CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> There is a growing interest in the integration of BIM and GIS. However, most of the research is focused on importing BIM data in GIS applications and vice versa. Real integration of BIM and GIS is using the strong parts of the GIS technology in BIM, and of course the strong parts from BIM technology in GIS. In this paper a mix of strong parts from both worlds is integrated in a single project. The paper describes the development of a CityGML extension called GeoBIM to get semantic IFC data into a GIS context. The conversion of IFC to CityGML (including the GeoBIM extension) is implemented in the open source Building Information Modelserver. <s> BIB001 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Virtual 3D city models are integrated complex compositions of spatial data of different themes, origin, quality, scale, and dimensions. Within this paper, we address the problem of spatial compatibility of geodata aiming to provide support for ad-hoc integration of virtual 3D city models including geodata of different sources and themes like buildings, terrain, and city furniture. In contrast to related work which is dealing with the integration of redundant geodata structured according to different data models and ontologies, we focus on the integration of complex 3D models of the same representation (here: CityGML) but regarding to the geometric-topological consistent matching of non-homologous objects, e.g. a building is connected to a road, and their geometric homogenisation. Therefore, we present an approach including a data model for a Geodata Join and the general concept of an integration procedure using the join information. The Geodata Join aims to bridge the lack of information between fragmented geodata by describing the relationship between adjacent objects from different datasets. The join information includes the geometrical representation of those parts of an object, which have a specific/known topological or geometrical relationship to another object. This part is referred to as a Connector and is either described by points, lines, or surfaces of the existing object geometry or by additional join geometry. In addition, the join information includes the specification of the connected object in the other dataset and the description of the topological and geometrical relationship between both objects, which is used to aid the matching process. Furthermore, the Geodata Join contains object-related information like accuracy values and restrictions of movement and deformation which are used to optimize the integration process. Based on these parameters, a functional model including a matching algorithm, transformation methods, and conditioned adjustment methods can be established in order to facilitate ad-hoc 3D homogenisation for consistent 3D city models. <s> BIB002 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> This article describes a research project that realised a national standard for 3D geo-information. The standard was developed as part of a pilot in which more than 65 private, public and scientific organisations collaborated to analyse and push 3D developments in the Netherlands run between March 2010 and June 2011. The 3D standard was established through several steps. First, a comparison between the existing 3D computer-aided design and GIS standards was carried out that selected the Open Geospatial Consortium OGC standard CityGML as the optimal 3D standard to align to. Second, the equivalent concepts in CityGML and the existing national standard for large-scale topography Information Model Geography [IMGeo] were identified. Third, IMGeo was extended to 3D following the principles of CityGML Application Domain Extensions. The model was tested by applying it to real data. Based on the experiences of this pilot, this article proposes a framework of guidelines and principles for extending CityGML for national purposes, deduced from the modelling experiences. This is a unique contribution since experiences on extending CityGML are new and not well described in the OGC CityGML specifications. Finally, this article presents the change requests CRs which have been submitted to OGC to make the CityGML standard more suited for integration with existing 2D topographic information models. The CRs were formulated based on experiences from developing this nationwide 3D standard. <s> BIB003 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Recently a national 3D standard was established in the Netherlands as a CityGML Application Domain Extension (called IMGeo). In line with the Dutch practice of modeling geo-information, the ADE is devel- oped using a model driven approach. The classes are designed in UML and automatically mapped to GML schema. The current OGC CityGML specification does not provide rules or guidance on correctly modeling an ADE in UML. This article fills this gap by studying how CityGML can be extended for spe- cific applications starting from the UML diagrams. Six alternatives for modeling ADEs in UML are intro- duced and compared. The optimal alternative is selected and applied to obtain the national 