International Journal of Geo-Information

Article Development of a Conceptual Mapping Standard to Link Building and Geospatial Information

Taewook Kang

Korea Institute of Civil Engineering and Building Technology, Ilsanseo-Gu Goyang-Si 10223, Korea; [email protected]; Tel.: +82-010-3008-5143



Received: 18 February 2018; Accepted: 19 April 2018; Published: 24 April 2018


Abstract: This study introduces the BIM (building information modeling)-GIS (geographic information system) conceptual mapping (B2GM) standard ISO N19166 and proposes a mapping mechanism. In addition, the major issues concerning BIM-GIS integration, and the considerations that it requires, are discussed. The B2GM is currently being standardized by the spatial-information international standardization organization TC211. Previous studies on BIM-GIS integration seem to focus on the integration of different types of model schemas and on the implementation of service interfaces. B2GM concerns the clear definition of the conditions and methods for mapping the object information required from the user’s use-case viewpoint for city-scale mapping. The benefits of the B2GM approach are that the user is able directly control the BIM-GIS linkage and integration process in order to acquire the necessary objection information. This can reveal cases of possibly unclear BIM-GIS integration outside the black box in an explicit and standard way, so that the user can distinctively predict the final output obtainable from the BIM-GIS integration. This study examined B2GM in terms of its development background, components, and several utilization examples, as well as the levels and considerations of the integration of different BIM-GIS models.

Keywords: BIM; GIS; conceptual mapping; ISO 19166; BG-IL

1. Introduction The integration of data through geographic information system (GIS)-based building information modeling (BIM) has emerged as an important area of research for the mining of valuable information that can support decision-making. In particular, in order to realize smart city services such as facilities including effective building and energy management, we need to consider the information perspective, which can be represented by considering use cases related to services and combining the BIM and GIS information that we want to use, including information on the building and infrastructure objects in a city. We also need to consider other heterogeneous data models, such as facility management (FM) database systems. These databases can be legacy systems. There have been some attempts to harvest the rich information in BIM and use it in GIS, but there is no established way to map the information elements between the two worlds. A proper mapping method is clearly required. From the viewpoint of GIS, there are many benefits related to using BIM information in GIS applications. Some examples are:

• Indoor service implementation, such as emergency management (for example, directing and finding evacuation paths in a fire situation); • Outdoor–indoor linking services, such as seamless navigation; and • Effective facility/energy/environment management considering objects related to BIM based on GIS.

ISPRS Int. J. Geo-Inf. 2018, 7, 162; doi:10.3390/ijgi7050162 www.mdpi.com/journal/ijgi ISPRS Int. J. Geo-Inf. 2018, 7, 162 2 of 22

However, an unclear BIM-GIS model integration method may cause the following problems. ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 2 of 22 • Difficulty for the user to predict the model integration results. • Difficulty for the user to predict the model integration results. • In the model integration process, the information necessary for the execution of the use-case may • In the model integration process, the information necessary for the execution of the use-case may be deleted. be deleted. • Information unnecessary for the execution of use-case may be retained. The unnecessary • Information unnecessary for the execution of use-case may be retained. The unnecessary information may make the management of the integrated model difficult and may increase information may make the management of the integrated model difficult and may increase the the time and cost of management. time and cost of management. • Erroneous integrated noise information may lead to bad results in the execution of services or • Erroneous integrated noise information may lead to bad results in the execution of services or in decision-making. in decision-making. The problems m mentionedentioned may may cause cause the user to hesitate to use the BIM-GISBIM-GIS model integration information.information. To To solve this this problem, problem, the user user should should be be able able to to define define the the BIM BIM-GIS-GIS integration integration process process inin a a standardized standardized way way [1] [1] from from the the point point of of view view of of use, use, and and the the result resultss should should be be clearly clearly predictable. predictable. Previous studies related to BIM-GISBIM-GIS integration often suggest the development of integrated models needed for specific specific usecases. This This approach approach fixes fixes the the integration integration method method or or part part of of the integrationintegration process process for for the the realiz realizationation of of a specific specific use case case,, such as an information query query method method using an ontology ontology model model [2 [2––66],], a a web web-service-based-service-based model model for for integration integration system system development development [7,8 [7,8],], data transformation methods methods using using commercial commercial tools tools [9 [9–12],], a andnd a model schema development metmethodhod [13 [13–17]. These These references references will be examined in more detail through a literature review.review. This studystudy proposesproposes the the BIM-GIM BIM-GIM integration integration method method based based on B2GM on B2GM (19166), (19166) which,is which a standard is a standardunder ISO/TC211. under ISO/TC211. B2GM B2GM enables enables flexible flexible information information mapping mapping and integrationand integration considering considering the therelevant relevant problems. problems. B2GM B2GM focuses focuses on the on clearthe clear definition definition of conditions of conditions and processes and process to mapes to the map object the objectinformation information necessary necessary from the from user’s the use-caseuser’s use viewpoint-case viewpoint onto the onto city the scale. city The scale. proposed The proposed method methodincludes includes the BIM-GIS the BIM element,-GIS element, geometry, geometry, and a property and a property set mapping set mapping method includingmethod including the external the externaldataset. dataset. Considering Considering the standardization the standardization of the BIM-GIS of the BIM mapping-GIS mapping requirements, requirements, the BIM the and BIM GIS andmodels GIS tomodels be mapped to be mapped were generalized were generalized and expressed and expressed if possible. if possible. In the case In the studies case studies and the and survey, the survey,the BIM-GIS the BIM integrated-GIS integrated information information type, utilization type, utilization and level and were level analyzed. were analyzed.

2. Materials Materials and and Methods Methods To develop the conceptual mapping, related current current research tr trendsends we werere studied and their characteristicscharacteristics werewere analyzedanalyzed toto compare compare and and investigate investigate the the respective respective technologies technologies in relationin relation to theto thepresent present study study like like Figure Figure1. 1.

Analysis of the study trend Research scope Related Studies trend Characteristic and definition studies analysis category analysis

Information Model Analysis Comparison BIM model GIS schema between BIM and schema study study GIS schema BIM-GIS integration level, consideration BIM-GIS Conceptual Mapping Design development Mapping concept Mapping and discussion Framework and mechanism component design design design Conclusion

Figure 1. Research flow. Figure 1. Research flow. The research progress situation and limits were reviewed through the examination of the existing literature. The scope of the literature survey was limited to the following keywords and purposes. • The literature surveyed includes BIM, GIS and similar keywords.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 3 of 22

The research progress situation and limits were reviewed through the examination of the existing literature. The scope of the literature survey was limited to the following keywords and purposes.

• The literature surveyed includes BIM, GIS and similar keywords. • The purpose of research includes integration and linkage, standardization, and service development.

Based on the literature review and the analysis of information models such as BIM and GIS, B2GM was designed to solve the integration problems. After comparing solutions that are similar to the B2GM concept, the benefits will be discussed. Finally, the BIM-GIS integration level, considerations and conclusions of the study are derived.

3. Results

3.1. Overview of Recent Research Trends For the GIS and BIM categories, standard models are proposed to support interoperability. Their respective model schema structures are different, making their integration difficult. Diverse approaches are used for the research on GIS-BIM integration, but this chapter summarizes the research contents from the perspectives of ontological modeling, integrated web services, schema mapping, and schema expansion and development.

1. Ontological modeling

Interoperability implementation based on ontological models enables data integration at the conceptual level. A method was proposed by which, after the extraction of IFC and GIS information, an RDF (resource description framework) model was created to ask questions [2]. In addition, a study was conducted to propose a method by which, after defining an RDF dictionary about the IFC wall structure, information is requested through SPARQL, and the results are expressed [3]. To apply this method, the components of the heterogeneous model composition should be converted to a triple structure. A study was conducted to propose a semi-automatic ontological method for geospatial integration [4]. It proposed heterogeneous data inter-model mapping operators and modeling tools for data integration. For the integration of GIS and CAD data, a study was conducted by applying the ontological modeling method [5]. It suggested that the use of the automated query interpreter (AQI) method makes a semantic interoperation between data models and processes possible. This method is operated by asking ontological questions about individual heterogeneous data and finally integrating the inquiry results. Yet another study was conducted on BIM-GIS integration based on RDF [6]. It converts IFC and GML (geography markup language) into RDF and expresses it in a graph model.

2. Integrated web service

Data extraction in BIM, GIS and other heterogeneous models can be provided as a web service in order to obtain the data required for the development of applications. The web services phase 4 (OWS-4) of the GIS standardization non-government council Open Geospatial Consortium (OGC) is currently developing IFC for GIS (IFG) in order to express BIM data in CityGML. IFC conversion to geography markup language (GML) and GML conversion to IFC are possible through a concept similar to extensible stylesheet language (XSLT) [7]. In addition, a study was conducted on the method of using web services to demonstrate building models in GIS [8].

3. Data mapping

BIM can be converted to another model, but with limitations. This conversion is a mapping-based process and usually consists of several mapping conditions and rules. ISPRS Int. J. Geo-Inf. 2018, 7, 162 4 of 22

There was a study where the IFC-based partial model was used in a co-work (teamwork) environment in connection with the mapping method [9]. It indicated that it is complicated and inconvenient to use approaches such as STEP (STandard for the Exchange of Product model data) tools and express data management (EDM), which are known as schema-based modeling tools. Instead, it proposed the mapping of source model elements into target model elements using the EXPRESS-X mapping schema. For mapping, STEP-P21 [10] implements interoperability using the IFC inter-printer. STEP-P21, known as the STEP physical file format, provides a clear text encoding method for information exchange, and the ISO 10303-21 clear text encoding of the exchange structure is the standard. This method, however, can be used only with in-depth knowledge of the STEP-P21 specifications, and it does not handle the methods of importing heterogeneous datasets into IFC and binding and mapping them. Yet another method of schema mapping is the information extraction technology using the generalised model subset definition schema (GMSD)-based partial model and the partial model query language (PMQL) [11]. GMSD was designed based on the object-oriented language concept, and is classified into the object filing division and the attribute view definition division. This method is similar to the SQL SELECT text and IFC IfcPropertySet. A study was conducted on mapping using ETL (extract, transform, and load) [12]. Using the ESRI commercial ETL software, it extracted the BIM data required for the implementation of a use case of landscaping planning.

