Gilles Valette

SoDA project: A simulation of soil surface degradation by rainfall

Abstract The main objective of the SoDA (Soil Degradation Assessment) project is to realize a simulator of soil surface degradation by rainfall at the meter scale and including visualization. Soil surface structure and morphology deeply influence a lot of processes of high agronomic and environmental relevance, such as mass and heat transfer through the soil–atmosphere interface, runoff and erosion, seed germination and seedling emergence. The soil surface structure of agricultural field is in continuous evolution: it is strongly affected by tillage, and in between tillage operations, erosion by rainfall and runoff causes a progressive degradation of the structure whose intensity and speed partly depend on the initial state associated to tillage modalities. A soil surface degradation model could allow one to predict this evolution of the soil surface structure, and even to help choosing adequate tillage practices and sowing dates. Erosion modeling has been addressed by soil scientists but also by computer graphic scientists in order to add realism to virtual landscapes. Mixing both of these points of view would be interesting to simulate and visualize the evolution of the soil surface of a cultivated soil. Based on a 3D cellular automata approach using the knowledge accumulated by soil scientists about the physical processes involved in erosion, the principles of our simulator and its first implementation are presented in this paper.

A Dynamic Model of Cracks Development Based on a 3D Discrete Shrinkage Volume Propagation

We attempt to model and visualize the main characteristics of cracks produced on the surface of a desiccating crusted soil: their patterns, their different widths and depths and their dynamics of creation and evolution. In this purpose we propose a method to dynamically produce three‐dimensional (3D) quasi‐static fractures, which takes into account the characteristics of the soil. The main originality of this method is the use of a 3D discrete propagation of ‘shrinkage volumes’ with respect to 2D precalculated paths. In order to get realistic cracks, we newly propose to take into account a possibly inhomogeneous thickness of the shrinking layer by using a watershed transformation to compute these paths. Moreover, we use the waterfall algorithm in order to introduce in our simulation a hierarchy notion in the cracks appearance, which is therefore linked with the initial structure of the surface. In this paper, this method is presented in detail and a validation of the cracks patterns by a comparison with real ones is given.

High-dynamic range video acquisition with a multiview camera

We propose a new methodology to acquire HDR video content for autostereoscopic displays by adapting and augmenting an eight view video camera with standard sensors. To augment the intensity capacity of the sensors, we combine images taken at dierent exposures. Since the exposure has to be the same for all objectives of our camera, we x the exposure variation by applying neutral density lters on each objective. Such an approach has two advantages: several exposures are known for each video frame and we do not need to worry about synchronization. For each pixel of each view, an HDR value is computed by a weighted average function applied to the values of matching pixels from all views. The building of the pixel match list is simplied by the property of our camera which has eight aligned, equally distributed objectives. At each frame, this results in an individual HDR image for each view while only one exposition per view was taken. The nal eight HDR images are tone-mapped and interleaved for autostereoscopic display.

Autostereoscopic visualization of 3D time-varying complex objects in volumetric image sequences

This paper presents 4dVizMed, a framework for interactive analysis and autostereoscopic visualization of 3d time-varying objects in volumetric image sequences. It combines a deformable surface model which automatically tracks volumetric features, real-time multi-view stereo volume rendering, and some interactive tools for manipulation and quantization. Our method is based on a topological feature tracking process, using a flow-based paradigm and a deformable surface model. It tracks through time the evolution of the components of an isosurface and their interaction with other components. We focus on the difficulties of visualizing 4d volume data, and we report the results of preliminary experiments designed to evaluate the utility of autostereoscopic displays for this purpose.

A discrete modelling of soil fragments transport by runoff

We aim to model and visualize the evolution of the surface structure of a cultivated soil surface during rainfall. In this paper,we briefly present our model, based on an Extended Cellular Automaton, and the different simulated processes. Among these processes, we focus on runoff which is of high relevance as it drives the evolution of the soil surface structure by transporting and depositing the detached fragments of soil and thus inducing an evolution in the granulometry of the surface material. We propose a simple algorithm to model, in a discrete way, runoff and also the transport and deposition of soil fragments according to their size. In that way we are able to derive information about the evolution of soil surface granulometry. A validation of the runoff model is proposed, based on the comparison of the results obtained with results from a numerical solution of the Saint Venants equations. Although no validation was attempted for transport, simulations yielded visually promising results.

A Non-Modular Cellular DEVS Model Of The Degradation Of A Cultivated Soil Surface By Rainfall

We aim to model and simulate the evolution of the surface structure of a cultivated soil surface during rainfall. The surface degradation is mainly the consequence of the creation and the transport of soil fragments, which are caused by the circulation of water, rainfall and runoff in particular. Our first intent was to use Cellular Automata (CA), but these processes cannot easily be modelled in a pure CA model because they are both discrete and continuous, local and global. We explain in this paper how non modular cellular DEVS can efficiently model this natural system and we present in detail the coupled model of the simulator and the atomic model of the terrain, and we give a sketch of the way we model the processes involved.

A preliminary approach of 3D simulation of soil surface degradation by rainfall

Soil surface structure and morphology deeply in uence a lot of processes of high agronomic and environmental relevance, such as mass and heat transfer through the soil-atmosphere interface, runoff and erosion, seed germination and seedling emergence. The soil surface structure of agricultural eld is in continuous evolution: it is strongly affected by tillage, and in between tillage operations, erosion by rainfall and runoff causes a progressive degradation of the structure whose intensity and speed partly depend on the initial state associated to tillage modalities. A soil surface degradation model could allow to predict this evolution of the soil surface structure, and even to help choosing adequate tillage practices and sowing dates. Erosion modelling has been addressed by soil scientists but also by computer graphic scientists in order to add realism to virtual landscapes. Mixing both of these points of view would be interesting to simulate and visualize the evolution of the soil surface of a cultivated soil. In this paper, we present our project of a simulator of soil surface degradation by rainfall at a small spatial scale (1 m2 or less), including visualization, and which is mainly based on a 3D cellular automata approach with a speci c type of cell. The choices made for the implementation of our model are discussed in the light of the results found in the literature with different modelling approaches.

A premixed autostereoscopic OptiX-based volume rendering

Present multi-view display techniques are often based on the use of multi-pass algorithms, one per view usually besides an additional step for image compositing. Generally linearly dependent on the number of views, these approaches introduce a bias by incorrectly considering that depth information is located at the pixel level, while the sub-pixel level would be more suitable to improve the intrinsic quality of the resulting images. In this paper, we introduce a new method for rendering multi-stereo views at interactive frame rates which is innovative on two main aspects: first it is based on an OptiX™ ray-tracing engine, second it uses a single premixed rendering pass operating at sub-pixel level. This approach has been tested on a specific volume rendering algorithm, natively supporting 3D displays. After a detailed description of our method, we present performance results for different use cases on an 8-view autostereoscopic 3D display. Quantitative aspects of the latency as well as resulting perceived image quality are measured for the proposed method and compared with a conventional multi-pass GPU approach.