CityGML is an international standard issued by the Open Geospatial Consortium (OGC) on the modeling, storage, and exchange of semantic 3D city models. Version 2.0 of the standard was adopted by the OGC in March 2012. The Chair of Geoinformatics is actively involved in the development of version 3.0 and coordinates the creation of the specification documents, the data models, and the GML application schemas.
Version 3.0 of the CityGML standard consists of several parts. The first part of the standard, Version 3.0.0 - Part 1: Conceptual Model Standard, was adopted by the OGC in September 2021. The second part on the GML Encoding is planned for publication by the end of 2022.
Project description
In order to increase the usability of CityGML for more user groups and areas of application, the OGC CityGML Standards Working Group (SWG) and the Special Interest Group 3D (SIG 3D) of the initiative Geodata Infrastructure Germany (GDI-DE) work since 2014 on the further development of CityGML.
This development results in the new major version CityGML 3.0 which is to be finalised by the end of 2022. The new version brings a number of improvements, extensions, and new functionalities.
Use of a model-driven approach: The data model is now fully based on the ISO 191xx standards. The software tool Enterprise Architect is used for creating the data model and the GML encoding will be fully automatically derived from the data model using the software tool ShapeChange.
Revised LOD concept: LOD4 has been removed, the interior of objects can be expressed in different LODs 0-3 now. It is e.g. possible to model the outside shell of a building in LOD1 while representing the interior structure in LOD2 or 3.
New and revised modules: CitygML 3.0 includes several new and revised modules which allow for better use of 3D city models in different areas of application such as urban planning, energy simulations, and traffic analyses, reduce redundancy by integrating and providing concepts used in several modules centrally via inheritance, simplify geometry handling, and improve the representation of physical and logical objects.
New Core model: All spatial representations base on the two new pivotal concepts Space and SpaceBoundary. The geometry can now also be given by point clouds. The new core model implements the new LOD concept.
New Construction module: Groups all classes which are similar over different types of constructions like buildings, tunnels, and bridges. Allows for representing constructions not being covered by any of the other modules.
New Versioning module: Allows to explicitly represent and exchange multiple versions of city objects (e.g. history or alternative designs) within one city model dataset. All objects can have bitemporal lifespan data.
New Dynamizer module: Defines concepts to represent and exchange time-varying data for city object properties (e.g. solar irradiation over the day) as well as to integrate sensors with 3D city models. Data sources can be timeseries data represented inline, in external files, or from sensor web services (OGC Sensor Web Enablement or Internet of Things, IoT, in general).
Revised Transportation module: Transportation objects like Roads, Tracks, or Railways can now be subdivided into sections and have an area as well as a center line representation for each LOD.
Revised Building module: Allows now for representing storeys and building units.
Improved interoperability with other standards: CityGML 3.0 allows for better interoperability with other relevant standards like IndoorGML, Industry Foundation Classes (IFC), Land Administration Domain Model (LADM), as well as with Semantic Web Technologies like Resource Description Framework (RDF) and with the EU Directive INSPIRE (Infrastructure for spatial information in Europe).
Backwards compatibility: All modifications to the new CityGML 3.0 model are carried out in a way to ensure backwards compatibility with CityGML 1.0 and 2.0
The CityGML 3.0 standard consists of at least two parts:
The specification "CityGML 3.0 Part 1: Conceptual Model Standard"
The specification "CityGML 3.0 Part 2: GML Encoding Standard"
Further encoding specifications (e.g. relational database schema, JSON-based representation) which may follow in the future
GML application schemata have been derived from the UML model using the software ShapeChange. The current draft of the GML application schemata can be downloaded from this github repository: https://github.com/opengeospatial/CityGML-3.0Encodings (Folder "CityGML")
Test data sets
Test data sets that are compliant to the CityGML 3.0 standard are available here:
New Webinars on New Features in CityGML 3.0 and its Graph-based Applications (CUT Academy)
GISPro_CityGML
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In October, two new CUT Academy videos on CityGML 3.0, its functions and application showcases have been published!
CityGML 3.0 and its new features
CityGML and its graph-based applications
Son H. Nguyen and Felix Olbrich from the Chair of Geoinformatics have contributed two new webinars to the CUT Academy in October 2024, which focus on the new features in CityGML 3.0 and its graph-based applications. In the “Connected Urban Twins” (CUT) project, Urban Digital Twins (UDT) are being jointly developed for integrated urban development. The CUT Academy serves as a platform for the exchange and discussion of knowledge - both between the partners of the CUT project and with the public, for example through webinars.
CityGML 3.0 is an official international OGC standard since 2023. This video summarizes the most important new features of the new version.
A brief overview:
New and revised modules: In addition to revised modules such as CityGML Core, Generics, Building and Transportation, CityGML 3.0 also has new modules such as Dynamizer, Versioning, PointCloud and Construction.
New concepts for spaces and space boundaries: All city objects are now based on the concept of Space and SpaceBoundary; all geometries are bound to it.
Interior modelling without LOD4: CityGML 3.0 enables interior modeling in any LOD. This eliminates the need for LOD4.
Modelling of changes: Fast, dynamic changes are handled by the Dynamizer module, while slow changes are handled by the Versioning module.
Improved representation of transportation infrastructure: CityGML 3.0 allows for a detailed representation of street space as part of a standardized and consistent semantic 3D city model.
City objects, especially those encoded in CityGML, are structured like graphs. This video presents two applications that use graph representations of CityGML datasets: (1) Identification and interpretation of changes to a city, and (2) Multimodal navigation using detailed street space modelling of a city.
A brief overview:
Graph structure of CityGML: CityGML objects are structured like graphs. Graph-based methods and algorithms can therefore be applied.
The Neo4j graph database: In the applications presented, graph representations of city objects are stored in the Neo4j graph database. Neo4j is currently one of the most popular graph databases worldwide.
Identification and interpretation of changes: Graphs can be used to compare CityGML datasets with each other to detect changes. These changes are then interpreted to identify meaningful patterns for specific stakeholders.
Multimodal navigation: Graph representations of street spaces in CityGML 3.0 can also be used to enable multimodal navigation.
Interactive Neo4j tutorials: This video is accompanied by interactive tutorials for Neo4j and its query language Cypher.
Further resources:
GitHub repository for identification and interpretation of changes in CityGML graphs
GitHub repository for the construction of knowledge graphs from semantic 3D city models