4. Schema extension and development

Attempts were made to resolve problems arising from the BIM-GIS schema difference by developing a new common schema. The IFC-CityGML schema structure difference was analyzed using the unified building model (UBM) for the purpose of proposing a new schema in a bid to resolve such problems [13]. There was a study on extending the BIM model using the application domain extension (ADE) method [14]. To implement GIS-based use cases such as site selection and fire management in the construction category, a study was conducted to propose a method of incorporating BIM information into GIS [15]. To convert data from IFC to the ESRI schema structure, the said study developed the persistent schema level model view schema. A method was proposed to convert this information into transient temporary object model data, incorporate it into the GIS geographical data model, and store it in ESRI’s shapefile and geodatabase structure [16]. The results of the study were verified by interviewing experts regarding the ISO 9126-1 quality factors. A study was conducted to demonstrate a flood model using ADE [17]. Most studies on ADE should focus on the implementation of the data required for special use cases, thus limiting their scope.

3.2. Research Review Analysis The research reviewed above can be divided into the following categories. As shown in Table1, most of studies on BIM-GIS model integration focus on the ontological model, schema expansion, the development of web services and applications, and the development of commercial-solution-based data extraction modules. This study focuses on the distinctive definition method for the conditions and processes to map the external data necessary from the user’s use-case viewpoint, as well as the BIM object information in the GIS model. ISPRS Int. J. Geo-Inf. 2018, 7, 162 5 of 22

Table 1. Analysis of research.

Category References Research Characteristics and Limitations For the integration of the BIM and GIS heterogeneous models, the ontological modeling technique is used. The RDF-based integrated model has the strength of expressing Ontological modeling [2–6] inter-object relationships. The ontological model links the management of the models thanks to its nature, giving it good scalability, but it has the weaknesses of requiring a bigger capacity of the model itself, and of lowering performance. For the integration of the BIM and GIS heterogeneous models, web services can be developed. This example adopts the pattern of using the developed web services in integrating the information required for each heterogeneous model. The web services can Integrated web [7,8] be called through a specific programming language. The web services are a method of services developing services based on the web; thus, as the services are operated through the web services, their performance can be significantly influenced by the network traffic or the amount of information transmitted. Data mapping involves mapping the information of the BIM and GIS heterogeneous models into a specific model schema, and it includes information conversion. The schema mapping method has the strength of being able to reuse services—which are used based Data mapping [9–12] on a specific model—as they are. Naturally, when using these services, it does not create problems such as lowering the performance. One-on-one mapping between these heterogeneous models is impossible in many cases, however; thus, when the information conversion process is executed, the type and content of the information can be changed. This method involves extending the schema to include other heterogeneous information based on a specific model. This method is used in the schema of object-oriented models. Compared to other methods, this model causes fewer problems involving lowering the Schema extension performance and being incompatible as a result of model integration. However, if the class [13–17] and development structure, which is the basis of extending the schema, is not generalized, conceptual conflicts may occur. When the object-oriented extension method is applied, myriads of class layers will be created, thus possibly making the model more complicated and making the maintenance and operation difficult.

3.3. Analysis of Standard Models

3.3.1. Overview The BIM and GIS schemas have different development purposes, concepts and structures, thus making it difficult to integrate data if specific criteria are not given. This chapter analyzes the schema structure to be considered from the BIM-GIS integration viewpoint. The existing BIM and GIS commercial data format has a binary structure and is not open. Thus, based on IFC and CityGML, which are the representative standard models of BIM and GIS, the schema structure and features are analyzed herein.

3.3.2. IFC Standard Model IFC is a data exchange format that was developed to describe building information. This format is neural and open. The IFC format was developed for the purpose of data exchange in 1995 by IAI (International Alliance Interoperability), a council formed in 1995 mainly by AEC (architecture, engineering and construction) companies in the U.S. and Europe. It has been developed and maintained in buildingSMART. IFC has now evolved into the IFC4 version, and it is described in the EXPRESS language, which is based on the entity relationship model, a model that can describe object-oriented structures. In IFC4, classes are defined by being extended into the kernel package (which defines the key object classes), into the three basic extended packages (i.e., control, product and process) extended from the kernel, and into the five AEC/FM common packages (i.e., building services, components, absence of buildings, management factors, and facility objects) extended from the extended packages. IFC4 consists of eight packages in the AEC/FM domain in individual common packages, and of 21 resource packages resulting from the basic object types (e.g., the quantity and material used to define the attributes of the construction elements) defined and classified by kind. IFC describes the information schema in the EXPRESS language based on the object-oriented concept. Focusing on the interoperation of architectural information to enable the reuse of the information, it provides a total of over 700 objects, including various architectural elements, materials, and processes, which are extended from the kernel objects. ISPRS Int. J. Geo-Inf. 2018, 7, 162 6 of 22

IFC is used together with IFD (International Framework for Dictionaries, ISO 12006-3) and with IDM (Information Delivery Manual, ISO 29481-1:2010), an IFC information exchange method. Here, IDM aims to define the construction project process and to provide guidelines for the inter-process information exchange required when using BIM. IDM is defined in terms of BPMN (business process model and notation) and ER (exchange requirement), which are part of BPM (business process management) technologies, to tailor the universal IFC to the mutual process relevancy, type of consumption information, information exchange method, etc. IFC provides the phase information that connects IfcProject to IfcBuildingStorey, thus enabling the search for hierarchically-related information like Figure2. ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 6 of 22

Figure 2. Major structure expression of IFC (BuildingSmart). Figure 2. Major structure expression of IFC (BuildingSmart).

3.3.3. CityGML Standard Model 3.3.3. CityGML Standard Model CityGML is a GIS-based open object information model developed by OGC (Open Geospatial CityGML is a GIS-based open object information model developed by OGC (Open Geospatial Consortium). It is the ISO TC211 standard and a GML-based application schema that functions as an Consortium). It is the ISO TC211 standard and a GML-based application schema that functions as information interoperation format in city object models. GML based on abstract specification was an information interoperation format in city object models. GML based on abstract specification was developed by OGC. developed by OGC. CityGML was developed to more efficiently develop three-dimensional spatial modeling by CityGML was developed to more efficiently develop three-dimensional spatial modeling by strengthening models, which GML lacks; it defines materials, features and models, as well as their strengthening models, which GML lacks; it defines materials, features and models, as well as their mutual phase relationships. GML, based on object-based classes, defines the geometry (expressing mutual phase relationships. GML, based on object-based classes, defines the geometry (expressing geometric models), the features (expressing geographic features), and the definition class (defining geometric models), the features (expressing geographic features), and the definition class (defining the the material dictionary). material dictionary). CityGML was developed with a focus on the object information model of city infrastructure. By CityGML was developed with a focus on the object information model of city infrastructure. considering the abstraction and performance of the model, it can express LOD (level of detail) By considering the abstraction and performance of the model, it can express LOD (level of detail) information like Figure 3. CityGML bases its schema hierarchy structure design on features. It uses information like Figure3. CityGML bases its schema hierarchy structure design on features. It uses CityObject, derived from the features, to extend the geographical feature models into facilities, CityObject, derived from the features, to extend the geographical feature models into facilities, transport means, water resources, terrain, etc.; in order to express these shapes, it extends the transport means, water resources, terrain, etc.; in order to express these shapes, it extends the geometry. geometry. CityModel is provided in order to be able to handle many city objects, and this class is CityModel is provided in order to be able to handle many city objects, and this class is derived from derived from FeatureCollection, where the feature is the basic class [18]. FeatureCollection uses the FeatureCollection, where the feature is the basic class [18]. FeatureCollection uses the composite design composite design pattern as an object container so that it can manage many city objects [19]. This pattern as an object container so that it can manage many city objects [19]. This serves a role similar serves a role similar to IFC’s relationship with IfcRelContainedInSpatialStructure. To effectively to IFC’s relationship with IfcRelContainedInSpatialStructure. To effectively demonstrate many city demonstrate many city facilities, CityGML divides the detailed shape expression levels into LOD 0– facilities, CityGML divides the detailed shape expression levels into LOD 0–5. This is significantly 5. This is significantly different from IFC’s shape expression method. At individual detailed levels, different from IFC’s shape expression method. At individual detailed levels, the geometry expression the geometry expression is defined as from lod0Geometry to lod4Geometry. Recently, to resolve the is defined as from lod0Geometry to lod4Geometry. Recently, to resolve the ambiguity of the CityGML ambiguity of the CityGML LOD, the CityGML 3.0 concept was proposed [20]. LOD, the CityGML 3.0 concept was proposed [20].

Figure 3. CityGML LOD model.

ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 6 of 22

Figure 2. Major structure expression of IFC (BuildingSmart).

3.3.3. CityGML Standard Model CityGML is a GIS-based open object information model developed by OGC (Open Geospatial Consortium). It is the ISO TC211 standard and a GML-based application schema that functions as an information interoperation format in city object models. GML based on abstract specification was developed by OGC. CityGML was developed to more efficiently develop three-dimensional spatial modeling by strengthening models, which GML lacks; it defines materials, features and models, as well as their mutual phase relationships. GML, based on object-based classes, defines the geometry (expressing geometric models), the features (expressing geographic features), and the definition class (defining the material dictionary). CityGML was developed with a focus on the object information model of city infrastructure. By considering the abstraction and performance of the model, it can express LOD (level of detail) information like Figure 3. CityGML bases its schema hierarchy structure design on features. It uses CityObject, derived from the features, to extend the geographical feature models into facilities, transport means, water resources, terrain, etc.; in order to express these shapes, it extends the geometry. CityModel is provided in order to be able to handle many city objects, and this class is derived from FeatureCollection, where the feature is the basic class [18]. FeatureCollection uses the composite design pattern as an object container so that it can manage many city objects [19]. This serves a role similar to IFC’s relationship with IfcRelContainedInSpatialStructure. To effectively demonstrate many city facilities, CityGML divides the detailed shape expression levels into LOD 0– 5. This is significantly different from IFC’s shape expression method. At individual detailed levels, theISPRS geometry Int. J. Geo-Inf. expression2018, 7, 162 is defined as from lod0Geometry to lod4Geometry. Recently, to resolve7 ofthe 22 ambiguity of the CityGML LOD, the CityGML 3.0 concept was proposed [20].

