Ibero-American Symposium on Computer Graphics

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Adaptive trimming of cubic triangular Bézier patches
(The Eurographics Association, 2006) García, Ángel Luis; Miras, Juan Ruiz de; Feito, Francisco R.; Pere Brunet and Nuno Correia and Gladimir Baranoski
We present a method to handle cubic trimmed triangular Bézier patches. This scheme makes use of levels of detail and surface subdivision to achieve a fast and flexible hierarchical data structure that is specially useful to compute surface intersections in a robust and efficient way. The accuracy of the results can be adjusted by adding or subtracting elements to the levels of detail hierarchy, and it is also easy to obtain a decomposition of a trimmed patch into single triangular Bézier patches.
ArTbitrating JaVox: Evolution Applied to Visual and Sound Composition
(The Eurographics Association, 2006) Moroni, Artemis Sanchez; Manzolli, Jonatas; Zuben, Fernando Von; Pere Brunet and Nuno Correia and Gladimir Baranoski
ArTbitrariness is presented here as an initiative of upgrading the esthetical judgment through interactive evolutionary computation techniques and other population based techniques. Computational creativity will be approached, moreover evolutionary algorithms will be described and applied to simulate creativity. ArTbitrating JaVox, an evolutionary interactive environment for artistic production in visual and sound domains will be presented. Besides, the features of the evolutionary systems, that were incorporated in ArTbitrating JaVox, VOX POPULI, in sound domain, Art Lab and Shape, in visual domain, will be described.
Augmented Reality Assistance in Forest Fire Fighting
(The Eurographics Association, 2006) Vicens, Fernando; Linares, Jordi; Sancho, Sergio; Pere Brunet and Nuno Correia and Gladimir Baranoski
Forest fire fighting is unfortunately a very important activity for many fire departments. A forest fire is always a very complex situation to manage, in which lots of ground teams and aircraft have to cooperate in order to control such an incident. Aircraft fleet has an important role: the identification, selection and notification of elements of interest. The current problem is the lack of a precise and effective technology to assist this task. In this work, we describe the definition and application of a low-cost augmented reality solution that allows an accurate selection of all the items an aircraft is able to visualize from its privileged position, and the integration of this information in a 3D terrain visualization system in real-time.
Automatic architectural 3D model generation with sunlight simulation
(The Eurographics Association, 2006) Mas, Albert; Besuievsky, Gonzalo; Pere Brunet and Nuno Correia and Gladimir Baranoski
Nowadays, 2D architectural design is provided with many good tools. But it lacks efficient tools that could help designers in early stages of a project for tasks such as virtual prototyping or 3D model simulation. The 3D model generation from 2D floorplans in general implies tedious manual effort. With a 3D model the designer could validate both the building structure and the space distribution. Natural lighting is also a basic feature in structures design as a correct sizing of the building openings allow a better exploration of daylight illumination, and consequently, could prevent artificial illumination needs. In this paper we present a tool that allows to obtain, in a highly automatic process, 3D architectural models from 2D floorplans. The system also provides sunlight simulation for visualization and interactive edition operations. It allows to re-model the openings of the structure with real-time sunlight visualization. The whole module can be integrated within a standard CAD architectural platform as a complement for fast virtual prototyping and validation designs in an early stage of the project. We present results showing its application for both conceptual designs and for a real building model.
Boolean Operations in Open-Source Blender Project
(The Eurographics Association, 2006) Freixas, Marc; Grau, Sergi; Silva, David; Pere Brunet and Nuno Correia and Gladimir Baranoski
This paper describes the work of a new implementation of the Boolean operations of Blender. Blender is a modelling and animation 3D software with GNU General Public License (GPL). Boolean operations are a useful tool for modelling. Previous implementations of Blender Boolean operations have some drawbacks and the Blender users are not totally satisfied with them. The proposed implementation avoids the existing drawbacks of previous implementations and helps users in their modelling stage.