3D standard. The approach was extensively discussed with international experts, who were members of both SIG3D and other working groups. As a consequence the approach was adopted by the SIG3D, the Special Inter- est Group 3D which, among other things, work on the 3D standard CityGML in cooperation with OGC. Therefore the approach contains many issues that can be generalized and reused by future domain exten- sions of CityGML. To further support this, the article formulates a model-driven framework to model CityGML ADEs. Open issues are described in the conclusions. <s> BIB004 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> The INSPIRE Data Specification on Buildings addressed in Annex III of the INSPIRE Directive is intended to meet the needs of use cases which involve buildings and other constructions in areas of application such as environment, security, infrastructure, spatial planning, census and public awareness. The Data Specification covers 2D as well as 3D representations of buildings and has strongly been influenced by CityGML, an application independent Geospatial Information Model for semantic 3D city and landscape models. CityGML is an international standard of the OGC and represents 3D geometry, 3D topology, semantics and appearance of buildings in five levels of detail. CityGML is both a data model defined in UML and an exchange format based on the international OGC GML standard. CityGML has been defined as a base model. For enriching this model with application specific data, the concept of Application Domain Extensions (ADEs) is provided by CityGML. Since many years CityGML is extensively employed in various projects worldwide and there are many software tools which support CityGML. However, these tools cannot be used straightaway with INSPIRE building data, since the INSPIRE encoding differs from the CityGML encoding. To enable the use of INSPIRE building data with CityGML tools, INSPIRE ADEs for the 3D profiles have been defined using UML. Furthermore, XML schemas of the ADEs have automatically been derived from the UML definitions by suitable encoding tools. These INSPIRE ADEs provide a practicable alternative to the native INSPIRE encoding, enabling INSPIRE building data to be identified and processed by currently available CityGML software. Furthermore ADEs for other applications such as facility management or noise emission simulation can be combined with the INSPIRE ADEs. The presentation will provide details on the INSPIRE ADEs and derived XML schemas and give examples for the use of INSPIRE building data encoded according to the ADEs. <s> BIB005 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> In many traffic and transportation models, data structures used for input and output do not adhere to common data formats. Consequently, many different architectures are used concurrently with little or no relation to the geographic information systems that carry and provide these data. As a result, the exchange of data between traffic models is often cumbersome. To improve the usability of geo-information, this paper studies the establishment of a standard for the transport domain that aligns to an existing international standard for geo-information, i.e. CityGML (Geographical Markup Language for city and landscape models). The Open Geospatial Consortium (OGC) established this standard as a generic standard for 3D modelling of topographic features. In this paper we propose a standard for traffic and transport modelling in the form of a CityGML Application Domain Extension (ADE). First, we analyse the data requirements for traffic and transportation models and present a description of objects that are necessary to build the traffic infrastructure for traffic models. By comparing these data with the CityGML data model concepts, we show a strong semantic match between concepts required in the transport domain and CityGML. Consequently, defining a standard for input data in the transport domain that aligns to CityGML will make it possible to reuse geo-information that was acquired for other purposes. This paper also shows the possibilities to extend CityGML to support properties that are specific to the transport domain. Further research will focus on further detailing the CityGML ADE for Transport and testing it in traffic and transportation models <s> BIB006 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Construction and maintenance activities of bridges often bring negative impacts to the urban environment in terms of disturbance, traffic jams and disruptions, noise, dust, and air pollution. Lack of coordination between the stakeholders in strategic, tactical and operational construction planning process has been identified as a key factor behind these negative impacts. Attempts to solve this issue critically depend on an effective interoperability between ICT tools from the building domain (based on Building Information Model or BIM) and the urban planning domain (based on three dimensional Geographical Information System or 3D GIS). Research on the interoperability between BIM and GIS requires knowledge of Open BIM as well as Open GIS and their