UDMV13: Eurographics Workshop on Urban Data Modelling and Visualisation

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NightLighting: a Nocturnal Urban Illumination Approach
(The Eurographics Association, 2013) Muñoz-Pandiella, Imanol; Andújar, Carlos; Patow, Gustavo; Vincent Tourre and Gonzalo Besuievsky
Real time rendering of cities with realistic global illumination is still an open problem. In this paper we propose a two-step algorithm to simulate the nocturnal illumination of a city. The first step computes an approximate aerial solution using simple textured quads for each street light. The second step uses photon mapping to locally compute the global illumination coming from light sources close to the viewer. Then, we transfer the local, highquality solution to the low resolution buffers used for aerial views, refining it with accurate information from the local simulation. Our approach achieves real time frame rates in commodity hardware.
Inverse-Procedural Methods for Urban Models
(The Eurographics Association, 2013) Musialski, Przemyslaw; Wimmer, Michael; Vincent Tourre and Gonzalo Besuievsky
Procedural modeling is an elegant and fast way to generate huge complex and realistically looking urban sites. Due to its generative nature it can also be referred to as forward-procedural modeling. Its major drawback is the usually quite complicated way of control. To overcome this difficulty a novel modeling paradigm has been introduced: it is commonly referred to as inverse procedural modeling, and its goal is to generate compact procedural descriptions of existing models-in the best case in an automatic manner as possible. These compact procedural representations can be used as a source for the synthesis of identical or similar objects, applied in various simulations and other studies of urban environments. We believe that this technology is still a widely unexplored ground and that it will prove itself as a very important tool in the reconstruction process. In this paper we sketch how inverse procedural modeling can be applied in the urban modeling field.
Taking Advantage of Low Radiative Coupling in 3D Urban Models
(The Eurographics Association, 2013) Beckers, Benoit; Vincent Tourre and Gonzalo Besuievsky
We examine different techniques able to enhance the efficiency of urban simulations. Condensation techniques like superelements - well known in the finite element community - are good candidates to improve the heat transfers simulations inside the city. Three typical situations are examined. In the first one, concerned with the interaction of inside and outside scenes through windows, the two problems can be analyzed successively. The second situation presents a weak coupling of radiation between built settings. The last one refers to the full radiative budget of a city; it is used to illustrate the possibility of applying superelement techniques to the linear part of the problem. The conclusion is that these techniques are able to help enhancing the efficiency of the simulations.
Interactive Techniques for Populating Large Virtual Cities
(The Eurographics Association, 2013) Jordao, Kevin; Pettré, Julien; Cani, Marie-Paule; Vincent Tourre and Gonzalo Besuievsky
For many applications, exploring empty virtual cities is not sufficient: streets and squares need to be populated by crowds of virtual humans. This position paper addresses the problem of generating such crowds when the scale of the city prevents the use of standard simulation methods. We first present the concept of crowd patches and review their advantages and drawbacks for animating large crowds of people. We then discuss the goals of our future work, namely being able to interactively design such large populations.
Indoor Scene Reconstruction using Primitive-driven Space Partitioning and Graph-cut
(The Eurographics Association, 2013) Oesau, Sven; Lafarge, Florent; Alliez, Pierre; Vincent Tourre and Gonzalo Besuievsky
We present a method for automatic reconstruction of permanent structures of indoor scenes, such as walls, floors and ceilings, from raw point clouds acquired by laser scanners. Our approach employs graph-cut to solve an inside/outside labeling of a space decomposition. To allow for an accurate reconstruction the space decomposition is aligned with permanent structures. A Hough Transform is applied for extracting the wall directions while allowing a flexible reconstruction of scenes. The graph-cut formulation takes into account data consistency through an inside/outside prediction for the cells of the space decomposition by stochastic ray casting, while favoring low geometric complexity of the model. Our experiments produces watertight reconstructed models of multi-level buildings and complex scenes.
Online Reconstruction of Textured Triangle Meshes from Aerial Images
(The Eurographics Association, 2013) Vierjahn, Tom; Roters, Jan; Moser, Manuel; Hinrichs, Klaus; Mostafawy, Sina; Vincent Tourre and Gonzalo Besuievsky
In this paper we present and evaluate a new online reconstruction algorithm to create a textured triangle mesh from a set of aerial images via an unorganized point cloud. Both the point cloud and the mesh are iteratively refined while allowing new aerial images to be added at any time during reconstruction. Texture coordinates are learnt to instantly visualize an initially rough approximation that gets refined as more data becomes available. The new algorithm improves upon other systems that require the complete data to be acquired beforehand, and that apply offline, non-iterative reconstruction and processing. Thus, our algorithm is perfectly suited for time-critical applications, e. g., strategical visualization platforms for disaster and emergency response.