FigureFigure 3. 3. CityGMLCityGML LOD LOD model. model.

3.3.4. Comparison of a Building and the GIS Standard Model Based on the aforementioned surveyed schema structure, the differences in the application purpose, development method, basic concept, shape definition structure, and LOD were examined. Table2 outlines the analyzed differences between the IFC and CityGML schemas.

Table 2. Comparison of the standard schema characteristics between IFC and LandXML.

Item IFC CityGML Developed to express the attributes and shapes of Specializes in building modeling and operational sites, buildings, roads, transport means, and other Application aspects, but does not consider civil alignment of city objects, but it does not contain detailed building digital terrains. information levels. Schema design methodology OOA/D (object-oriented analysis and design) OOA/D IfcObject-based schema developed as a structure Designed as an ISO 19109 GML (geographic markup Basic concept designed to express the object attributes, acts, language)-based schema structure. The features can and shape. be roads, rivers, people, vehicles, etc. Defined as a B-Rep geometry structure in IfcProductRepresentation of the Geometry; derived from the GM class package; Geometry IfcRepresentationResource package. IFC defines the B-Rep structure including primitive supports parametric models depending on the geometry such as point, curve and surface. specific element such as IfcWallStandardCase. Consists of over 700 objects related to the entire life of a building, such as CityGML element is based on feature abstraction Building: IfcBuildingElement, IfcSpace, IfcRoof, class in GML. If based on the CityGML 2.0 version, IfcWindow, IfcDoor, IfcStair, etc.; and it consists of 14 packages (bridge, building, tunnel, Process: IfcProcedure, IfcTask, IfcWorkPlan, etc.) and two external packages (GML, address Object type IfcWorkControl, etc. language). Does not separately classify LOD schema for Considering the information demonstrability and LOD object shapes in advance. LOD is determined at performance for large numbers of city objects, the the designer’s modeling time, and is stored in the information is managed by dividing it into LOD 0–4. IfcProductRepresentation object. Detailed building member materials, modeling Manages the string, integer, double, date, uri, and parameters, and attribute information measure data types, which are derived from the representation listed as follows. genericAttribute defined in the <> Attributes Pset_BuildingCommon: BuildingID, stereotype as an aggregation design pattern. By ContructionMethod, CrossPlannedArea, utilizing these, the user can use the CityObject NetPlannedArea, IsLandMark, etc. attributes on his own.

3.4. B2G Conceptual Mapping

3.4.1. Overview The BIM-to-GIS conceptual mapping (B2GM) proposed herein focuses on mapping the facility model (including buildings) on the city scale from BIM. To help implement the mapping technology from the ISO standardization perspective, B2GM defines the requirements and logical mapping mechanisms for the physical implementation of heterogeneous data models. ISPRS Int. J. Geo-Inf. 2018, 7, 162 8 of 22

These mechanisms consists of three components that have specific purposes, such as (1) BIM-to-GIS element mapping (B2G EM); (2) BIM-to-GIS LOD mapping (B2G LM); and (3) BIM-to-GIS perspective definition (B2G PD).

1. B2G EM supports element mapping from the BIM model to the GIS model. As the BIM model and GIS model schema are different, B2GM EM needs mapping rules determining how to transform from BIM model to a GIS model element. 2. B2G LM supports LOD definition and generation from a BIM model to a GIS model. “LOD”, as defined in the GIS model, consists of LODs to represent the geometry information depending on an object in GIS. The LOD models defined a visualization mechanism and classes, which is similar to the concept of B-Rep based on a surface. However, there are no LOD objects in BIM objects in the BIM standard model. To represent BIM object in GIS, LOD information needs to be extracted from the BIM model considering each LOD concept in the GIS model. It can be defined by the LOD mapping rule set. 3. B2G PD supports the perspective of information representation depending on the specific use ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 8 of 22 cases, such as the urban facility management (UFM). “Perspective” depends on the use case. For example,be extracted when from we managethe BIM model urban considering facilities, each the LOD required concept data in the should GIS model. be collected It can be from the various datadefined sources, by the LOD including mapping BIM rule models,set. and be transformed and presented in a user-specific 3. B2G PD supports the perspective of information representation depending on the specific use way. PDcases defines, such a as data the urban view facility to extract management the needed (UFM).data “Perspective and transform” depends on the the information use case. For from the various dataexample, sources. when we manage urban facilities, the required data should be collected from the various data sources, including BIM models, and be transformed and presented in a user-specific 3.4.2. Frameworkway. PD defines a data view to extract the needed data and transform the information from the various data sources. The B2GM defines the conceptual framework and mechanisms for the mapping of information elements from3.4.2. Framework building information modeling (BIM) to geographic information systems (GIS) in order to access the necessaryThe B2GM informationdefines the conceptual based onframework specific and user mechanisms requirements. for the mapping The main of information purpose of B2GM is to define theelements basic from mapping building requirement information m betweenodeling (BIM) BIM to and geographic GIS, including information the systems external (GIS) dataset. in B2GMorder uses to existingaccess the necessary international information standards based on such specific as user geography requiremen markupts. The main language purpose (GML)of (ISO B2GM is to define the basic mapping requirement between BIM and GIS, including the external 19136:2007),dataset. CityGML (OGC 12-019) and Industry Foundation Classes (IFC) (ISO 16739:2013). It is applicableB2GM uses to existing information international query standards services such such as geography as urban markup facility language management (GML) (ISO operation. BIM object19136:2007), visualization CityGML in GIS (OGC and 12 other-019) and application Industry Foundation services Classes that require (IFC) (ISO query 16739:2013). processing depending on the relationshipIt is applicable between to BIMinformation and GIS query objects, services either such as in urban the facility real or management virtual world, operation. will BIM be able to use object visualization in GIS and other application services that require query processing depending the mechanismson the relationship to map the between required BIM informationand GIS objects, elements either in the between real or virtual the two world, systems. will be able to Figureuse4 thepresents mechanisms a conceptual to map the required overview information of the elements B2G mappingbetween the andtwo systems. the relationship of the mapping mechanisms.Figure 4 presents a conceptual overview of the B2G mapping and the relationship of the mapping mechanisms.

B2G Perspective Definition (PD)

B2G Mapping B2G B2G LOD Element Mapping Mapping (LM) (EM)

FigureFigure 4. 4.B2GM B2GM conceptualconceptual overview. overview. It is impossible to perfectly integrate the physical mapping of myriads of BIM and GIS models considering the various actual limitations. Thus, B2GM focuses on providing the concept and method that can conceptually define the information required for BIM-GIS heterogeneous model mapping. B2GM considers the following: 1. Perspective information representation, depending on specific use cases, such as user facility management: “Perspective” depends on the use case to extract the needed data. PD consists of three parts to extract the needed external FM data.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 9 of 22

It is impossible to perfectly integrate the physical mapping of myriads of BIM and GIS models considering the various actual limitations. Thus, B2GM focuses on providing the concept and method that can conceptually define the information required for BIM-GIS heterogeneous model mapping. B2GM considers the following:

1. Perspective information representation, depending on specific use cases, such as user facility management: “Perspective” depends on the use case to extract the needed data. PD consists of ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 9 of 22 three parts to extract the needed external FM data. 2. 2. ElementElement mapping mapping from from BIM BIM to to the the GIS GIS model: model: As As there there are are differences differences between between the the BIM BIM model model andand the the GIS GIS model model schema, schema, B2G B2G EM EM needs needs the the mapping mapping rule rule to to determine determine the the transformation transformation fromfrom the the BIM BIM to to a GISa GIS model model element. element. 3. 3. LODLOD definition definition and and mapping mapping from from the the BIM BIM to to the the GIS GIS model: model: The The LOD LOD models models define define a a visualizationvisualization mechanism. mechanism. However, However there, there is is no no LOD LOD concept concept in in BIM BIM objects objects of of the the BIM BIM model model standard.standard. To To represent represent BIM BIM geometry geometry in in GIS, GIS, LOD LOD needs needs to to be be extracted extracted from from the the BIM BIM model model consideringconsidering each each LOD. LOD. 4. 4. Connection-orientedConnection-oriented approach: approach: For For all theall elementsthe elements involved involved in the mapping,in the mapping, the mapping the mapping source issource specified. is specified. Thus, if the Thus, integrated if the modelintegrated needs mod to beel renewed,needs to thebe renewed, defined B2GM the defined mechanism B2GM canmechanism synchronize can the synchronize data. the data. FigureFigure5 shows 5 shows the the process process whereby, whereby, using using B2GM B2GM PD, PD, LM, LM, and and EM, EM, the the heterogeneous-data heterogeneous-data modelsmodels are are integratedintegrated so that that the the necessary necessary information information can canbe extracted be extracted from froma specific a specific use-case use-caseperspective. perspective.

SELECT * FROM IfcBuilding, Alignment WHERE Information Data Buffer(Alignment, IfcBuilding, ’20m’) AND Mining Facility Alignment.Name = ‘Main Ave’ Manager

BIM-GIS integrated query considering use case SELECT * FROM IfcBuilding, Site WHERE perspective Meet(IfcBuilding, Site) AND Site.Name = ‘K’

SELECT * FROM IfcBuilding, Alignment WHERE Path(Alignment, IfcBuilding, ‘A’, ‘B’) Decision Making Support

Information Ex) Web Service Query JSON … BIM-based B2G EM GIS DB DB B2G LM Heterogeneous Ex) File IO … System B2G PD B2GM Conceptual Mapping External DB B2G Data Flow Database integration and query based on B2GM. FigureFigure 5. Database5. integration and query based on B2GM.