interconnection. Unfortunately, Open BIM and Open GIS have been developed separately and they have pursued different standards and technologies. Open BIM for civil infrastructure projects is still limited, especially due to the fact that the IFC open standard currently targets the building sector. Open GIS mainly relies on the use of GML/CityGML standard. This paper focuses on research to develop a solution for the interoperability of BIM and GIS, especially for the purpose of low-disturbance construction. It reports the on-going EU FP7 collaborative research project PANTURA. The preliminary achievements include a prototype solution that consists of: an architecture for the integration solution between BIM and GIS data and tools; an Application Domain Extension (ADE) that connects BIM data from the bridge with the computational parameters on disturbance in a GIS-based planning tool Urban Strategy; a configuration of open-source Deegree 3D model server; and a query interface between the model server and the decision-support tool. The prototype solution is verified using two case studies: on-site assembly of a new bridge on La Palma island, Spain; and refurbishment of existing bridges in Rotterdam, the Netherlands. <s> BIB007 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> The rapid evolution of integral schemes, accounting for geometric and semantic data, has been importantly motivated by the advances in the last decade in mobile laser scanning technology; automation in data processing has also recently influenced the expansion of the new model concepts. This paper reviews some important issues involved in the new paradigms of city 3D modelling: an interoperable schema for city 3D modelling (cityGML) and mobile mapping technology to provide the features that composing the city model. This paper focuses in traffic signs, discussing their characterization using cityGML in order to ease the implementation of LiDAR technology in road management software, as well as analysing some limitations of the current technology in the labour of automatic detection and classification. <s> BIB008 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> In infrastructural projects, communication as well as information exchange and (re-)use in and between involved parties is difficult. Mainly this is caused by a lack of information harmonisation. Various specialists are working together on the development of an infrastructural project and all use their own specific software and definitions for various information types. In addition, the lack of and/or differences in the use and definition of thematic semantic information regarding the various information types adds to the problem. Realistic 3D models describing and integrating parts of the earth already exist, but are generally neglecting the subsurface, and especially the aspects of geology and geo-technology. This paper summarises the research towards the extension of an existing integrated semantic information model to include surface as well as subsurface objects and in particular, subsurface geological and geotechnical objects. The major contributions of this research are the definition of geotechnical objects and the mechanism to link them with CityGML, GeoSciML and O&M standard models. The model is called 3D-GEM, short for 3D Geotechnical Extension Model. Innovative model (3D-DEM) for semantic and geometric properties of geo-technical data.First model to reflect needs of users involved in infrastructural projects.The model can be easily integrated with above surface data via CityGML.The models provide links to other geological models GeoSciML and O&M. <s> BIB009 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> The level of detail in 3D city modelling, despite its usefulness and importance, is still an ambiguous and undefined term. It is used for the communication of how thoroughly real-world features have been acquired and modelled, as we demonstrate in this paper. Its definitions vary greatly between practitioners, standards and institutions. We fundamentally discuss the concept, and we provide a formal and consistent framework to define discrete and continuous levels of detail (LODs), by determining six metrics that constitute it, and by discussing their quantification and their relations. The resulting LODs are discretisations of functions of metrics that can be specified in an acquisition–modelling specification form that we introduce. The advantages of this approach over existing paradigms are formalisation, consistency, continuity, and finer specification of LODs. As an example of the realisation of the framework, we derive a series of 10 discrete LODs. We give a proposal for the integration of the framework within the OGC standard CityGML (through the Application Domain Extension). <s> BIB010 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> European Historic Urban Districts are highly appreciated by their inhabitants and visitors and they can be considered as one of the most valuable collective achievements of the European culture. The preservation of our urban heritage requires the protection of the social context as well as the preservation of the