Robust Intrinsic and Extrinsic Calibration of RGB-D Cameras

Color-depth cameras (RGB-D cameras) have become the primary sensors in most robotics systems, from service robotics to industrial robotics applications. Typical consumer-grade RGB-D cameras are provided with a coarse intrinsic and extrinsic calibration that generally does not meet the accuracy requirements needed by many robotics applications (e.g., highly accurate 3D environment reconstruction and mapping, high precision object recognition and localization, ...). In this paper, we propose a human-friendly, reliable and accurate calibration framework that enables to easily estimate both the intrinsic and extrinsic parameters of a general color-depth sensor couple. Our approach is based on a novel two components error model. This model unifies the error sources of RGB-D pairs based on different technologies, such as structured-light 3D cameras and time-of-flight cameras. Our method provides some important advantages compared to other state-of-the-art systems: it is general (i.e., well suited for different types of sensors), based on an easy and stable calibration protocol, provides a greater calibration accuracy, and has been implemented within the ROS robotics framework. We report detailed experimental validations and performance comparisons to support our statements

Sublinear algorithms for local graph centrality estimation

We study the complexity of local graph centrality estimation, with the goal of approximating the centrality score of a given target node while exploring only a sublinear number of nodes/arcs of the graph and performing a sublinear number of elementary operations. We develop a technique, that we apply to the PageRank and Heat Kernel centralities, for building a low-variance score estimator through a local exploration of the graph. We obtain an algorithm that, given any node in any graph of $m$ arcs, with probability $(1-\delta)$ computes a multiplicative $(1\pm\epsilon)$-approximation of its score by examining only $\tilde{O}(\min(m^{2/3} \Delta^{1/3} d^{-2/3},\, m^{4/5} d^{-3/5}))$ nodes/arcs, where $\Delta$ and $d$ are respectively the maximum and average outdegree of the graph (omitting for readability $\operatorname{poly}(\epsilon^{-1})$ and $\operatorname{polylog}(\delta^{-1})$ factors). A similar bound holds for computational complexity. We also prove a lower bound of $\Omega(\min(m^{1/2} \Delta^{1/2} d^{-1/2}, \, m^{2/3} d^{-1/3}))$ for both query complexity and computational complexity. Moreover, our technique yields a $\tilde{O}(n^{2/3})$ query complexity algorithm for the graph access model of [Brautbar et al., 2010], widely used in social network mining; we show this algorithm is optimal up to a sublogarithmic factor. These are the first algorithms yielding worst-case sublinear bounds for general directed graphs and any choice of the target node.Comment: 29 pages, 1 figur

REPENSANDO A EDUCAÇÃO NA CONTEMPORANEIDADE:O SER DOCENTE

International audienceEste trabalho relata o andamento de um projeto de pesquisa, o qual é composto por professores doCentro Universitário Franciscano, Santa Maria - RS. Atualmente todos atuam no ensino superior,desenvolvendo atividades docentes diretamente com os alunos em sala de aula, orientações de TrabalhosFinais de Graduação e Pós-Graduação e em pesquisas nas suas diferenciadas áreas de atuação. Foi justamentea inscrição como docentes no ensino superior a condição que permitiu uma aproximação de olharesinteressados a este tema de pesquisa formação de professores: repensando a educação nacontemporaneidade. Incontestavelmente somos interpelados por estas formações discursivas que desenhammodos de ser professor nas configurações atuais do mundo, ao passo que também interpelamos a conjunturadiscursiva que nos atravessa. Esta discussão também é perpassada por nossas vivências docentes e peloenredamento discursivo que tem delineado nossas representações sobre o sujeito pedagógico nacontemporaneidade, em especial, o sujeito-aluno do/no ensino superior. Interpelados principalmente pelasdiscussões do filósofo francês Michel Foucault se tece um produtivo embate de ideias em relação as suasáreas de atuação (Pedagogia e Educação Especial), mesclando as particularidades de cada campo cominquietações quanto à formação de professores e a constituição desses sujeitos. Interessou-nos problematizaralgumas questões que tomam a centralidade da cena educacional contemporânea, principalmente no que dizrespeito as práticas de formação de professores. A objetividade continua em aprofundar os conhecimentosconstruídos por FOUCAULT, pensando a formação dos professores, problematizar a constituição do professorna contemporaneidade e buscar a compreensão das relações entre o sujeito, a escola e o período modernoimplicados no contexto da educação

