Portuguese Meeting on Computer Graphics 2002

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30 Texture-based Hybrid Visualízations
(The Eurographics Association, 2022) Soada, lmma; Navazo, Isabel; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
ln this paper the visualization of hybrid scenes that contain volume data anda fitted extracted surface is addressed. The proposed algorithm is based on a integrated octree-based representation: the "Hybrid Octree ". The Hybrid Octree allows to obtain multiresolution representation of the volume data and it also maintains a decimated surjace codification. The proposed visualization approach uses 3D-textures for the visualization of the volume data and integrates the surface polygons using the information represented in the octree structure. The main characteristics of the method are: its capabilities to perform multiresolution hybrid visualizations and its efficient use of texture memory space.
Algorithms for Point-Polygon Collision Oetection in 20
(The Eurographics Association, 2022) Delgado, Juan J. Jiménez; Sánchez, Rafael J. Segura; Higueruela, Francisco R. Feito; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
ln this article, several algorithms for the collision detection between a point and a polygon on a plane are presented. Coverings by triangles and barycentric coordinates are used. Temporal and geometric coherence are usedfor reducing their performance times. A study of times has been carried out; it shows that these simple and robust algorithms are efficient. Also, these algorithms can be used for non convex figures and they have the advantage of being easily extended to JD.
Case study: full-size virtual models of trains
(The Eurographics Association, 2022) Serón, Francisco José; Gutiérrez, Diego; Magallón, Juan Antonio; Sobreviela, Emilio José; Gutiérrez, José Antonio; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Simulation of models, in all different areas, is an expanding, attractive fine ofwork. More and more applications are taking advantage of the improving technology and knowledge in this field, achieving results that would have been impossible to achieve with a real model, or foreseeingfacts that would have been encountered too late in the production process otherwise. The train industry is one possible beneficiary of this approach. Usually, before commencing the fabrication process of a new train, the construction of a full-size model is mandatory. lnstead of building this full-size real model, which leaves little room for !ater, last-minute modifications, a virtual model could be built in the digital realm, thus offering a new platform for easier interaction with it. ln this article, a simulation of a train is presentedfor visual, aesthetics and ergonomic issues. The simulation runs on a PC-based CAVE-like architecture, and combines static and dynamic computer generated imagery, both with and without stereoscopy for JD visualization, as well as Augmented Virtuality techniquesfor the integration ofthe train with its environment.
A Constraint Manager to Support Virtual Maintainability
(The Eurographics Association, 2022) Marcelino, Luis; Murray, Norman; Fernando, Terrence; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Virtual prototyping tools have already captivated the industry's interest as a viable design tool. One of the key challenges for the research community is to extend the capabilities of Virtual Reality technology beyond its current scope of ergonomics and design reviews. The research presented in this paper is part of a larger research programme that aims to perform maintainability assessment on virtual prototypes. This paper discusses the design and implementation of a geometric constraint manager that has been designed to support physical realism and interactive assembly and disassembly tasks within virtual environments. The key techniques employed by the constraint manager are direct interaction, automatic constraint recognition, constraint satisfaction and constrained motion. Various optimisation techniques have been implemented to achieve real-time interaction with large industrial models.
A Density Estimation Technique for Radiosity
(The Eurographics Association, 2022) Lastra, Miguel; Urefía, Carlos; Revelles, Jorge; Montes, Rosana; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Radiosity computation on scenes including objects with a complex geometry, or with a large number of faces and meshes with very different sizes, is very complex. We presenta new method (based on the Photon Maps method [7]) where density estimation on the tangent plane at each surface point is performed for irradiance computation by using photon paths (fine segments traveled by a ray) instead of photon impacts. Therefore we improve the results for scenes containing small objects which receive only afew impacts. Also, geometry is completely decoupledfrom radiosity computation.