Challenges and Ideas in Procedural Modeling of Interiors
(The Eurographics Association, 2013) Ilcik, Martin; Wimmer, Michael; Vincent Tourre and Gonzalo Besuievsky
While the creation of convincing cityscapes from the outside is already possible, there is a lack of robust and efficient techniques for modeling the interior of buildings. In particular, we focus on challenges for the subdivision of the interior space into rooms and for placement of furniture in those rooms.
Challenges in Procedural Modeling of Buildings
(The Eurographics Association, 2013) Patow, Gustavo; Besuievsky, Gonzalo; Vincent Tourre and Gonzalo Besuievsky
The use of procedural modeling for building generation has risen dramatically over the last years, being an elegant and fast way to generate huge, complex and realistically looking urban sites. However, due to its generative nature there are still unsolved problems that limits they usage. In this paper we report on the challenges still pending on procedural modeling of buildings. We provide a state of the art on most recent solution and we draw possible research avenue that could be taken for spreading the use of procedural modeling in current applications.
Toward Automated Façades Generation from Oblique Aerial Images
(The Eurographics Association, 2013) Vahl, Matthias; Lukas, Uwe von; Vincent Tourre and Gonzalo Besuievsky
In this paper we introduce an approach for automatic recognition and description of building façades from oblique aerial images. This approach does not use street-side images, like Google StreetView, but aerial images to derive photorealistic city models. The paper starts with a short summary of the state of the art in the domain of imagebased modeling, automated recognition and description of façades from (oblique aerial) images. Then the context of the research project is described including the hardware setup and and application requirements for complex façade analysis. Afterwards a novel approach of a grid graph model with traversers is suggested to solve the problem of façade recognition. The framework that implements the approach in a flexible manner is introduced. Finally, the paper ends with a conclusion and an outlook to future works.
Understanding City Dynamics through Spatio-temporal Visualization
(The Eurographics Association, 2013) Dias, Luís; Silva, Nelson; Cardoso, Tiago; Fonseca, Manuel J.; Vincent Tourre and Gonzalo Besuievsky
Every time we visit a new city there is a huge effort made in understanding its dynamic, i.e. what are the relevant locations within that city in each time period, for there are large amounts of data to sift through. Although several attempts have been made to combine information from various sources, the majority focus on geographic data, lacking on time representation. In this paper we describe and evaluate three representation approaches for spatiotemporal data, to understand which is better to convey the dynamics of a city at a glance. We devised 2D and 3D visualizations to understand their adequacy to our objectives. Based on the results from the evaluation with users we noticed that they preferred the 2D visualization of the data, but on the other hand there was no significant difference to the 3D representation.
Dual-Domain Visual Exploration of Urban Solar Potential
(The Eurographics Association, 2013) Seipel, Stefan; Lingfors, David; Widén, Joakim; Vincent Tourre and Gonzalo Besuievsky
Traditional methods for estimating the solar energy potential in buildings determine energy yields on an annual base and make use of highly aggregated geo-spatial data. This work proposes a method for detailed assessment of the potential solar energy yield in the temporal and spatial domain. Solar irradiance is evaluated using numerical methods based on hourly variation of solar irradiance and on actual building geometry. Results of our initial studies allow exploration of the variation patterns in solar yield depending on local and time-varying factors, which cannot be seen in coarse level solar planning tools. This helps identifying surfaces with good solar yield that are deemed unfavorable according to traditional planning practices.
A General Strategy for Semantic Levels of Detail Visualization in Urban Environment
(The Eurographics Association, 2013) Zhang, Fan; Tourre, Vincent; Moreau, Guillaume; Vincent Tourre and Gonzalo Besuievsky
Applications based on urban environments are applied frequently in daily life which increases the needs for a high quality visualization result. It combines the urban environment and the special application-related topic together. The urban environment can be visualized with different scales, namely with different levels of detail to improve rendering and processing performance of the application. Visualization for the special topic, semantics, similarly is in need of a smart strategy to stay consistent with information density. This paper proposes a general strategy to handle semantic levels of detail visualization in urban environment. An example is given to illustrate how it is applied. Later, a mapping between urban environment levels of detail and semantic levels of detail is discussed. In the last part, the limitations of the general strategy are stated. And visualization issues for semantics are listed such as the proper visualization form and technique for a given semantic level of detail. This paper aims to bring about a wider discussion on semantic levels of detail visualization in urban environment.

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