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In-Depth Information
discuss the segmentation technique for 3D city models which decomposed the
model based on semantic and geometric values. The
Sect. 4
will discuss the future
work and conclusion that can be drawn from this chapter.
2 Related Works
2.1 3D City Models and CityGML
CityGML is a data model and an exchange format that represents 3D spatial data
i.e. 3D city models, especially urban objects. According to Kolbe (
2009
), Groger
and Plumer (
2012
), CityGML is in XML-based format and an application schema
for the Geography Markup Language version 3.1.1 (GML3). The Open Geospatial
Consortium (OGC) has accepted CityGML specifications as one of the interna-
tional standards for representing and exchanging spatial data, along with GML3.
CityGML represents the semantics, geometry, topology and appearance of 3D city
models in five well-defined Level-of-Details (LoD), namely LoD0 to LoD4. The
accuracy and structural complexity of the 3D objects increases with the LoD level
where LoD0 is the simplest LoD (2.5D Digital Terrain Model (DTM)) while LoD4
is the most complex LoD (architectural details with interior structures). Kolbe
(
2009
) discussed in detail the role of CityGML in exchanging and representing 3D
city models, the aim of CityGML development, its modelling aspects, recent
applications and its relation to other 3D standards such as IFC and KML.
Previously, 3D city models have been used mainly for visualization purposes
but the rapid development in 3D city modelling has prompted some applications
such as facilities management, building information model and simulations to
utilize additional information about the city objects with standardized represen-
tations as suggested by Kolbe (
2009
). Meanwhile, Groger and Plumer (
2012
)
elaborated on the current development in CityGML, its features being the inter-
operable semantic 3D city model and current researches that aim to enhance the
format for geospatial purposes. They provided several key points that differentiate
CityGML with other graphically-focused format such as KML and X3D. Kolbe
(
2009
), Groger and Plumer (
2012
) also stated the importance of semantic infor-
mation supported in CityGML which is crucial in geospatial applications. In
explaining the semantic aspect supported in CityGML, Groger and Plumer (
2012
)
had provided UML diagrams that shows hierarchical structures of the semantic
information for every LoDs which emphasized that coherent semantical-geomet-
rical modelling is a very important aspect in CityGML.
2.2 3D Buildings Generation
The emergence of better hardware and software in the computer-related industries
makes it easier for the users to generate 3D buildings. Some researchers even