authenticity and integrity of its physical materiality. That means to improve the quality of life of their inhabitants as well as the sustainability of the historic districts. This dissertation analysed the Historic Urban Districts as complex energy and informational systems in order to address the challenge to improve their sustainability and liveability while protecting their cultural values. First, a methodological framework for energy retrofitting in all its phases has been defined based on a strategic information management and from a multiscale perspective. Secondly, a decision making methodology that allows the modelling of the historic city and the selection of the best strategies has been developed. In order to support the whole system a multiscale data model has been designed. Finally, the historic city of Santiago de Compostela has been selected for the implementation. <s> BIB011 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Abstract In this study, we propose software architecture for the effective integration of building information modeling (BIM) into a geographic information system (GIS)-based facilities management (FM) system. This requires the acquisition of data from various sources followed by the transformation of these data into an appropriate format. The integration and representation of heterogeneous data in a GIS are very important for use cases involving both BIM and GIS data, such as in the management of municipal facilities. We propose a BIM/GIS-based information Extract, Transform, and Load (BG-ETL) architecture that separates geometrical information from that related to the relevant properties. The property required for each use-case perspective is extracted and transformed from information for the BIM with FM to GIS using the ETL concept. In consideration of the viewpoint of geometry, the surface model for several representations in the GIS, we designed BG-ETL, developed a prototype, and verified the results through interviews. The results show that BG-ETL considering BIM/GIS integration issue has benefits such as reusability and extensibility. <s> BIB012 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> This paper presents the generation of the 3D national building geo-data model of Turkey, which is compatible with the international OGC CityGML Encoding Standard. We prepare an ADE named CityGML-TRKBIS.BI that is produced by extending existing thematic modules of CityGML according to TRKBIS needs. All thematic data groups in TRKBIS geo-data model have been remodelled in order to generate the national large scale 3D geo-data model for Turkey. Specific attention has been paid to data groups that have different class structure according to related CityGML data themes such as building data model. Current 2D geo-information model for building data theme of Turkey (TRKBIS.BI) was established based on INSPIRE specifications for building (Core 2D and Extended 2D profiles), ISO/TC 211 standards and OGC web services. New version of TRKBIS.BI which is established according to semantic and geometric rules of CityGML will represent 2D-2.5D and 3D objects. After a short overview on generic approach, this paper describes extending CityGML building data theme according to TRKBIS.BI through several steps. First, building models of both standards were compared according to their data structure, classes and attributes. Second, CityGML building model was extended with respect to TRKBIS needs and CityGML-TRKBIS Building ADE was established in UML. This study provides new insights into 3D applications in Turkey. The generated 3D geo-data model for building thematic class will be used as a common exchange format that meets 2D, 2.5D and 3D implementation needs at national level. <s> BIB013 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Normal 0 21 false false false TR X-NONE X-NONE This paper presents the generation of the 3D national geo-data model of Turkey, which is compatible with the international OGC CityGML Encoding Standard. We prepare an ADE named CityGML-TRKBIS that is produced by extending existing thematic modules of CityGML according to TRKBIS needs. All thematic data groups in TRKBIS geo-data model have been remodeled in order to generate the national large scale 3D geo-data model for Turkey. Within the concept of reference model-driven framework for modelling CityGML ADEs in UML, the first step is conceptual mapping between CityGML and national information model. To test all stages of the framework for Urban GIS Turkey, Building data theme is mapped with CityGML-Building thematic model. All classes, attributes, code lists and code list values of the TRKBIS is tried to be mapped with related CityGML concept. New classes, attributes and code list values that will be added to CityGML Building model are determined based on this conceptual mapping. Finally the new model for CityGML-TRKBIS.BI is established in UML with subclassing of the related CityGML classes. This study provides new insights into 3D applications in Turkey. The generated 3D geo-data model for building thematic class will be used as a common exchange format that meets 2D, 2.5D and 3D implementation