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defines mechanisms, conventions and syntax in
XML Schema., which provide an open framework
for the definition of schemas and objects for
geospatial applications.
The Keyhole Markup Language (KML) is an
XML language focused on geographic visualization,
including annotation of maps and images.
Geographic visualization includes not only the
presentation of graphical data on the globe, but also
the control of the user’s navigation in the sense of
where to go and where to look.
The City Geography Markup Language
(CityGML) is an open data model structure and
standardized code based on XML for storing and
exchanging virtual 3D city models. The common
information model behind CityGML defines classes
and relationships for the most relevant topographic
objects in cities and regional models with respect to
their geometrical, topological, semantic and
appearance properties.
In comparison to GML, CityGML represents not
only the geometry of the urban objects, but also
represents the semantic and thematic properties of
the city. The KML and CityGML overlap in the
functionality, but they differ in other important
issues. Both standards use similar geometry
elements to represent the characteristics of the real
world, but the KML lacks many of the semantic
properties included in CityGML.
Finally, Kolbe et al. (Kolbe, Konig, Nagel, &
Stadler, 2009) present a 3D geodatabase for
CityGML. The CityGML data model is mapped into
a relational database schema, allowing users to store,
represent and manage virtual models of the cities.
Additionally, this work provides a tool which
imports and exports data in CityGML and GML
structures.
3 WORK DESCRIPTION
The model of a city has certain characteristics that
favor the use of procedural modeling for its
generation, such as the existence of several repeated
patterns in their shape or the possibility to structure
its content hierarchically. Additionally, due to their
size and complexity, these models require many
resources, making it appealing to apply procedural
modeling techniques in order to reduce the
development time and costs.
Thus, the developed methodology intends to
integrate multiple real world data sources, from
different municipal GIS, into an unified data model
mapped based on an urban ontology oriented for
procedural modeling. The proposed urban ontology
allows the integration of different data on the same
data model, allowing the interpretation of this data to
be always the same. This facilitates the later
representation of urban information in three-
dimensional format by using procedural modeling
techniques, where the geometric information does
not need to be stored, but can rather be generated
when needed, producing the same results.
3.1 Definition of Urban Ontology
Having as base specification the CityGML (Groger,
Kolbe, Czerwinski, Nagel, 2008) and the work of
Kolbe et al. (Kolbe et al., 2009), an ontology was
defined which meets the expectations presented in
this paper. The selection of CityGML was used since
it is an OGC standard and a very flexible and
complete data schema, capable of describing urban
environments in detail. However, whereas the
CityGML specification is very focused on the
representation of urban objects, through the
association of geometric properties, this new urban
ontology is oriented to the description of the main
urban elements, in order to be used by procedural
modeling methods. Thus, it is important that the
procedural modeler is fed with all the semantic
information of the city rather than a large quantity of
geometric information, since it can (aside from some
base geometries) generate automatically such
tridimensional data.
Figure 1: Core data model, defining the basic concepts and
components.
The proposed urban ontology was materialized in
an unified data model for procedural modeling of
urban environments. Similarly to the CityGML
standard, the new data model includes the geometric
model, the appearance model and the different
thematic models of the urban environment (Groger
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