Environmental Objects for Authoring Procedural Scenes

International audienceWe propose a novel approach for authoring large scenes with automatic enhancement of objects to create geometric decoration details such as snow cover, icicles, fallen leaves, grass tufts or even trash. We introduce environmental objects that extend an input object geometry with a set of procedural effects that defines how the object reacts to the environment, and by a set of scalar fields that defines the influence of the object over of the environment. The user controls the scene by modifying environmental variables, such as temperature or humidity fields. The scene definition is hierarchical: objects can be grouped and their behaviours can be set at each level of the hierarchy. Our per object definition allows us to optimize and accelerate the effects computation, which also enables us to generate large scenes with many geometric details at a very high level of detail. In our implementation, a complex urban scene of 10 000 m², represented with details of less than 1 cm, can be locally modified and entirely regenerated in a few seconds

Simulating How Salt Decay Ages Buildings

International audienceSalt-based aging plays an important part in the realism of scenes featuring stone structures and monuments. A proposed model, based on physical behaviors and principles, replaces the simulation of complex physical formulations with ad hoc algorithms. It leads to plausible results, ultimately helping designers create aging patterns on affected objects

Phenomenological Simulation of Efflorescence in Brick Constructions

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A survey of aging and weathering phenomena in computer graphics

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Interactive solar irradiance estimation in urban scenes

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Heat Transfer Simulation for Modeling Realistic Winter Sceneries

International audienceThis paper presents a physically based method for simulating the heat transfers between the different environmental elements to synthesize realistic winter sceneries. We simulate the snow fall over the ground, as well as the conductive, convective and radiative thermal transfers using a finite volume method according to the variations of air and dew point temperatures, the amount of snow, cloud cover and day-night cycles. Our approach takes into account phase changes such as snow melting into water or water freezing into ice

A BRDF Post-Process to Integrate Porosity on Rendered Surfaces

International audienceThe behavior of light interacting with materials is a crucial factor in achieving a high degree of realism in image synthesis. Local illumination processes, describing the interactions between a point of the surface and a shading ray, are evaluated by bidirectional reflectance distribution functions (BRDFs). Current theoretical BRDFs use surface models restricted to roughness only, sometimes at different scales. We present a more complete surface micro-geometry description, suitable for some common surface defects, including porosity and micro-cracks; both of them are crucial surface features since they strongly influence light reflection properties. These new features are modeled by holes inserted in the surface profile, depending on two parameters: the proportion of surface covered by the defects and the mean geometric characteristic of these defects. In order to preserve the advantages and characteristics of existing BRDFs, a postprocessing method is adopted (we integrate our technique into existing models, instead of defining a completely new one). Beyond providing graphical results closely matching real behaviors, this method moreover opens the way to various important new considerations in computer graphics (for example, changes of appearance due to the degree of humidity

Real-Time Solar Exposure Simulation in Complex Cities

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Surface scratches : Measuring, Modeling and Rendering

International audienceOne of the most important criticisms that can be made concerning synthesized images is the brand new and too clean aspect of objects. Surface color modifica- tions can be used to introduce dirtiness or other aging- linked characteristics. Also, techniques such as bump or displacement mapping allow users to improve sur- face aspects by introducing geometrical perturbations. In parallel, the bidirectional reflectance distribution function (BRDF) is a crucial factor in achieving a high degree of realism. It turns out that surfaces are very often covered by defects such as scratches that are re- lated to both textures and BRDFs due to their size. Scratches do not always affect the apparent geometry but nevertheless can remain strongly visible. None of the previously mentioned methods is suited for ren- dering these defects efficiently. We propose a new method, based on extensions to existing BRDFs and classical 2D texture mapping techniques, to render efficiently individually visible scratches. We use phys- ical measurements on "real objects" to derive an ac- curate geometric model of scratches at small scale range (roughness scale), and we introduce a new ge- ometric level between bump mapping and BRDFs. Beyond providing graphical results closely matching real cases, our method opens the way to a new class of considerations in computer graphics based on defects that require the coupling of both BRDFs and texturing techniques