needs at national level. <s> BIB014 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Abstract. The federal governments of Germany endeavour to create a harmonized 3D building data set based on a common application schema (the AdV-CityGML-Profile). The Bavarian Agency for Digitisation, High-Speed Internet and Surveying has launched a statewide 3D Building Model with standardized roof shapes for all 8.1 million buildings in Bavaria. For the acquisition of the 3D Building Model LiDAR-data or data from Image Matching are used as basis in addition with the building ground plans of the official cadastral map. The data management of the 3D Building Model is carried out by a central database with the usage of a nationwide standardized CityGML-Profile of the AdV. The update of the 3D Building Model for new buildings is done by terrestrial building measurements within the maintenance process of the cadaster and from image matching. In a joint research project, the Bavarian State Agency for Surveying and Geoinformation and the TUM, Chair of Geoinformatics, transformed an AdV-CityGML-Profilebased test data set of Bavarian LoD2 building models into an INSPIRE-compliant schema. For the purpose of a transformation of such kind, the AdV provides a data specification, a test plan for 3D Building Models and a mapping table. The research project examined whether the transformation rules defined in the mapping table, were unambiguous and sufficient for implementing a transformation of LoD2 data based on the AdV-CityGML-Profile into the INSPIRE schema. The proof of concept was carried out by transforming production data of the Bavarian 3D Building Model in LoD2 into the INSPIRE BU schema. In order to assure the quality of the data to be transformed, the test specifications according to the test plan for 3D Building Models of the AdV were carried out. The AdV mapping table was checked for completeness and correctness and amendments were made accordingly. <s> BIB015 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> In addition to buildings, the terrain forms an important part of a 3D city model. Although in GIS terrains are usually represented with 2D grids, TINs are also increasingly being used in practice. One example is 3DTOP10NL, the 3D city model covering the whole of the Netherlands, which stores the relief with a constrained TIN containing more than 1 billion triangles. Due to the massive size of such datasets, the main problem that arises is: how to efficiently store and maintain them? While CityGML supports the storage of TINs, we argue in this paper that the current solution is not adequate. For instance, the 1 billion+ triangles of 3DTOP10NL require 686 GB of storage space with CityGML. Furthermore, the current solution does not store the topological relationships of the triangles, and also there are no clear mechanisms to handle several LODs. We propose in this paper a CityGML extension for the compact representation of terrains. We describe our abstract and implementation specifications (modelled in UML), and our prototype implementation to convert TINs to our CityGML structure. It increases the topological relationships that are explicitly represented, and allows us to compress up to a factor of ∼ 25 in our experiments with massive real-world terrains (more than 1 billion triangles). <s> BIB016 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Smart cities provide effective integration of human, physical and digital systems operating in the built environment. The advancements in city and landscape models, sensor web technologies, and simulation methods play a significant role in city analyses and improving quality of life of citizens and governance of cities. Semantic 3D city models can provide substantial benefits and can become a central information backbone for smart city infrastructures. However, current generation semantic 3D city models are static in nature and do not support dynamic properties and sensor observations. In this paper, we propose a new concept called Dynamizer allowing to represent highly dynamic data and providing a method for injecting dynamic variations of city object properties into the static representation. The approach also provides direct capability to model complex patterns based on statistics and general rules and also, real-time sensor observations. The concept is implemented as an Application Domain Extension for the CityGML standard. However, it could also be applied to other GML-based application schemas including the European INSPIRE data themes and national standards for topography and cadasters like the British Ordnance Survey Mastermap or the German cadaster standard ALKIS. <s> BIB017 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Abstract CityGML, as the standard for the representation and exchange of 3D city models, contains rich information in terms of geometry, semantics, topology and appearance. With respect to topology, CityGML adopts the XLink approach to represent topological relationships between different geometric aggregates or thematic features; however, it is limited to shared objects. This paper proposes a two-level model for representing 