3.4.3. Conceptual Mapping Mechanism 3.4.3. Conceptual Mapping Mechanism By using the mapping framework, it is possible to query the information from the linked By using the mapping framework, it is possible to query the information from the linked database database that utilizes the mapped BIM information. Figure 6 shows use cases for querying that utilizes the mapped BIM information. Figure6 shows use cases for querying information that information that includes both GIS and BIM information elements from an integrated database. includes both GIS and BIM information elements from an integrated database. As mentioned above, it is impossible to define mapping mechanisms considering the myriads of physical BIM and GIS models, and it is also difficult to standardize them. B2GM conceptually defines the mapping requirements; thus, the BIM and GIS models do not need to be generalized. To generalize the BIM and GIS models, the packages were defined as in Figure 7. The geometries of the BIM and GIS models should be able to define the B-rep by referring to GFM (general feature model). The BIM and GIS models, if they meet the package requirements shown in Table 3, can define the B2GM mapping requirements.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 10 of 22

As mentioned above, it is impossible to define mapping mechanisms considering the myriads of physical BIM and GIS models, and it is also difficult to standardize them. B2GM conceptually defines the mapping requirements; thus, the BIM and GIS models do not need to be generalized. To generalize the BIM and GIS models, the packages were defined as in Figure7. The geometries of the BIM and GIS models should be able to define the B-rep by referring to GFM (general feature model). The BIM and GIS models, if they meet the package requirements shown in Table3, can define

ISPRSthe B2GM Int. J. Geo mapping-Inf. 2018, requirements.7, x FOR PEER REVIEW 10 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 10 of 22 Set connection information with Define B2GM PD Set connectionthe external information database with Define B2GM PD the external database Set link information with BIM Define B2GM EM Set link informationdatabase with BIM Define B2GM EM database Define B2GM LM Define B2GM LM

Link and map elements and LoDs from BIM to GIS model Link and map elements and LoDs from BIM to GIS model

Query information from BIM-GIS linked model Query information from BIM-GIS linked model Figure 6. B2GM use cases. Figure 6. B2GM use cases. Figure 6. B2GM use cases.

GFM BIM mode l B2GM GIS mode l GFM BIM mode l B2GM GIS mode l

Figure 7. BIM and GIS concept model and B2GM package diagram. Figure 7.7. BIM and GIS concept model and B2GM package diagram. Table 3. Package requirements. Table 3. Package requirements. Package Table 3. PackageRequirement requirements. Package It should be able to define the following Requirementobject information: Package Requirement BIMIt should model be element: able to define It should the befollowing able to defineobject theinformation: runtime of construction components, It should be able to define the following object information: geometry,BIMBIM model model element:property, element: It should and It should be relationship. able to definebe able the runtimeto define of construction the runtime components, of construction geometry, property, components, and relationship. The runtime information should be able to identify the types of BIM element. The types are building information components Thegeometry,such runtime as walls, property, doors,information and rooms. and shouldrelationship. be able to identify the types of BIM element. The types are buildingTheThe runtime geometry information information information shouldcomponents should contain the be B-repsuch able (boundary as to walls, identify representation) doors, the andtypes information. rooms. of BIM B-rep element. must support The the types vertex, edge, are loop, and faces, which are supported by GFM. BIM model ThebuildingThe geometry property information information information should components be should able to categorize contain such as the thewalls, attributes B-rep doors, of the(boundary BIM and elements rooms. representation) and to define the {name, information. value type, BThe-repand geometry initialmust value} support pairs.information the vertex, should edge, contain loop, andthe Bfaces,-rep (boundarywhich are supportedrepresentation) by GFM. information. The system properties of the property information should be defined. The system properties are automatically created when BIM model TheB-creatingrep property must a BIM support model.information the vertex, should edge, be able loop, to andcategorize faces, which the attributes are supported of the BIMby GFM. elements BIM model andTheThe toproperty system define properties the information {name, are the BIM value elementshould type, name be and andable the initial to GUID. categorize value} pairs. the attributes of the BIM elements The relationship information defines the relationships between the BIM elements. The relationships follow the UML relationships. TheandThe system to relationships define properties the covered {name, in thisof the standardvalue property type, are association, and information initial dependency, value} should and pairs. generalization. be defined. The system properties areTheIt a should utomaticallysystem be able properties to define created the of following whenthe property object creating information: information a BIM model. should be defined. The system properties GIS model element: It should be able to define the runtime, geometry, property, and relationship, which are the GIS Thearemodel asystemutomatically components. properties created are thewhen BIM creating element a BIMname model. and the GUID. TheTheThe relationship system runtime information properties information should are be the able defines toBIM identify element the the typesrelationships name of BIM element.and betweenthe The GUID. types the include BIM the site,elements. building, wall,The door, and room, which are the same architectural information components. relationshipsTheThe relationship geometricinformation follow information the should UML be able definesrelationships. to contain the the relationships LOD. The The relationships LOD should between contain covered thethe B-rep BIM (boundaryin elements.this standard representation). The are The B-rep should support the vertex, edge, loop, and face, which are supported by GFM. GIS model association,relationships dependency, follow the UML and generalization. relationships. The relationships covered in this standard are The property information should be able to categorize the attributes of the BIM element and to define the {name, value type, Itassociation, shouldinitial value} be pairs. abledependency, to define andthe followinggeneralization. object information: The system properties of the property information should be defined. The system properties are automatically created when GISIt creatingshould model a BIMbe element: able model. to Itdefine should the be following able to define object the information: runtime, geometry, property, and relationship,GISThe model system properties element: which are are theIt should BIMthe elementGIS be model nameable and tocomponents. thedefine GUID. the runtime, geometry, property, and The relationship information defines the relationships between the BIM elements. The relationships follow the UML relationships. Therelationship,The runtime relationships information which covered are in this the should standard GIS aremodelbe association, able components. to dependency,identify the and types generalization. of BIM element. The types includeThe runtime the site, information building, wall,should door, be able and toroom, identify which the are types the ofsame BIM architectural element. The types informationinclude the site,components. building, wall, door, and room, which are the same architectural Theinformation geometr iccomponents. information should be able to contain the LOD. The LOD should contain the BThe-rep geometr (boundaryic information representation). should The be Bable-rep to should contain support the LOD. the Thevertex, LOD edge, should loop, contain and face, the GIS model whichB-rep are(boundary supported representation). by GFM. The B-rep should support the vertex, edge, loop, and face, GIS model Thewhich property are supported information by GFM. should be able to categorize the attributes of the BIM element and toThe define property the {name, information value type,should initial be able value} to categorize pairs. the attributes of the BIM element and Theto define system the properties {name, value of the type, property initial information value} pairs. should be defined. The system properties areThe automatically system properties created of whenthe property creating information a BIM model. should be defined. The system properties Theare automaticallysystem properties created are thewhen BIM creating element a BIMname model. and the GUID. TheThe relationshipsystem properties information are the defines BIM element the relationships name and betweenthe GUID. the BIM elements. The relationshipsThe relationship follow information the UML definesrelationships. the relationships The relationships between covered the BIM in elements.this standard The are association,relationships dependency, follow the UML and generalization. relationships. The relationships covered in this standard are association, dependency, and generalization.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 11 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 11 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 11 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 11 of 22 TheThe BIMBIM and GIS model model class class structures structures reflecting reflecting the the requirements requirements described described in inTable Table 3 3can can be The BIM and GIS model class structures reflecting the requirements described in Table 3 can be beexpressed expressedThe BIM as shown asand shown GIS in modelFigure in Figures classs 8 and8 structures and 9. The9. The B2GM reflecting B2GM packages packagesthe requirements have have the relationships the described relationships inshown Table shown in 3 Figurecan in be expressed as shown in Figures 8 and 9. The B2GM packages have the relationships shown in Figure Figure10expressed and 10 Table and as shown Table4. Each4 .in Each packageFigure packages 8must and must 9.meet The meet theB2GM the requirements requirementspackages have described described the relationships in in Table Table 22 shown toto perform perform in Figure the the 10 and Table 4. Each package must meet the requirements described in Table 2 to perform the mappingmapping10 and Table function.function. 4. Each package must meet the requirements described in Table 2 to perform the mapping function. mapping function. runtime runtime +type:stringruntime +type:string +type:string

BIM_model element geometry B-rep BIM_model * element * geometry * B-rep BIM_model * element * geometry * B-rep * * *

* * property relationship* * property_set property relationship * property_set * +name: stringproperty relationship * property_set +name: string +name:string * +name:+type: {integer,string real, string} +name:+type: {association,string dependency, generalization} +name:string+type: {system, general} * +name: string +name: string +name:string +type:+value {integer, real, string} +type: {association, dependency, generalization} +type: {system, general} +value+type: {integer, real, string} +type: {association, dependency, generalization} +type: {system, general} +value

Figure 8. BIM DB conceptual model. FigureFigure 8.8. BIMBIM DBDB conceptualconceptual model.model. Figure 8. BIM DB conceptual model. runtime runtime +type:stringruntime +type:string +type:string

LOD GIS_model element geometry B-rep * * LOD * * GIS_model element * LOD geometry B-rep GIS_model * element +name: string * geometry * B-rep * * +name: string * * +name: string * * property relationship* * property_set property relationship * property_set * +name: stringproperty relationship property_set +name: string * +name:string * +name:+type: {integer,string real, string} +name:+type: {association,string dependency, generalization} +name:string+type: {system, general} * +name: string +name: string +name:string +type:+value {integer, real, string} +type: {association, dependency, generalization} +type: {system, general} +value+type: {integer, real, string} +type: {association, dependency, generalization} +type: {system, general} +value

Figure 9. GIS DB conceptual model. Figure 9. GIS DB conceptual model. FigureFigure 9.9. GISGIS DBDB conceptualconceptual model.model.

