Vieillissement interactif pour la synthèse d'image réaliste des environnements urbains

Abstract : Being able to capture and synthesize realistic materials is an important research topic in Computer Graphics. In order to render realistic images it is not enough to represent materials reliably, but we also need to represent its temporal component. Simulation of weathering effects is the research area that pursues the incorporation of decay to virtual models. After studying the previous work, we have found that there is a lack of estimation methods for some important environmental parameters and a need of global models that consider the interactions of the environmental factors in big scenes. Moreover, we have observed that the improvement of current techniques need to incorporate real effects characteristics to avoid the current disconnection from the real processes. But, this need to be first analyzed and understood. In this thesis, we aim to improve weathering simulation in Computer Graphics in these three fronts. Concerning weathering factors estimation, we first propose to deal with an undervalued factor in weathering literature which is very important in aging processes: the sun. More specifically, we propose an interactive technique that estimates solar exposure on detailed urban scenes. Given a directional exposure map computed over a given time period, we estimate the sky visibility factor that serves to evaluate the final exposure at each visible point. This is done using a screen-space method based on a two-scale approach, which is geometry independent and has low storage costs. Our method results in an interesting technique not only in weathering simulations, but also in architecture, in sustainable building design and in the estimation of buildings’ energy performance. After that, we introduce a global model to simulate the changes of appearance of buildings due to pollution deposition. This process is very noticeable on urban scenes and, so far, no technique has dealt with it using a global approach. We propose a physically-based technique that considers pollution effects to depend on three main factors: wind, rain and sun exposure, and that takes into account three intervening steps: deposition, reaction and washing. With a low-cost pre-computation step, we evaluate the pollution distribution through the city. Based on this distribution and the use of screen-space operators, our method results in an efficient approach that generate realistic images of polluted surfaces at interactive rates. In addition, the pre-computation demands a reduced amount of memory to store the pollution map and, as it is independent from scene complexity, it can suit large and complex models adapting its resolution. Finally, in order to improve the understanding of weathering processes, we present a method to identify and map “scaling” weathering effects on stone monuments with very little user interaction.
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Imanol Muñoz Pandiella. Vieillissement interactif pour la synthèse d'image réaliste des environnements urbains. Graphics [cs.GR]. Université de Limoges, 2017. English. ⟨NNT : 2017LIMO0089⟩. ⟨tel-01707902⟩

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