3D topological relationships in CityGML: high-level (semantic-level) topology between semantic features and low-level (geometric-level) topology between geometric primitives. Five topological relationships are adopted in this model: touch , in , equal , overlap and disjoint . The semantic-level topology is derived from the geometric-level topology on the basis of the shared geometric primitives. To maintain the 3D topology, topological consistency rules are presented. An Application Domain Extension, called TopoADE, is proposed for the implementation of the topological model. The TopoADE consists of three modules: Topology, Feature and Geometry. Finally, 3D city models with LoD1 to LoD4 are used to test this model. Experimentation on those data sets indicates a validation of the proposed topological model in CityGML. <s> BIB018 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Abstract The Building Information Modeling (BIM) domain and the Geographic Information System (GIS) domain share a mutual need for information from each other. Information from GIS can facilitate BIM applications such as site selection and onsite material layout, while BIM models could help generate detailed models in GIS and achieve better utility management. The mapping between the key schemas in the BIM domain and the GIS domain is the most critical step towards interoperability between the two domains. In this study, Industry Foundation Classes (IFC) and City Geography Markup Language (CityGML) were chosen as the key schemas due to their wide applications in the BIM domain and the GIS domain, respectively. We used an instance-based method to generate the mapping rules between IFC and CityGML based on the inspection of entities representing the same component in the same model. It ensures accurate mapping between the two schemas. The transformation of coordinate systems and geometry are two major issues addressed in the instance-based method. Considering the difference in schema structure and information richness between the two schemas, a reference ontology called Semantic City Model was developed and an instance-based method was adopted. The Semantic City Model captures all the relevant information from BIM models and GIS models during the mapping process. Since CityGML is defined in five levels of detail (LoD), the harmonization among LoDs in CityGML was also developed in order to complete the mapping. The test results show that the developed framework can achieve automatic data mapping between IFC and CityGML in different LoDs. Furthermore, the developed Semantic City Model is extensible and can be the basis for other schema mappings between the BIM domain and the GIS domain. <s> BIB019 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Ancient Chinese-style architecture has received increased attention during the last century as a segment of cultural heritage and is of great significance, specifically in regard to the process of digitizing and modeling these buildings to preserve and protect this heritage. Because the roof form reflects the age of the structure, the structural character and the historical culture of the ancient building, constructing a refined model for the roof is a primary aspect of the 3D modeling procedure. To avoid cumbersome traditional modeling approaches that use geometry units, such as points, lines and triangles, a flexible semantic method is proposed in this study to improve modeling efficiency and reduce the professional requirements. In this method, a two-level semantic decomposition of the roof is presented according to the characteristics of ancient Chinese-style architecture. The structural level reveals the basic components that determine its structural shape, and the decorative level refers to the attached components that influence the exterior appearance. The assembly validity of the decomposed elements and the combined diversity of the integrated entities are ensured by topological constraints and derived transformations of the semantic components. This proposed method was implemented by utilizing CityGML (City Geography Markup Language) via the ADE (Application Domain Extension) mechanism and was tested by modeling the principal buildings included in the Palace Museum. <s> BIB020 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Abstract. This paper presents a geometric approach for modelling tree roots with different Levels of Detail, suitable for analysis of the tree anchoring, potentially occupied underground space, interaction with urban elements and damage produced and taken in the built-in environment. Three types of tree roots are considered to cover several species: tap root, heart shaped root and lateral roots. Shrubs and smaller plants are not considered, however, a similar approach can be considered if the information is available for individual species. The geometrical approach considers the difficulties of modelling the actual roots, which are dynamic and almost opaque to direct observation, proposing generalized versions. For each type of root, different geometric models are considered to capture the overall shape of the root, a simplified block