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GEOMETRIC AND THEMATIC ENRICHMENT OF FRONTAGES IN 3D CITY-MODELS 
M. Koehl*, V. Gaiotti 
INSA de Strasbourg, UMR MAP-PAGE n°694 CNRS/MCC, 24 Boulevard de la Victoire, F-67084 Strasbourg 
Cedex, France, 
Mathieu. Koehl@insa-strasbourg.fr 
gaiotti.vincent@libertysurf.fr 
Commission III, WG III/7 
KEY WORDS : Modeling, Reconstruction, City, Model, Urban, GIS, Geometry, Thematic 
ABSTRACT : 
Urban space is a three-dimensional space. That is why the 3D is often required when it is a question of representing it. G.I.S. existing 
applications already propose 3D tools, but actually, these tools are only visualization tools, mainly designed to facilitate the 
understanding of the urban space. The tools developed within the laboratory MAP-PAGE propose to enrich the urban models 
generally resulting from aerial photogrammetry by using photographs of the frontages of the buildings. Indeed, these images make it 
possible to integrate a certain number of data by describing three-dimensional phenomenon pushed aside by the mono-surface 
representation of the frontages (number of stories, overhanging parts of the building, balconies, etc). Beside contributing to a 
thematic enrichment of the urban model, the possibility of measuring on the pictures will also allow a geometrical enrichment of the 
model. 
RESUME : 
L'espace urbain est tridimensionnel. Ainsi a-t-on trés souvent recours à la 3D quand il s'agit d'en faire une représentation. Les 
applications fonctionnant dans des environnements S.I.G. proposent une large panoplie d'outils 3D, mais ces outils sont souvent 
restreints à des outils de visualisation permettant une représentation et une compréhension plus aisée de l'espace urbain. Les outils 
qui ont été développés dans le laboratoire MAP-PAGE proposent d'enrichir les modèles urbains généralement issus de la 
photogrammétrie aérienne en utilisant des photographies des façades des bâtiments. En effet, ces images rendent possible 
l'intégration d'un certain nombre de données complémentaires concernant des phénomènes 3D. La simple face de la façade peut ainsi 
être enrichie de données thématiques concernant notamment le nombre d'étages, la présence de parties en surplomb, de balcons, etc. 
Enfin, l'enrichissement thématique du modèle est accompagné d'un enrichissement géométrique du modèle à partir des mêmes 
images qui permettent d'y faire des mesures. 
I. INTRODUCTION thematic aspects of the buildings. Like it will be demonstrated 
in the following part of this paper, images allow also to perform 
measurements on geometric data and so to extend the models 
with a more detailed geometry of the frontages, which are, 
together with the rooves the visible parts of the city models. 
c 
1.1 Aim of the system 
The MAP-PAGE laboratory has now a good experience in the 
construction of 3D city models. These models are realized by 
using techniques and initial measurements from aerial 1.2 Method 
photogrammetry. They are then build by using some projection 
algorithms developed internely. In a first time, the models are 
only geometric models and are based on constitution and 
construction concepts developed in different works like Koehl 
[1999]. 
The models have a precision in keeping with the initial data in 
particular with the resolution of the aerial photographs used. 
Even if the use of the models seems to be easy and the needs of - not too much information, but only relevant information, 
vizualization of urban scenes seems to be good in adequation - the photographs provide also the texture material later used for 
with these models particularly for small scales, we must the texturing of the model, 
conclude that these models are really poor structured and offers 
no real possibilities to make thematic queries. : 
The aim of the system designed is to enrich the models by using 
the techniques of the terrestrial photogrammetry and images of 
the frontage of the buildings described in the models. These 
complementary data are packed full of new information which 
allows in the same time to understand and to complete a lot of 
The method decided to be used to perfom the integration of 
suplementary information and which is the central point of this 
project is the using of images (photographies, snapshots) of the 
frontages of the buildings. 
This idea find his justification in some interests : 
- very fast data acquisition, 
- the accuracy of the GIS for the later exploitation of the model 
does not often need to use specific methods for the shooting of 
the images. This makes it possible to use existing images. 
The aim of the tools we have developed is to perform the data 
extraction from a set of images and the data integration in the 
3D model and in an associated database. 
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