Publications

Consistent Handling of Linear Features in Polyline Simplification
Authors:Adler Cardoso Gomes da Silva and Wu Shin-Ting
Published as chapter in Advances in GeoInformatics, DAVIS JR., C. A., MONTEIRO, A. M. V. (eds.)

A Robust Strategy for Handling Linear Features in Topologically Consistent Polyline Simplification [pdf|ps]
Authors:Adler Cardoso Gomes da Silva and Wu Shin-Ting
Published in Proceedings of Simpósio Brasileiro de Geoinformática - GEOINFO 2006
Abstract
Polyline simplification is a technique that reduces the number of vertices of a polygonal chain for the purpose of map generalization and for speeding up processing and visualization in GIS. Unfortunately, the majority of simplification algorithms does not preserve the topological consistency of the map, namely the spatial placement of a polyline with respect to itself and to its neighbouring features. To overcome this problem, some approaches based on the consistency of a point feature have been proposed. For the sake of simplicity, they unify the handling of linear and point features by considering a linear feature as a sequence of point features. This solution, however, fails in a few particular cases. In this paper, we firstly examine the reason for it to fail and then present a robust strategy for remedying the remaining problems without abandoning the basic principle of reducing a linear feature to a sequence of point features.

Preserving Coincidence and Incidence Topologies in Saalfeld's Polyline Simplification Algorithm[pdf|ps]
Authors:Adler Cardoso Gomes da Silva and Wu Shin-Ting
Published in Proceedings of Simpósio Brasileiro de Geoinformática - GEOINFO 2005
Abstract
In this paper, we firstly describe two topological configurations that are not considered by Saalfeld's polyline simplification algorithm: the coincidence topology, concerning the overlapping of two polylines or the overlapping of a feature point and a polyline, and the incidence topology, concerning the incidence of two polylines without having the incidence point represented as a common vertex. Afterwards, we suggest a simple modification in Saalfeld's algorithm for preserving these topologies. Finally, we give some results of our simplification procedure and compare them to the ones of Saalfeld's algorithm.

Using Geospatial Data to Generate One-line Diagrams of Electrical Power Systems[pdf]
Authors:Lia Toledo Moreira Mota, Alexandre de Assis Mota, and Wu Shin-Ting
Published in Proceedings of Simpósio Brasileiro de Geoinformática - GEOINFO 2005
Abstract
One-line diagrams are widely used to represent the electrical power system current state and its probable performance in the case of studies and simulations. Hence, its adequate construction is of great importance to avoid inaccurate decisions of the network operators. In order to reduce the human errors and the huge effort in a manual generation technique (usually adopted nowadays), the work proposes a methodology to automatically build these diagrams. The method is based on the usage of the geospatial data related to the network buses and branches with a graph algorithm that permits the elimination of superpositions of buses. The approach was successfully testes with the Institute of Electrical and Electronics Engineers (IEEE) 30 buses standard system and with a portion of the Brazilian network.

The Douglas-Peucker Algorithm: Sufficiency Conditions for Non-Self-Intersections [pdf|ps]
Authors: Wu Shin-Ting, Adler Cardoso Gomes da Silva, and Mercedes G. Márquez
Published in Journal of the Brazilian Computer Society
Abstract
The classic Douglas-Peucker line-simplification algorithm is recognized as the one that delivers the best perceptual representations of the original lines. It may, however, produce simplified polyline that is not topologically equivalent to the original one consisting of all vertex samples. On the basis of properties of the polyline hulls, Saalfeld devised a simple rule for detecting topological inconsistencies and proposed to solve them by carrying additional refinements. In this paper, we present an alternative form for the classic Douglas-Peucker to produce a simplified polyline which is homeomorphic to the original one. Our modified Douglas-Peucker algorithm is based on two propositions: (1) when an original polyline is star-shaped, its simplification from the Douglas-Peucker procedure cannot self-intersect; and (2) for any polyline, two of its star-shaped sub-polylines may only intersect if there is a vertex of one simplified sub-polyline inside the other's corresponding region.

