"Bacchus" Methodological approach for vineyard inventory and management. Chap.4: Textural and structural analysis

Ce chapitre présente les méthodes qui ont été développées dans le projet Bacchus pour la détection et la caractérisation des parcelles de vigne en imagerie aérienne en se basant sur leur structure. Une analyse texturale est d'abord mise en oeuvre, et complétée par l'introduction de contraintes de régularité des contours pour améliorer la segmentation. Finalement, les parcelles issues de ces premières étapes sont vérifiées et caractérisées au moyen d'une analyse de leur spectre de Fourier. Les résultats obtenus sur diverses zones d'étude du projet Bacchus sont présentés et discutés. / This chapter presents the methodologies that have been developed during the Bacchus project concerning the automatic detection and characterisation of vineyard plots in satellite and aerial images, based on their structural properties. First, a textural analysis has been used. Then shape regularity constraints have been introduced to improve the image segmentation. Finally, the vineyard plots issued from these previous steps are checked and characterised using a Fourier spectrum analysis. Results on various study areas of the Bacchus project are presented and discussed

Dual back-stepping observer to anticipate the rollover risk in under/over-steering situations. Application to ATVs in off-road context

International audienceIn this paper an ATV (All-Terrain Vehicle) rollover prevention system is proposed. It is based on the online estimation and prediction of the Lateral Load Transfer (LLT), allowing the evaluation of dynamic instabilities. Using a vehicle model based on two 2D representations, the LLT can be estimated and predicted. As we consider off road vehicle, grip conditions must be encountered and are here estimated thanks to observation theory. Nevertheless, two main behaviours (over/under-steering) may be encountered pending on grip, and vehicle configuration. Because of the low cost sensor, these two opposite dynamics cannot be explicitly discriminated. As a result, two observers are used according to the vehicle behaviour. Based on a bicycle model and a low cost perception system, they estimate on-line the terrain properties (grip conditions, global sideslip angle and bank angle). A "supervisor" selects on-line the right observer. Associated to a predictive control algorithm, based on the extrapolation of rider's action and the selected estimated dynamical state, the risk can be anticipated, enabling to warn the pilot and to consider the implementation of active actions. Simulations and full-scale experimentations are presented to discuss about the efficiency of the proposed solution

On-line estimation of a stability metric including grip conditions and slope: Application to rollover prevention for all-terrain vehicles

International audienceRollover is the principal cause of serious accidents for All-Terrain Vehicles (ATV), especially for light vehicles (e.g.quad bikes). In order to reduce this risk, the development of active devices, contributes a promising solution. With this aim, this paper proposes an algorithm allowing to predict the rollover risk, by means of an on-line estimation of a stability criterion. Among several rollover indicators, the Lateral Load Transfer (LLT) has been chosen because its estimation needs only low cost sensing equipment compared to the price of a light ATV. An adapted backstepping observer associated to a bicycle model is first developed, allowing the estimation of the grip conditions. In addition, the lateral slope is estimated thanks to a classical Kalman filter relying on measured acceleration and roll rate. Then, an expression of the LLT is derived from a roll model taking into account the grip conditions and the slope. Finally, the LLT value is anticipated by means of a prediction algorithm. The capabilities of this system are investigated thanks to full scale experiments with a quad bike

Rollover prevention system dedicated to ATVs on natural ground

In this paper, an algorithm dedicated to light ATVs, which estimates and anticipates the rollover, is proposed. It is based on the on-line estimation of the Lateral Load Transfer (LLT), allowing the evaluation of dynamic instabilities. The LLT is computed thanks to a dynamical model split into two 2D projections. Relying on this representation and a low cost perception system, an observer is proposed to estimate on-line the terrain properties (grip conditions and slope), then allowing to deduce accurately the risk of instability. Associated to a predictive control algorithm, based on the extrapolation of riders action, the risk can be anticipated, enabling to warn the pilot and to consider the implementation of active actions

On stability of discretizations of the Helmholtz equation (extended version)

We review the stability properties of several discretizations of the Helmholtz equation at large wavenumbers. For a model problem in a polygon, a complete $k$-explicit stability (including $k$-explicit stability of the continuous problem) and convergence theory for high order finite element methods is developed. In particular, quasi-optimality is shown for a fixed number of degrees of freedom per wavelength if the mesh size $h$ and the approximation order $p$ are selected such that $kh/p$ is sufficiently small and $p = O(\log k)$, and, additionally, appropriate mesh refinement is used near the vertices. We also review the stability properties of two classes of numerical schemes that use piecewise solutions of the homogeneous Helmholtz equation, namely, Least Squares methods and Discontinuous Galerkin (DG) methods. The latter includes the Ultra Weak Variational Formulation

Plant Responses to Extreme Climatic Events: A Field Test of Resilience Capacity at the Southern Range Edge

