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3D VISUALIZATION AND QUERY TOOL FOR 3D CITY MODELS 
R. Dogan", S. Dogan?, M. O. Altan? 
"Directorate of 12nd Region of Village Services, Samsun, Turkey - dogan_rukiye@hotmail.com 
’Ondokuz Mayis University, Engineering Faculty, Dept. of Geodesy and Photogrammetry, 55 139, Kurupelit, Samsun, 
Turkey - (sedatdo@omu.edu.tr) 
‘ITU, Civil Engineering Faculty, 80626 Maslak Istanbul, Turkey - oaltan@itu.edu.tr 
Commission II, WG III/7 
KEY WORDS: 3D, city, modelling, GIS, databases, photorealism, query, analysis 
ABSTRACT 
For 3D city management visualization, query and the analysis of 3D data related to cities are very important tasks. In this paper, we 
present a tool (3D-City VAQS/ 3D-City Visualization Analyse and Query System) that can effectively visualize and query 3D city 
models. We use relational database model to represent geometry and topology of 3D city data. We organize 3D data in layers and 
themes and each theme has their own attribute tables. Our tool provides to query both geometry and attribute information of 3D data. 
We use V3D data structure and implement it in a relational database. 
1. INTRODUCTION 
Use of 3D spatial information for modern city management 
plays important role, especially for the tasks of spatial planning, 
communication, emergency management etc. These tasks can 
be realized easily and effectively by the 3D representations of 
the spatial and thematic attribute information together with in a 
geographic database. The generic idea of GISs is to incorporate 
geometric and semantic information in one system and to 
support analysis in both domains, (Zlatanova, 1999). A 3D GIS 
should satisfy various spatial operations. These operations can 
be summarized as follows: (Goodchild, 1987; Aronoff, 1995; 
Zlatonova, 1999). 
e Access to semantic properties of one type object, 
e Access to both semantic and location information, 
e Operations which create object-pairs. (e.g. buildings 
in a given parcel that have one owner.) 
e Operations analyse semantics of object pairs from 
one or more types. 
* Operations which create a new type of object from 
existing objects. 
* Retrieval operations. (e.g. what is the current 
information about a particular building.) 
e Query operations retrieve data which satisfies some 
given conditions. 
e Retrieval and query of semantic data. 
* Integrated analysis of spatial and semantic data, 
(classification, measurement, overlay operations.) 
e Neighbourhood operations, (search, topographic 
operations, contour generation etc.) 
* Connectivity operations, (contiguity measurements, 
buffering, networking etc.) 
e Output formatting, (map annotation, text labels, etc.) 
For the above operations, firstly the geometric and the 
thematic characteristics of objects and their spatial 
relationships should be integrated in a database. 
559 
Geometry defines the location and shape of the 3D 
objects in space. On the other hand, topology allows to 
take into account various relationships between the 
objects in the space. Examples for these relationships can 
be given as adjacency, inclusion, overlapping etc. Here, 
topology can be considered as complement of the 
geometry. Topological relations of objects are deduced 
from their geometry. For example, in order to find 
adjacency of objects, one should look at the geometry and 
find the adjacent points, edges, facet surfaces etc. This 
operation requires expensive searches, computations and 
comparisons in the geometric domain. To overcome this 
costly expensive operation processes, it is a good solution 
approach to store topological relations in an explicit 
form. Thus, for one time expensive operations are 
performed and at the result of these operations, the 
constructed or found topological relations are stored in to 
a database for further query and analyse operations 
without repeating the complex processes. Here, the 
requirement of a database to be used for storing of the 
topological relations, can be seen easily. But on the other 
hand, to visualize 3D data on the computer's graphics 
hardware (on the screen), geometry of the spatial objects 
should be presented to the graphic displays in the proper 
rendering primitives, which are supported by OpenGL 
standards. For the rendering of the 3D data, geometry 
information should also be represented effectively in the 
database. 
Research in the GIS community is trying to work out a 
conceptual model capable of integrating geometric and 
thematic characteristics of objects and mutual spatial 
relationships. These models can be considered as an 
explicit description of cells (or objects), (Zlatanova, 
1999). In the past, several methods for 3D object 
description have been investigated. These models can be 
grossly subdivided into wire-frame, B-Rep, VBR, cell- 
decomposition, FBR, CSG, (Gruen and Wang, 1999). 
Another efficient model is Molenaar's 3D topological 
vector structure, the formal data structure (FDS), (Gruen :