Portuguese Meeting on Computer Graphics 2009

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    BEDS: Uma Estrutura de Dados para Malhas Triangulares
    (The Eurographics Association, 2021) Silva, Frutuoso; Gomes, Abel; Coelho, António and Cláudio, Ana Paula
    As malhas triangulares tem um papel fundamental na ComputafiiO Grafica. Este artigo apresenta uma nova estrutura de dados geometrica para representar malhas triangulares, designada de Butte,jly Edge Data Structure ( BEDS). Esta estrutura de dados representa apenas os vertices e as arestas, sendo as faces representadas impli- citamente por vertices. Esta estrutura de dados implementa uma representarao CJ para malhas triangulares, o que significa que tem dois acessos directos e sete indirectos para aceder a toda a informarao topol6gica da malha. Apesar disso, permite o acesso as faces directamente atra ves das arestas como um conjunto de tres vertices. Esta estrutura de dados permite tambem representar malhas triangulares niio-manifold.
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    Blaze - Automatizando a Interacção em Interfaces Gráficas
    (The Eurographics Association, 2021) Barata, Gabriel; Guerreiro, Tiago; Gonçalves, Daniel; Coelho, António and Cláudio, Ana Paula
    Operating system users are constantly facing situations where repetitive tasks arise and there is no trivial way to automate them. It is tme that there are several application launchers currently available, but they are no match to the uniqueness of the repetitive tasks that emerge from eve,yday usage. 1\1ost of the times, to maximize their pe,formance, users struggle to find workarounds, resorting to scripting languages and macro editors. However, these are bey ond the common user's knowledge, leading them to accomplish the remainder of the task by hand. We present Blaze, a new system which is able to automate user's repetitive tasks, not in a single application but operating system-widely. Blaze brings the application launcher concept to a new level, enhancing other applica-tion launchers' features and adding the ability to be constantly monitoring users' actions, without intermpting their work. Blaze is able to establish relationships between actions and, resorting to an algorithm, based on common prefix search in a suffix-tree, detect repetition patterns in the user interaction hist01y. These repetitions are used to dynamically generate comprehensive narratives and to fi,lfi/1 the remaining of the task in the user's place. Furthermore, these automations can be stored in script files, which can later be reproduced, even in dif ferent situations from the one in which the repetition was detected.
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    Comparação de Dispositivos de Interacção em Ambientes de Realidade Virtual: Desenvolvimento de um Setup Experimental e Estudos com Utilizadores
    (The Eurographics Association, 2021) Lino, Filipe; Dias, Paulo; Oliveira, Arnaldo; Santos, Beatriz Sousa; Coelho, António and Cláudio, Ana Paula
    A Realidade Virtual (RV) tem despertado um interesse crescente nos ultimos anos. Contudo a sua evolup'io tem sido mais lenta que o esperado, provavelmente devido a.o custo dos equipamentos, mas tambem as capacidades dos dispositivos de interacrao que ainda estiio em muitos aspectos aquem do esperado. Exist em jd vdrios dispositivos de interaccao para ambientes de RV, sendo um dos mais recentes o comando da Wii, o Wiimote, que tem permitido de alguma forma vulgarizar uma interacrao mais natural. Contudo a utilizar;iio deste tipo de ambientes e dispositivos para tarefas como a manipularao e selecrao de objectos numa aplicarao ainda tem muitas dificuldades para ultrapassa1; 0 ganho que esses dispositivos podem trazer relativamente a dispositivos mais tradicionais como o rato ainda niio estd hem quantificado. 0 trabalho apresentado neste artigo tem como objectivo estudar a interacrao num ambiente de RV comparando vdrios dispositivos de entrada, mais concretamente, o Wiimote, o rato e o GamePad. Para talfoi adaptada uma aplicacao Ja existente cujo objectivo ea manipularao e selecrao de polfgonos num modelo. Foram ainda realizadas duas experiencias com utilizadores para validar os tipos de interacr;iio escolhidos assim como comparar o desempenho dos utilizadores com os diferentes dispositivos. Uma das conclusoes e que para este tipo de interacrao, os utilizadores tem um desempenho muito pr6ximo usando o Wiimote e o rato, sendo o gamepad nitidamente pio1; Por outro lado, a evolufiiO do desempenho com o Wiimote entre as duas experiencias apresentadas tambem mostra a importtincia que tem a configurarao do dispositivo e o tipo de interacrao definido no desempenho final do utilizador.