Direct Modelíng: from Sketches to 3D Models
(The Eurographics Association, 2022) Naya, Fernando; Jorge, Joaquim A.; Conesa, Julián; Contera, Manuel; Gomis, José Maria; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
ln spite of recent advances in Computer Aided Design, Graphical User Interfaces (GUJ) are, by and large, still at the stage of the so-called WIMP (Window, Icon, Menu, Pointing device) approach. ln recent years, our research team has developed different algorithms in Geometric Reconstruction. The aim of this effort is to obtain an automatic (or, at least, easy-to-use) means to generate 3D models from freehand 2D drawings. This approach serves as the basis to a calligraphic interface, based onfreehand sketches and gestures, described as a prototype application capable of modeling special kinds of objects such as normalon and quasi-normalon polyhedra. Using our system users can directly draw the axonometric view of an object to yield a 3D model. White much work remains to be done, the current application already shows gains with respect to more traditional forms ofmodeling in that it embodies a drawing approachfamiliar to most draflspeople, who can start modeling relatively complex shapes without much training. Preliminary studies show that our modeling system compares favorably to commercial grade CAD systems both in number of operations required to creating objects and time to accomplish simple modeling tasks.
Free-Form Solid Modellíng Based on Extended Simplícial Chains Using Triangular Bézier Patches
(The Eurographics Association, 2022) García, Ángel Luis; Miras, Juan Ruiz de; Feito, Francisco R.; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
We present a mathematical model for geometric modelling based on the concept of extended simplicial chain (ESC) defined in previous works. With this model, a solid is defined by means of an algebraic sum of nondisjoint extended cells, applying the divide and conquer concept. This allows us to obtain the traditional Boolean operations in geometric modelling through the operations defined for ESC's. The model enables us to represent free-form solids whose boundaries are free-form swfaces represented by a set of low degree triangular Bézier patches and operate with them. ln fact, this model allows us to solve basic problems in solid modelling, like the point-in-solid test. ln this case we make use of the generality of the definition of ESC to particularize it to the use of triangular Bézier patches in 3D.
Hoops Fusion: Synthesis of View-dependent Convex Occluders from a Set of Objects
(The Eurographics Association, 2022) Ríos, Àlex; Navazo, Isabel; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Visibility determination is a requirement to navigate through complex scenes. Occluder fusion algorithms generate convex occluders that are contained in the umbra cast by a group of objects given an area light. Hoops are non-convex, but view-dependent convex, non-planar closed polylines that can be used to compute occlusion for objects that not necessarily have large interior convex sets. ln this paper we present an efficient, robust, and incremental octree-based algorithm to synthesize hoops for a set of objects and to compute the hoopís umbra. Experimental results demonstrate the techniqueís effectiveness to compute occluder fusion of non-convex objects.
INTERCOMUNICANDO - Computer Assisted Communication for Severely Handicapped Persons
(The Eurographics Association, 2022) Lopes, João Brisson; Amaro, Ricardo; Pereira, António; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
This paper presents project INTERCOMUNICANDO whose aim is to provide computer assisted pictogram based communication as a rehabilitation toolfor severely handicapped persons. The project developed a suite of integrated applications that use autonomous agents with speech and animation to provide on-line help, feedback and motivation to users. The paper addresses user interface design. It also addresses the user requirements and the development methodology used to provide users with ali services, including input, that smoothly adapt to the kind and degree of disability of each user. The current state of the project is described along with results. Conclusions and recommendations for the following project (RECRIA) are presented.
Marching Edges: A Method for lsosurface Extraction
(The Eurographics Association, 2022) Velasco, Francisco; Torres, Juan Carlos; Cano, Pedro; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Volumetric data can be represented as a rectilinear structured grid and can be displayed by the rendering of an isosurface that is built from the grid and defining a threshold value. The know marching cubes method builds the isosurface cell by cell. However, from a set of cells that comply with some conditions, a bigger cell can be built. ln these cases, the volume is represented by a set of cells of different size. Then, the isosurface built by marching cubes will have holes on the borders between cells of different size. ln this paper, we show a new method, called marching edges, to build the isosurface edge by edge, that generates a hole-free isosurface.