Coherent Hierarchical Level-of-Detail (HLOD) Refinement Through Hardware Occlusion Queries
(The Eurographics Association, 2006) Charalambos, Jean Pierre; Pere Brunet and Nuno Correia and Gladimir Baranoski
We present a coherent hierarchical level of detail (HLOD) culling algorithm that employs a novel metric to perform the refinement of a HLOD-based system that takes into account visibility information. The information is gathered from the result of a hardware occlusion query (HOQ) performed on the bounding volume of a given node in the hierarchy. Although the advantages of doing this are clear, previous approaches treat refinement criteria and HOQ as independent subjects. For this reason, HOQs have been used restrictively as if their result were boolean. In contrast to that, we fully exploit the results of the queries to be able to take into account visibility information within refinement conditions. We do this by interpreting the result of a given HOQ as the virtual resolution of a screen space where the refinement decision takes place. In order to be able to use our proposed metric to perform the refinement of the HLOD hierarchy as well as to schedule HOQs, we exploit the spatial and temporal coherence inherent to hierarchical representations. Despite the simplicity of our approach, in our experiments we obtained a substantial performance boost (compared to previous approaches) in the frame-rate with minimal loss in image quality.
Data-driven Tetrahedral Mesh Subdivision
(The Eurographics Association, 2006) Rodríguez, Lyudmila; Navazo, Isabel; Vinacua, Álvar; Pere Brunet and Nuno Correia and Gladimir Baranoski
Given a tetrahedral mesh immersed in a voxel model, we present a method to refine the mesh to reduce the discrepancy between interpolated values based on either scheme at arbitrary locations. An advantage of the method presented is that it requires few subdivisions and all decisions are made locally at each tetrahedron. We discuss the algorithm s performance and applications.
Efficient Conservative Collision Detection for Populated Virtual Worlds
(The Eurographics Association, 2006) Fernandes, A. Ramires; Deusdado, L.; Pere Brunet and Nuno Correia and Gladimir Baranoski
Large virtual worlds, with considerable level of detail are starting to emerge everywhere, from large areas of actual cities to archaeological detailed reconstructions of sites. Populating a virtual world adds an extra touch to the visualization of these worlds, but unfortunately it also brings an extra burden to the system. Several tasks are required when adding animated characters to a virtual world, such as collision detection, path planning and other AI algorithms, rendering of dynamic geometry, amongst others. In here a method for efficient and scalable conservative collision detection, that is able to deal with large scenes and thousands of avatars, is presented. This method does not perform exact collision detection, hence it is conservative. The method is suitable as a basis for path planning algorithms and other AI algorithms where an avatar is often regarded as something that can be bounded by a cylinder, or a box. The algorithm is capable of dealing with arbitrarily complex 3D worlds, and does not require any a priori knowledge of the geometry.
Efficient focus+context visual exploration of volume datasets
(The Eurographics Association, 2006) Campos, Jordi; Puig, Anna; Tost, Dani; Pere Brunet and Nuno Correia and Gladimir Baranoski
We propose a hierarchical representation of volume data sets based on a user-given definition of features. The model is general and it can be used for various types of feature definitions such as rendering queries, topological skeletons and property-based classification. We use this model to interactively select features of the volume and to render them providing focus+context information. In addition, our model provides a mechanism to index directly the feature voxels, therefore it considerably speeds up rendering.
Expeditious Modelling of Virtual Urban Environments with Geospatial L-systems
(The Eurographics Association, 2006) Coelho, António; Bessa, Maximino; Sousa, A. Augusto de; Ferreira, F. Nunes; Pere Brunet and Nuno Correia and Gladimir Baranoski
This paper presents Geospatial L-systems, a new extension of L-systems that incorporates geospatial awareness, and shows an application of this new tool in the expeditious modelling of urban environments, integrated with a modelling system with interoperable access to data sources. L-systems have been used in Computer Graphics for the modelling of plants, and in a few experiments to model urban environments. However, the lack of geospatial awareness is a limitation and in spite of some developments like open l-systems introduced the ability to communicate with the environment, there was a need for more flexibility. A new modelling system, named XL3D, generates virtual urban environments automatically from a XL3D document with a modelling specification. This modelling system accesses data sources in a interoperable way and the modelling processes are based on Lsystems. The integration of geospatial L-systems with the XL3D modelling system has increased its potential for automation and improved the potential to generate virtual urban environments with a higher level of detail and visual fidelity, with a lower level of complexity of the modelling processes. These facts are shown in a case study where a virtual urban environment taken from an area in the Porto downtown is generated by this solution.
