparisons were introduced without architectural drawings. The reality of artifacts was enhanced in 3D data. A connection between architectural artifacts and virtual representation was obtained as an extended sustainable application of as-built data. A variety of 3D mesh model types (wireframe-like, semi-transparent) was applied for enhanced comparison results. The study applied a common environment of Cloud access, a markerless AR, and a convenient smartphone to architecture field study. The integration enabled a situated comparison to correlate the results under geographic differences. A combinative approach of complicated scan data and popular app was applied. The general-purposed platform was feasible for situated architectural study. The application was made possible for on-site comparisons even in remote sites. The visualization and communication of 3D models was incorporated to reduce development and maintenance effort, with more emphasis placed on preparation of 3D models. A set of models converted from as-built scenes created a more coherent appearance to the environment. Twenty (20) sets of models were created and compared in seven sites with different numbers of adjustments and findings. The situated operation involved researchers in a local environment replete with both contemporary human settings and reconstructed building styles. The operations contributed to the environmental awareness and cultural sustainability of building style. This approach can be conducted individually or as a team at any location with the support of a Cloud database. The entire adjustment process can be recorded for post-visit review. Live broadcasting is also possible in the current pandemic situation between researchers and team members, or students and instructors. A collaborate environment should be established for architectural styles and construction components as real-time situated studies of geographic differences in the future.

10.2. Field Comparisons Situated comparisons succeeded in identifying component-related variations, such as the discovery of different building bay widths, extended ceiling heights on ground floors, or level distances between indoors and outdoors. The recognition of the subject and environment was always enhanced by the surrounding urban fabric and furniture. With the extended support of media, video recording of the operating process was made possible for the entire adjustment process. Situated comparisons, however, did not always succeed. For example, a drifting problem occurred, which may cause inconsistent viewing perspectives. Depth display was another issue which created a certain model overlaying effect over pedestrians or vehicles at near depth. Moreover, restriction of operation clearance occurred when the smartphone camera was barely wide enough to include the whole façade in a narrow alley. Ground level selection and anchoring can also be tolerance-prone in a few cases in which the ground floor and façade were not at a perfect 90 degrees. In addition, during recording site activity, a third-person picture of situated operation by researchers could be difficult in terms of balancing the brightness between the façade and smartphone screen. Furthermore, Sensors 2020, 20, x FOR PEER REVIEW 22 of 26 smartphone screen. Furthermore, interference of pedestrians, tourists, and vehicles frequently occurred (Figure 16), and each comparison took approximately 18–30 min to complete. Lighting conditions may also change the saturation of models upon automatic adjustments performed by the phone camera. In contrast, it was relatively easy to re-situate comparisons in the laboratory or indoors.Sensors 2020 , 20, 5628 22 of 26 The success rate of taking photographs for post-visit evaluation was near 90% for one-person screen shots of the model and the façade from the app. This rate, however, dropped to half when photographsinterference of were pedestrians, taken with tourists, the screen and vehicles and the frequentlyfaçade cross occurred street included (Figure 16 at), the and same each comparisontime with a cleartook approximatelydisplay of content 18–30 on minthe screen. to complete. The rate Lighting dropped conditions even lower may when also taking change photographs the saturation with of themodels screen, upon the automatic researcher, adjustments and the façade performed included by the simultaneously. phone camera. The In contrast,SLR camera it was function relatively of narrowingeasy to re-situate the aperture comparisons to cover in longer the laboratory focal lengths or indoors. was not applicable in a smartphone.

Figure 16. 16. OneOne of of the the factors factors that that affected affected the the situated situated comparison comparison by byinterference interference of ofpedestrians pedestrians or vehicles.or vehicles.