B2GM PD B2GM EM B2GM LM B2GM PD B2GM EM B2GM LM B2GM PD B2GM EM B2GM LM

Figure 10. GIS DB conceptual model. Figure 10. GIS DB conceptual model. FigureFigure 10.10. GISGIS DBDB conceptualconceptual model.model. Table 4. B2GM package requirements. Table 4. B2GM package requirements. Table 4. B2GM package requirements. Package Requirement Package Requirement Package It supports external legacy data associationsRequirement and views that require BIM from a use-case It supports external legacy data associations and views that require BIM from a use-case perspective.It supports external The external legacy legacy data associationsdata required and for views B2GM that mapping require should BIM from be capable a use-case of perspective. The external legacy data required for B2GM mapping should be capable of beingperspective. uniquely The linked external to thelegacy PK (primarydata required key), for such B2GM as the mapping BIM element should GUID. be capable of being uniquely linked to the PK (primary key), such as the BIM element GUID. B2GM PD Thebeing data uniquely view must linked be to able the to PK define (primary an external key), such legacy as the data BIM item element to link GUID. to the BIM model B2GM PD The data view must be able to define an external legacy data item to link to the BIM model B2GM PD element.The data view must be able to define an external legacy data item to link to the BIM model element. Theelement. value of the associated data item must be changeable into a format that can be used in The value of the associated data item must be changeable into a format that can be used in theThe use value-case. of the associated data item must be changeable into a format that can be used in the use-case. Thethe usefollowing-case. mapping operators must be defined for element mapping. Predefined The following mapping operators must be defined for element mapping. Predefined operatorsThe following can bemapping used to operators create mapping must be rules. defined The formapping element rules mapping. can be Predefinedconfigured B2GM EM operators can be used to create mapping rules. The mapping rules can be configured B2GM EM differentlyoperators can depending be used tono create the use mapping-case. rules. The mapping rules can be configured B2GM EM differently depending on the use-case. differently depending on the use-case. ( ) ( ) ( 𝐵𝐵 𝐺𝐺 ) 𝐸𝐸𝐸𝐸 𝐸𝐸𝐵𝐵 → 𝐸𝐸𝐺𝐺 𝐸𝐸𝐸𝐸 𝐸𝐸𝐵𝐵 → 𝐸𝐸𝐺𝐺 𝐸𝐸𝐸𝐸 𝐸𝐸 → 𝐸𝐸 ISPRS Int. J. Geo-Inf. 2018, 7, 162 12 of 22

Table 4. B2GM package requirements.

Package Requirement It supports external legacy data associations and views that require BIM from a use-case perspective. The external legacy data required for B2GM mapping should be capable of being uniquely linked to the PK B2GM PD (primary key), such as the BIM element GUID. The data view must be able to define an external legacy data item to link to the BIM model element. The value of the associated data item must be changeable into a format that can be used in the use-case. The following mapping operators must be defined for element mapping. Predefined operators can be used to create mapping rules. The mapping rules can be configured differently depending on the use-case. B2GM EM EM(EB → EG)

The following mapping operator must be defined for LOD mapping. B2GM LM LM(LB → LG, LOD)

3.5. B2G PD

3.5.1. Overview B2GM PD supports the method of perspective information representation depending on the specific use cases, such as a facility management (FM). The B2GM PD structure used BPD (BIM perspective definition) from previous related research [21]. BPD research focuses only on the external data mapping required from the BIM perspective. PD is a concept similar to MVD (model view definition) from buildingSMART, but focuses on the definition of the BIM data-binding requirements for mapping BIM into GIS. To define the information perspective for binding and using BIM, GIS and external data sets such as FM data, B2GM PD includes methods to determine which data is needed for the use-case from the BIM model, how to extract and integrate the data between BIM-GIS and an external data set, and how to represent the integrated information. Each method uses data view, logic view and style view.

3.5.2. Mechanism To map the information required from the user perspective into the BIM model, PD should have a BIM model destination in the form of a URL (uniform resource locator). The PD views have been divided into stages of information processing, such as DataView according to perspective, LogicView for information conversion, and StyleView for information expression in order to acquire the information viewed using each perspective.

1. Data view: Defines the data view, which expresses the extracted data as BIM object properties. Properties are combined with BIM objects defined with a primary key (PK), such as objectGUID (object globally unique identifier). Properties are expressed by category, name, value, and type. The property to be extracted is formalized into the categories property name, property value, and property type using metadata and scripts. Types are defined as integer, real, and character string.

Property = {Category, Name, Value, Type}

2. Logic view: As this is the part that extracts and converts data, it is applied using the ETL concept. To process BIM-based FM, the aggregated FM data in the dispersed DB must be extracted, converted, and stored in a form that can be easily used. This process is carried out in the ETL. Through extracting and refining data from various geospatial sources, and converting data and storing it in the DB, the extracted property data can be used to extract or analyze information that supports the perspectives of different project stakeholders. Data must have a defined PK such as objectGUID to be combined with BIM objects. 3. Style view: The style view is the formatting method by which the data is displayed on the user interface. Formatting can be expressed in XML form. For instance, it can include a ISPRS Int. J. Geo-Inf. 2018, 7, 162 13 of 22

formatting operator designed to convert the data to the unit of measurement required from the user’s perspective.

Figure 11 and Table5 show the B2G PD concept. ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 13 of 22

PD +na me +BIM_model_destination: URL

* PD_logic_view PD_style_view PD_data_view +external_data_source: URL +ETL_module: string

* PD_property_style * * PD_property PD_element PD_category +category: string * * +name: string +property: string +objectGUID: GUID +name: string +value: string +formattingOperation: string +type: string

Figure 11. B2G PD concept diagram (UML). Figure 11. B2G PD concept diagram (UML).

Table 5. P2G PD class description. Table 5. P2G PD class description. Class Requirement ClassPerspective definition (PD) manages the Requirement logic view (PD_logic_view), data view PD Perspective definition (PD) manages the logic view (PD_logic_view), data view (PD_data_view) and style PD (PD_data_view) and style view (PD_style_view). view (PD_style_view). PD style view defines how to format the data to understand meaning. PD_style_view PDIt styleincludes view the defines formatting how to format operation the data designed to understand to convert meaning. the data value form from the user PD_style_view It includes the formatting operation designed to convert the data value form from the user perspective, togetherperspective, with the together unit. with the unit. PDPD data data view view which which is similar is similar to data to filters data defines filters whether defines the w datahether set shouldthe data be linkedset should withthe be BIMlinked elementwith the and BIM imported element from and the externalimported database. from Elementsthe external that aredatabase. mapped Elements into data view that have are anmapped object PD_data_viewPD_data_view GUIDinto d (globallyata view unique have identifier). an object To GUID connect (globally external dataunique with identifier). the BIM elements, To connect PK should external be definable data forwith the datathe BIM binding. elements, PK should be definable for the data binding. PDPD logic logic view view defines defines how tohow import to import the data the set fromdata theset external from the database. external database. External data source is defined as the external_data_source of the URL type. The execution path of the PD_logic_view External data source is defined as the external_data_source of the URL type. The PD_logic_view operation module that extracts data from the URL and loads it into the Pset (property set) BIM database is definedexecution in the path ETL_module. of the operation module that extracts data from the URL and loads it into the Pset (property set) BIM database is defined in the ETL_module. 3.6. B2G EM 3.6. B2G EM 3.6.1. Overview 3.6.1. Overview To transform the elements from the BIM model to the GIS model, it is necessary to define the objectTo mapping transform mechanism the elements in terms from of the how BIM to model transform to the from GIS BIM model, to GIS it modelis necessary elements. to define B2G EMthe canobject handle mapping a rule mechanism set related toin theterms object of how mapping to transform mechanism from from BIM the to viewpointGIS model of elements. specific use B2G cases. EM can handle a rule set related to the object mapping mechanism from the viewpoint of specific use 3.6.2.cases.Mechanism B2G EM defines the rule set related to how to transform from BIM model to GIS model elements such3.6.2. asMechanism buildings, floors, walls, windows, etc., as described in Figure 12. B2G EM defines the rule set related to how to transform from BIM model to GIS model elements such as buildings, floors, walls, windows, etc., as described in Figure 12.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 14 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 14 of 22

ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 14 of 22 ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 14 of 22

Figure 12. B2G EM-basedEM-based element transform concept and relationship between B2GM EM and B2G

LM (e.g., dictionary model such as RDBMS). Figure 12. B2G EM-based element transform concept and relationship between B2GM EM and B2G Figure 12. B2G EM-based element transform concept and relationship between B2GM EM and B2G To implementLM (e.g., dictionary the transformation model such as RDBMS). of the elements from the BIM model to the GIS model, the To implementLM (e.g., dictionary the transformation model such as RDBMS). of the elements from the BIM model to the GIS model, the LOD LOD mapping method needs to be considered. For example, a wall in BIM DB can be mapped to a mappingTo method implement needs the to transformation be considered. of For the example, elements afrom wall the in BIM model DB can to bethe mapped GIS model, to a the wall in wall in LOD2To implement or LOD3 the of transformation a GIS model of depending the elements on from the thespecific BIM modeluse-cases. to the For GIS this model, reason, the it is LOD mapping method needs to be considered. For example, a wall in BIM DB can be mapped to a LOD2LOD or LOD3mapping of method a GIS model needs dependingto be considered. on the For specific example, use-cases. a wall in ForBIM this DB reason,can be mapped it is necessary to a to necessarywall into LOD2 consider or LOD3 the method of a GIS formodel transform dependinging onLODs the specificfrom the use BIM-cases. model For this to reason,the GIS it model, is considerwall thein LOD2 method or LOD3 for transforming of a GIS model LODs depending from the on BIM the modelspecific to use the-cases. GIS model,For this which reason, is it B2G is LM, whichnecessary is B2G LM, to consider when we the carry method out for the transform B2G EM.ing LODs from the BIM model to the GIS model, whennecessary we carry to out consider the B2G the EM.method for transforming LODs from the BIM model to the GIS model, Thewhich B2G is B2G EM LM,concept when can we becarry represented out the B2G using EM. UML, as shown in Figure 13. whichThe B2G is B2G EM LM, concept when canwe carry be represented out the B2G usingEM. UML, as shown in Figure 13. The B2G EM concept can be represented using UML, as shown in Figure 13. The B2G EM concept can be represented using UML, as shown in Figure 13. EM_source EM_ruleset EM_source EM_rule EM_source+element: string EM_ruleset +element: string +name: stringEM_ruleset EM_rule +name: stringEM_rule +element: string +description:+name: string string * +name: string *+descriptoin:+name: string string +BIM_model_source:+description: string URL +name: string +description: string * +descriptoin: string +BIM_model_source: URL +PSet_operation:+descriptoin: string {replace, append} EM_destination +GIS_model_destination:+BIM_model_source: URL URL +PSet_operation: {replace, append} EM_destination +GIS_model_destination: URL +PSet_operation: {replace, append} +GIS_model_destination: URL EM_destination +element:+element: string string +element: string

FigureFigure 13. 13. B2G B2G EM EM concept concept diagramdiagram (UML). (UML). FigureFigure 13. 13. B2GB2G EM concept concept diagram diagram (UML). (UML). The mappingThe mapping source source and and destination destination ofof B2GMB2GM EM areare defined defined as asURL URL so sothat that for elementfor element The mapping source and destination of B2GM EM are defined as URL so that for element Theattribute mapping data synchronization source and destination and source of B2GMdata change EM are it can defined propagate as URL to the so destination, that for element as shown attribute attributeattribute data data synchronization synchronization and and source source data changechange it it can can propagate propagate to theto thedestination, destination, as shown as shown data synchronizationin Figure 14. and source data change it can propagate to the destination, as shown in Figure 14. in Figurein Figure 14. 14.