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    A Comparison of Orthographic and Perspective Projections in the Generation of Textures for Billboards
    (The Eurographics Association, 2021) Saraiva, Carlos; Oliveira, João Fradinho; Pereira, João Madeiras; Araújo, Bruno Rodrigues de; Coelho, António and Cláudio, Ana Paula
    Image-based rendering techniques take the approach of rendering new images based on existing ones, effec­tively separating the rendering complexity from the geometric complexity of the scene they represent. With the advance of hardware capabilities, these techniques have regained interest. However, the creation of images pre­viously mentioned is error-prone, so computation must be done in order to correct them. This paper presents a comparison between the uncorrected errors apparent in billboards when the applied texture is generated with a perspective or with orthographic projection.
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    Dados Geotécnicos e Geofísicos: Exploração de novas formas de visualização
    (The Eurographics Association, 2021) Gonçalves, Vítor; Dias, Paulo; Almeida, Fernando; Batista, João; Santos, Beatriz Sousa; Coelho, António and Cláudio, Ana Paula
    Este artigo visa a explorar:ao de novas formas de visualizar:ao de dados geotecnicos que possam ser mais enri­quecedoras e mais interactivas que as oferecidas pelos actuais sistemas informar:ao geografica (SIG). Desta forma os dados siio simplesmente um mode lo para a construr:ao de uma potencial ferramenta. Na pratica pre­tende-se a implementar:ao de metodos de visualizar:ao e interacr:ao que permitam a visualizar:ao simultanea dos varios tipos de dados disponibilizados. Este trabalho ainda se encontra numa fase experimental e tern como ob­jectivo explorar varias formas de visualizar:ao, verificar a sua validade/adaptabilidade ao caso concreto dos dados geotecnicos. Neste caso de estudo, foram utilizados dados geotecnicos adquiridos atraves de diferentes modalidades.
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    Desenvolvimento de um operador de tone mapping para dispositivos com ecrã pequeno
    (The Eurographics Association, 2021) Urbano, Carlos; Magalhães, Luís; Moura, João Paulo; Bessa, Maximino; Marcos, Adérito Fernandes; Coelho, António and Cláudio, Ana Paula
    Dada a forte divulgação e crescente adesão à criação e utilização de imagens HDR (High Dynamic Range), quer de fotografias do mundo real quer imagens geradas por computador através de software específico, tornase necessário permitir a sua adequada visualização nos dispositivos de visualização convencionais, incluindo os pequenos e limitados, mas amplamente difundidos, dispositivos com ecrã pequeno (DEP) como os Personal Digital Assistants (PDA). Apesar do considerável esforço na melhoria destes dispositivos, as suas limitações continuam a ser notórias, salientando-se o reduzido tamanho, resolução e gama de cores disponíveis. Conforme demonstrámos em experiências anteriores, este tipo de dispositivos necessitam de um operador de mapeamento de tons (Tone Mapping Operator - TMO) adequado que maximize a percepção de imagens HDR. Neste artigo expomos o estado actual do desenvolvimento deste novo TMO para DEP.
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    Dispositivo de Interacção para Ecrã de Grandes Dimensões
    (The Eurographics Association, 2021) Araújo, Bruno; Jota, Ricardo; Fernandes, João; Ferreira, Alfredo; Pereira, João Madeiras; Coelho, António and Cláudio, Ana Paula
    A interacriio corn ecrans de grande dimensiio e um tema que tern despertado a atenriio de investigadores, niio apenas na academia, mas tambem na industria. No entanto, os dispositivos tratlicionais, como o teclado ou o rato, sao claramente inadequados para este tipo de ambientes. Neste contexto concebemos um inovador dispositivo de interaci;iio sem fios esferico, desenhado para caber na m[io de um adulto. Este dispositivo fornece seis graus de liberdade em conjunto corn um sensor de pressiio e um botcio tradicional. Des ta f orma o utilil,Cldor controla niio apenas a posiriio no esparo tri-dimensional, mas tambem a rotai;lio ao Longo dos tres eixos. Nesta comunicarlio apresentamos o dispositivo jl:.sico em conjunto corn o prot6tipo de interacrao.
