UDMV: EG 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.
Hierarchical Radiosity for Procedural Urban Environments
(The Eurographics Association, 2014) Roure, Ferran; Besuievsky, Gonzalo; Patow, Gustavo; Gonzalo Besuievsky and Vincent Tourre
In this paper we present a novel solution for the computation of diffuse global illumination in urban environments that takes advantage of the underlying structure of the procedural building models used for generating the city, using them to compute a realistic global illumination solution based on the well known hierarchical radiosity algorithm. As we generate the geometry procedurally, we take advantage of the generation hierarchy to be the base of the hierarchical radiosity algorithm, without using the classic quad-based subdivision scheme. This structure is used for low-frequency global illumination, being later combined with a shadow-map-like system for the highfrequency component, thus resulting in a complete global illumination solution for procedural urban environments.
Ground Temperature Modelling: The Case Study of Rue des Maraîchers in Geneva
(The Eurographics Association, 2014) Upadhyay, Govinda; Kämpf, Jérôme; Scartezzini, Jean Louis; Gonzalo Besuievsky and Vincent Tourre
This paper presents a methodology to approximate the urban heat island effect by using a PostgreSQL database and CitySim software, a simulation tool to evaluate urban energy flows. A ground temperature model has been developed for shallow depths (until 4m), which reproduces the phenomena of heat transfer into the ground on an hourly basis. This model is further used to predict the outdoor ground surface temperature, which is an indicator of the urban heat island effect. A PostgreSQL database which contains information such as the building footprints, geographical location, address, construction date, energy system etc. of the buildings was modified to include data relative to this model. A case study has been performed in a small neighbourhood, Rue des Maraîchers, in Geneva (Switzerland) in order to illustrate the usage of this tool to analyse the surface temperature of asphalted roads and green alleys. Finally, a methodology has been introduced to predict the urban heat island effect using this temperature.
Managing Temporal Change of Cities with CityGML
(The Eurographics Association, 2014) Morel, Maxime; Gesquière, Gilles; Gonzalo Besuievsky and Vincent Tourre
An increasing number of cities are developing digital models. It becomes thus necessary to take into account changes over time. Interoperability and thus the use of standards is also recommended. In this paper, we propose a new method, based on CityGML to take into account changes in the objects which compose the city. This method is efficient for any kind of changes of the city objects (semantic, geometry, topology or appearance). We then propose an extension of our method in order to consider more frequent changes as it is the case with sensors data that can be linked with part of city objects.
A Configurable LoD for Procedural Urban Models intended for Daylight Simulation
(The Eurographics Association, 2014) Besuievsky, Gonzalo; Barroso, Santiago; Beckers, Benoit; Patow, Gustavo; Gonzalo Besuievsky and Vincent Tourre
In many applications, such as in massive urban models visualization or in the study of the impact of urban simulation at different scales, models with different levels of detail are required. In this paper we propose a flexible system for configuring level of details models using Procedural Modeling aiming to generate only the geometry required for each specific need. We test our system for a solar simulation analysis at urban scale. We evaluate the solar irradiation and the Sky View Factor in order to study the impact at different scales. We show that our tool provides a way to handle the complexity of urban scale models, and specifically to study the sensitivity of the geometry.
Applying Level-of-detail and Perceptive Effects to 3D Urban Semantics Visualization
(The Eurographics Association, 2014) Zhang, Fan; Tourre, Vincent; Moreau, Guillaume; Gonzalo Besuievsky and Vincent Tourre
Urban environment consists of various types of data, both geometric ones and non-geometric ones, among which urban semantics are important sources for non-geometric data. The modelling and visualization of urban semantics is one type of information visualization (InfoVis). In both 2D and 3D environment, a lot of work has been done, which use different kinds of representation forms to illustrate knowledge and information stored in the original abstract dataset. This paper aims to apply the idea of information level-of-detail (LoD) to urban semantics visualization and a text-based semantic database is built to illustrate how the idea works. Then in the implementation process, four perceptive factors for text visualization are chosen, while we mainly test, compare and analyse text size, aiming to better aid users find new knowledge and make decisions.
Topological Reconstruction of Complex 3D Buildings and Automatic Extraction of Levels of Detail
(The Eurographics Association, 2014) Diakité, Abdoulaye A.; Damiand, Guillaume; Maercke, Dirk Van; Gonzalo Besuievsky and Vincent Tourre
This paper describes a new method allowing to retrieve the indoor and outdoor topology of a detailed 3D building model from its geometry and to extract different levels of detail (LoD) from the resulting topological description. No prior information about the initial model, except its geometric information is needed as input, and using the combinatorial maps data structure, the method recovers the topological information of the identified parts of the building. The topology is needed for most of the applications using 3D building models after the architects design it. While classical models available are mainly furnished in a Boundary Representation (B-Rep) format, we discuss how to recover the components that allow to distinguish the several parts of the building (defined as volumes) then the spatial relationships linking them.
Visualizing Street Orientation and Solar Radiation in Relation to Complex Topography
(The Eurographics Association, 2014) Mohajeri, Nahid; Gudmundsson, Agust; Kämpf, Jérôme H.; Scartezzini, Jean Louis; Gonzalo Besuievsky and Vincent Tourre
Street networks can be visualized in various ways depending on the purpose. Here we introduce (in the present context) a new technique for visualizing the orientation of street networks in relation to complex topography. The technique is tested on the city of Sheffield, England, with a current population of about 555,500 (in 2010) and a total street number of 23,500. Using digital elevation maps and unique historical datasets, we show how the street network of Sheffield has expanded in a complex topographical environment for close to three centuries, that is, since 1736. The results demonstrate how the topography has affected the spatial orientation of the evolving network. We quantify the network geometry through entropy analysis; entropy is a measure of dispersion or spreading. The results show that the orientation entropy of the network has gradually increased with time. In 1736 the network was primarily composed of orthogonal streets, and had comparatively low entropy. As the network expanded the topographical constraints have contributed to the street orientation becoming more uniform on the rose, resulting in increasing entropy. The analysis also shows that the entropy of the central part of the present network is lower than that of the outer and younger parts. The potential solar radiation for Sheffield is also calculated, visualized, and compared with the topography model and the street network density. The results show that the network density (number of streets per unit area) correlates solar radiation; high-density parts of the network tend to coincide with high-intensity solar radiation.
Incremental Plane-based Reconstruction and Exploration of Buildings in old Postcards
(The Eurographics Association, 2014) Younes, Lara; Romaniuk, Barbara; Bittar, Eric; Gonzalo Besuievsky and Vincent Tourre
We present an approach for 3D reconstruction of a city model over the time from a collection of old postcards of the city of Reims. The planar structure of the buildings façades constraints the dense reconstruction of the city. We use a feature matching technique while proposing the registration of façades in the images and there use for the reasoning about there visibility in the images. This system is semi-automatic, it requires a user control in the complicated case where no matches are found to link an image to the dataset. The image data set is sparse and the urban space evolves over time.

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