GPU-based Evaluation of Boolean Operations on Triangulated Solids
(The Eurographics Association, 2006) Ogayar, Carlos Javier; Feito, Francisco R.; Segura, Rafael J.; Rivero, Marilina; Pere Brunet and Nuno Correia and Gladimir Baranoski
This paper presents a robust method for evaluating boolean operations on triangle meshes. It is based on a fast and reliable point-in-solid algorithm that works with B-Rep representations. With this method, several boolean operations can be performed with almost the same processing cost as a single boolean operation. Moreover, the presented approach can take advantage of the modern programable graphics hardware.
Grid Architecture for Distributed Rendering
(The Eurographics Association, 2006) Fernández-Sorribes, Jose Antonio; González-Morcillo, Carlos; Jiménez-Linares, Luis; Pere Brunet and Nuno Correia and Gladimir Baranoski
Rendering is the process by means of which a raster 2D image can be obtained from the definition of a 3D scene. This process is computationally intensive and requires a lot of time to be done when the source scene has certain complexity or when high-quality realistic images are required. YAFRID (Yet Another Free Render grID) is a system that takes advantage of the characteristics of computational grids by distributing the rendering of a scene among a large number of heterogeneous computers connected to the Internet. With that kind of systems, the time a scene takes to be rendered is drastically decreased because the parts in which the complete work has been divided (called workunits) can be processed in parallel and finally joined using an interpolation function to obtain the image result. As we will discuss on the final section of this article, the selection of the workunit size is a key step in this class of work division. With this approach, local optimizations in each workunit could be made to obtain a better rendering time per frame.
Individualizing the New Interfaces: Extraction of User's Emotions from Facial Data
(The Eurographics Association, 2006) Hupont, Isabelle; Cerezo, Eva; Pere Brunet and Nuno Correia and Gladimir Baranoski
When developing new multimodal user interfaces emotional user information may be of great interest. In this paper we present a simple and computationally feasible method to perform automatic emotional classification of facial expressions. We propose the use of 10 characteristic points (that are part of the MPEG4 feature points) to extract relevant emotional information (basically five distances, presence of wrinkles and mouth shape). The method defines and detects the six basic emotions (plus the neutral one) in terms of this information and has been fine-tuned with a database of 399 images. We analyze the effect of different facial parameters and other issues like gender and ethnicity in the classification results. For the moment, the method is applied to static images.
Interactive Cutting in Voxel-Based Objects. Application to Simulate Transurethral Resection of the Prostate
(The Eurographics Association, 2006) Joan-Arinyo, Robert; Vilaplana, Josep; Pere Brunet and Nuno Correia and Gladimir Baranoski
Simulating cutting processes of human tissue is an important feature in virtual reality systems for medical training and rehearsal. In this paper we present a method to simulate the cutting operation in voxel-based virtual reality objects intended to simulate volume cutting in transurethral resection of the prostate. The method allows the user to directly interact with the three dimensional model in a manner that simulates dragging a resectoscope loop through the tissue, performing the task in an intuitive, natural manner.
It's all in the Face: Studies on Monitoring Users' Experience
(The Eurographics Association, 2006) Branco, Pedro; Encarnação, L. Miguel; Marcos, Adérito; Pere Brunet and Nuno Correia and Gladimir Baranoski
We propose to observe users spontaneous facial expressions as a method to identify adverse-event occurrences at the user interface level. We discuss an experiment designed to investigate the association between incidents during a word processing task and users facial expressions monitored using electromyogram sensor devices. The results suggest that an increase of task difficulty is related to an increase in specific facial muscle activity. A second study is presented where an application offers assistance based on the users facial expressions. This study evaluates a social agent that reacts to the users spontaneous display of emotions, in an attempt to reduce the frustration caused by usability problems. The results indicate that for highly frustrated users the agent often increased their frustration, while those experiencing a moderate level of frustration stated that it somewhat reduced their frustrations.
Kit Assembly Helper in Augmented Reality
(The Eurographics Association, 2006) Almeida, Miguel Vieira; Dias, Jose Miguel Sales; Pere Brunet and Nuno Correia and Gladimir Baranoski
This paper describes an augmented reality application that aids users in assembling an object originally in a kit format, i.e. the object is received unassembled, with ordered instructions steps on how to connect each piece. We have used XML to define the objects, the object pieces and the assembly rules; thus, the Kit Assembly Helper (KAH) becomes flexible and can assemble any given 3D physical object. We have adopted a hierarchical structure similar to that used in a theatre, based on puppets and puppeteers. By using augmented reality and pre-recorded speech prompts, the cognitive distance between the user and the assembly instructions is reduced, allowing a better perception of the problem, as well as of the solution. The system is developed in MX Toolkit, an in-house C++ software platform oriented to the Augmented Reality/Mixed Reality application developer. The paper discusses system architecture aspects and provides a usability evaluation framework that shows the benefits of the approach for helping users in kit assembly tasks.
