Comment calibrer extrinsèquement des caméras à champs non-recouvrants ? Application pour un robot mobile

National audienceMulti-camera systems are more and more used in visionbased robotics. An accurate extrinsic calibration (camera relative poses) is usually required. In most of cases, this task is done by matching features through different views of the same scene. However, if the camera fields of view do not overlap, such a matching procedure is not feasible anymore. This article deals with a simple and flexible extrinsic calibration method, for non-overlapping camera rig. The aim is the calibration of non-overlapping cameras embedded on a vehicle, for visual navigation purpose in urban environment. The cameras do not see the same area at the same time. The calibration procedure consists in manoeuvring the vehicle while each camera observes a static scene. Previously, the camera were intrinsically calibrated. The main contributions are a study of the singular motions and a specific bundle adjustment which both reconstructs the scene and calibrates the cameras. Solutions to handle the singular configurations, such as planar motions, are exposed. The proposed approach has been validated with synthetic and real data. This article is translated from [19].Les systèmes multi-caméras sont de plus en plus utilisés en robotique mobile. Il est souvent nécessaire que l'étalonnage extrinsèque (poses relatives des caméras) soit précis. Pour cela, on utilise généralement des appariements entre différentes vues, ce qui est impossible à réaliser si les champs de vue des caméras sont disjoints. Dans cet article, nous exposons une méthode simple et flexible pour étalonner extrinsèquement un système multicaméras dont les champs de vue sont disjoints. Le but est de calibrer des caméras embarquées sur un véhicule pour des applications de navigation en milieu urbain. Les caméras observent donc des régions différentes à un instant donné. La procédure d'étalonnage consiste à manoeuvrer le véhicule pendant que chaque caméra, intrinsèquement calibrée au préalable, observe une scène statique. Les principales contributions sont l'étude des mouvements singuliers, et un ajustement de faisceaux spécifique qui affine les scènes, les poses du système multi-caméras, et calibre extrinsèquement les caméras. Nous étudions comment traiter les mouvements singuliers, comme les mouvements plans. La méthode proposée est validée avec des données synthétiques et réelles. Traduction depuis l'anglais de l'article [19]

Comparative and statistical analysis between the CERN conference database and three other bases

This is a comparison between three scientific conference databases and CERN data. High Energy Physics institutes DESY and SLAC databases and the STN-FIZ commercial one's are described and analysed by statistical tables. We plan to work out a co-operation policy especially with DESY for exchange or data import

NIMBUS-7 CZCS. Coastal Zone Color Scanner Imagery for Selected Coastal Regions. North America - Europe. South America - Africa - Antarctica. Level 2 Photographic Product

The Nimbus-7 Coastal Zone Color Scanner (CZCS) is the first spacecraft instrument devoted to the measurement of ocean color. Although instruments on other satellites have sensed ocean color, their spectral bands, spatial resolution, and dynamic range were optimized for geographical or meteorological use. In the CZCS, every parameter is optimized for use over water to the exclusion of any other type of sensing. The signal-to-noise ratios in the spectral channels sensing reflected solar radiance are higher than those required in the past. These ratios need to be high because the ocean is such a poor reflecting surface that the majority of the signal seen by the reflected energy channels at spacecraft altitudes is backscattered solar radiation from the atmosphere rather than reflected solar energy from the ocean. The CZCS is a conventional multichannel scanning radiometer utilizing a rotating plane mirror at a 45 deg angle to the optic axis of a Cassegrain telescope. The mirror scans 360 deg; however, only 80 deg of data centered on the spacecraft nadir is collected for ocean color measurements. Spatial resolution at spacecraft nadir is 825x825 m with some degradation at the edges of the scan swath. The useful swath width from a spacecraft altitude of 955 km is 1600 km

An Analysis of Topographic Effects on LANDSAT Thematic Mapper Image Using Digital Terain Data

A comprehensive literature review on the simulation and corrections of topographic variations in remote sensing data was presented. The effects of topography on the scene radiance of LANDSAT thematic mapper (TM) image were examined in the context of the remote sensing of vegetation m Great Smoky Mountains National Park (GSMNP). To simulate the image intensity component due to varying orientation of surface elements, two reflectance models were adopted to generate the synthetic images from a Digital Elevation Model (DEM). Visual and analytical procedures were developed to register the TM image to the DEM data. The dark tones of scene radiance of most TM bands effective to vegetation classification were found to be caused by the terrain relief surface with incidence angle more than 55° rather than the intrinsic scene properties. Statistically significant correlation were found between LANDSAT TM data and the synthetic brightness values. The best correlation coefficient was 0.854. This result indicated that a simple linear model gives a good prediction of measured brightness as a function of the cosine of the incident angle of the direct solar beam. The residual images were produced from the linear regression model of real LANDSAT TM and synthetic images. The segmentation of residual images was performed based on the two segmenting criteria to extract ground spectral patterns. The outcome is discussed with a view to achieving a better understanding of the nature of problem

