Portuguese Meeting on Computer Graphics 2011 - SIACG 2011

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3D Visualization of Sparse Geophysical Data Representing Uncertainty
(The Eurographics Association, 2021) Gonçalves, Vítor; Dias, Paulo; Almeida, Fernando; Madeira, Joaquim; Santos, Beatriz Sousa; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Geophysical data are sparse and by nature difficult to analyze. Usually domain experts use "mental models" to infer missing data according to the surrounding data and their own knowledge. The main goal of this work is to explore the best way to represent uncertainty in geophysical data. Given the sparse nature of the represented data, it is important to provide a 3D volumetric representation of the whole subsoil, based on a geostatistical process. We use kriging interpolation to generate a structured grid from the original sparse data. However, the analysis of such an interpolated representation must be careful, since the uncertainty varies significantly according to the distance to real measurements. We use different representations to emphasize data uncertainty during the analysis stage. The different visualization techniques implemented in our prototype, as well as methods used to simultaneously visualize resistivity and uncertainty information, are presented.
3DWikiU - 3D Wiki For Urban Environments
(The Eurographics Association, 2021) Melo, M.; Silva, P.; Magalhães, L.; Bessa, M.; Coelho, A.; Moura, J.; Rocha, A.; Ferreira, F.; Cruz, J.; Sousa, A.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Virtual Reality (VR) systems may be used with great effectiveness in applications such as urban planning, virtual tourism, cultural heritage and education. In fact, the VR systems allow the visualization and interaction with 3D models, which can work as a natural metaphor due to their similarities with the objects that they intend to recreate. This is the perfect scenario for this project which intends to recreate virtual urban environments and complement them with digital services useful for people's everyday tasks. On the other hand, the implementation and management of a virtual environment is complex and requires a numerous development team with different skills to build it properly. The purpose of this project is to build a collaborative environment where the users have the power to contribute and edit objects in the referred environment, exploring the wiki concept. This paper presents a collaborative VR system that aims to provide a more natural and intuitive interface to access diversified services on 3D urban environments - 3D Wiki for urban environments. These services shall contemplate citizenship activities, entrepreneurship activities, promotion of the natural and cultural heritage and support of the cooperation and data sharing among citizens.
Augmented Reality for Web - A New Interaction Method Without Markers
(The Eurographics Association, 2021) Silva, Luis F. A.; Silva, Frutuoso G. M.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
In the new age of omnipresent internet, browsers are accessible on every device in everyday's life. Thus it is also needed new interaction methods to facilitate the interaction through browser. Augmented reality is one of the techniques that is available now via browser. In this paper we present a new method of interaction without physical markers for augmented reality via browser. The first part of the paper describes the use of augmented reality via browser using physical markers and its limitations. In the second part, we propose a solution to solve the limitations of augmented reality using physical markers, i.e. we propose a new interaction method to manipulate virtual objects without using physical markers. Finally, we show a simple augmented web game based on the new interaction method proposed.
BlenderCAVE: Easy VR Authoring for Multi-Screen Displays
(The Eurographics Association, 2021) Gascón, Jorge; Bayona, José M.; Espadero, José M.; Otaduy, Miguel A.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
BlenderCave is a framework for the fast creation of virtual reality applications for multi-screen display systems. It consists of a set of extensions to the open-source Blender Game Engine (BGE), leveraging the scene creation and real-time rendering capabilities of BGE, and augmenting them with easy-to-setup support for CAVE or Powerwall-type displays. The framework is implemented in a distributed manner, and it contains a virtual camera setup to control the display output, and a lightweight network communication protocol to manage events and synchronize the application state. We demonstrate that, with BlenderCAVE, 3D applications can easily be written in Blender and displayed on multi-screen displays.
Coded Apertures for Defocus Deblurring
(The Eurographics Association, 2021) Masia, Belen; Corrales, Adrian; Presa, Lara; Gutierrez, Diego; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
The field of computational photography, and in particular the design and implementation of coded apertures, has yielded impressive results in the last years. Among their applications lies defocus deblurring, in which we focus in this paper. Following the approach of previous works, we obtain near-optimal coded apertures using a genetic algorithm and an existing quality metric. We perform both synthetic and real experiments, testing the performance of the apertures along the dimensions of depth, size and shape. We additionally explore non-binary apertures, usually overlooked in the literature, and perform a comparative analysis with their binary counterparts.
