CityGML

CityGML. It is an open data model and XML-based exchange format for the storage and interchange of virtual 3D city models, standardized by the Open Geospatial Consortium. The format is designed to represent the geometry, topology, semantics, and appearance of urban objects, supporting applications across fields like urban planning, environmental simulation, and facility management. Unlike purely graphical models, it encodes rich thematic information about buildings, terrain, vegetation, water bodies, and transportation networks, enabling complex spatial analyses and simulations.

Overview

CityGML provides a common semantic framework for describing 3D urban landscapes, facilitating interoperability between different Geographic Information System applications. It is implemented as an application schema of the Geography Markup Language, the extensible modeling language for geographic systems defined by the Open Geospatial Consortium. The standard is crucial for initiatives like Smart City projects and national spatial data infrastructures, such as the German AAA-Standard and the Dutch IMGeo. Its adoption supports the work of organizations like the International Organization for Standardization through standards such as ISO 19107 and ISO 19109, which relate to spatial schema and rules for application schemas.

Data Model and Concepts

The core of the standard is a multi-level Level of Detail concept, ranging from regional footprints to highly detailed architectural models with interior structures. Thematic modules define object classes for key domains: the Building Module describes structural parts and functions; the Transportation Module covers objects like roads, railways, and squares; the Vegetation Module represents plants and solitary vegetation objects; the Water Body Module models rivers, lakes, and canals; and the CityFurniture Module includes items like streetlights and benches. Each object carries attributes, relationships, and can be aggregated, such as a Building being part of a Building Complex. The model also supports textures and materials via the Appearance Module, linking to standards like X3D and Collada for visualization.

Application Domains

CityGML data is utilized in diverse sectors. In urban planning and architecture, it aids in shadow analysis, line of sight studies, and planning compliance checks. Environmental simulations use it for noise mapping, airflow analysis, and energy demand forecasting, often integrated with tools like ENVI-met and SimStadt. For disaster management and risk analysis, models support flood simulation and evacuation planning. Infrastructure and facility management applications include network planning for telecommunications and maintenance of utility networks. Furthermore, it serves as a base for augmented reality applications, autonomous vehicle navigation systems, and cultural heritage documentation of sites like the Acropolis of Athens.

Versions and Development

The development began in 2002 within the Special Interest Group 3D of the Initiative Geodata Infrastructure North-Rhine Westphalia. Version 1.0 was released in 2008, followed by the widely implemented CityGML 2.0 in 2012, which introduced the ADE mechanism for domain-specific extensions. The current CityGML 3.0, released in 2021, represents a major evolution, introducing a new Space Partitioning concept, a revised Level of Detail definition, and improved support for dynamic data and point clouds. The standard is maintained by the Open Geospatial Consortium's CityGML Standards Working Group, with significant contributions from institutions like the University of Bonn, the Karlsruhe Institute of Technology, and companies such as virtualcitySYSTEMS.

Related Standards and Formats

CityGML exists within an ecosystem of complementary geospatial standards. It is inherently linked to Geography Markup Language and aligns with the ISO 19100 series. For visualization, it connects to 3D graphics formats like X3D, Collada, and glTF, often through converters. The IndoorGML standard specializes in indoor navigation, while InfraGML covers civil infrastructure. The Industry Foundation Classes format, used in Building Information Modeling, is a key related format, with ongoing work on interoperability through projects like the BuildingSmart Data Dictionary. Other relevant formats include KML for Google Earth and the open data ecosystem of OpenStreetMap.

Category:Geographic Information Systems Category:Open Geospatial Consortium standards Category:XML-based standards Category:3D computer graphics