MIXDesign, Tangible Mixed Reality for Architectural Design
(The Eurographics Association, 2022) Salles Dias, J. Miguel; Santos, Pedro; Bastos, Rafael; Monteiro, Luis; Silvestre, Rui; Diniz, Nancy; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
MIXDesign, provides a tangible Mixed-Reality system oriented towards tasks in Architectural Design, in severa! usage scenarios, such as Conceptual Design, Client Brief or even Architectural Design education. With MIXDesign, an architect can intuitively interact with a real scale model of the design, in normal working settings, where he can observe an enhanced version of the scale model, with JD virtual objects registered to the real ones. The architect is then able to use intuitive tangible interfaces, such as a paddle, to choose menu options, select a JD virtual object, transport a virtual object within the scale model surroundings and geometrically transform an object (by rotation or scaling). MIXDesign provides a platform for testing new design concepts while seamlessly transporting the Architect from Reality (RE) to Augmented Reality (AR) and then through Augmented Virtuality (AV), towards afull Virtual Environment (VE), and back, where he can perceive andjudge both the virtual and the real models, interactively and in real-time.
Oetermining orientation of Laser scanned surfaces
(The Eurographics Association, 2022) Oliveira, João Fradinho; Steed, Anthony; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Real 3D data acquired from scanning technology provide interesting 3D models for research and industrial applications. However before these models can be used, a surface needs to be jitted to a point cloud of an unknown object, this process might create some undesirable properties, such as triangle normais pointing in incorrect directions. We present a robust algorithm that reliably fixes these triangle normal problems on nonmanifold, and self-interesting surfaces of scanned objects.
Optimal Software-based Projector Alignment
(The Eurographics Association, 2022) Baier, Pablo A. S.; Carvalho, Paulo C. P.; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
We present a software-based method for alignment of projectors, both for side-by-side (mosaic) and stereo projections. The projectors are assumed to be positioned in such a way that their axes are not perpendicular to the screen plane and their projection areas do not adjust exactly to each other. We consider the problem of modifying each projected image in such a way that the projected areas become perfectly adjusted rectangles, without any physical repositioning. We model the problem of finding the largest possible projection rectangles as a linear program and show how to appropriately pre-warp each image so that they project exactly anta these optimal areas.
Powering Multiprojection lmmersive Environments with Clusters of Commodity Computers
(The Eurographics Association, 2022) Soares, Luciano Pereira; Cabral, Márcio Calixto; Bressan, Paulo Alexandre; Lopes, Roseli de Deus; Zuffo, Marcelo Knörich; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Multiprojection lmmersive Environments are used in many fields such as science, engineering and art. Virtual Reality (VR) oriented systems have been powered traditionally by high-end graphics workstations or supercomputers but recently, clusters of commodity computers (PCs, Macintoshes, low cost workstations) have become a practical alternative. The advantages of a commodity cluster include low cost, flexibility, access to technology, and performance scalability. ln this paper we describe the family of graphics clusters developed to power Multiprojection lmmersive Environments. Design issues and results are presented considering the CAVERNA DigitalTM, the first five-sided cubic Multiprojection lmmersive Environment implemented in South America.
Proceedings Info
(The Eurographics Association, 2022) Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Simulating E-Garments Oressed on Personalísed Avatars
(The Eurographics Association, 2022) Dias, José Miguel Salles; González, David Muifíos; Gamito, Manuel Noronha; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
We present a general computational architecture that solves the problem of the production of physical-based virtual textiles and garments (so called electronic garments or e-garments), applicable in lnternet-based electronic-commerce scenarios. We focus in the evaluation of their visual and mechanical precision, relatively to the textile quality control procedures adopted by the industry. Our proposed architecture includes a client that authors an e-garment dressed onto a personalised avatar, establishing the boundary conditions of the mechanical system and, a server, that solves the equilibrium equations through time of such system, using optimised numerical procedures. The client inputs 2D cutting patterns from apparel CAD vendors, defines the seams between the CAD patterns, sets fabric material proprieties, loads a personalised avatar into a JD scene, places the patterns relative to the JD avatar, configures simulation parameters and instructs the remate server to simulate the e-garment dressing process. We conclude with the validity of our new computationalframework for modelling e-garments made of plain-woven fabrics and the applicability of the system in a more global lnternet-based electronic commerce solutionfor on-line shopping of apparel andfashion goods.
