Visualizing 2D Flows with Animated Arrow Plots

Flow fields are often represented by a set of static arrows to illustrate scientific vulgarization, documentary film, meteorology, etc. This simple schematic representation lets an observer intuitively interpret the main properties of a flow: its orientation and velocity magnitude. We propose to generate dynamic versions of such representations for 2D unsteady flow fields. Our algorithm smoothly animates arrows along the flow while controlling their density in the domain over time. Several strategies have been combined to lower the unavoidable popping artifacts arising when arrows appear and disappear and to achieve visually pleasing animations. Disturbing arrow rotations in low velocity regions are also handled by continuously morphing arrow glyphs to semi-transparent discs. To substantiate our method, we provide results for synthetic and real velocity field datasets

Un splendide isolement: Les politiques françaises du maintien de l’ordre

La Vie des IdéesSur les politiques de maintien de l'ordre menées en France depuis le début des années 1980 au regard des politiques à l'oeuvre dans l'espace ouest-européen

Retour d'expérience sur l'instrumentation d'un glacier du Baounet : quels apports de la traçabilité des mesures environnementales ?

Les campagnes de mesures hydro-météorologiques réalisées sur le glacier du Baounet (Savoie, France) depuis 2002 ont posé les bases d'un développement de techniques métrologiques inspirées du milieu industriel. Ces méthodes ont pour objectif de fiabiliser les mesures environnementales et de caractériser la qualité des résultats. Le retour d'expérience de l'exploitation de la station du Baounet montre que les pertes de temps induites par la mise en place de ces procédures sont largement compensées par les facilités d'exploitation qui en découlent. Le point le plus important demeure un progrès appréciable dans la traçabilité des résultats scientifiques des expérimentations de terrain. Les perspectives de ces travaux s'orientent vers une évolution de l'instrumentation couplée à des télémesures et vers la mise en place d'une charte métrologique

Police, du plébiscite à l'abandon

National audienceTantôt loués quand ils protègent des attentats, tantôt détestés quand ils s'en prennent aux manifestants, les policiers entretiennent une relation ambiguë avec la population. Pourquoi ? La mesurerait-on à sa relation à la police, la société française contemporaine offrirait un visage bien versatile et, de prime abord, difficilement compréhensible. Comme ils l'ont eux-mêmes souligné, en appelant le 18 mai 2016 à une manifestation contre « la haine anti-flics », les Français étreignaient les policiers en janvier 2015, après les attaques à la rédaction de Charlie Hebdo, puis quelques mois après les massacres du 13 novembre, mais se retournaient et les affrontaient dans la rue, au cours des mobilisations contre la loi dite « travail » au printemps 2016. Aussi puissants soient-ils, les événements terroristes de 2015 n'ont pas terrassé les paradoxes constitutifs de toute institution policière. La police française a cette particularité, dans le contexte européen, de ne susciter qu'une confiance prudente de la part de ses concitoyens. Depuis le début des années 1980, la police jouit d'un solde positif de confiance : les deux tiers de la population interrogée dans les sondages successifs disent faire confiance à la police. Mais les Français, en dépit d'une confiance générale plutôt élevée, doutent plus que leurs voisins européens des vertus de leurs policiers, notamment en matière d'équité

Le nouveau mandat policier : Faire la police dans les zones dites de « non-droit »

Les quinze dernières années ont été marquées, en France, par l’importance prise par les enjeux policiers dans l’arène des luttes politiques. Cela se mesure principalement à la concentration de l’attention politique et des forces policières sur des zones dites de « non-droit », zones urbaines touchées par la crise économique engagée depuis le début des années 1970, et par des explosions récurrentes de violences collectives ou d’émeutes urbaines. Cette radicalisation croissante des politiques policières dans le sens d’un maintien de l’ordre agressif a été accompagnée d’un resserrement du lien entre les policiers intervenant dans ces zones et leur mandant qui est « le » politique. Ainsi, l’article examine à partir d’une description ethnographique approfondie d’une intervention policière dans une zone de « non-droit », la nature d’un « nouveau mandat policier » en voie de définition. Nous utilisons la notion de souveraineté policière, nécessaire pour penser l’intervention policière dans ces zones, mais nous nous efforçons également d’en repérer les limites.Over the last fifteen years, a growing importance has been given in France to policing and security issues by political authorities. This evolution can be perceived above all in the focusing of government attention on economically depressed urban neighbourhoods that seem to be no man’s lands beyond the reach of the law and in the attendant saturation policing now occurring in these zones. This increasing radicalization of “law and order” policies in France has implied closer linkages between the police officers deployed on these troubled sites and the political power holders that are posting them there. The object of the article is to describe this newly emerging police mandate that is characterized by its high politicization through a comprehensive ethnographical thick description of a police intervention in such a city. The article makes use of the notion of police sovereignty as tentative theoretical explanation, and attempts as well to assess the limits of such an explanation