In What Order Should Learners Learn Japanese Vocabulary? A Corpus-based Approach

This thesis attempts to answer the following two main research questions:1) In what order should learners of Japanese as a second language learn words and characters in order to be able to read Japanese? 2) How will the order vary according to the purpose of learning? To answer these questions, a Vocabulary Database for Reading Japanese (VDRJ) and a Character Database of Japanese (CDJ) were first developed from the Balanced Contemporary Corpus of Written Japanese (BCCWJ) 2009 monitor version (NINJAL, 2009) which contains book texts and internet-forum site texts with 33 million running words in total. Word and character rankings for international students, non-academic learners and general written Japanese were included in these databases. These rankings were proven to be valid for their respective purposes as they provided higher text coverage for the target texts than other texts. After analysing the use of vocabulary and characters in Japanese, three groups of domain-specific words, namely common academic words, limited-academic-domain words and literary words were extracted. In order to test the expected efficiency for learning these groups of words, an index entitled Text Covering Efficiency (TCE) in different types of texts was proposed. The TCE represents the expected return per unit of text length from learning a group of words. As such, the TCE score in the target text domain should determine the order in which words in this domain are most efficiently learned. Indeed, the extracted common academic words and limited-academic-domain words showed significantly higher text coverage and TCE scores in academic texts than in other texts. Literary words also provided high text coverage and high TCE scores in literary texts, despite a lower efficiency level than that of academic vocabulary in academic texts. Learning domain-specific words is expected to be much more efficient than learning other words at the intermediate level. At the advanced level or above, learning domain-specific words will be further more efficient in some domains such as the natural sciences. In sum, the TCE has been shown to provide useful information for deciding on the learning order of various groups of words. Other findings based on the analyses using the databases and word lists include the features of some indices for dispersion and adjusted frequency, lexical features of different media and genres, indexicality of the distributions of word origins and parts of speech, and the discrepancy between learning orders of words and Kanji. A Lexical Learning Possibility Index for a Reading Text (LEPIX) was also proposed for the simplification of a text as a vocabulary learning resource

Expert system development for hard disk drive failure analysis

The Computer\u27s Hard Disk Drive is a complex high technology device, diagnosis of a failure is difficult even using sophisticated test equipments. These Drives are expensive and returning a new one when it fails within the warranty period is not an option. The failed drive must be tested and repaired. In the repair process the analysis and diagnosis of the failures is a key point in the process where decisions regarding the repair process that the failed Drive will follow. Therefore, there is a requirement to perform an effective analysis and provide an accurate diagnosis. The standard system utilized for diagnosis was based on human capacity, this study proves that the deficiencies of the standard failure analysis method does not provide satisfactory results. On the other hand, this study proposes alternatives that incorporate the expert\u27s knowledge and makes it available for analysis technicians, analyzing every Drive

Infestations as a Natural Disaster: The Economic Impacts of the Fonterra Whey Protein Concentrate Contamination Incident

This paper presents the results from an investigation into the economic implications for New Zealand of the 2013 Whey Protein Concentrate contamination incident (popularly known as the Fonterra Botulism scare). It assesses the impact of this incident to dairy exports using synthetic control methods. A synthetic counterfactual scenario where the incident did not occur is developed using weighted averages of the dairy exports of countries unaffected by the scare. The research finds that there was an initial negative shock to the exports of products that were thought to have been contaminated, but that there were no significant sustained impacts on other dairy products. The affected products make up only a small proportion of New Zealand dairy exports, with the vast majority of dairy exports being unaffected products. Infant formula exports appear to have recovered somewhat in the long run, however whey product exports remain lower than they otherwise would have been

"So, you're from Brixton?": towards a social psychology of community

This thesis examines the social psychological significance of 'community', as it is experienced and talked about in Brixton, a culturally diverse area in South London. There are two points of entry into the social psychology of a community: (1) the negotiation of social representations of the community and (2) the co-construction of community identities. The theoretical perspective that I have developed through this research is grounded in the theory of social representations (Moscovici, 1984, 1988; Farr, 1987) and draws on other theories of representation (Hall, 1997a), community (Cohen, 995), identity and self-consciousness (Hall, 1991a; Tajfel, 1982; Mead, 1934), stigma (Goffman, 1968) and the media (Thompson, 1995). It is an ethnographic study which combines ongoing participant-observation, 7 focus groups with 44 adolescents aged between 12 and 16, 5 in-depth interviews with deputy-heads of Brixton's schools, a media analysis of a documentary set in Brixton, and follow-up discussions. These accounts are woven together to answer the principal research question: how is `community' lived in Brixton? This study shows that communities emerge as sites of struggle in the negotiation of self-identity, belonging and difference. Community identities are constructed through and against social representations of the community, particularly those in the media. Two competing representations of Brixton - 'Brixton as Diverse' and 'Brixton as Bad' — were found in the same representational field. The data illustrate the different ways in which people affirm, manipulate and contest these ambivalent social representations in order to defend their perspective on Brixton, and so either claim or reject community membership. I examine how these representations both reflect and construct the social reality of Brixton. This reveals the potential of social representations to construct, delimit and empower the living of community. The systematic analysis of social representations of community and community identities demonstrates the pressing need for a social psychology of community