A Colour Rotation Based Detector for Bleeding Gastric Pathologies
(The Eurographics Association, 2021) Coelho, P.; Cunha, A.; Costa, P.; Hadjileontiadis, L.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Colour is one the distinct features in computer vision systems and can be represented in several colour spaces. The most commonly used is the RGB colour space, since most high-quality cameras used in computer vision systems provide RGB signals, for example endoscopic capsule cameras. This work describes a computer vision algorithm intended to assist the physician in the diagnosis of endoscopic diseases, such as gastrointestinal bleeding, using a colour space rotation-based method. This algorithm modifies the images RGB representation channels in such way that the bleeding information can be effectively enhanced in a single channel. Tests in endoscopic images were performed and results have shown that the proposed colour-based rotation approach successfully increases the detection of bleeding regions in endoscopic images, corroborating the usefulness in physician diagnosis assistance.
Cortical 3D Face Recognition Framework
(The Eurographics Association, 2021) Rodrigues, J.; Lam, R.; Buf, J. du; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Empirical studies concerning face recognition suggest that faces may be stored in memory by a few canonical representations. In cortical area V1 exist double-opponent colour blobs, also simple, complex and end-stopped cells which provide input for a multiscale line/edge representation, keypoints for dynamic routing and saliency maps for Focus-of-Attention. All these combined allow us to segregate faces. Events of different facial views are stored in memory and combined in order to identify the view and recognise the face including facial expression. In this paper we show that with five 2D views and their cortical representations it is possible to determine the left-right and frontal-lateral-profile views and to achieve view-invariant recognition of 3D faces.
Digital Cartographic Generalization in Spatial Databases: application issues in Power Grids CAD tools
(The Eurographics Association, 2021) Rodríguez, Javier Novo; Pereira, Elena Hernández; Canosa, Mariano Cabrero; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
This work presents the results of applying several digital cartographic generalization techniques to improve the performance of an Electrical Power Grids Computer-Aided-Design application. The performance increase is attained by adjusting the level of detail of the grid topology being visualized in the CAD application. This adjustment takes place at the database level using a multi-scale architecture and the available spatial extensions of Geographic Information Systems databases. The data volume is minimized to fit the exact requirements of the scale being used in the visualization so that no processing time is wasted on representing irrelevant elements. Results show that up to a 90 % of the data can be skipped and thus, a 84 % of the time required to render the visualization can be saved on average, enabling the CAD application to render it in real-time. Furthermore, the optical legibility of the grid visualization is enhanced as a consequence of applying cartographic generalization.
Efficient Propagation of Light Field Edits
(The Eurographics Association, 2021) Jarabo, Adrian; Masia, Belen; Gutierrez, Diego; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Light field editing is a complex task, due to the large amount of data and the need to keep consistency between views. This has hampered the creation of efficient edit propagation methods, similar to those existing for single images. We propose a framework to edit light fields at interactive rates, by propagating some sparse user edits in the full light field. This propagation is guided by a novel affinity function, which forces similar pixels (defined by our affinity space) to receive similar edits, thus ensuring consistency. To manage the light field's large amount of data, we propose a novel multi-dimensional downsampling technique: we first cluster pixels with high affinity, and then perform edit propagation over the downsampled data. We finally upsample back to the original full resolution, maintaining visual fidelity and view consistency between views.
GPU Collision Detection in Conformal Geometric Space
(The Eurographics Association, 2021) Roa, Eduardo; Theoktisto, Víctor; Fairén, Marta; Navazo, Isabel; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
We derive a conformal algebra treatment unifying all types of collisions among points, vectors, areas (defined by bivectors and trivectors) and 3D solid objects (defined by trivectors and quadvectors), based in a reformulation of collision queries from R3 to conformal R4,1 space. The algebraic formulation in this 5D space is then implemented in GPU to allow faster parallel computation queries. Results show expected orders of magnitude improvements computing collisions among known mesh models, allowing interactive rates without using optimizations and bounding volume hierarchies.
