Laurent Lucas

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.

Multiview Shooting Geometry for Multiscopic Rendering with Controlled Distortion

A fundamental element of stereoscopic and/or autostereoscopic image production is the geometrical analysis of the shooting and viewing conditions in order to obtain a qualitative 3D perception experience. This paper firstly compares the perceived depth with the shot scene depth from the viewing and shooting geometries for a couple of shooting and rendering devices. This yields a depth distortion model whose parameters are expressed from the geometrical characteristics of shooting and rendering devices. Secondly, these expressions are inverted in order to design convenient shooting layouts yielding chosen distortions on specific rendering devices. Thirdly, this design scheme provides three shooting technologies (3D computer graphics software, photo rail, and camera box system) producing qualitative 3D content for various kinds of scenes (real or virtual, still or animated), complying with any prechosen distortion when rendered on any specific multiscopic technology or device formerly specified.

Toward an immersion platform for the world wide web using autostereoscopic displays and tracking devices

A few years ago, the introduction of the WebGL API has allowed displaying 3D content in web browsers very efficiently by using the power of 3D accelerators. Nowadays, 3D web applications, from games to medical imaging, tend to compete with their desktop counterparts. Among the main factors that can improve the feeling of presence in terms of impressiveness, immersion and natural interaction play a prominent role in enhancing the quality of the user experience. Both immersion and natural interaction rely on dedicated hardware like 3D displays and tracking devices. Unfortunately, browser makers do not supply JavaScript mechanisms for accessing hardware for security reasons. In this paper, we propose a plugin-free solution using the new features of HTML5 (WebGL and WebSockets) in order to handle autostereoscopic displays and widespread tracking devices like IR depth sensors for providing immersion and natural interaction within the web browser.

3D displays and tracking devices for your browser: A plugin-free approach relying on web standards

The emergence of 3D screens and their tailored 3D contents played a key role in improving the perception of depth. Coupled with tracking devices, these 3D displays are the central components of an immersion platform. According to this new trend called “cloud computing”, it has become straightforward to adapt this kind of immersion platform for the World Wide Web. A major issue resides in the ability to handle dedicated hardware (tracking devices and 3D displays) from within a web browser. Indeed, for security reasons, browser makers prevent developers from accessing hardware components via JavaScript. In this paper, we propose a pluginfree solution using the new features of HTML5 (WebGL and WebSockets) in order to handle autostereoscopic displays and widespread tracking devices like IR depth sensors for providing immersion and natural interaction within a web browser.

A new pixel-oriented visualization technique through color image

Color image is often considered as a fundamental perceptual unit of visualization. In this paper, we suggest using this medium (color image) to summarize multidimensional data and thus to turn a data set into a meaningful insight. The methodology we use is based on the theory of Keim for designing pixel-oriented visualization techniques. The technique we propose consists in a three-step pipeline. The first one is devoted to dimensionality reduction by projecting multidimensional data into a three-dimensional space. In this work, we use the classical principal component analysis (PCA) to reduce the dimension to three. The second step, called color mapping, is based on the reverse color information transformation defined by Ohta et al. This stage is the main novelty of this work in addition to the pipeline itself. The third step consists in a pixel-oriented method to display large data sets with an image using space-filling curve techniques. The combination of these steps (first, dimensionality reduction with PCA, second, color mapping with color information of Ohta et al., and third, space-filling curve with Peano–Hilbert curve) allows us to obtain a new unsupervised visualization technique through color images. This blind (i.e. unsupervised) technique using a color image gives a previsualization that can be used before exploring the data set or choosing more effective colors. Some applications are proposed in the field of multicomponent image visualization.

A new unsupervised cube-based algorithm for iso-surface generation

This paper introduces a new algorithm which automatically produces polygonal representations of 3D structures within a volume data set built from a stack of parallel cross-sections. Several methods of 3D surface reconstruction have already been proposed ranging from heuristic approaches for constructing 3D surfaces from 2D contours to the Marching Cubes (MC) approach where the different configurations are checked systematically. Instead, we define a cube-to-cube connection based upon geometrical closeness provided by convex hulls computation. We further evaluate the precision of 3D models reconstructed from synthetic and real data obtained in confocal microscopy and compare it with the conventional MC algorithm. We also discuss improvements that allow to reduce the number of generated surface patches and the ability to be used in 3D quantitative tasks.

3D volume matching for mesh animation of moving actors

4D multiview reconstruction of moving actors has many applications in the entertainment industry and although studios providing such services become more accessible, efforts have to be done in order to improve the underlying technology to produce high-quality 4D contents. In this paper, we enable surface matching for an animated mesh sequence in order to introduce coherence in the data. The context is provided by an indoor multi-camera system which performs synchronized video captures from multiple viewpoints in a chroma key studio. Our input is given by a volumetric silhouette-based reconstruction algorithm that generates a visual hull at each frame of the video sequence. These 3D volumetric models differ from one frame to another, in terms of structure and topology, which makes them very difficult to use in post-production and 3D animation software solutions. Our goal is to transform this input sequence of independent 3D volumes into a single dynamic volumetric structure, directly usable in post-production. These volumes are then transformed into an animated mesh. Our approach is based on a motion estimation procedure. An unsigned distance function on the volumes is used as the main shape descriptor and a 3D surface matching algorithm minimizes the interference between unrelated surface regions. Experimental results, tested on our multiview datasets, show that our method outperforms approaches based on optical flow when considering robustness over several frames.

3D Video: From Capture to Diffusion

While 3D vision has existed for many years, the use of 3D cameras and video-based modeling by the film industry has induced an explosion of interest for 3D acquisition technology, 3D content and 3D displays. As such, 3D video has become one of the new technology trends of this century.The chapters in this book cover a large spectrum of areas connected to 3D video, which are presented both theoretically and technologically, while taking into account both physiological and perceptual aspects. Stepping away from traditional 3D vision, the authors, all currently involved in these areas, provide the necessary elements for understanding the underlying computer-based science of these technologies. They consider applications and perspectives previously unexplored due to technological limitations.This book guides the reader through the production process of 3D videos; from acquisition, through data treatment and representation, to 3D diffusion. Several types of camera systems are considered (multiscopic or multiview) which lead to different acquisition, modeling and storage-rendering solutions. The application of these systems is also discussed to illustrate varying performance benefits, making this book suitable for students, academics, and also those involved in the film industry.