Portuguese Meeting on Computer Graphics 2011 - SIACG 2011

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https://diglib.eg.org/handle/10.2312/2633063

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Real-Time Modelling and Rendering of Sprayed Concrete
(The Eurographics Association, 2021) Vélez, G.; Matey, L.; Amundarain, A.; Ordás, F.; Marín, J.A.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
This paper presents a new real-time method to model and render how sprayed concrete is spread on a surface. The method not only models and renders deposits sprayed from any angle, any distance and with any concrete flow, but it is also able to compute the amount of deposited volume taking into account the percentage of material that rebounds. The proposed method has been developed for a real-time training simulator for concrete spraying machinery, where most of the algorithm is parallelised and computed in the GPU, leaving the CPU free for other computations. In this research, the method has been validated for its use on plain surfaces and tunnel walls, but it can be extended to other types of surfaces.
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.
Neural Data Exploration with Force Feedback
(The Eurographics Association, 2021) Raya, Laura; Otaduy, Miguel A.; García, Marcos; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
The behavior of the brain depends to a large extend on its neural structure. Therefore, understanding this neural topology is a high-priority research line for neurobiologists. Due to complexity of the brain's neural structure, visual representations look tangled, and extracting knowledge from them is a difficult task. In this work, we propose the use of multimodal interfaces to enhance neurobiologists' understanding of neural data. Our system is based on four pillars: a stereo rendering module, a camera control system, a visual aid unit, and a haptically constrained navigation tool. We observe that haptically aided navigation helps neurobiologists analyze the brain's topology. Our system uses stylus-based haptic devices with two purposes: they provide a natural interface to deal with 3D data (controlling camera motion) and they constrain the user's motion. The system was built trying to keep user interactions as intuitive as possible.
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.
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.
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.
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.
Procedural Modeling of Suspension Bridges
(The Eurographics Association, 2021) Patow, Gustavo; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
In this paper we introduce a method for designing a class of engineering structures, namely suspension bridges. These bridges are ubiquitous in the industrialized countries, often appearing in known city landscapes, yet they are complex enough that hand-based modeling is tedious and time consuming. We present a method that finds the right proportions for such a structure through an optimization method that tries to distribute the tower positions while maintaining cable width to be a finite number. By simultaneously optimizing the span and sag of the cables of a bridge, we optimize the geometry and soundness of the structure. We present the details of our technique together with examples illustrating its use, including comparisons with real structures.
Procedural Modelling of Destructible Materials
(The Eurographics Association, 2021) Gestel, J. van; Bidarra, R.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Traditional content creation for computer games is a costly process. In particular, current techniques for authoring destructible behaviour are often limited to a single object basis. In this paper, we build on previous research results to develop a novel method for designing reusable destructible behaviour which can be applied in real-time to a variety of objects. To separate the destructible behaviour from particular objects, we introduce the concept of destructible materials: where the material of an object usually defines the way an object looks, a destructible material will determine how it breaks. Destructible materials provide a reusable definition and intuitive way of designing and tweaking destructible behaviour of objects in game development, which can then be applied in real-time.
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.
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.
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.
Volume-Surface Collision Detection
(The Eurographics Association, 2021) Ortegano, J.; Navarro, H.; Carmona, R.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
The presence or not of collisions between objects is usually required to study the interaction between them, increasing the realism in virtual environments. Collision detection between polygonal objects has been widely studied, and more recently some studies have been made concerning collisions between volume objects. Collision detection between volume datasets and polygonal objects is introduced in this work. This kind of mixed scenes appears naturally in many applications such as surgery simulation and volume edition. To detect the collision, first the volume dataset is represented by a single 3D texture. Then, a mapping from eye space to volume space is established, such as each mesh fragment has a 3D texture coordinate. The collision is verified by fragment during the rasterization stage. We use OpenGL R occlusion query extension to count the number of mesh fragments colliding with the volume. Our tests show that up to 3800 pairs of volume-mesh may be evaluated in one second.
Parallel Collision Detection Oriented to Distributed Memory Architectures for High-Resolution Meshes
(The Eurographics Association, 2021) Novalbos, Marcos; Sánchez, Alberto; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Higher resolution meshes should be used in graphics applications to make them as realistic as they can. However, they imply a high computational. Several approaches have been built to solve collision detection, although most of them do not take into account this feature. This paper presents a scalable parallel algorithm for collision detection designed for working with high resolution meshes. The algorithm is based on distributed memory architectures taking advantage of their benefits and overcoming their drawbacks.
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.
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.
A Moving Least Squares Method for Implant Model Deformation in Computer Aided Orthopedic Surgery for Fractures of Lower Extremities
(The Eurographics Association, 2021) Ramírez, Esmitt; Coto, Ernesto; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Preoperative planning is an essential step before performing any surgical procedure. Computer Aided Orthopedic Surgery (CAOS) systems are extensively used for the planning of surgeries for fractures of lower extremities. These systems are input an X-Ray image and the planning can be digitally overlaid onto the image. The planning includes reassembling the fractured bone and possibly adding implants to reduce the fracture. In many cases, the implant does not fit perfectly in the patient's anatomy and it must be bended to adjust the implant to the bone. This paper presents a new method for the deformation of implants in CAOS systems, based on the Moving Least Squares (MLS) method for 2D images. Several improvements over the original MLS method are introduced to achieve visual results similar to the real procedure and make the deformation process easier and simpler for the surgeon. The improvements are explained in detail and all parameter values are provided. Over 100 clinical surgeries have been already planned successfully using a CAOS system that employs the proposed technique.
Mobile Computational Photography: Exposure Fusion on the Nokia N900
(The Eurographics Association, 2021) Echevarria, Jose I.; Gutierrez, Diego; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
This paper explores the Nokia N900 platform as a versatile playground for mobile computational photography. We present the implementation of a simple yet practical application to acquire high quality tone mapped HDR images, and a relatively straightforward white balance selection. We have built everything from scratch: from the capture of the bracketed sequence of images with different exposures, to the final tone mapping algorithm. Completed in less than one week, showcasing the flexibility and productivity of the platform, our experiments have encouraged us to continue exploring all the possibilities this kind of devices offer.
Linear-Time Dynamics of Characters with Stiff Joints
(The Eurographics Association, 2021) Hernández, Fernando; Garre, Carlos; Casillas, Rubén; Otaduy, Miguel A.; Silva, F. and Gutierrez, D. and Rodríguez, J. and Figueiredo, M.
Characters, like other articulated objects and structures, are typically simulated using articulated dynamics algorithms. There are efficient linear-time algorithms for the simulation of open-chain articulated bodies, but complexity grows notably under additional constraints such as joint limits, loops or contact, or if the bodies undergo stiff joint forces. This paper presents a linear-time algorithm for the simulation of open-chain articulated bodies with joint limits and stiff joint forces. This novel algorithm uses implicit integration to simulate stiff forces in a stable manner, and avoids drift by formulating joint constraints implicitly. One additional interesting feature of the algorithm is that its practical implementation entails only small modifications to a popular algorithm.

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