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In the field of computer graphics, the simulation of the visual appearance of materials requires an accurate computation of the light transport equation. Consequently, material models need to take into account various factors which may influence the spectral radiance perceived by the human eye. Though numerous relevant studies on the reflectance properties of materials have been conducted to date, environment maps used to simulate visual behaviors remain chiefly trichromatic. Whereas questions regarding the accurate characterization of natural lighting have been raised for some time, there are still no real sky environment maps that include both spectral radiance and polarization data. Under these conditions the simulations carried out are approximate and therefore insufficient for the industrial world where investment-sensitive decisions are often made based on these very calculations., Workshop on Material Appearance Modeling, Measurement and Fluorescence, 11, 14, Philippe Porral, Laurent Lucas, Thomas Muller, and Joël Randrianandrasana, Categories and Subject Descriptors (according to ACM CCS): I.3.1 [Computer Graphics]: Hardware Architecture-Input devices I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism-Raytracing I.6.8 [Simulation and Modeling]: Types of Simulation-Visual J.2 [Computer Applications]: Physical Sciences and Engineering-Engineering

Most recent crowd simulation algorithms equip agents with a synthetic vision component for steering. They offer promising perspectives through a more realistic simulation of the way humans navigate according to their perception of the surrounding environment. In this paper, we propose a new perception/motion loop to steering agents along collision free trajectories that significantly improves the quality of vision-based crowd simulators. In contrast with solutions where agents avoid collisions in a purely reactive (binary) way, we suggest exploring the full range of possible adaptations and retaining the locally optimal one. To this end, we introduce a cost function, based on perceptual variables, which estimates an agent’s situation considering both the risks of future collision and a desired destination. We then compute the partial derivatives of that function with respect to all possible motion adaptations. The agent then adapts its motion by following the gradient. This paper has thus two main contributions: the definition of a general purpose control scheme for steering synthetic vision-based agents; and the proposition of cost functions for evaluating the perceived danger of the current situation. We demonstrate improvements in several cases. T. B. Dutra acknowl1edges CAPES for the fellowship (PDSE Proc. 0130/13-3) and J. Ondˇrej for helping in the implementation of his model. R. Marques acknowledges the projects Percolation (ANR- 13-JS02-0008), and Kristina (H2020-RIA-645012) for partially financing this research.

This thesis present an efficient approach for performing smoke simulation on curvilinear grids. The solution of the Navier-Stokes equations on curvilinear is made on three steps: advection, pressure solving and velocity projection. The proposed advection method is simple, fast and unconditionally-stable. Our solution is able to maintain a staggered-grid variable arrangement, and includes an efficient solution to enforce mass conservation. Compared to approaches based on regular grids traditionally used in computer graphics, our method allows for better representation of boundary conditions, lending to more realistic results, with just a small increment in computational cost. Moreover, we are able to condensate cells where interesting artifacts tend to appear, like swirling vortices or turbulence. We demonstrate the effectiveness of our approach, both in 2-D and 3-D, through a variety of high-quality smoke simulations and animations. These examples show the integration of our method with overlapping grids and multigrid techniques.

Multi-resolution representations are widely used in many data visualization contexts and applications. The adoption of a multi-resolution approach provides the optimal management of a data representation, using at each instant of time a level of detail that is more adequate for the given action or task to be performed. Recently, multi-resolution has also been introduced into the interactive physically-based simulation of deformable objects (e.g. in virtual surgery applications). In these applications, the processing resources available are often insufficient and pose a critical constraint. The adoption of multi-resolution allows one to improve the accuracy of the simulation in the proximity of the action focus while maintaining computations under a given bound. In this particular context, the user should be able to perform cuts in the object. The problem is that most multi-resolution models need a pre-processing phase in which the data structure is constructed. Such a construction strictly depends on the topology of the object, which is supposed to be invariable. We propose a new approach for the dynamic topological modification of a multi-resolution model, which allows easy updating of the multi-resolution data structure (based on the multi-resolution triangulation framework), and efficient decomposition of the cells intersected by the cut. With respect to previous methods, our solution supports a much lower degree of fragmentation of the decomposition and very short processing times, due to the design of a lookup table (LUT) based splitting solution.