AN URBAN ONTOLOGY TO GENERATE COLLABORATIVE

VIRTUAL ENVIRONMENTS FOR MUNICIPAL PLANNING

AND MANAGEMENT

Tiago Martins

, Pedro Brandão Silva

, António Coelho

1,2

and A. Augusto Sousa

1,2

INESC Porto, DEI, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

3Decide / Palcos da Realidade, UPTEC - PINC, Praça Coronel Pacheco, 2, 4050-453 Porto, Portugal

Keywords: Urban Ontology, Interactive Collaborative Virtual Environment, Procedural Modeling, Virtual Reality.

Abstract: The municipal planning and management tasks are generally performed based on text documents or through

digital maps provided by geographic information systems (GIS). However, most municipal GIS follow

different data models, leading to interoperability problems when there is a need to combine data from

different sources. Furthermore, most of the time these tasks are performed in a collaborative way between

the municipal technicians, emerging some difficulties in decision making due to the three-dimensional

nature of urban space. Thus, this paper describes a methodology which can integrate multiple sources of real

data from diverse municipal GIS, in a unified data model based on the CityGML specification. This model

is mapped onto an urban ontology oriented for procedural modeling, which, in turn, produces the three-

dimensional models of the urban environments. The system developed operates in a client-server approach,

where the server is responsible for mapping the urban information to the unified data model and the client

represents the procedural modeling technology that generates the urban environment in three-dimensional

format, allowing users to interact and amplify the existing urban information.

1 INTRODUCTION

GIS systems are very common in urban planning

and management, since they enable and facilitate the

analysis, administration and representation of the

urban spaces. However, most municipal GIS follow

different data models, leading to integration

problems, and in addition, these tasks are often

performed in a collaborative way between the

municipality technicians emerging thereby some

difficulties in decision making due to the three-

dimensional nature of urban space. In this sense,

virtual urban environments can be used with great

effectiveness, since 3D models are natural

metaphors for the interaction with the urban

environments.

Due to these factors, new perspectives arise

concerning new ways of exploration and

development of urban spaces, such as the use of

automatic techniques to generate the virtual urban

environments. Thus, this work has as its main goal

the development of a methodology which allows the

integration of real world data sources, from different

municipal GIS, in an unified data model, mapped

onto an urban ontology oriented for procedural

modeling. This information is then displayed in

three-dimensional format by employing procedural

modeling methodologies, providing a more natural

and intuitive system to operate on the virtual urban

environments.

2 RELATED WORK

The main reason to use urban ontologies is because

they can help extracting information related to the

vocabulary used in the municipal planning and

management, in order to minimize interoperability

and cooperation issues between databases with

urban information from different sources (Laurini,

2007). Over the years, several standard data models

have focused on the issue of interoperability, such as

the GML (Portele, 2007), KML (Wilson, 2008) and

CityGML (Groger et al., 2008).

The Geography Markup Language (GML) is an

XML data model for transport and storage of

geographical information, including spatial and non-

spatial characteristics and whose specification

507

Martins T., Brandão Silva P., Coelho A. and Augusto Sousa A..

AN URBAN ONTOLOGY TO GENERATE COLLABORATIVE VIRTUAL ENVIRONMENTS FOR MUNICIPAL PLANNING AND MANAGEMENT.

DOI: 10.5220/0003849705070510

In Proceedings of the International Conference on Computer Graphics Theory and Applications (GRAPP-2012), pages 507-510

ISBN: 978-989-8565-02-0

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

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

GRAPP 2012 - International Conference on Computer Graphics Theory and Applications

508

et al., 2008). The geometric model is responsible for

storing the geometrical information of urban

elements while the appearance model is responsible

to store the information about the appearance of

urban elements, such as the visible properties that

reinforce their 3D representation. The thematic

models allow the definition of classes which

represent the different types of objects contained in a

city, allowing the storage of the thematic and

semantic concepts of the entities that characterize

the urban space (Figure 1).