Graph-Based Reflectance Segmentation
(The Eurographics Association, 2021) Garces, Elena; Gutierrez, Diego; Lopez-Moreno, Jorge; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Most of the unsupervised image segmentation algorithms use just RGB color information in order to establish the similarity criteria between pixels in the image. This leads in many cases to a wrong interpretation of the scene since these criteria do not consider the physical interactions which give raise to of those RGB values (illumination, geometry, albedo) nor our perception of the scene. In this paper, we propose a novel criterion for unsupervised image segmentation which not only relies on color features, but also takes into account an approximation of the materials reflectance. By using a perceptually uniform color space, we apply our criterion to one of the most relevant state of the art segmentation techniques, showing its suitability for segmenting images into small and coherent clusters of constant reflectance. Furthermore, due to the wide adoption of such algorithm, we provide for the first time in the literature an evaluation of this technique under several scenarios and different configurations of its parameters. Finally, in order to enhance both the accuracy of the segmentation and the inner coherence of the clusters, we apply a series of image processing filters to the input image (median, mean-shift, bilateral), analyzing their effects in the segmentation process. Our results can be transferred to any image segmentation algorithm.
GraphJudge: A System for Assisted Assessment of Computer Graphics Assignments
(The Eurographics Association, 2021) Rocha, Lindomar; Rodrigues, Rui; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
We describe a system for submission, automated validation and assisted evaluation of Computer Graphics' assignments. This type of assessments has a series of specific challenges associated to it, namely the analysis of graphical output and the variations between implementation in different development platforms and operating systems. When considering a large number of submitted programs (in the order of hundreds), preparing and evaluating the submissions quickly becomes a very time-consuming task. The goals of the system are therefore to allow submission and early validation for the students, and to ease the teachers' burden of compiling and executing, while automatically providing visual information of the submissions in an integrated and effective way.
HaloDot: Visualization of the Relevance of Off-Screen Objects
(The Eurographics Association, 2021) Gonçalves, Tiago; Afonso, Ana Paula; Carmo, Maria Beatriz; Pombinho, Paulo; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
The increasing usage of maps on mobile devices reinforce the need to solve some visualization and usability issues that constraint the user's interaction with information visualization applications. When exploring map information on a small screen device, the points of interest are often located off -screen. Despite the existence of several techniques for the visualization of off-screen objects, most of them use representations to indicate the direction and/or the distance towards these objects but none of them represent their relevance. This paper describes the work in progress to achieve a visualization that provides clues about the relevance of off-screen objects.
High-quality Compression of Mipmapped Textures
(The Eurographics Association, 2021) Andujar, C.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
High-quality texture minification techniques, including trilinear and anisotropic filtering, require texture data to be arranged into a collection of prefiltered texture maps called mipmaps. In this paper we present a compression scheme for mipmapped textures which achieves much higher quality than current native schemes by exploiting image coherence across mipmap levels. The basic idea is to use a high-quality native compressed format for the upper levels of the mipmap pyramid (to retain efficient minification filtering) together with a novel compact representation of the detail provided by the highest-resolution mipmap. Key elements of our approach include delta-encoding of the luminance signal, efficient encoding of coherent regions through texel runs following a Hilbert scan, a scheme for run encoding supporting fast random-access, and a predictive approach for encoding indices of variable-length blocks. We show that our scheme clearly outperforms native 6:1 compressed texture formats in terms of image quality while still providing real-time rendering of trilinearly-filtered textures.
Inexpensive 3D Stereo for Two Users Using a Single Display
(The Eurographics Association, 2021) Re, Armando de la; Martorell, Eduardo; Camahort, Emilio; Abad, Francisco; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Multiuser computer systems allow several users to collaborate on the same task. Medium sized displays, like workbenches or tabletops provide a shared view of the task and a set of input devices to interface with the system. Some of the existing installations also provide 3D stereoscopic viewing, often also shared by all the participants and therefore incorrect for all of them but one. In these cases a different stereoscopic view for each user is desirable. We implemented two hardware configurations that support independent stereo viewing for two users sharing a common display using a 120Hz monitor and a 120Hz projector. Our prototypes use off-the-shelf parts to create a functional, responsive and inexpensive two-user 3D stereo display system. We also apply our systems to a competitive game, where each user has a private stereoscopic view of the game table, and a two-user multimedia player, where each user can watch and hear a different video on the same display.