model, and a planar or surface projected version. Lower detail versions are considered as compatibility version for 2D systems while higher detail models are suitable for 3D analysis and visualization. The proposed levels of detail are matched with CityGML Levels of Detail, enabling both analysis and aesthetic views for urban modelling. <s> BIB021 </s> CityGML Application Domain Extension (ADE): overview of developments <s> Generic <s> Terrains form an important part of 3D city models. GIS practitioners often model terrains with 2D grids. However, TINs (Triangulated Irregular networks) are also increasingly used in practice. One such example is the 3D city model of the Netherlands (3DTOP10NL), which covers the whole country as one massive triangulation with more than one billion triangles. Due to the massive size of terrain datasets, the main issue is how to efficiently store and maintain them. The international 3D GIS standard CityGML allows us to store TINs using the Simple Feature representation. However, we argue that it is not appropriate for storing massive TINs and has limitations. We focus in this article on an improved storage representation for massive terrain models as TINs. We review different data structures for compactly representing TINs and explore how they can be implemented in CityGML as an ADE (Application Domain Extension) to efficiently store massive terrains. We model our extension using UML, and XML schemas for the extension are automatically derived from these UML models. Experiments with massive real-world terrains show that, with this approach, we can compress CityGML files up to a factor of ~20 with one billion+ triangles, and our method has the added benefit of explicitly storing the topological relationships of a TIN model. <s> BIB022
Many ADEs have been developed also as a general extension of CityGML without a specific application in focus. For example, some of these ADEs have been implemented for adapting CityGML supporting a national standard or enabling interoperability between a national standard and CityGML. Furthermore, it is relevant to note that national 3D geographic information models can be developed entirely as a CityGML ADE   BIB013 . The Netherlands has a national 3D standard (Information Model Geography -IMGeo) that is established as a CityGML ADE BIB003   . The IMGeo ADE is designed as an extension of the existing 2D standard, utilising concepts from CityGML. It is expressed as UML, describing adaptations that give means to fitting the Dutch context and enabling extensions to the previously established 2D standard. A relevant detail to note about the work behind IMGeo is that it is one of the earliest ADEs defined with an UML model, and a byproduct of the project are the publicly available guidelines on modelling ADEs using UML BIB004 . Similarly, an extension of CityGML according to the requirements of the Turkish Urban Information System (TRKBIS) has been developed BIB013 BIB014 . The ADE has been established in UML, with currently available documentation focusing on enhancing the building and trasportation modules. For example, the attribute describing roof material of a building and the maintenance authority of a transportation entity have been enabled in the ADE. Classes have been extended as well, e.g. the class OtherConstruction 3 not available in CityGML but a part of the TRKBIS is available owing to the ADE. The European INSPIRE Building specification is partially based on CityGML, hence an ADE was developed fostering interoperability between the two standards  BIB005 . The ADE focuses on the 3D portion of the INSPIRE Data Specification on Buildings, and it extends CityGML with building attributes that are not available in the data model, e.g. number of dwellings, building nature, and metadata on data quality such as the accuracy of the height. The specification is available as XSD and UML, and work in practice is mostly focused on implementations in Germany BIB015 . Adapting the CityGML data model to a local context is not exclusive to national standards and efforts of government agencies. For example, Li et al. BIB020 extend CityGML for modelling ancient Chinese-style architecture. Specifically, the RoofSurface feature of Building has been extended in the ACRoofADE entertaining Chinese-style roofs, e.g. include information about dynasty and type of ridge. It is also interesting to note that this comprehensive work focusing on a particular component (roofs) of a particular architecture (ancient Chinese) doubles as a data modelling guideline as it provides instructions on data acquisition in different LODs. ADE has been employed also in enhancing thematic modules without a national context in mind. The work of Kumar et al. BIB016 BIB022 presents a solution for enhancing the efficiency of storing terrain in CityGML. CityGML iTINs ADE introduces new geometry types in the GML schema which are extended to existing CityGML features for compact representation of massive terrains, resulting in a compression factor of 20. Guerrero Iñiguez BIB021 suggested an ADE for the inclusion of geometric and semantic properties of tree roots in solitary vegetation