Political activity of brazilian adjudication: some dimensions

Since de advent of what is known as new constitucionalism, jurists have faced a difficult task in order to overcome some failures of normative positivism. In this context, the judiciary has played a renewed role, which can be justified on grounds of legal theory and on institutional reasons. However, this new role has led legal philosophers to several concerns, such as the relationship between law and ethics. On one hand, Critical Legal Studies points out that the judge always acts informed by his own convictions. On the other hand, according to R. Forst (within another context, but also relevant here), this is not really a problem, because a rule can be provided with ethics, but not ethically justified. This openness of law to moral makes it difficult for the interpretative judicial discourse to be taken as claimed by K. Günther: as a discourse of application only, and not of justification. All these controversies, however, lead to a common statement: the constitutional adjudication has been exercising a different activity. Some legal systems allows such activity legitimacy in some extent, like Brazilian’s, for example, which i) states a very broad adjudication, ii) provides an extensive catalog of basic rights, and iii) contains several procedural mechanisms for their protection. This empowers the adjudication to exercise what can be called a political activity. Therefore, a series of moral issues which were once exclusive to the political arena have been brought to the judiciary, such as: gay marriage, abortion, affirmative action, religious freedom, federation, separation of powers, distribution of scarce resources. In a democracy, these moral questions ought to be mainly decided through deliberation outside the judiciary, but not always this is what happens. The paper discusses these issues, showing also how the Brazilian Supreme Court has dealt - technically, or not - with this relationship between law and justice in a complex and pluralist society

CONHECIMENTOS DE NATUREZA MATEMÁTICA E SUAS REPRESENTAÇÕES EM SITUAÇÕES DE EXCLUSÃO SOCIAL

National audienceThis paper shows how men and women construct mathematical knowledge when subjected to social exclusion in a community peripheral in southern Brazil. Through a questionnaire administered to 103 subjects, different activities of work developped in this context were analyzed. Garbage recycling was approached, studying implicit mathematical knowledge developed by individuals working in this practice. The theoretical framework used appeals to the sociology, the educational, and developmental psychology of Vergnaud. We used a crossing between quantitative and qualitative methods for the data construction, namely, questionnaire, individual and group interviews recorded in video. Results show that according to the different problems faced in the community, individuals develop skills that appear to be maintained on the basis of contextual variables. We observed and differentiated knowledge called as concepts in action in the theory of conceptual fields of Vergnaud.Neste artigo, apresenta-se como homens e mulheres constroem conhecimentos matemáticos quando submetidos a situações de exclusão social, em uma comunidade periférica do Sul do Brasil. Por meio de um questionário aplicado a 103 sujeitos, analisaram-se diferentes atividades de trabalho desenvolvidas nesse contexto. Abordou-se a reciclagem de lixo, estudando os conhecimentos matemáticos implícitos, desenvolvidos pelos sujeitos nessa prática de trabalho, sendo essa atividade central investigada e desenvolvida nesse artigo. O quadro teórico utilizado faz apelo à sociologia, à educação, e à psicologia do desenvolvimento de Vergnaud. Utilizou-se um cruzamento de métodos quantitativos e qualitativos para a construção dos dados, quais sejam: o questionário, entrevistas videografadas individuais e coletivas. Os resultados mostram que, face aos diferenciados problemas enfrentados na comunidade, os sujeitos desenvolvem conhecimentos que parecem ser mantidos em função de variáveis contextuais. Observaram-se conhecimentos diferenciados e denominados como conceitos em ação na teoria dos campos conceituais de Vergnaud

Analizar las historias de vida: reflexiones metodológicas y epistemológicas

Este artículo reseña las diversas formas de analizar los textos realizados a partir de entrevistas biográficas (historias de vida)

Plane extraction for indoor place recognition

In this paper, we present an image based plane extraction method well suited for real-time operations. Our approach exploits the assumption that the surrounding scene is mainly composed by planes disposed in known directions. Planes are detected from a single image exploiting a voting scheme that takes into account the vanishing lines. Then, candidate planes are validated and merged using a region grow- ing based approach to detect in real-time planes inside an unknown in- door environment. Using the related plane homographies is possible to remove the perspective distortion, enabling standard place recognition algorithms to work in an invariant point of view setup. Quantitative Ex- periments performed with real world images show the effectiveness of our approach compared with a very popular method