CityGML

Definition

CityGML is an open standardized data model and exchange format used for the storage and exchange of virtual 3D city and landscape models. It is based on the Geography Markup Language (GML) and has been developed as an official standard by the Open Geospatial Consortium (OGC). The model includes definitions for the geometry, topology, semantics, and appearance of city models, facilitating the sharing and analysis of urban and landscape data in 3D.

What is CityGML?

CityGML is designed to represent urban environments by encoding 3D models of cities, towns, or neighborhoods in a highly detailed and semantically enriched way. This includes buildings, roads, railways, city furniture, vegetation, water bodies, and terrain surfaces. CityGML organizes these components into different thematic layers that come with various levels of detail (LoD), allowing for incremental complexity in the data representation. CityGML is extensively used in applications such as urban planning, disaster management, environmental simulations, and as a foundation for building information modeling (BIM).

CityGML facilitates interoperability between different geographic information systems (GIS) and supports extensive attributes for individual city elements. These attributes can provide additional information such as construction year, height, function of buildings, or materials used, enabling a comprehensive analysis of urban datasets. By providing a shared conceptual foundation, CityGML allows different stakeholders, such as municipalities, architects, and engineers, to effectively collaborate and utilize 3D city models in their respective disciplines.

FAQs

What are the Levels of Detail in CityGML?

CityGML specifies five levels of detail (LoD) ranging from LoD0 to LoD4. LoD0 represents a two-dimensional digital terrain model with height references, while LoD1 to LoD4 progressively add more geometric details and semantic information, from block models without roofs to detailed architectural features in LoD4.

How does CityGML handle semantic information?

CityGML encodes semantic information by associating attributes and thematic classes with 3D model components. This semantic data includes the types of objects (e.g., buildings, roads), their functions, and relationships between model elements, allowing users to perform complex analyses beyond pure geometric calculations.

Is CityGML compatible with other 3D formats?

CityGML is designed to be interoperable with other 3D formats and systems. While it might require conversion or transformation processes, CityGML's basis in GML and its adherence to international standards facilitate compatibility and data exchange with other GIS and 3D modeling formats.

What applications use CityGML?

CityGML is widely used in urban planning, environmental analysis, infrastructure management, and disaster risk assessment. It serves as a foundation for creating detailed city models that can be used in simulations for energy and climate studies, noise mapping, and infrastructure management.