objects at different LODs. A new concept 'dynamizer' has been proposed by Chaturvedi and Kolbe BIB017 for enabling the representation of dynamic information in semantic 3D city models for different purposes. Examples of such dynamic properties are real-time information on electricity consumption from smart meters. Dynamizers are currently realised in CityGML with an ADE. However, the integration of this concept in the next version of CityGML 3.0 is being currently discussed in the CityGML Standards Working Group (SWG). The evolvement of a concept implemented as an ADE into a native component of CityGML is not uncommon (i.e. see Tunnel ADE), as discussed earlier. For another related ADE, the reader is referred to the Dynamic ADE  BIB011 . Kaden et al. BIB002 developed Geodata Join ADE to enrich the CityGML data model with additional information about the relationship between the adjacent city objects (e.g. a building and a road) in order to remove geometric inconsistencies. TopoADE was developed by Li et al. BIB018 to enrich the CityGML data model with topological relationships, i.e. relationships between geometric primitives and between semantic features. Tamminga et al. BIB006 study the establishment of a standard for exchanging traffic and transportation models as a CityGML ADE. In this work in progress, researchers point out that CityGML provides a geographical context, which many existing traffic and transportation models currently lack. Examples of attributes that are added to the CityGML thematic module representing roads are maximum speed of a road segment, gradient, and capacity. With that, this ADE opens the door for different uses of CityGML in transportation applications. Varela-González et al. BIB008 proposed the Traffic Sign ADE for modelling traffic signs with specific feature types, attributes, and their relationship with road network models defined in the Transportation module. On the subsurface, Tegtmeier et al. BIB009 developed the 3D Geotechnical Extension Model (3D-GEM), an ADE for handling information on subsurface geological and geotechnical features. ADE has also been used to extend CityGML with a custom LOD specification and richer semantic structure (e.g. allowing balconies to be denoted) BIB010 . Besides the harmonisation of national standards, a subcategory that may be identified in this group are ADEs developed in the frame of the conversion from IFC to CityGML. Because CityGML and IFC are inherently different formats conceived for different purposes and scale, there is large disparity between them in terms of object types, geometry, attributes, and relationships BIB012 . Therefore, ADEs have been developed supporting their interoperability. Deng et al. BIB019 introduce the Semantic City Model ADE for capturing the semantic information from IFC that would normally not be possible to store in CityGML. The ADE allows storing the structural properties and component relationships in CityGML. An interesting aspect to note is the support of multiple LODs, as the conversion results in multiple instances differentiated by their spatio-semantic grade. Perhaps the most prominent ADE in the context of IFC ↔ CityGML interoperability, is the one introduced in 2011 by De Laat and Van Berlo BIB001 . The extension GeoBIM is developed for integrating IFC semantics and properties in CityGML. It works in the way that existing CityGML features such as Room are extended with rich information from IFC. Their work identifies a subset of IFC classes that are of relevance for IFC (less than 10% of the total number), and focuses on mapping them onto CityGML. For example, the IFC class ifcDoor is mapped onto the CityGML Door extending the attributes OverallWidth and OverallHeight, originally not available in CityGML. Another identified work utilising ADE in the domain of BIM-GIS integration is the PANTURA ADE BIB007 . This ADE partially captures IFC data types and hierarchy. It has been tested on an IFC model of a bridge, and the resulting model is tested in a use case for analysing the disturbance induced by bridge construction. Finally, the 3D Metadata ADE was recently developed focusing on adding metadata related to 3D city models in CityGML standard . It incorporates ISO 19115  metadata elements and several other elements related to 3D city models such as LODs, feature count, and metadata related to CityGML thematic models, e.g. the total number of building parts and installations in Buildings. It also defines attributes to store information about any other ADE(s) already present in a dataset, which is an interesting functionality in the context of this paper. The 3D Metadata ADE has a modular structure and can be extended by other ADEs to incorporate their metadata. Figure 5 illustrates such an example. A new class MDnoiseBuilding is created by extending the Metadata ADE MDBuilding class. MDnoiseBuilding has a new attribute to store information such as the number of buildings enriched with Noise ADE attributes (numberOfNoiseBuildings). Similarly, MDnoiseRoads is a subclass of MDRoads with a new attribute to store the number of noise road segments present in the data (numberOfNoiseSegments).