Showing papers in "Revista Brasileira de Cartografia in 2003"

Map-matching in complex urban road networks

Abstract: Global Navigation Satellite Systems (GNSS) such as GPS and digital road maps can be used for land vehicle navigation systems. However, GPS requires a level of augmentation with other navigation sensors and systems such as Dead Reckoning (DR) devices, in order to achieve the required navigation performance (RNP) in some areas such as urban canyons, streets with dense tree cover, and tunnels. One of the common solutions is to integrate GPS with DR by employing a Kalman Filter (Zhao et al., 2003). The integrated navigation systems usually rely on various types of sensors. Even with very good sensor calibration and sensor fusion technologies, inaccuracies in the positioning sensors are often inevitable. There are also errors associated with spatial road network data. This paper develops an improved probabilistic Map Matching (MM) algorithm to reconcile inaccurate locational data with inaccurate digital road network data. The basic characteristics of the algorithm take into account the error sources associated with the positioning sensors, the historical trajectory of the vehicle, topological information on the road network (e.g., connectivity and orientation of links), and the heading and speed information of the vehicle. This then enables a precise identification of the correct link on which the vehicle is travelling. An optimal estimation technique to determine the vehicle position on the link has also been developed and is described. Positioning data was obtained from a comprehensive field test carried out in Central London. The algorithm was tested on a complex urban road network with a high resolution digital road map. The performance of the algorithm was found to be very good for different traffic maneuvers and a significant improvement over using just an integrated GPS/DR solution.

Correction to helmert’s orthometric height due to actual lateral variation of topographical density

Abstract: Helmert (1890) used Poincare-Prey’s gravity gradient for the definition of the orthometric height. According to this approach the gravity value needed for the evaluation of the height is obtained from the observed gravity at the earth surface reduced to the mid-point between the earth surface and the geoid, considering that the gravity gradient is con-stant along the plumbline. Moreover, the mean topographical density p. = 2.67 g.cm -3 is assumed to approximate the actual distribution of topographical density. The correction to Helmert’s orthometric height due to the lateral variation of topographical density has been introduced by Vanicek et al. (1995). In this paper, some numerical aspects of this correction are investigated.

Far-zone contribution to upward continuation of gravity anomalies

Abstract: Based on a theoretical formulation of the far-zone contribution to the upward continuation of geoid-generated gravity anomalies the numerical aspects are investigated. Moreover, the numerical result over the part of the Canadian Rocky Mountains is presented in this paper.

Geografia e representações gráficas: uma breve abordagem crítica e os novos desafios técnico- metodológicos perpassando pela climatologia

Abstract: O presente artigo faz uma breve abordagem critica da relacao entre as representacoes graficas e os estudos geograficos, contextualiza historicamente a origem de certos equivocos na consideracao da cartografia, dos procedimentos matematicos e estatisticos e do uso das ferramentas tecnicas no sistema brasileiro de ensino de Geografia e aponta alguns novos desafios da Cartografia quanto processo de conhecimento cientifico, inserindo a Climatologia como ponte exemplificativa para a discussao.

Metodologia automática para extração de cruzamento de rodovias em imagens de alta resolução

Abstract: Pesquisas em extracao de rodovias em imagens digitais nao sao recentes, sendo as primeiras da decada de 70. Os metodos desenvolvidos normalmente sao classificados em duas classes: semi-automatico e automatico. Esta ultima classe nao preve a intervencao de um operador. Neste contexto, a extracao automatica de cruzamentos de rodovias e fundamental, embora muito poucos trabalhos sao encontrados na literatura sobre extracao de rodovias. A razao principal e a grande diversidade de cruzamentos de rodovias, gerando algumas dificuldades para construir um conhecimento a priori sobre cruzamentos. Esta pesquisa propoe uma metodologia automatica para resolver este problema, combinando segmentos de rodovias extraidos de uma imagem de alta resolucao (pixel 2m), reamostrada da imagem original de alta resolucao. A metodologia proposta foi testada em um conjunto de imagens de alta resolucao, mostrando-se confiavel e eficiente. Desde que as bordas das rodovias sejam satisfatoriamente definidas, o metodo se mostrou capaz de extrair totalmente os cruzamentos de rodovias. Alem disso, gerou uma significante melhora na malha viaria (aproximadamente 20%) extraida pela metodologia automatica de extracao de segmentos de rodovias.

Hierarchical data fusion with photogrammetric applications

Abstract: When two datasets are fused using least-squares adjustment, usually all the results will be affected by some change, even the reference data that are meant to provide information of such high quality that they should remain stable. In order to avoid this effect, the sequential adjustment is to be replaced by a strictly hierarchical method in which the esti-mation procedure is designed to reproduce everything that belongs to a “higher category” and to perform an adjustment in the least-squares sense for everything else. After presenting such a suboptimal estimator, but with the “reproducing property,” this technique is applied to the integration of photogrammetric networks of substantially different scales.