EPSAT-SG: a satellite method for precipitation estimation; its concepts and implementation for the AMMA experiment

International audienceThis paper presents a new rainfall estimation method, EPSAT-SG which is a frame for method design. The first implementation has been carried out to meet the requirement of the AMMA database on a West African domain. The rainfall estimation relies on two intermediate products: a rainfall probability and a rainfall potential intensity. The first one is computed from MSG/SEVIRI by a feed forward neural network. First evaluation results show better properties than direct precipitation intensity assessment by geostationary satellite infra-red sensors. The second product can be interpreted as a conditional rainfall intensity and, in the described implementation, it is extracted from GPCP-1dd. Various implementation options are discussed and comparison of this embedded product with 3B42 estimates demonstrates the importance of properly managing the temporal discontinuity. The resulting accumulated rainfall field can be presented as a GPCP downscaling. A validation based on ground data supplied by AGRHYMET (Niamey) indicates that the estimation error has been reduced in this process. The described method could be easily adapted to other geographical area and operational environment

The check and the guardianship: A comparison of surveillance at an airport and a housing-estate area in the Paris outskirts

International audienceThis chapter approaches the question of government and surveillance through a comparison between the control practices observable in two types of places. First, we focus on international airports, specifically the French international airport of Orly. Airports are maximum security zones where persons perceived as having no legitimate business are expelled and where suspicious objects are destroyed. The second kind of places are the ones labeled as "no-go areas", violent pockets within urban space. Social housing projects located in the bleak suburbs of French cities are such dangerous zones. Both kinds of places - airports and no-go areas - have very different time and space features: people briefly pass through anonymous airports where relationships are kept at an impersonal minimum, whereas the population of a housing estate area is made of "permanent transients" pinned down by a shared fate of which there seems no escape

Évaluer et prendre en compte le renforcement orographique

International audienceCe texte présente les premiers résultats obtenus à partir de la base VIRS/PR. Un moyen simple d'analyse des biais systématiques et en particulier des effets orographiques est proposé

Parallel extraction and simplification of large isosurfaces using an extended tandem algorithm

International audienceIn order to deal with the common trend in size increase of volumetric datasets, in the past few years research in isosurface extraction has focused on related aspects such as surface simplification and load-balanced parallel algorithms. We present a parallel, block-wise extension of the tandem algorithm by Attali et al., which simplifies on the fly an isosurface being extracted. Our approach minimizes the overall memory consumption using an adequate block splitting and merging strategy along with the introduction of a component dumping mechanism that drastically reduces the amount of memory needed for particular datasets such as those encountered in geophysics. As soon as detected, surface components are migrated to the disk along with a meta-data index (oriented bounding box, volume, etc.) that permits further improved exploration scenarios (small component removal or particularly oriented component selection for instance). For ease of implementation, we carefully describe a master and worker algorithm architecture that clearly separates the four required basic tasks. We show several results of our parallel algorithm applied on a geophysical dataset of size 7000 × 1600 × 2000

Isosurface extraction and interpretation on very large datasets in geophysics

International audienceIn order to deal with the heavy trend in size increase of volumetric datasets, research in isosurface extraction has focused in the past few years on related aspects such as surface simplification and load balanced parallel algorithms. We present in this paper a parallel, bloc-wise extension of the tandem algorithm [Attali et al. 2005], which simplifies on the fly an isosurface being extracted. Our approach minimizes the overall memory consumption using an adequate bloc splitting and merging strategy and with the introduction of a component dumping mechanism that drastically reduces the amount of memory needed for particular datasets such as those encountered in geophysics. As soon as detected, surface components are migrated to the disk along with a meta-data index (oriented bounding box, volume, etc) that will allow further improved exploration scenarios (small components removal or particularly oriented components selection for instance). For ease of implementation, we carefully describe a master and slave algorithm architecture that clearly separates the four required basic tasks. We show several results of our parallel algorithm applied on a 7000×1600×2000 geophysics dataset