10.3. TheSwitch success of AR rateDevelopment of taking Environment photographs for post-visit evaluation was near 90% for one-person screen shots of the model and the façade from the app. This rate, however, dropped to half when Former app development required substantial time and effort, as well as periodic software photographs were taken with the screen and the façade cross street included at the same time with a development kit (SDK) updates. Customized needs led to predefined architecture and data, which clear display of content on the screen. The rate dropped even lower when taking photographs with the may not be exchangeable among studies without redevelopment. It also did not accept all kinds of screen, the researcher, and the façade included simultaneously. The SLR camera function of narrowing data, such as point cloud, or formats for the best representation of reality. In the present study, a the aperture to cover longer focal lengths was not applicable in a smartphone. different application approach emerged for an app which is relatively simple and capable of working10.3. Switch with of most AR Development kinds of data Environment with higher visual fidelity. For the adoption of the ready-made app, the experience of interface, Cloud access, and QR Former app development required substantial time and effort, as well as periodic software code access were consistent with similar app experiences. It is similar to a webpage tool, development kit (SDK) updates. Customized needs led to predefined architecture and data, which may subscription e-commerce platform, or virtual store or classroom with which students are familiar not be exchangeable among studies without redevelopment. It also did not accept all kinds of data, and use frequently. This transferrable experience and familiarity of tools lowers the learning curve such as point cloud, or formats for the best representation of reality. In the present study, a different benchmark. The instructor was also a content provider who presented students with forms of application approach emerged for an app which is relatively simple and capable of working with most models made by different mesh creation tools. A customized app may achieve the result more kinds of data with higher visual fidelity. rapidly, but offers less flexibility to explore the subject in real time. For the adoption of the ready-made app, the experience of interface, Cloud access, and QR code Fast development of contents from creation to application was made possible using different access were consistent with similar app experiences. It is similar to a webpage tool, subscription content development approaches. A user can select a simpler CloudCompare® approach or a e-commerce platform, or virtual store or classroom with which students are familiar and use Geomagic Studio® approach with more variable control of mesh quality. The access of contents was frequently. This transferrable experience and familiarity of tools lowers the learning curve benchmark. sharable and yet secured. It is similar to a shared AR study group that can have models contributed by The instructor was also a content provider who presented students with forms of models made by a number of involved people, and discuss shared experiences through screenshots or different mesh creation tools. A customized app may achieve the result more rapidly, but offers less video-conferencing. flexibility to explore the subject in real time. The advantage of the scan data provider in this study is that it enables an AR environment Fast development of contents from creation to application was made possible using different with a realistic model for architectural situated-study environments. Instead of a customized content development approaches. A user can select a simpler CloudCompare® approach or a Geomagic application for a specific purpose, it is an open app that hosts a general-purpose application. The Studio® approach with more variable control of mesh quality. The access of contents was sharable and data or models that we provided were relatively convincing. As a consequence, more emphasis can yet secured. It is similar to a shared AR study group that can have models contributed by a number of involved people, and discuss shared experiences through screenshots or video-conferencing. The advantage of the scan data provider in this study is that it enables an AR environment with a realistic model for architectural situated-study environments. Instead of a customized application for a specific purpose, it is an open app that hosts a general-purpose application. The data or models Sensors 2020, 20, 5628 23 of 26 that we provided were relatively convincing. As a consequence, more emphasis can be placed on the contents. While the flexibility of interaction created new findings, the transfer to a ready-developed app also enabled an accurate assessment of building styles.

10.4. Limitations The study also possessed certain limitations. The model may have shadow-casted differently from as it appears on the façade, depending on the weather or the time of day. On/off display switches were also not supported individually for each object without additional scripting effort, same was the customized annotations added in mixed reality (MR). In addition, the device display was small. Finally, it could not accept a 3D point cloud model, and its conversion can be effort-intensive.

11. Conclusions The study applied a common environment of Cloud access, a markerless AR, and integration with a convenient device for architecture field study. This research applied a combination approach of complicated scan data and a popular app. The application of a general-purpose app for architectural study was made possible with specific models for on-site comparisons, and further extended the study to remote sites. A set of models, which was converted from 3D scans of as-built scenes, was made with a more coherent appearance to the environment. An optimal combination of sensor data and architectural manipulation of historical space was achieved in a user-friendly AR interface. Moreover, the application of 3D as-built data is demonstrated to be sustainable, even for the purposes of knowledge tours and pedagogy of architectural history. Future works would investigate cross-application interaction platforms that support different architectural contents and issues. AR should accept all kinds of data, including point cloud, as a more direct connection from one reality to another reality, or from different input devices to reality. An open environment should also be established for self-contained study of individuals at any location with group support of a domain-specific Cloud database.

Author Contributions: Both N.-J.S. and Y.C. were involved in every part of the research. Additional resources, supervision, project administration, funding acquisition, and writing—review and editing were conducted by N.-J.S. Both authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Ministry of Science and Technology of Taiwan, the second year of the grant number MOST 107-2221-E-011-029-MY3. Acknowledgments: The authors are very thankful to Tzu-Yu Chen and Yi-Ting Qiu for their involvements in field comparisons and analysis. Conflicts of Interest: The authors declare no conflict of interest.

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