Magic in Augmented Reality
(The Eurographics Association, 2006) Batalha, Joao; Dias, Miguel S.; Pere Brunet and Nuno Correia and Gladimir Baranoski
In this paper we suggest a new approach for playing the "Magic The Gathering" game. This approach allows the user to perform a set of game moves within this popular card game using a Tangible Augmented Reality (AR) environment. Each move represents a new interaction involving real and virtual worlds. We try to make the game more realistic and interactive, through the usage of a tangible user interface. Therefore, interaction with virtual objects is simple and natural. Magic in AR, consists of a camera, a computer, a video projection screen and a deck of cards to play the game. The original Magic card deck has been changed to include visual tags to be used within an AR system. However, the changes performed in this card deck don t modify the philosophy found within a common "Magic The Gathering" card deck. Consequently, we propose a new paradigm to play the game, keeping the traditional and known elements of the game that are now part of a system that frees our imagination. We describe the system requirements, its architecture, involving the integration of ArTooKit in the Virtools authoring environment, and finally extract conclusions of the system use and usefulness, drawn from usability evaluation.
A Mesh-Particle Model for Fluid Animation
(The Eurographics Association, 2006) Suárez, Nuria; Susín, Antonio; Pere Brunet and Nuno Correia and Gladimir Baranoski
We use our adapted versions of the two most used methods in Computer Fluid Animation, Marker and Cell and Smoothed Particle Hydrodynamics, to develop a new method taking advantage of the calculation speed of the first and the great level of detail and controllability of the second. Such a method is very useful in animations with a great volume of fluid where the events needing high-level detail take place on the surface. Finally, we present some simulation examples made with this new method.
Perceived Quality of Simplified Polygonal Meshes: Evaluation using Observer Studies
(The Eurographics Association, 2006) Silva, Samuel; Ferreira, Carlos; Madeira, Joaquim; Santos, Beatriz Sousa; Pere Brunet and Nuno Correia and Gladimir Baranoski
The complexity of a polygonal mesh model is usually reduced by applying a simplification method, resulting in a similar mesh having less vertices and faces. Although several such methods have been developed, it is not yet clear how the choice of a given method, and the level of simplification achieved, influence the quality of the resulting mesh, as perceived by the final users. Following on work carried out by the authors, but only for mesh models of the lungs [SSSMF05, SSFM05], a comparison among the results of three mesh simplification methods, for a few generic models and two simplification levels, was performed through a controlled experiment involving 65 observers. The goal was to ascertain whether the main findings previously obtained for lung models, through a study with 32 subjects, could be generalized to other types of models and confirmed for a larger number of observers. This was verified through the analysis of the data collected from the experiment, which shows that, regarding perceived quality, users are indeed sensitive to the mesh simplification method used and that this sensitivity varies with the simplification level.
Perception-based painterly rendering: functionality and interface design
(The Eurographics Association, 2006) Nunes, Samuel; Almeida, Daniel; Brito, Vera; Carvalho, Joao; Rodrigues, Joao; Buf, J. M. Hans du; Pere Brunet and Nuno Correia and Gladimir Baranoski
Painterly rendering (non-photorealistic rendering or NPR) aims at translating photographs into paintings with discrete brush strokes, simulating certain techniques (im- or expressionism) and media (oil or watercolour). Recently, our research into visual perception and models of processes in the visual cortex resulted in a new rendering scheme, in which detected lines and edges at different scales are translated into brush strokes of different sizes. In order to prepare a version which is suitable for many users, including children, the design of the interface in terms of window and menu system is very important. Discussions with artists and non-artists led to three design criteria: (1) the interface must reflect the procedures and possibilities that real painters follow and use, (2) it must be based on only one window, and (3) the menu system must be very simple, avoiding a jungle of menus and sub-menus. This paper explains the interface that has been developed.

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