A non-self-intersection Douglas-Peucker Algorithm[pdf|ps]
Authors: Wu Shin-Ting and Mercedes R. G. Márquez
Published in Proceedings of SIBGRAPI 2003 by IEEE, São Carlos, Brazil, 2003 (selected to be published in Journal of the Brazilian Computer Society)
Abstract
The classical Douglas-Peucker line-simplification algorithm is recognized as the one that delivers the best perceptual representations of the original lines. It is used extensively for both computer graphics and geographic information systems. There are two variants of this algorithm, the original O(nm) method, where n denotes the number of input vertices and m the number of output segments, that works in any dimension, and the O(nlog{n}) one, which only works for simple 2D planar polylines. In the both variants, a self-intersecting simplified line may be yielded if the accepted approximation is not sufficiently fine. Based on star-shaped subsets, we present in this paper yet another O(mn) variant of Douglas-Peucker algorithm which preserves the non-self-intersection property for any predefined tolerance.

Scientific Visualization of Poincaré Maps [compressed PostScript]
Authors: Wu, Shin - Ting, Sidney Pio de Campos and Marcus A. M. de Aguiar
Published in Computers & Graphics: An International Journal of Systems & Applications in Computer Graphics Vol. 22 No. 2/3 - a Special Issue on "Selection of the Best Papers from the WSCG'97 Int. Conf. on Computer Graphics and Visualization" - 1998
Abstract
Poincaré maps have been proved to be a valuable tool in the analysis of several dynamical systems modeled by differential equations. These maps are generated by reducing the continuous flow to a two-dimensional discrete dynamics. From a map it is possible to identify the chaos phenomena in a system under the influence of an external parameter. If this external parameter is variable, one can study the behaviour of the system by interpolating the set of corresponding Poincaré maps. Despite of its usefulness, the computer graphics work carried out so far has been limited to display and plot of Poincaré maps. In this paper a prototype for the computer analysis of Poincaré maps is described. We show that, from the point-of-view of computer graphics, we can process Poincaré maps as noisy images. This approach not only facilitates the partition of Poincaré maps into regular and chaotic regions but also offers possibilities to visualize the continuous evolution of a system by varying the external parameter. Some results are given to illustrate the funcionalities of the prototype.

Simplificação Consistente de Linhas em Mapas Cartográficos[pdf]
Author: Adler Cardoso Gomes Da Silva
Type: Mestrado

Um Modelo de Interação Gráfica para Suporte ao Pré-Despacho de Sistemas de Energia Elétrica[pdf]
Author: Célio Flores Siqueira Júnior
Type: Mestrado

Visualização Científica de Mapas de Poincaré[gziped ps|gziped pdf]
Author: Sidney Pio de Campos
Type: Mestrado

Relatório Técnico RT-DCA-06[pdf]
Author:Adler C. G. da Silva

Visualização de Dados Elétricos da Rede de Transmissão Brasileira[pdf(in Portuguese)]
Authors:Paulo César Magalhães Meira and Wu Shin-Ting
Published in Sibgrapi 2007 - Trabalhos de Iniciação Científica
Abstract
Uma proposta de visualização de dados elétricos da rede transmissão brasileira, baseado em diagramas unifilares, é apresentada. Para contemplar, de um lado, um número elevado de barras e conexões e, de outro lado, a baixa qualidade de dados disponíveis, propomos utilizar dois níveis de visualização: um nível até as cidades, baseado em dados geográficos, e um outro nível de maior detalhamento dentro das cidades, no qual são utilizados dados da topologia de sub-redes para alimentar geradores automáticos de diagramas unifilares.

VisciPower: Um Ambiente de Interação com os Dados Elétricos Georeferenciados[gz (in Portuguese)]
Authors: Paulo C. M. Meira; Rajiv Andrade and Wu Shin-Ting
Presentedx in the event Unicamp de Portas Abertas - 2006
Abstract
In this poster we present the overview of the architecture of VisciPower.

VisciPower: Uma Interface Interativa para o Planejamento Energético[pdf (in Portuguese)]
Authors: Célio Flores Siqueira Jr., Wu Shin-Ting, Anésio dos Santos Junior, and Takaaki Ohishi
Published in the Proceedings of SisPot 2005
Abstract
In this work we present the project of a graphical interface that supports a power engineer in elaborating the diary predispatch on the basis of the estimated demand and the system's generation and transmission capability.