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    Effective Algorithm for Building and Solving Linear Systems
    (The Eurographics Association, 2021) Serna, Sebastian Pena; Silva, João; Stork, Andre; Marcos, Adérito Fernandes; Coelho, António and Cláudio, Ana Paula
    Several mesh-based techniques in computer graphics such as shape deformation, mesh editing, animation and simulation, build and solve linear systems. The most common method to build a linear system consists in traversing the topology (connectivity) of the mesh, producing in general a representation of the set of equations in form of a sparse matrix. Similarly, the solution of the system is achieved, by means of iterating over the set of equations in the default sequence of the vertices (unknowns). This paper presents a new algorithm, which optimizes the build of the linear system and its storage, and which allows the iteration over the set of equations in any arbitrary order. Additionally, our algorithm enables rapid modifications to the linear system, avoiding a complete rebuild.
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    Efficient use of Multiple Hardware Components for Image Synthesis
    (The Eurographics Association, 2021) Pereira, Francisco; Moura, João Paulo; Magalhães, José Afonso Bulas Cruz Luís; Chamers, Alan; Coelho, António and Cláudio, Ana Paula
    With the advent of affordable and powerful computers systems, even in desktop configurations, the rapid render­ing of complex scenes using global illumination algorithms is within reach. However, some significant problems still must be dealt with when performing such physically based lighting simulations i we are to achieve real time performance on current technology. The power offered by modern computer systems is not only due to the in­creasing CPU capabilities, but also to the fast development of others system elements, including graphics proc­essing units (GPU) and other additional processing boards. Ray tracing implementations in such environments typically target only one hardware component, or at best map specific type of work to particular elements within the system. This approach leads to an unbalanced work distribution and marginalisation of certain types of resources. Jn this paper we present a framework for managing and interfacing all the available computational power within a modern PC in a balanced and efficient way. At the centre of proposed approach is an abstraction layer between the main rendering stage and the primitives of the rendering process. Several advantages of such organisation are discussed, including portability and ea.ry extendibility to newer powerful hardware resources as they become available, optimizations at resource level, modularity, and load balancing. More practical issues regarding the management strategy and implementation for heterogeneous environments below this level o ab­ straction, where performance is a key aspect, are also presented. To validate this model a set of experiments were conducted. The results have shown that the introduction of an abstraction layer into the rendering system can improve the performance and better use the available resources.
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    Ensaio de Avaliação Preditiva para Utilizadores com Necessidades Especiais
    (The Eurographics Association, 2021) Artífice, Andreia; Lopes, João Brisson; Jorge, Joaquim; Fonseca, Manuel João; Coelho, António and Cláudio, Ana Paula
    This paper addresses the prediction of likely user moves in a practical case study where user interaction is pre­dicted on the basis of lambda-parameters acquired from users with special needs playing a software game. A model was built to reproduce actions performed by such users in a 3D world to overcome the difficult set-up of tests due to user reduced availability, mobility and varying/erratic behaviour. User actions data was obtained from usability tests where users played a game requiring them to move around a virtual house and perform some ac­tivities. The tests were carried out with users with disabilities such as severe physical injuries, cerebral palsy and Down syndrome. A three level simulator was developed with data extracted from part o the data collected during experiments, the remaining raw experimental data serving as reference for validation. Data analysis cal­culated the λ-parameter required by the Poisson and Exponential Distributions used by the statistical approach adopted. The tests performed showed an excellent statistical flt of the simulated data to the reference data.
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    Estratégias para a Representação de Pontos de Interesse sobre Mapas
    (The Eurographics Association, 2021) Paiva, Bruno; Cláudio, Ana Paula; Carmo, Maria Beatriz; Pombinho, Paulo; Catita, Cristina; Coelho, António and Cláudio, Ana Paula
    0 objectivo do nosso trabalho e mostrar pontos de interesse sabre um mapa de um modo que seja inteligivel para o utilizador quando este utiliza um computador de secretaria ou um computador portatil. Sao tidos em considera9ao dais aspectos, para os quais se apresentam abordagens: primeiro, os simbolos relativos aos pon­tos de interesse podem ocultar zonas do mapa que o utilizador necessita visualizar; segundo, os simbolos, ape­sar da aplica9ao da fun9ao de grau de interesse, podem ser em numero sign(ficativo em determinadas zonas do mapa, tornando d[ficil obter informacao util de forma rapida e simples.