The expected and already observed increment in frequency of extreme climatic events may result in severe vegetation shifts. However, stabilizing mechanisms promoting community resilience can buffer the lasting impact of extreme events. The present work analyzes the resilience of a Mediterranean mountain ecosystem after an extreme drought in 2005, examining shoot-growth and needle-length resistance and resilience of dominant tree and shrub species (Pinus sylvestris vs Juniperus communis, and P. nigra vs J. oxycedrus) in two contrasting altitudinal ranges. Recorded high vegetative-resilience values indicate great tolerance to extreme droughts for the dominant species of pine-juniper woodlands. Observed tolerance could act as a stabilizing mechanism in rear range edges, such as the Mediterranean basin, where extreme events are predicted to be more detrimental and recurrent. However, resistance and resilience components vary across species, sites, and ontogenetic states: adult Pinus showed higher growth resistance than did adult Juniperus; saplings displayed higher recovery rates than did conspecific adults; and P. nigra saplings displayed higher resilience than did P. sylvestris saplings where the two species coexist. P. nigra and J. oxycedrus saplings at high and low elevations, respectively, were the most resilient at all the locations studied. Under recurrent extreme droughts, these species-specific differences in resistance and resilience could promote changes in vegetation structure and composition, even in areas with high tolerance to dry conditions.This study was supported by Ministerio de Ciencia e Innovación (Spanish Government) Projects CGL2008-04794 and CGL2011-29910 to R.Z., and by grant FPU-MEC (AP2005-1561) to A. H

Lois de commande pour le contrôle et la mobilité de machines agricoles

This doctoral thesis shows the different methods we use to control two agricultural vehicles on a line built by a mowing vegetation. We describe an help guidance system which has two parts. The first one gives some informaiton about the environment of the robots using a CCD camera and an non supervised image processing algorithm. The second one deals with the control algorithms and the vehicles models. It is developed in this thesis. The first chapter describes the environment of the vehicles and its consequences about some control laws which are used in the litterature. The second chapter proposes a cinematic model for the two vehicles which makes simple the application of control laws calculated for a two whieels axle. The third chapter develops the theories of two control laws. The first one defines a trajectory between two positions of the vehicles. These positions are calculated in the space of the scene. The second one is deduced from the vision based control theory and applied to the control of non-holonomic mobile robots in the image space. The fourth chapter shows the result obtained with the help guidance system and proposes an original approach of the model and the correction in the image space of the sliding effects induced by a transverse slope of the ground. The last chapter gives some elements of the future work about the help guidance system robustness and its application to other vehicles. / Ce mémoire vise à exposer les méthodes utilisées pour asservir deux véhicules agricoles sur une ligne symbolisant une interface de végétation. Dans ce cadre, nous décrivons un système d'aide à la conduite composé de deux modules principaux. Le premier concerne la perception de l'environnement qui se fait au moyen d'une caméra CCD et d'une segmentation markovienne non supervisée d'images texturées. Le second fait l'objet des développements théoriques et pratiques de ce mémoire concernant les différents modèles et lois de commande appliqués aux véhicules. Le premier chapitre traite de l'environnement des robots mobiles et plus particulièrement des conséquences de celui-ci sur quelques lois de commande couramment utilisées. Le second chapitre propose une modélisation cinématique des engins qui permettra de leur appliquer facilement des lois de commandes calculées pour l'essieur rigide à deux roues. Le troisième chapitre expose les développements théoriques de deux lois de commande. La première permet de générer une trajectoire à partir de deux positions d'un véhicule reconstruitres dans l'espace de la scène. La seconde est déduite du formalisme de la commande référencée vision et propose un contrôle de véhicules non holonomes dans l'espace image. Le quatrième chapitre est consacré aux résultats obtenus avec le système d'aide à la conduite et propose une approche originale de la modélisation et de la correction dans l'espace image du glissement d'un robot mobile sur un terrain comportant une pente transversale. Enfin, le cinquième chapitre donne les différents travaux futurs concernant la robustesse du système d'aide à la conduite et de son application à d'autres robots mobiles

Integrity of an autonomous agricultural vehicle according the definition of trajectory traversability

International audienceIn this article we address the problem of the traversability of the trajectory of an agricultural robot defining the conditions insuring a safe displacement according the notion of "obstacle". Unlike other approaches that try to detect and to avoid obstacle, we propose the concept of Allowable Speed Trajectories which depends on the vehicle capabilities, its dynamics constraints, its speed and the 3D rendering of the environment. We make a dynamic study to estimate the acceleration of inertial center of vehicle taking into account geometry of the environment and the trajectory to follow. Then we propose some solutions to adapt the speed and/or the trajectory of the agricultural vehicle according criteria linked to the mission objective. Results in simulation and real conditions show the performance of our algorithm in different scenarios

Evaluation de la qualité des tranches de jambon cuit par vision numérique : appel à proposition

This document aims to find industrial partners for the realization of a system of quality sort for the cooked ham slides, following a feasibility study carried out by Cemagref.Ce document a pour objectif de trouver des partenaires industriels pour la réalisation d'un système de tri qualité pour les tranches de jambon cuit, suite à une étude de faisabilité réalisée par le Cemagref