Section: New Results

Efficient visualization of very large scenes

Participants : Sébastien Barbier, Georges-Pierre Bonneau, Christian Boucheny, Eric Bruneton, Alexandre Coninx.

Visualisation of large numerical simulation data sets

Participants : Sébastien Barbier, Georges-Pierre Bonneau.

Sébastien Barbier has developed a set of GPU implemented algorithms that enable to dynamically extract a BiResolution mesh from any given tetrahedral mesh. A specific out-of-core simplification algorithm is performed in preprocessing. During exploration of the data, a single consistent mesh is extracted on-the-fly from a Volume-Of-Interest (VoI) and a coarse contextual mesh outside the VoI. Sébastien has defended his PhD thesis on October 26 2009 [1] . He is is still working with the team until december 2009, and will be working at CEA in Bordeaux from January 2010. There he will work on Visualization with Fabien Vivodtzev, a former PhD student of Georges-Pierre Bonneau.

Perceptive visualization

Participants : Georges-Pierre Bonneau, Christian Boucheny, Alexandre Coninx.

This project is part of a collaboration with EdF R& D, and with LPPA (Laboratoire de Physiologie de la Perception et de l'Action, Collège de France). EdF runs massive numerical simulations in hydrodynamics, mechanics, thermodynamic, neutronic... Postprocess, and in particular visualization of the resulting avalanche of data is a bottleneck in the engineering pipeline. Contrary to the numerical simulation itself, this postprocessing is human-time consuming, with engineers spending several hours to explore the result of their simulation, trying to catch the knowledge hidden behind the numbers computed by the simulation. The focus of our collaboration with EdF and the College de France is to incorporate our knowledge of the human visual perception system in the development of more efficient visualization techniques. We also deal with the evaluation of existing visualization algorithms, based on perceptive criteria.

This year we have published a journal paper at ACM Transactions on Applied Perception [4] , perceptive evaluation of volume rendering algorithms. Christian Boucheny has also defended his PhD thesis on February 13th [2] . Christian has been hired by EdF R&D, where he will continue to work on Visualization. We have started in January 2009 a new PhD thesis by Alexandre Coninx. Alexandre will focus his work on the Visualization of data with uncertainty.

Real-time realistic ocean lighting

Participant : Eric Bruneton.

Figure 27. Some real-time results obtained with our ocean lighting algorithm, showing Sun reflections, sky reflections and local reflections from a boat. The lighting is correct at all distances thanks to accurate transitions from geometry to BRDF.

We developped a new algorithm for modelling, animation, illumination and rendering of the ocean, in real-time, at all scales and for all viewing distances. Our algorithm is based on a hierarchical representation, combining geometry, normals and BRDF. For each viewing distance, we compute a simplified version of the geometry, and encode the missing details into the normal and the BRDF, depending on the level of detail required. We then use this hierarchical representation for illumination and rendering. Our algorithm runs in real-time, and produces highly realistic pictures and animations (see Figure 27 ). This work has been accepted for publication at the next Eurographics conference (Eurographics 2010). It has also been integrated in the Proland software (see Section  5.4 ).

Real-time quality rendering of clouds

Participant : Eric Bruneton.

Laurent Belcour worked during his Master thesis on the real-time, realistic rendering of Earth-scale clouds. Its goal was to extend the work of Antoine Bouthors (a former Phd student at Evasion) on the rendering of stratiform clouds. Laurent extended Antoine's model to account for the curvature of the Earth, as well as to support mountains and other non flat terrains (Antoine's model was limited to flat terrains). His model uses spherical harmonics to simulate the light bounces between the clouds and the ground (radiosity). Laurent is now a PhD student in the Aeris team.

Efficient representation of plants and trees

Participants : Philippe Decaudin, Fabrice Neyret.

Figure 28. Our Volumetric Billboards model allows us to represent very complex detailled scenes very efficiently and with high visual quality, handling a volumetric-wise filtering of 'geometry'.

We developed a new representation for the efficient representation and filtering of complex data, typically, vegetal elements in a landscape [5] . The volumetric Billboard, which is based on a multiscale volume of voxels. Our rendering algorithm is able to render seemlessly and efficiently a complex self-intersecting distribution of such base volumes relying on common adaptive slicing of then parallel to screen. Equivalent mesh-based seen are more costly to render, more prone to aliasing. Moreover, Volumes allow to properly define the filtering of thin objects (which become fuzzy), see Figure 28 . This work has been done by Philippe Decaudin and Fabrice Neyret before 2009, while they were members of the team.