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    Exploração da Remoção Hierárquica por Oclusão em Simulações em Tempo Real
    (The Eurographics Association, 2021) Cunha, Vitor; Leitão, Miguel; Coelho, António and Cláudio, Ana Paula
    As aplicacoes de simulacao grafica em tempo real podem apresentar um fraco desempenho devido a complexi­dade de ambientes virtuais de muito grandes dimensoes. Um exemplo ea simulacao de conducao em ambientes urbanos onde se utilizam cenas extensas corn densidade de geometria tipicamente muito elevada. Nesta perspec­tiva, o desenvolvimento de metodos que permitem a seleccao apenas da geometria visivel, eliminado toda a res­tante, e de importancia crucial pois ira diminuir a quantidade de trabalho a realizar pelo hardware grafico. Neste grupo de metodos, que determinam a visibilidade da geometria mediante um ponto de vista sabre a cena, existe um conjunto cujo prop6sito e o de determinar se um dado objecto no ambiente virtual se encontra ocluso por outro(s), logo, niio visivel. Este tipo de algoritmos de remocao por oclusiio, em particular os que usam Hardware Occlusion Queries, tornou atractiva a determinacao de visibilidade em tempo real sem necessidade de extensos calculos em pre-processamento. Neste artigo e abordada a infl.uencia na pe,formance que o uso da remocao por oclusiio, quando aplicada a cenas organizadas em estruturas de dados hierarquicas, tern em simu­la98es de ambientes virtuais complexos de muito grandes dimensoes. A aplicacao de suporte desenvolvida usa as fimcionalidades base que a API OpenSceneGraph disponibiliza para o render da cena e determinacao de visibilidade.
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    Fast CUDA-Based Triangulation of Molecular Surfaces
    (The Eurographics Association, 2021) Dias, Sérgio; Gomes, Abel; Coelho, António and Cláudio, Ana Paula
    Modeling molecular surfaces enables us to extract useful information about interactions with other molecules and measurements of areas and volumes. Over the years many types of algorithms have been developed to represent and rendering molecular surfaces, but all these algorithms have problems related to time performance in triangulating molecular surfaces. One possible solution to solve this problem is using parallel computing systems, but until recently they have been very expensive. Fortunately, the appearance of the new generation of low-cost GPUs with massive computational power opens up an opportunity window to solve this problem. So, in this paper, we present a GPU-based algorithm to speed up the triangulation and rendering of molecular surfaces. Besides we carry out a study that compares a sequential version (CPU) and a parallel version (GPU) of a molecular surface representation using the Marching Cubes (MC) Algorithm.
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    FlexiXML - Um animador de modelos UsiXML
    (The Eurographics Association, 2021) Mendes, Sandrine A.; Campos, José Creissac; Coelho, António and Cláudio, Ana Paula
    Uma parte consideravel do desenvolvimento de software e dedicada a camada de interacc;:ao corn o utilizador. Face a complexidade inerente ao desenvolvimento desta camada, e importante possibilitar uma analise tao cedo quanto possivel dos conceitos e ideias em desenvolvimento para uma dada interface. 0 desenvolvimento baseado em modelos fornece uma soluc;:ao para este problema ao facilitar a prototipagem de interfaces a partir dos modelos desenvolvidos. Este artigo descreve uma abordagem a prototipagem de interfaces e apresenta a primeira versao da ferramenta FlexiXML que realiza a interpretar;:ao e animac;:ao de interfaces descritas em UsiXML.
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    GeniusPhone: A Personal Companion for Everyday Situations
    (The Eurographics Association, 2021) Guerreiro, João; Guerreiro, Tiago; Gonçalves, Daniel; Coelho, António and Cláudio, Ana Paula
    Mobile devices have become faithful companions that keep track of most o_f our daily interactions and are al­ways available to interact with. However, considering their capabilities, mobile devices play an insufficient role helping the user in his comnzon daily tasks. The in;formation they have access to is limited, as is the context in which it can be used. We present GeniusPhone, a system that inter-relates the users' personal information and interactions with others from their computers and mobile devices, using it to gather additional data .from online public sources. The information retrieved from the personal devices, due to its personal and trustable character, helps us filter the in;formation retrieved from other less trustable and structured sources. GeniusPhone is able to provide the users with relevant summaries about someone or something, from their point of view, at the time they want or need them. An example application that presents condensed information about a person is presented, as well as scenarios revealing its potentialities.