Figure 14. Information connection approach for element data synchronization, propagation-enabled. FigureFigure 14. Information14. Information connection connection approach approach for for element element data data synchronization synchronization,, propagation propagation-enabled.-enabled. Figure 14. Information connection approach for element data synchronization, propagation-enabled.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 15 of 22

3.7. B2G LM

3.7.1. Overview B2G LM defines the method for transforming LODs from the BIM to the GIS model. In the GIS model, there is an LOD schema for representing the level of details, which have the purpose of decreasing the information complexity and improving the information visualization performance, such as rendering. The GIS model LOD schema supports various LODs when representing geometric information, depending on the object on GIS. The LODs defines the visualization mechanism and information, which is similar to the B-Rep structure. However, there is no LOD schema in the BIM model. To represent a BIM object in GIS, the LOD information needs to be extracted from the BIM model. It can be defined by the LOD mapping rule set.

3.7.2. Mechanism Before mapping the LOD from the BIM to GIS model, we should consider the mechanism that determines how to generate LOD information from the BIM model’s geometry. B2G LM defines the mapping rule to transform LODs from the BIM to the GIS model. In the GIS model, there is LOD schema for representing level of details, which have the purpose of decreasing the information complexity and improving the information visualization performance, such as rendering. To generate the BIM model LOD, we should define the LOD information to transform it into the LOD of the GIS model element. This LOD information definition method can be a rule set including simple solid operators such as extrusion, projection, etc., such as the B2G LM ruleset operator. Table6 shows the operator required for the definition of the B2GM LM ruleset. LOD, extracted from BIM, is created from the perspective of the LOD required for GIS, using the LM ruleset operator in Table6. Figure 15 shows the class diagram that defines the LOD mapping (LM) rule.

Table 6. B2G LM rule set operators.

Class Member Description LM_Ruleset name: string Ruleset name definition footprint(el: element): geometry Returns the footprint geometry of Building element el OBB(el: element): OBB Returns OBB (oriented bounding box) of Building element el projection(el: element, base: enum plane{XZ, XY, Returns the geometry2D mapped onto the reference surface that YZ}): geometry2D designates the geometry of Building element el in the enum plane type boundary(g: geometry, base: enum plane{XZ, XY, Creates the geometry gboundary on the reference surface designated in YZ}): geometry2D the base, and returns the geometry2D extrude(g: geometry2D, v: vector3D, height: Returns geometry2D g to the geometry protruded as much as the real): geometry height, using the vector direction v Extracts only the outside surface of geometry g, then returns exterior(g: geometry): geometry LM_Rule to geometry interior(g: geometry): geometry Extracts only the inside surface of geometry g, then returns to geometry Returns only the void-type elements of the Building element. VOID(e: element): element The void-type elements refer to the windows, doors, and other openings. Returns the results of the union operation of geometry g1 and g2 union(g1: geometry, g2: geometry): geometry to geometry Returns the results of the geometry g1 and g2subtraction operation subtract(g1: geometry, g2: geometry): geometry to geometry Returns the results of the geometry g1 and g2intersection operation intersect(g1: geometry, g2: geometry); geometry to geometry x_direction: vector3D Member that defines OBB’s X axis OBB y_direction: vector3D Member that defines OBB’s Y axis extent: vector3D Member that defines OBB’s width, depth, and height vector3D v[3]: real Defines the 3D vector elements The member that can define the 2D shape should be geometry2D - implemented The member that can define the 3D shape should be geometry3D - implemented ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 16 of 22

ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 16 of 22 x_direction: vector3D Member that defines OBB’s X axis y_direction: vector3D Member that defines OBB’s Y axis OBB x_direction: vector3D Member that defines OBB’s X axis y_direction: vector3D MemberMember thatthat definesdefines OBB’sOBB’s Ywidth, axis depth, and OBB extent: vector3D Memberheight that defines OBB’s width, depth, and extent: vector3D vector3D v[3]: real heightDefines the 3D vector elements The member that can define the 2D geometry2Dvector3D v[3]: real Defines- the 3D vector elements Theshape member should that be implemented can define the 2D geometry2D The member that can define the 3D - ISPRSgeometry3D Int. J. Geo-Inf. shape2018, 7should, 162 be implemented - 16 of 22 Theshape member should that be implemented can define the 3D geometry3D - shape should be implemented LM_Rule

+name: string LM_Rule +name:+footprint(el: string element): geometry OBB LM_Ruleset +OBB(el: element): OBB * +footprint(el:+projection(g: element): geometry, geometry base: enum plane{XZ, XY, YZ}): geometry +x_direction:OBB vector3D +y_direction: vector3D +name:LM_Ruleset string +OBB(el:+extrude(g: element): geometry2D, OBB v: vector3D, height: real): geometry * +projection(g:+exterior(g: geometry): geometry, geometry base: enum plane{XZ, XY, YZ}): geometry +x_direction:+extent: vector3D vector3D +name: string +extrude(g:+VOID(g: geometry): geometry2D, element v: vector3D, height: real): geometry +y_direction: vector3D +exterior(g:+union(g1: geometry, geometry): g2: geometry geometry): geometry +extent: vector3D +VOID(g:+subtract(g1: geometry): geometry, element g2: geometry): geometry +union(g1:+intersect(g1: geometry, geometry, g2: g2:geometry): geometry): geometry geometry +subtract(g1: geometry, g2: geometry): geometry +intersect(g1: geometry, g2: geometry): geometry

BIM_model element geometry B-rep * * BIM_model element geometry B-rep * *

geometry2D geometry3D

geometry2D geometry3D Figure 15. B2G LM concept diagram (UML). Figure 15. B2G LM concept diagram (UML). Figure 15. B2G LM concept diagram (UML). By using the rule set and operators, the method for generating each LODs of the GIS element By using the rule set and operators, the method for generating each LODs of the GIS element fromBy the using geometr the icrule representation set and operators, of the BIMthe methodgeometry for can generat be defined.ing each LODs of the GIS element from the geometric representation of the BIM geometry can be defined. from Inthe example, geometr toic definerepresentation LOD from of IFCthe toBIM CityGML geometry semantically, can be defined. a set of mapping rules is required. In example, to define LOD from IFC to CityGML semantically, a set of mapping rules is required. The Inrule example, set for toB2G define LM LOD consists from ofIFC rules to CityGML, including semantically, operators asuch set of as mapping simple rulessolid is modelling required. The rule set for B2G LM consists of rules, including operators such as simple solid modelling functions Thefunctions rule setand for set B2Goperators LM consists(union ∪, of intersect rules, including∩), as described operators in Figure such 16.as simple solid modelling and set operators (union ∪, intersect ∩), as described in Figure 16. functions and set operators (union ∪, intersect ∩), as described in Figure 16.

Figure 16. B2G LM rule set concept. Figure 16. B2G LM rule set concept. 4. Case Studies and Discussion Figure 16. B2G LM rule set concept. 4. Case Studies and Discussion 4. CaseB2GM, Studies which and supports Discussion BIM-GIS model integration, has thus far been described in terms of its concept,B2GM, structure, which supportsand operation BIM-GIS mechanism. model integration, B2GM is has not thus a perfect far been solution described that in supports terms of theits B2GM, which supports BIM-GIS model integration, has thus far been described in terms of concept,integration structure, of heterogeneous and operation models. mechanism. As mentioned B2GM earlier,is not ait perfectis not esolutionasy to perfectlythat supports map andthe its concept, structure, and operation mechanism. B2GM is not a perfect solution that supports the integration of heterogeneous models. As mentioned earlier, it is not easy to perfectly map and integration of heterogeneous models. As mentioned earlier, it is not easy to perfectly map and integrate

heterogeneous models, for various reasons. Instead of perfect BIM-GIS integration, it may be practical to define the integration level to make it fit into use-cases before system implementation, and to define the integration mapping mechanism. Together with the integration requirements considered in B2GM, to derive the BIM-GIS integration level and considerations, the existing BIM-GIS integration solutions were examined in this study in ISPRS Int. J. Geo-Inf. 2018, 7, 162 17 of 22 terms of their strengths and weaknesses, and the difference between these and the proposed B2GM [1] was analyzed. Through the survey of previous literature, individual studies were surveyed. This case study targets solutions that support the BIM-GIS linkage or integration method from the platform viewpoint. Thus, the considerations for BIM-GIS integration were also examined. Table7 shows a comparison of the BIM-GIS integration solutions thus far studied.

Table 7. Comparison of the BIM-GIS integration technology characteristics.

No Solution Description Outline: A BIM-GIS operation platform that was studied by KICT (Korea Institute of Civil Engineering and Building Technology). BIM-GIS Characteristics: Demonstration of lightweight BIM and GIS 3D shape information. Support for lightweight technology for the S1 platform individual LOD of BIM. BIM/GIS object spatial inquiry is possible using coordinate values [22]. Limitations: Data utilization perspective, and the external-data binding implementation method is fixed; focused on demonstration. There are no LoD and coordination mapping definition methods. Outline: A BIM-GIS middleware software for data mining that has been studied by KICT. Characteristics: The data mining function designed to extract information from BIM/GIS is integrated into the middleware. When extracting external data from the perspective of the use of such data, definition and the user’s own use and reuse are S2 BIM cube possible [23]. Limitation: The elements that map BIM into GIS, and such mapping methods, are limited, and hard coding is required, making it lack scalability. Outline: Developed by ESRI, a commercial program for support service development. Characteristics: Provides convenient API for implementing smart-city spatial information services; can import commercial BIM S3 CityEngine models such as Autodesk Revit as they are Limitations: The BIM-GIS integration process is not standardized. Data can be missed in the process of converting BIM into a CityEngine-supportive format [24]. Outline: Developed by Autodesk, a program for use in infrastructure. Characteristics: Facilitates road and other infrastructure modeling; can import BIM models of self-developed software. S4 Infraworks Limitation: The BIM-GIS integration process is already being implemented by the developer, making it difficult for the user to use it according to his requirements. The Infraworks is one way to connect BIM and GIS by an export/ import process of the models [25]. Outline: Developed by Safe software, an ETL (extract, transform, and load) middleware. Characteristics: Supports the ETL of geographical information shape; supports the user’s own BIM-GIS integration development. S5 FME Limitations: The development of the new data schema based on FME requires a significant amount of time and efforts [26]. Also, The BIM-GIS data integration process is not standardized. Apart from the purchase of software, ETL process development costs for integration may be incurred separately. Outline: BIM server developed as an open source by bimserver.org. Characteristics: Open source; the implementation process has been disclosed; can support the IF standard format and can make S6 BIMserver complex inquiries about the BIM shape, attributes, and phase information; a CityGML ADE (application domain extend) method that considers BIM information schema extension [27]. Limitations: Lacks GIS data and BIM-GIS integration function support.