Sketching User Interfaces with Visual Patterns
(The Eurographics Association, 2022) Caetano, Anabela; Goulart, Neri; Fonseca, Manuel; Jorge, Joaquim; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
This paper presents an approach to layout static components of user interfaces as hand-drawn compositions of simple geometric shapes, using sketch recognition and visual languages. The system uses a visual grammar built from drawings collectedfrom users. We tried to understand how people sketch interfaces and what combinations of shapes they are more likely to used when sketching widgets. From there we implemented a prototype system, for creating user interfaces through hand-drawn geometric shapes, identified by a gesture recognizer. This prototype generates a Java interface, whose layout can be beautified using an a posteriori set of grammar rufes ( e.g. to align and group objects, etc.). We have conducted usability assessments with ten users to compare our approach with a commercial system (JBuilder). Besides a measurable speed advantage in drawing interfaces, users found our system more comfortable, satisfactory and efficient to use than the commercial product, as demonstrated by post-experiment questionnaires.
Surface Collision Detection for Maintenance Support in Virtual Environments
(The Eurographics Association, 2022) Marcelino, Luis; Figueiredo, Mauro; Fernando, Terrence; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
Detecting collision between surfaces is an important feature for supporting interactive assembly operations based on the geometric constraint-based simulation. CAD models define the geometry of components using surfaces as the basic primitive while current collision detection toolkits, disregard this information and use only polygons. The automatic recognition of geometric constraints can use colliding surfaces to simulate realistic behaviour interactively. This paper presents our research into supporting surface based collision detection for use in immersive Virtual Environments. That resulted in the implementation of a surface collision detection module built on top of RAPID.
Towards Content-Based Retrieval of Technical Orawings through High-Oimensional lndexing
(The Eurographics Association, 2022) Fonseca, Manuel J.; Jorge, Joaquim A.; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
This paper presents a new approach to classify, index and retrieve technical drawings by content. Our work uses spatial relationships, visual elements and high-dimensional indexing mechanisms to retrieve complex drawings from CAD databases. This contrasts with conventional approaches which use mostly textual metadata for the sarne purpose. Creative designers and draftspeople often re-use data from previous projects, publications and libraries of ready to use components. Usually, retrieving these drawings is a slow, complex and error-prone endeavor; requiring either exhaustive visual examination, a solid memory, or both. Unfortunately, the widespread use of CAD systems, while making it easier to create and edit drawings, exacerbates this problem, insofar as the number of projects and drawings grows enormously, without providing adequate retrieval mechanisms to support retrieving these documents. ln this paper we describe an approach that supports automatic indexation of technical drawing databases through drawing simplification techniques based on geometric features and efficient algorithms to index large amounts of data. We describe in detail the indexing structure (NB-Tree) we have developed within the context of a more general approach. Experimental evaluation reveals that our approach outperforms some of the best indexing structures published, enabling us to search very large drawing databases.
Towards Fully Reconfígurable Multimedia Platforms
(The Eurographics Association, 2022) Poz, Marco A. S. Dai; Leitão, Ricardo B. Vidigal; Faria, Regis Rossi Alves; Lopes, Roseli de Deus; Zuffo, Marcelo Knörich; Xavier Pueyo; Manuel Próspero dos Santos; Luiz Velho
This paper describes a novel approach to implement multimedia access platforms: reconfigurable oriented codesign. Nowadays we observe a rapid and mutant evolution of multimedia standards and its de facto adoption into many consumer electronics, such as audiolvideo appliances, digital set-top boxes for TV access networks, mobile technologies and portable digital assistants (PDAs). Among the disadvantages of current multimedia access platforms, we can mention the relative high cost, the very short obsolescence cycles, the communication and computational performance limitations, the large sizes of software components, and system architectures that do not match future multimedia standards requirements. To overcome these, we propose the use of a reconfigurable computing architecture to implement a family of multimedia access platforms. As an example, we present an implementation of a multimedia access platform that runs a web browser (HTML 3.2 compatible) over a 32-bit RISC microprocessor, described using less than 256 Kbytes of data to represent software and hardware components on a FPGA (Field Programmable Gate Array).

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