3.2 Data Mapping

Since the information about urban elements is not

centralized on a single data source and, furthermore,

knowing that this information is not common to the

majority of GIS data sources of the municipalities

and government institutions, different levels of

mapping were defined, according to the available

information detail of the urban elements. Thus, the

concept of LOM (Level of Mapping) was introduced

which refers the minimum information that an entity

must possess for a certain kind of procedural method

to be used. This allows the definition of more

specific model generation rules, therefore

eliminating the need to check for the existence and

validity of each data field.

Besides the definition of LOMs, it becomes

necessary to create processes that map the

information from the municipal GIS into the defined

data model, which is not a simple task, mainly due

to the size and complexity of urban information.

Additionally, data from the information sources of

the municipalities have different formats and data

models. These problems are derived by the lack of a

unique and uniform data model.

Thus, a methodology was specified, allowing the

mapping of the information onto the data model. The

first stage is not automated, and human intervention

is required in order to interpret the original data to

be mapped, since most of documentation is only

intended for humans. So, it is required that the

meaning of the original data is interpreted, for which

the data model tables and columns of these tables

will be mapped, and the type of operations that will

Figure 2: Mapping the original data (left) in the data

model (right).

focus on these data. This information represents the

settings for the mapping of the original data and it

can be specified through external files such as XML,

for example. Figure 2 illustrates an example of this

process.

3.3 Implementation

The developed system operates in a client-server

architecture, where the server is responsible for

mapping the urban information and the client

represents the procedural modeling technology. The

mapping server was implemented with a

PostgreSQL database management system, equipped

with the spatial extension PostGIS and the

procedural language PL/pgSQL. In addition to the

mapped data, the server provides, through Web

Services, a set of operations that allow the

procedural modeling technology to access, edit and

amplify the existing urban data. The procedural

modeling technology, represented by the PG3D

modeler (Silva, Coelho, 2011) has the responsibility

for generating the information of urban space in

three-dimensional format. After the procedural

generation, users can view and interact with the

urban environment. In order to achieve this, the

mapping server contains a version control system

capable of storing different instances of the same

object, which means a previous version can be

retrieved at any time.

Figure 3 shows an overview of the architecture

of the implemented system.

Figure 3: Overview of the architecture.

4 RESULTS

A proof of concept has been developed, consisting in

the demonstration of each involved step. The

original data was obtained from two different

sources of information representing buildings that

were defined in two levels of mapping (LOM0 and

LOM1). This information was then mapped into the

AN URBAN ONTOLOGY TO GENERATE COLLABORATIVE VIRTUAL ENVIRONMENTS FOR MUNICIPAL

PLANNING AND MANAGEMENT

509

defined data model. Out of it, the visualization of an

urban environment was achieved, which was created

based on real data, and which allowed users to

interact and to amplify the existing urban

information. Figure 4 shows the final result.

Figure 4: Viewing and editing of

urban

inf

ormation.

After confirming the edition, the PG3D modeler

requests an operation to the web service provided by

the mapping server, so that it records the changes in

the database of urban ontology. These changes

involve the creation of a new version for the

manipulated building. The previous version goes to

an inactive state, but can be retrieved.

5 CONCLUSIONS AND FUTURE

WORK

This paper presents a unified data model based on

the CityGML specification oriented towards the

procedural modeling of collaborative virtual urban

environments.

Due to the size and complexity of the urban

environments there is still much work to do. The

real data used in the proof of concept represented

only the buildings. In addition to these, a city

consists of other entities such as streets, water

bodies, vegetation, and city furniture, among others.

Each entity requires a detailed and independent

study about the mapping process of information

sources of these objects. Therefore, future work will

concern the study of the mapping data for these

entities, allowing the development of a prototype

with a higher quality of information about the urban

environment. Additionally, it is necessary to refine

and create new features for manipulating the existing

urban information in order to perform tests that

confirm the visual fidelity of the urban environment.

ACKNOWLEDGEMENTS

This work is partially supported by the Portuguese

government, through IAPMEI, and the European

Union (QREN and FEDER) through the project

QREN 2010/12319 SI I&DT entitled “GIS2R –

Geração e Exploração de Ambientes 3D Urbanos

Reais”.

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