Interacting with Outdoor Sports Performance Data
(The Eurographics Association, 2021) Lopes, J. M. Brisson; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
This paper presents a portable application to visualize performance data obtained from GPS devices in outdoor sports (e.g., ski, running, BTT) that also record data as heartbeat rate. GPS file formats are analyzed and a data structure that enables easy and flexible data manipulation is presented. Several data representation (chart, map and table) and visualization issues are addressed. Results show that the set of interaction design requirements was appropriate. The application is portable to due the development tools adopted (OpenGL, GLUI and TinyXML).
Interactive Elastic Deformation of 3D Images
(The Eurographics Association, 2021) Prados, Francisco J. R.; Salas, Alejandro León; Torres, Juan Carlos; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
The standard workflow of a haptic device takes the position of the effector in space and sends a force vector in return. This paradigm naturally meets the behaviour shown in elastic materials, where the resistant force of a body is proportional to the displacements created. In fact many works have designed methods to simulate interaction with linear-elastic bodies, covering different techniques from spring-mass structures to specific volumetric representations. However, realistic simulation of volumetric data is still an open issue. Not only is it challenging due to the complex relations that govern the real elastic behaviour, but also because of the huge amount of data that needs to be processed. In this paper we propose a technique to interactively deform 3D images, such as those acquired by a CT scanner. While producing a physically plausible haptic feedback, deformation and visualization algorithms produce an efficient and natural feeling. Using a free form deformation structure as a wrapper, it is possible to deform complex structures at high frame rates, independently of the size of the volume.
Interactive Visualizations of Automatic Debugging Reports
(The Eurographics Association, 2021) Riboira, André; Rodrigues, Rui; Abreu, Rui; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Automated debugging techniques, based on statistical analysis of historical test executions data, have recently received considerable attention due to their diagnostic capabilities. However, current automatic debugging tools suffer from a common shortcoming that may affect their adoption and correct use: the lack of effective visualizations of their output. This paper explores the use of interactive visualization techniques applied to automatic debugging results, and integrated in a common development environment (Eclipse), to improve the efficiency of the debugging process. The proposed tool – GZOLTAR– is an Eclipse plug-in that includes an automatic debugging algorithm and generates interactive visualizations of the resulting hierarchical data, with direct links to the IDE's source code editor.
Investigating the Differences Between European Portuguese Sounds: An Approach Using Polygonal Mesh Comparison
(The Eurographics Association, 2021) Martins, Paula; Silva, Samuel; Oliveira, Catarina; Ferreira, Carlos; Silva, Augusto; Teixeira, António; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
With the main purpose of studying the articulatory configuration of the European Portuguese (EP) sounds and to evaluate coarticulatory effects, a large 3D MRI database from several speakers and contexts have been acquired. Segmentation, visualization and interpretation of all the available data, essential to a detailed characterization of these sounds, are complex and time-consuming tasks. To perform the segmentation, a semi-automatic method was used. Meshes of the tongue were created from the segmented volumes and a polygonal mesh comparison tool (PolyMeCo) was used to compare: different sounds, the same sound produced in different contexts and syllabic positions, and productions from different speakers, providing a qualitative measure of these differences. To the best of our knowledge this is the first study in the literature using such an approach to analyze and compare tongue shape. Furthermore, these first results are very promising allowing a proper analysis and depiction of the main differences between EP sounds and further insight into their production.
Left-Ventricle Global and Regional Functional Analysis from MDCT Images
(The Eurographics Association, 2021) Silva, Samuel; Santos, Beatriz Sousa; Madeira, Joaquim; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Left-ventricle functional analysis is of paramount importance for the assessment of coronary artery disease. Non-invasive coronary artery imaging using multiple-detector computed tomography (MDCT) provides a wealth of data concerning multiple cardiac phases. These have still to be explored in order to assess if further insight is possible regarding regional and functional analysis of the left ventricle leading to a more informed diagnosis and prognosis. Following on previous work regarding left-ventricle segmentation of all available cardiac phases in MDCT exams this article presents several parameters characterizing global and regional left ventricle function, computed for several cardiac phases and represented over time. Synchronized viewing of the different parameters is also supported.

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