ınbul 2004
ons, seven
en applied
nonstrated
operations
cell tuple
ve the way
entation of
nt Trends)
velopment
ies", USA.
ed 13 April
! geometric
ice, 1994.
les, JJGIS
n Science),
topological
61-273.
pproach for
Urban and
1), Vol. 14,
s for object-
onal Society
Amsterdam,
.
ed approach
oceedings of
Association,
tio-temporal
Proceedings
{ Knowledge
Geographic
souri, USA,
REPRESENTATION OF A 3-D CITY MODEL IN SPATIAL
OBJECT-RELATIONAL DATABASES
G. Gróger ^, M. Reuter, L. Plümer?
* [nstitute for Cartography and Geoinformation, University of Bonn, Meckenheimer Allee 172, 53115 Bonn, Germany -
(groeger, pluemer)@ikg.uni-bonn.de
? AED-SICAD, Mallwitzstr. 1-3, 53177 Bonn, Germany - reuter@aed-sicad.de
Commission IV, WG IV/1
KEY WORDS: Databases, GIS, Modeling, Three-dimensional, Performance, Query, Data Structures
ABSTRACT:
Three-dimensional city models become more and more important in many GIS applications. Examples are, apart from simple
visualization, city and land use planning as well as telecommunication planning and disaster management. Currently, there are no
3-D GIS available, which are suitable for these applications. For managing large spatial data sets in an efficient and sustainable way,
spatial databases are suitable, but in general restricted to two dimensions. The paper answers the questions how to represent a 3-D
city model in an object-relational spatial database, and to what degree the modeling, analysis and query mechanism of the database
can be used for 3-D models and applications. Our geometrical-topological 3-D city model is based on existing standards of the ISO
and the Open GIS Consortium to ensure interoperability with other systems and data providers. Recent 'object-relational' databases
support sophisticated object models closing the gap between relational databases and object-oriented models. Furthermore, spatial
extensions are available for database systems. Based on the widespread commercial database system Oracle 9.21 Spatial, the
functionality and efficiency of analysis, access and queries is examined. In our paper we will demonstrate which kind of 3-D spatial
queries are feasible using Oracle Spatial, and how exact the query results are with respect to geometry, especially when using three-
dimensional spatial indices. Likewise, the system's performance is considered by means of miscellaneous benchmarks and their
dependency on individual factors such as the recursive aggregation of objects.
1. INTRODUCTION
Three-dimensional city models are important ‘in many
applications of geographic information systems (GIS).
Examples are telecommunications planning, disaster manage-
ment, or urban planning (Kóninger & Bartel; 1998, Zlatanova,
2000; Zlatanova & Holweg, 2004). On one hand, most GIS
currently available, however, cope only with two or two and a
half dimensional data. Most systems from Computer Aided
Design (CAD) or Computer Graphics (Foley et al., 1995) can
handle 3-D data, but are limited since they do not handle
topology and semantic properties adequately and do not offer
the GIS functionality required for the applications mentioned.
Relational databases are, on the other hand, suitable for storing
and managing data in an efficient and sustainable way (Ullman,
1988). Transaction mechanisms enable consistent updates of the
database, and powerful access structures guarantee efficient
execution of queries. Object-relational extensions close the gap
between conceptual models and their implementation in a
database. Add-ons to handle spatial data are available for the
most commercial databases, for example the Spatial Extender
for IBM's DB/2, PostGIS for PostgreSQL, Spatial Data Blade
for Informix, or Spatial for Oracle. Most of these extensions are
restricted to. 2-D or 2.5-D data and offer only a few
functionalities to handle 3-D data.
This paper addresses the question how to store, manage and
query 3-D city models in object-relational spatial databases and
to which degree the required 3-D functionalities are supported.
In addition, the performance of 3-D queries is analyzed. The
focus is on a widespread commercial system, Oracle 9i Spatial
(Oracle, 2002a; Oracle, 2002b).
The 3-D city model on which the implementation is based
(Kolbe & Gróger, 2003) is a multifunctional model, which may
be used for analysis and simulation purposes as well as for
visualization. To reach this objective, the model has explicit
topologic relations between its geometric components, and a
hierarchical structure to model aggregated thematic objects
recursively. To support interoperability, it is based on
international GIS standards, for example ISO 19107 ‘Spatial
Schema’ (Herring, 2001). It can casily be interchanged using
the Geography Markup Language (GML 3) (Cox et al, 2003),
which will be one of the most important GIS transfer formats in
the future.
The implemented 3-D city model was developed based on
discussions within the “Special Interest Group 3D” (SIG 3D) of
the initiative “Spatial Data Infrastructure North Rhine-
Westphalia” (GDI NRW). In this group, municipalities,
scientists and software devclopers cooperate to develop a
unified approach for 3-D city models.
In the last decade, the suitability of databases for 3-D GIS
models has been studied several times. (Molenaar, 1992:
Rikkers et al, 1994) employ a database to implement a 3-D
formal data structure. A pure relational model without spatial
extensions is used. A similar approach is the prototype SOMAS
(Pfund, 2002), which focuses on the thematic aspects and, in
particular, 3-D city models. In contrast to our approach,
recursive aggregates are not considered in both prototypes.
(Arens et al., 2003) analyze the suitability of Oracle Spatial 9i