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    Getting a Glimpse of your Pictures using Dominant Colors
    (The Eurographics Association, 2021) Rodrigues, Pedro; Lopes, Luís; Fonseca, Manuel J.; Coelho, António and Cláudio, Ana Paula
    Nowadays, we have a lot o_f digital images in our collections o_ften scattered in a disorganized way. This paper presents a new way to structure and visualize our database of.pictures based on the two most dominant colors of· each image. Our solution combines mechanisms .from image retrieval with visualization techniques to give users an overview o_ftheir picture collection and also to allow them to search.for similar images by using the dominant colors. To speed up the overall process, we use an inverted index where we replace the typical textual terms by the dominant colors.
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    Global Terrorism Database Vizualization: um projecto de arte digital suportado por visualização de informação
    (The Eurographics Association, 2021) Moura, João Martinho; Sousa, Jorge; Branco, Pedro; Marcos, Adérito Fernandes; Coelho, António and Cláudio, Ana Paula
    Esta comunicação apresenta uma aplicação de visualização da informação, o Global Terrorism Database Visualization (GTDV) abordando a questão do terrorismo. O projecto GTDV recorre a técnicas e processos de visualização da informação, dando ênfase á estética, além da funcionalidade, exibindo dados de eventos terroristas ocorridos entre 1970 e 2004, compilados a partir do Global Terrorism Database, da Universidade de Maryland, E.U.A.. É descrita a interface do GTDV, sendo realizada uma análise crítica e especificadas as técnicas estruturais e de visualização utilizadas. O projecto GTDV visa contribuir para a emergência de um conhecimento aprofundado sobre a problemática do terrorismo.
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    GPU Ray Casting
    (The Eurographics Association, 2021) Marques, Ricardo; Leškovský, Peter; Santos, Luís Paulo; Paloc, Céline; Coelho, António and Cláudio, Ana Paula
    For many applications, such as walk-throughs or terrain visualization, drawing geometric primitives is the most efficient and effective way to represent the data. In contmst, other applications require the visualiza-tion of data that is inherently volumetric. For example, in biomedical imaging, it might be necessary to visualize 3D datasets obtained from GT or J\1RI scanners as a meaningful 2D image, in a process called volume rendering. As a result of the popularity and usefulness of volume data, a broad class of volume rendering techniques has emerged. Ray casting is one of these techniques. It allows for high quality volume rendering, but is a computationally expensive technique which, with current technology, lacks interactivity when visualizing large datasets, if processed on the CPU. The advent of efficient GPUs, available on almost every modern workstations, combined with their high deg ree of programmability opens up a wide field of new applications for the graphics cards. Ray casting is among these applications, exhibiting an intrinsic parallelism, in the form of completely independent light rays, which allows to take advantage of the massively parallel architecture of the GPU. This paper describes the implementation and analysis of a set of shaders which allow interactive volume rendering on the GPU by resorting to my casting techniques.
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    Infrared Tracking System for Immersive Virtual Environments
    (The Eurographics Association, 2021) Gaspar, Filipe; Dias, Miguel Sales; Bastos, Rafael; Coelho, António and Cláudio, Ana Paula
    In this paper, we describe the theoretical foundations and engineering approach of an infrared-optical tracking system specially design for large scale immersive virtual environments (VE) or augmented reality (AR) settings. The system described is capable of tracking independent retro-reflective markers arranged in a 3D structure (artefact) in real time (25Hz), recovering all possible 6 Degrees of Freedom (DOF). These artefacts can be adjusted to the user's stereo glasses to track his/her pose while immersed in the VE or AR, or can be used as a 3D input device. The hardware configuration consists in 4 shutter-synchronized cameras attached with band-pass infrared filters and the artefacts are illuminated by infrared array-emitters. The system was specially designed to fit a room with sizes of 5.7m x 2.7m x 3.4 m, which match the dimensions of the CAVE-Hollowspace of Lousal where the system will be deployed. Pilot lab results have shown a latency of 40ms in tracking the pose of two artefacts with 4 infrared markers, achieving a frame-rate of 24.80 fps and showing a mean accuracy of 0.93mm/0.52º and a mean precision of 0.08mm/0.04º, respectively, in overall translation/rotation DOFs, fulfilling the system requirements initially defined.
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    Interactive Collision Detection for 3D Environments
    (The Eurographics Association, 2021) Figueiredo, Mauro; Coelho, António and Cláudio, Ana Paula
    This paper presents a collision detection algorithm for 3D simulated environments. It describes the implementa­tion of a collision detection approach using the Overlapping Axis-Aligned Bounding Box (OAABB) and R-trees to improve petformance. Experimental results show that this implementation is effective in determining interac­tively intersections between 3D models.