Section: New Results
Efficient visualization of very large scenes
Visualisation of large numerical simulation data sets
The energy industry sector has to perform numerical simulation on very large data sets, in thermodynamics, mechanics, aerodynamics, neutronics, etc. Visualization of the results of these simulations is crucial in order to gain understanding of the phenomena that are simulated. The visualization techniques need to be interactive - if not real time - to be helpful for engineers. Therefore multiresolution techniques are required to accelerate the visual exploration of the data sets. In the PhD of Fabien Vivodtzev (who is now working at CEA on Visualization systems) we have developed multiresolution algorithms devoted to volumetric data sets based on tetrahedral grids in which inner structures of dimension 2, 1 or 0 are preserved. Typically these algorithms are used to compute a sequence of simplified volumetric meshes with good properties. Sebastien Barbier is now starting a PhD on the interactive rendering of these simplified meshes. The aim is to integrate today's standard visualization algorithms - including slicing, iso-surfacing, volume rendering - with the multiresolution models developed previously.
This project is part of a collaboration with the research and development department of EDF, and with LPPA (Laboratoire de Physiologie de la Perception et de l'Action, Collège de France). The general context is similar to the collaboration with CEA (Section 6.3.1 ), i.e., the visualisation of large numerical data sets. The focus in this project in on the following problem: How should human perception be taken into account in Visualization algorithms, and more specifically in algorithms based on multiresolution techniques. Previous works in this area are mostly based on image analysis techniques, that are used to measure important features in a static image resulting from some visualization algorithm. These results do not take into account information on the specific person using the visualization system. We are especially interested in taking into account such information, like the point where the user is looking at. We also want to insert dynamic parameters in the perceptive measure, like the movement of the user's head, since such parameters greatly influence the actual perception of the rendered scene. In the framework of this collaboration, EDF is funding a PhD grant on these topics, started by Christian Boucheny in December 2005.
Efficient representation of landscapes
In September, Eric Bruneton joined the team as a researcher, on the topic or lanscape representation and rendering. The goal of this work is the real time rendering of large landscapes with forests, rivers, fields, roads, etc. with high rendering quality, especially in term of details and continuity. A first step toward this goal is the modeling, representation and rendering of the terrain itself (i.e., without taking into account the vegetation - see Section 6.3.4 - the rendering of rivers - see Section 6.2.5 - etc.). Since an explicit representation of the whole terrain elevation and texture at the maximum level of detail would be impossible, we generate them procedurally on the fly (completely from scratch or based on low resolution digital elevation models). Our main contribution, in this context, is to use vector based data to efficiently and precisely model linear features of the landscape (such as rivers, hedges or roads), from which we can compute in real time the terrain texture and the terrain elevation (in order to correctly insert roads and rivers in the terrain - see figure 11 ).
Efficient representation of forest
This year, we obtained a European Marie-Curie OIF "mobility" funding (see Section 8.4 ) allowing Philippe Decaudin to start (in October) a long stay in Beijin (CN) to collaborate with LIAMA on the topic of the real time realistical exploration of forestry landscape. The idea is to extend our volumetric models of forest combined with GPU-based rendering algorithms to visualize the huge data sets obtained by the LIAMA and CIRAD ecosystem simulations.
Real-time quality rendering of clouds layers
Antoine Bouthors continues his PhD on Cumulus clouds. This year, we developped an illumination model embedding the main local and global lighting effects in reflectance and transmitance (halo, glory, pseudo-specular, diffusion, etc.) in the form of a local shader such that a cloud layers (represented as a height-field) can be rendered on the fly on the GPU without precomputations or global simulation. We also accounted for inter-reflections between the clouds base and the floor through a real-time GPU-adapted radiosity algorithm. This work has been published at Eurographics Workshop on Natural Phenomena'2006  .
This year, Antoine also did a long stay at UC Davis (California, USA) to work with Nelson Max, thanks to a EURODOC Regional funding plus a France-Berkeley funding (see Section 8.4 ). In this collaboration, we intend to generalize the approach to non layer kinds of clouds.