1SPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
3D MODELLING FOR AUGMENTED REALITY 
Siyka ZLATANOVA 
Department of Geodesy, Delft University of Technology 
Thijsseweg 11,2629 JA, Delft, The Netherlands 
s.zlatanova@qeo.tudelft.nl 
KEYWORDS 3D topology, 3D model, spatial objects, 3D visualisation, 3D GIS, real-time 
ABSTRACT 
This paper addresses an approach for storing 3D spatial objects with respect to the requirements of an outdoor augmented reality 
application. The presented 3D data structure focuses spatial objects of urban areas, as the aim is support of 3D topology, high level of 
details and appropriate performance. To satisfy these contradictory requirements, only the outlines of spatial objects are organised in a 
3D topological model. Details on façades (e.g. doors, windows) are modelled as line features. An explicit relationship “line on face" 
indicates the link between the lines and the corresponding façades. The paper concentrates on the 3D topological data structure, which 
a typical example of so called boundary representations. The 3D data structure is implemented in Oracle 8/ DBMS using three different 
approaches, i.e. relational, relational with object views and object-relational. The tests have showed that the proposed data structure 
can be tuned to meet the needs of real-time rendering and positioning for augmented reality. We consider our results a promising step 
toward extending 3D GISs to serve real-time applications. 
1 INTRODUCTION 
Augmented reality is a mixture of reality and virtuality that allows 
real world to be augmented with additional information. Virtual 
objects (text or graphics) are visualised in the field of view via 
special transparent glasses. The user can observe the 
surrounding world and the virtual objects simultaneously (see 
Figure 1). Until recently, the augmented reality application were 
restricted to indoor applications e.g. surgery, inspection of 
hazardous spaces. With the advances of the computer and 
vision technology, augmented reality systems attempt to leave 
the world of indoor applications, which rises new challenging 
topics for research. Among them, structuring and database 
organisation of the 3D model required for positioning and 
visualisation of virtual objects is most pressing. Augmented 
reality aiming at outdoor urban applications (e.g. rescue 
operations, utility management, urban development, guided 
navigation) needs a 3D model of size comparable to a town, i.e. 
thousands of houses, streets, parking lots, etc. For example, the 
national 2D topographic map of The Netherlands contains about 
31 million line objects (see [12]). In residential areas this number 
might increase three or four times for the corresponding 3D 
model. Such an application faces all the problems in processing 
and maintaining large 3D data sets. 
This paper presents a 3D model aiming at both maintenance of 
3D topology (one of the most important features of a 3D GIS) 
and efficient organisation of 3D data for augmented reality 
applications. The paper is organised in four sections: first the 
requirements to the data structure are specified with respect to 
the tasks of the vision system, second the proposed data 
structure is discussed, then the 3D re-construction procedures 
are briefly explained and finally some initial experiments within 
Oracle database are reported. The research is a part of the 
interdisciplinary UbiCom project carried out at Delft University of 
Technology, The Netherlands (see [11]). 
Figure 1: A person with mobile equipment and the observed 
view 
2 REQUIREMENTS 
Discussions related to the content and the structuring of data in 
3D GIS can be found in many publications on 3D GIS (see [2], 
[3], [8], [13], [15]). Therefore, in this paper, we focus the specific 
requirements to the 3D model with respect to the vision system 
intended in the UbiCom project. 
The 3D model is to be used for two critical subsystems of the 
system architecture, i.e. positioning and visualisation (rendering) 
of virtual objects. The expected types of data retrieved from the 
database are different for both subsystems. 
• Line features. The positioning system in UbiCom relies on 
line features (straight lines) supplied by the database. The 
term positioning refers to determining the accurate location 
of the user (i.e. the person using the system) in the real 
world. The movement of the user is followed (tracked) by 
mobile equipment (GPS, accelerator and inertial system) 
that provides an approximate positioning at range of 2-10 
meters. The accurate positioning is to be achieved by 
establishing the correspondence between lines extracted 
from video images (provided by the video camera that is 
also a part of the mobile unit) in real-time and lines 
retrieved from the 3D model (see [8]). The success of the 
line matching (and thus the accurate positioning) is closely 
related to the amount of details maintained in the 3D 
model. 
• 3D topology. In contract to positioning, the visualisation of 
virtual objects requires no details but correct shape and 
orientation of the real objects. Since the virtual object is 
“mixed” with the real world, it is very likely a real object to 
appear between the virtual one and the user. In this case 
the real object is said to be an occluder of the virtual object 
(see [7]). The user should not see the occluded parts of the 
virtual object. In other words, the rendering engine has to 
be able to compute which parts of the virtual object are not 
visible in that particular moment and remove them from the 
scene. The computations require the accurate location of 
the user (provided by the positioning system) and the 3D 
model of the real objects (retrieved from the 3D GIS). The 
3D model has to ensure connectivity and continuity. 
• Performance. The mobile equipment is capable of tracking 
the movement in certain period of time without reference to 
the database. This period depends on the speed of walking 
and the movements of the head. The estimation is that 
every 6-7 sec the system has to receive new data sets from 
the database. Within this time (called lag of the system), a 
query has to be sent to the database, processed and the 
retrieved data has to be transmitted back to the mobile unit. 
The performance of the database is one of the critical 
issues influencing the lag of the system. 
• Vector representation. Since both rendering and 
positioning system use vector representation, we 
concentrate on vector data structures. 
. VRML. The Virtual Reality Modelling Language was chosen 
as a standard to exchange data between the individual 
subsystems. The language provides a full and flexible