The following considerations can be confirmed from the overall research trends and related studies: C1—The model integration levels may be different according to the use-case. The types of BIM-GIS integration data are varied to support individual BIM-GIS integration solutions. This is because only the data required in the use cases that individual solutions intend to support are integrated. C2—Inter-model integration can be considered from the lowest level, shape, and model integration to high-level semantic integration. C3—Model integration entails diverse overhead costs. For instance, the integrated model may cause problems such as heaviness, slow processing, data loss, unnecessary data input, and re-work costs. C4—Several commercial software solutions involve the model integration process as a black box. It is difficult for the users, however, to guess the data integration process occurring inside a black box, and the corresponding integrated model quality level. C5—If the heterogeneous-model integration method and process are opened as a white box and can be standardized, they can be constructed and reused as libraries in similar model integration projects. In addition, this can facilitate the checking and management of the quality of the model integration output. If this is not standardized, costs will continue to be incurred to execute the detailed design required for model integration and to implement the solution. C6—Model integration does not necessarily mean the method of physically combining data at the schema level. For instance, linkage models such as topology manage only the data source references required for model integration, and filter the necessary data used; thus, it can reduce the efforts to ISPRS Int. J. Geo-Inf. 2018, 7, 162 18 of 22

ensure data consistency and synchronization between models. Physical model integration does not need to handle this process in the system, thus facilitating data management and utilization, but should handle data consistency and synchronization problems. B2GM has benefits related to each consideration, as shown in Table8.

Table 8. B2GM benefits and solutions related to consideration.

No Consideration Benefit and Solution Using B2GM PD and EM, specify the method of integrating BIM-GIS from the use B1 C1 case perspective B2 C2 Using B2GM EM, define element integration levels B3 C3 Using B2GM LM, define the LoD integration method B2GM is a white box-based integration, standardized to define integration B4 C4, C5 methods, transparently. The B2GM PD supports a method of integrating only the needed data for use. By using B2GM PD, unnecessary data management costs are lowered in the integrated model. In B5 C6 addition, data synchronization is considered by specifying the data reference source by using URL.

The heterogeneous-model integration level should be able to be defined on a use-case-driven basis. High-level model integration, unnecessary for use-cases, may entail unnecessary costs and cause unnecessary problems. For instance, If BIM-GIS integration is required for the development of spatial-information services for the operation of a smart city, the integration level should be defined in the requirements before the integration process is executed. Before implementing the integrated model output, the user should be able to forecast it and to inspect the quality not only of the model ISPRS Int.integration J. Geo-Inf. 2018 output, 7, x but FOR also PEER of the REVIEW integration process. 19 of 22 From this perspective, the following illustrates the BG-IL (BIM-GIS integration level) division. In BG-IL, the upper level must includeGIS— theSite, lower Terrain, level. Building, For instance, Alignment in urban element facility (Road, management Bridge, Tunnel) Relationship (Topology) BG-IL4use cases, the facility management historyContain, attribute Aggregation, is more important Dependency, than Generalization the shape information, as only certain casesIntegration may require (RI) shape information. In this case, efforts to integrate the shape information Semantic Information Ontology Directionary, Semantic Triple Model in RDF (Resource BG-IL5are not necessarily needed. Figure 17 shows the BG-IL expression, and Table9 shows examples of implementableIntegration use cases (SIM) according to BG-IL.Description Framework), Linkage Model with Legacy Dataset

BIM BG-IL L5 Semantic Information Integration

L4 Relationship Integration

L3 Element Data Integration

L2 Geometry Model Integration Coordinate Reference System L1 Integration GIS

FigureFigure 17. 17. B2GB2G LM rulerule set set and and concept. concept.

Table 10 shows the use-cases available in BG-IL, but there may be a large deviation in the requirements for the information required between the use-cases at each level. For instance, the corresponding related historical information is needed to analyze and manage the facility energy. With only the basic attributes of building elements (e.g., name, area, volume, boundaries, etc.), such use-cases cannot be implemented.

Table 10. BG-IL use-case examples.

Level Possibility Use Cases BG-IL1 CRS mapping CRS mapping considering element position and orientation BG-IL2 Visualization City visualization, rendering and viewing, landscape analysis City facility management(FM), energy management(EM), construction BG-IL3 Management management, life-cycle cost analysis(LCCA) Query and Navigation service, evacuation simulation, element relationship-based BG-IL4 simulation information query and navigation from city to building facility scale Semantic information query, data source reference identification and BG-IL5 Knowledge synchronization, knowledge development and management

BG-IL does not mean the completeness of model integration. As mentioned, the level of integration should be properly defined according to the use-case perspective. In some use-cases, element data integration may be more important than geometry and coordinate reference system integration. For example, in applications such as facility management, attribute information is more important than geometry information. To check the level of integration, the reference cases in Table 7 were analyzed. For the analysis, 34 practitioners with BIM or GIS experience for more than five years were interviewed. The interviewed occupations were city, architecture and maintenance. As the results show, most solutions related to the cases have a lower level of relationship and semantic integration. In general, relationship and semantic integration are more difficult than coordinate system and geometry integration. This is because the relationship and semantics have a great deal of variability depending on the use perspective. Developing an integrated model that can represent all use perspectives is very difficult. This is why semantic integration is defined as the highest level of integration. Also, this result shows that the BIM-GIS integrated model use case is still biased toward a specific purpose. In addition, the effects on B2GM was also investigated. The participants in the interview responded that B2GM was beneficial in the order of LoD, element, legacy data, and use perspective integration.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 19 of 22

Table 9. BG-IL definition.

Level Indicator Information LOD Coordinate Reference System Integration Local Coordinate Reference System (CRS), Building BG-IL1 (CRSI) CRS, Site CRS, World CRS (WGS84, IRTF, CRS80 ... ) 2D geomertry, 3D geometry, CSG (Constructive Solid BG-IL2 Geometry Model Integration (GMI) Geometry), B-Rep (Boundry Representation), Parametric Geometry Model BIM—Structrual element (Column, Slab), Architectural element (Wall, Door, Floor, Ceiling, BG-IL3 Element Data (Property) Integration (EDI) Window, Roof) GIS—Site, Terrain, Building, Alignment element (Road, Bridge, Tunnel) BG-IL4 Relationship (Topology) Integration (RI) Contain, Aggregation, Dependency, Generalization Ontology Directionary, Semantic Triple Model in BG-IL5 Semantic Information Integration (SIM) RDF (Resource Description Framework), Linkage Model with Legacy Dataset

Table 10 shows the use-cases available in BG-IL, but there may be a large deviation in the requirements for the information required between the use-cases at each level. For instance, the corresponding related historical information is needed to analyze and manage the facility energy. With only the basic attributes of building elements (e.g., name, area, volume, boundaries, etc.), such use-cases cannot be implemented.

Table 10. BG-IL use-case examples.

Level Possibility Use Cases BG-IL1 CRS mapping CRS mapping considering element position and orientation BG-IL2 Visualization City visualization, rendering and viewing, landscape analysis City facility management(FM), energy management(EM), construction BG-IL3 Management management, life-cycle cost analysis(LCCA) Query and Navigation service, evacuation simulation, element relationship-based BG-IL4 simulation information query and navigation from city to building facility scale Semantic information query, data source reference identification and BG-IL5 Knowledge synchronization, knowledge development and management

BG-IL does not mean the completeness of model integration. As mentioned, the level of integration should be properly defined according to the use-case perspective. In some use-cases, element data integration may be more important than geometry and coordinate reference system integration. For example, in applications such as facility management, attribute information is more important than geometry information. To check the level of integration, the reference cases in Table7 were analyzed. For the analysis, 34 practitioners with BIM or GIS experience for more than five years were interviewed. The interviewed occupations were city, architecture and maintenance. As the results show, most solutions related to the cases have a lower level of relationship and semantic integration. In general, relationship and semantic integration are more difficult than coordinate system and geometry integration. This is because the relationship and semantics have a great deal of variability depending on the use perspective. Developing an integrated model that can represent all use perspectives is very difficult. This is why semantic integration is defined as the highest level of integration. Also, this result shows that the BIM-GIS integrated model use case is still biased toward a specific purpose. In addition, the effects on B2GM was also investigated. The participants in the interview responded that B2GM was beneficial in the order of LoD, element, legacy data, and use perspective integration. However, respondents are expected to benefit from data integration similar to the results in Figure 18. ISPRS Int. J. Geo-Inf. 2018, 7, x FOR PEER REVIEW 20 of 22

ISPRSHowever, Int. J. Geo-Inf.respondents2018, 7, 162 are expected to benefit from data integration similar to the results in Figure20 of 22 18.

