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Section: Scientific Foundations

3D cities reconstruction

Participants : Cédric Guiard, Chun Liu, Emilia Lombardo, André Gagalowicz.

Cities are of multi-dimensions, highly functional and with visual complexity. They are the concentration of history, culture, economy, and ecology, etc. Therefore, modeling and visualizing realistically 3D cities using computers covers various disciplines and is a real challenge to researchers in different research domains. The potential applications for creating 3D cities range from research and educational purposes like urban planning and global navigation to entertainment like tourism and 3D computer games. Buildings, as one of the main objects in cities, differ from one another in many aspects like motif, style, dimensions, etc. Facades can to a great extent reflect most aspects of one building. Therefore, our research will mainly focus on 3D facade reconstruction based on multi-source informations (including aerial images, ground images, architectural knowledge, etc.). Our goal is to create a real time 3D facade reconstruction system with a user friendly interface. Three major challenges will be tackled:

Ranging from the generation of typical buildings appearance considered to populate the environment to the accurate reconstruction of existing ones regarding specific fidelity and precision constraints, the production of 3D buildings representation draws a bridge between Computer Graphics and Computer Vision approaches.

Techniques in Computer Graphics are interested in large-scale modeling making use of procedural schemes. Introduced in the 70's [39] as a formal approach to architectural design, Shape Grammars have recently evolved to extend their derivation mechanisms ( [36] , [41] , [33] , [34] ). Shape grammars can be complemented by cellular textures [30] and generative mesh modeling to generate facade ornaments. Meanwhile; these techniques do not allow to account for precise similarity constraints to a real environment.

Conversely, there is a wide spectrum of strategies for urban reconstruction in Computer Vision. Depending on considered input data : single image [35] , ground-based facade images ( [21] , [40] ), interactive editing using aerial images [37] , aerial images combined with ground-based panorama images [42] , ground-based laser scans combined with aerial images or airborne laser scans [24] , [25] , these systems still resort to semi-automatic and notorious fragile methods having quite difficulties to extract the structural characterization of the considered constructions.

All these different acquisitions types (geo-referenced through the help of the numerical foot print; cadastre delivered by ING) are considered and accessible in the scope of the TERRA NUMERICA project. In this context, our scientific objective is to establish a virtuous loop linking image-based analysis techniques to model-based building characterization through the introduction of an innovative reconstruction scheme counting for the simultaneous registration of planimetric, 2D photo and 3D scans acquisitions. This approach is foreseen to couple the respective advantages carried by these techniques able to resolve their respective weaknesses in order to:


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