
Copyright © 2012 Open Geospatial Consortium.
or built structures can be represented. This coherent model structure facilitates the similar understanding of
semantic entities and helps to reduce software implementation efforts. Both the Bridge and the Tunnel model
introduce further concepts and model elements which are specific to bridges and tunnels respectively.
Additions to existing thematic modules
CityGML Core module (cf. chapter 10.1)
Two new optional attributes have been added to the abstract base class core:_CityObject within the
CityGML Core module: relativeToTerrain and relativeToWater. These attributes denote the feature’s
location with respect to the terrain and water surface in a qualitative way, and thus facilitate simple and
efficient queries (e.g., for the number of subsurface buildings) without the need for an additional digital
terrain model or a model of the water body.
Building module (cf. chapter 10.3)
o LOD0 representation
Buildings can now be represented in LOD0 by footprint and/or roof edge polygons. This al-
lows the easy integration of existing 2D data and of roof reconstructions from aerial and satel-
lite imagery into a 3D city model. The representations are restricted to horizontal, 3-
dimensional surfaces.
o Additional thematic boundary surfaces
In order to semantically classify parts of the outer building shell which are neither horizontal
wall surfaces nor parts of the roof, two additional boundary surfaces are introduced:
OuterFloorSurface and OuterCeilingSurface.
o Additional relations to thematic boundary surfaces
In addition to _AbstractBuilding and Room, the surface geometries of BuildingInstallation and
IntBuildingInstallation features can now be semantically classified using thematic boundary
surfaces. For example, this facilitates the semantic differentiation between roof and wall sur-
faces of dormers which are modeled as BuildingInstallation.
o Additional use of implicit geometries
Implicit geometries (cf. chapter 8.3) are now available for the representation of _Opening,
BuildingInstallation, and IntBuildingInstallation in addition to BuildingFurniture. A prototyp-
ical geometry for these city objects can thus be stored once and instantiated at different loca-
tions in the 3D city model.
Generics module (cf. chapter 10.12)
Two generic attributes have been added to the Generics module: MeasureAttribute and
GenericAttributeSet. A MeasureAttribute facilitates the representation of measured values together with
a reference to the employed unit. A GenericAttributeSet is a named collection of arbitrary generic at-
tributes. It provides an optional codeSpace attribute to denote the authority organization who defined
the attribute set.
LandUse module (cf. chapter 10.10)
The scope of the feature type LandUse has been broadened to comprise both areas of the earth’s surface
dedicated to a specific land use and areas of the earth’s surface having a specific land cover with or
without vegetation.
Attributes class, function, and usage (all modules)
In order to harmonize the use of the attributes class, function, and usage, this attribute triplet has been
complemented for all feature classes that at least provided one of the attributes in CityGML 1.0.
Additions to the CityGML code list mechanism
In CityGML, code lists providing the allowed values for enumerative attributes such as class, function, and
usage can be specified outside the CityGML schema by any organization or information community according to
their specific information needs. This mechanism is, however, not fully reflected in the CityGML 1.0 encoding
schema, because in a CityGML 1.0 instance document a corresponding attribute cannot point to the dictionary
with the used code list values. This has been corrected for CityGML 2.0: All attributes taking values from code
lists are now of type gml:CodeType following the GML 3.1.1 mechanism for the encoding of code list values (cf.