4.5 CRSI 4.5 4.3 4.09 4.1 4 3.9 3.5 3.71 3.66 3.7 SIM EDI 3.5 3.43 3 3.3 3.16 2.5 3.1 2.9 2.7 2.5 CRSI EDI GMI RI SIM RI GMI Figure 18. BIM-GIS model integration level survey results. Figure 18. BIM-GIS model integration level survey results. Another aspect of the results can mean that users are exploring how to use the BIM-GIS integrationAnother model, aspect or of that the results the focus can meanof the thatuse userscase is are one exploring-sided due how to to the use lack the BIM-GISof integration integration level. model,Standard ors thatorganization the focuss ofsuch the as use ISO/ caseTC211 is one-sided will discuss due these to the issues lack ofregarding integration BIM level.-GIS i Standardsntegration organizationsmethod development such as, ISO/TC211such as B2GM. will discuss these issues regarding BIM-GIS integration method development, such as B2GM. 5. Conclusions 5. Conclusions Decision-making based on BIM-GIM use-cases such as smart city services and city integration modelDecision-makings is becoming increasingly based on BIM-GIM important use-cases. This study such proposes as smart a method city services designed and to city clearly integration define modelsthe BIM is-GIS becoming integration increasingly process. important. The unclear This integration study proposes of different a method-type designeds of model to method clearly defines may thecause BIM-GIS the user integration to hesitate process. to use the The outputs unclear of integrationintegration. of B2GM different-types defines the of integration model methods conditions may causeand process the useres between to hesitate different to use the-type outputs models of using integration. a formal B2GM method defines, so as theto create integration a white conditions box. This andapproach processes helps between the user different-typeto check that nothing models has using been a omitted formal method,before using so as the to integrated create a white model. box. In Thisaddition, approach the possibility helps the user can tobe checkreduced that that nothing the object has been information omitted before required using for the the integrated execution model. of the Inuse addition,-cases may the not possibility be obtained can be or reducedthat wrong that services the object may information be executed required due to for noise. the execution of the use-casesTo handle may not the be problems obtained surrounding or that wrong the services integration may beof executedBIM (building due to information noise. modeling) and ToGIS handle (geographic the problems information surrounding system) heterogeneous the integration mod of BIMels, the (building relevant information research trends modeling) were andsurveyed GIS (geographic and their characteristics information system) were analyzed. heterogeneous The methods models, of the schema relevant integration, research trends extension, were surveyedlinkage, etc. and have their their characteristics respective limitations, were analyzed. and it The is not methods easy to of integrate schema heterogeneous integration, extension, models. linkage,According etc. to have the u theirse-case, respective the necessary limitations, model andintegration it is not levels easy toand integrate procedures heterogeneous may vary. BIM models.-GIS Accordingconceptual to mapping the use-case, (B2GM), the necessary instead of model integrating integration heterogeneous levels and procedures model schemas, may vary. attempts BIM-GIS to conceptualstandardize mappingthe BIM-GIS (B2GM), model instead integration of integrating process to heterogeneousmake it fit the modeluser’s requirements schemas, attempts from the to standardizeuse-case perspective. the BIM-GIS B2GM model divides integration the heterogeneous process to makeprocess it fitinto the PD, user’s EM, requirementsand LM, and links from and the use-casemaps BIM perspective. models on B2GMthe city divides scale. the heterogeneous process into PD, EM, and LM, and links and mapsThe BIM case models analysis on the and city discussion scale. analyzed the research trends, derived considerations for heterogeneousThe case analysis-model integration and discussion based analyzed on the experience the research gained trends, from derived the B2GM considerations research, and for heterogeneous-modeldefined the integration integration level (i.e., based BG-IL). on In the addition, experience examples gained fromof applicable the B2GM use research,-cases according and defined to thethe integration level level were (i.e., presented. BG-IL). In It addition, was thus examples confirmed of that applicable clearer m use-casesodel integration according goals to and the integrationstrategies need level to were be derived. presented. It was thus confirmed that clearer model integration goals and strategiesIn the need future, to be considering derived. the insights obtained from this study, research will be conducted on a methodIn the of future,clearly consideringdescribing the the BIM insights-GIS obtainedmodel integration from this study,levels and research information will be conductedused. It is onthus a methodexpected of that clearly the model describing integration the BIM-GIS levels modeland level integration of detail levels (LOD) and of the information integrated used. output It is at thus the expectedrequirement that definition the model level integration will be clearly levels described, and level of and detail that (LOD)the quality of the of integrated information output models at can the requirementbe properly managed. definition level will be clearly described, and that the quality of information models can be properly managed.

Acknowledgments: This research was supported by a grant (18AUDP-B127891-02) from the Architecture & Urban Development Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government.

ISPRS Int. J. Geo-Inf. 2018, 7, 162 21 of 22

Conflicts of Interest: The authors declare no conflicts of interest.

References

1. International Organization for Standardization. ISO/AWI 19166 Geographic Information—BIM to GIS Conceptual Mapping (B2GM); ISO TC211; International Organization for Standardization: Geneva, Switzerland, 2016. 2. Karan, E.P.; Irizarry, J. Developing a spatial data framework for facility management supply chains. In Construction Research Congress 2014@, Construction in a Global Network; ASCE: Reston, VA, USA, 2014; pp. 2355–2364. 3. Beetz, J.; Coebergh, W.; Botter, R.; Zlatanova, S.; De Laat, R. Interoperable data models for infrastructural artefacts—A novel IFC extension method using RDF vocabularies exemplified with quay wall structures for harbors. In eWork and eBusiness in Architecture, Engineering and Construction; CRC Press: Boca Raton, FL, USA, 2014; p. 354. 4. Cruz, I.F.; Sunna, W.; Chaudhry, A. Semi-automatic ontology alignment for geospatial data integration. In Geographic Information Science; Springer: Berlin/Heidelberg, Germany, 2004; pp. 51–66. 5. Peachavanish, R.; Karimi, H.A.; Akinci, B.; Boukamp, F. An ontological engineering approach for integrating CAD and GIS in support of infrastructure management. Adv. Eng. Inform. 2006, 20, 71–88. [CrossRef] 6. Hor, A.H.; Jadidi, A.; Sohn, G. BIM-GIS integrated geospatial information model using semantic web and RDF graphs. ISPRS Ann. Photogramm. Remote Sens. Spat. Inf. Sci. 2016, 3, 73. [CrossRef] 7. The Web Site for City GML: An Information Model for Exchange and Storage of Virtual 3D City Models. 2006. Available online: http://www.citygml.org/ (accessed on 24 April 2018). 8. Hagedorn, B.; Döllner, J. High-Level Web Service for 3D Building Information Visualization and Analysis. In Proceedings of the 15th Annual ACM International Symposium on Advances in Geographic Information Systems, Seattle, WA, USA, 7–9 November 2007; p. 8. 9. Nour, M. Manipulating IFC Sub-models in Collaborative Teamwork Environments. In Proceedings of the 24th CIB W-78 Conference on Information Technology in Construction, Maribor, Slovenia, 27–29 June 2007. 10. Li, Y. Development Architecture for Industrial Data Management; KTH Royal Institute of Technology: Stockholm, Sweden, 2013. 11. Scherer, R.J. Product-model-based Collaboration. In Proceedings of the 24th CIB W78 Conference, Maribor, Slovenia, 27–29 June 2007. 12. Schaller, J.; Gnaedinger, J.; Reith, L.; Freller, S.; Mattos, C. GeoDesign: Concept for Integration of BIM and GIS in Landscape Planning. J. Digit. Landsc. Archit. 2017, 2, 102–112. 13. El-Mekawy, M.; Östman, A.; Hijazi, I. An evaluation of IFC-CityGML unidirectional conversion. Int. J. Adv. Comput. Sci. Appl. 2012, 3, 159–171. [CrossRef] 14. Sebastian, R.; Böhms, M.; Van den Helm, P. BIM and GIS for Low-Disturbance Construction. In Proceedings of the 13th International Conference on Construction Applications of Virtual Reality, London, UK, 30–31 October 2013. 15. Isikdag, U.; Underwood, J.; Aouad, G. An investigation into the applicability of building information models in a geospatial environment in support of site selection and fire response management processes. Adv. Eng. Inform. 2008, 22, 504–519. [CrossRef] 16. Pickard, R. ArcView Shape Files: A Read/Write OCX, Help File. 2004. Available online: http://arcscripts. esri.com/details.asp?dbid=11810/ (accessed on 24 April 2018). 17. Amirebrahimi, S.; Rajabifard, A.; Mendis, P.; Ngo, T. A data model for integrating GIS and BIM for assessment and 3D visualisation of flood damage to a building. Locate 2015, 15, 10–12. 18. Open Geospatial Consortium. Available online: https://www.citygml.org/files/CityGML_2_0_0_UML_ diagrams.pdf (accessed on 24 April 2018). 19. Johnson, R.; Vlissides, J.; Helm, R.; Gamma, E. Design Patterns: Elements of Reusable Object-Oriented Software; Pearson Education; Addison-Wesley: Boston, MA, USA, 1994. 20. Löwner, M.-O.; Gröger, G.; Benner, J.; Biljecki, F.; Nagel, C. Proposal for a new LOD and multi-representation concept for CityGML. Remote Sens. Spat. Inf. Sci. 2016, 4, 3–13. [CrossRef] 21. Kang, T.W.; Choi, H.S. BIM perspective definition metadata for interworking facility management data. Adv. Eng. Inform. 2015, 29, 958–970. [CrossRef] ISPRS Int. J. Geo-Inf. 2018, 7, 162 22 of 22

22. Kang, T.W.; Hong, C.H. A study on software architecture for effective BIM/GIS-based facility management data integration. Autom. Constr. 2015, 54, 25–38. [CrossRef] 23. Kang, T.W.; Choi, H.S. BIM-based data mining method considering data integration and function extension. KSCE J. Civ. Eng. 2017, 1–12. [CrossRef] 24. Dimopoulou, E.; Tsiliakou, E.; Kosti, V.; Floros, G.; Labropoulos, T. November. Investigating integration possibilities between 3D modeling techniques. In Proceedings of the 9th 3DGeoInfo Conference, Dubai, UAE, 11–13 November 2014; pp. 1–16. 25. Moghadam, S.T.; Lombardi, P.; Mutani, G.; Osello, A.; Ugliotti, F.M. BIM-GIS modelling for sustainable urban development. In Proceedings of the Towards Post-Carbon Cities (SBE16), Turin, Italy, 18–19 February 2016; pp. 18–19. 26. Kim, H.; Chen, Z.; Cho, C.S.; Moon, H.; Ju, K.; Choi, W. Integration of BIM and GIS: Highway cut and fill earthwork balancing. In Proceedings of the Computing in Civil Engineering, Austin, TX, USA, 21–23 June 2015; pp. 468–474. 27. Deng, Y.; Cheng, J.C.; Anumba, C. Mapping between BIM and 3D GIS in different levels of detail using schema mediation and instance comparison. Autom. Constr. 2016, 67, 1–21. [CrossRef]

© 2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).