Short Papers 2007

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https://diglib.eg.org/handle/10.2312/261

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Virtual Agent Navigation in Open Spaces using Iterative Shrinking Polygons
(The Eurographics Association, 2007) Haciomeroglu, Murat; Laycock, Robert; Day, Andy; Paolo Cignoni and Jiri Sochor
Populating an urban environment with a virtual crowd provides a dynamic element to an otherwise static scene; bringing the virtual environment to life. One of the fundamental components governing the fidelity of the scene is the realistic simulation of the crowd behaviour. To create a believable crowd simulation one group of methods considers constructing a graph covering the space available to the virtual agents and subsequently performing path planning to allow the agents to navigate their environment by traversing the edges of the graph. To avoid computationally expensive path planning algorithms there exists a tradeoff between the number of edges in the graph and the amount of available space which an agent can visit. In order to alleviate this problem we propose to compute the straight skeleton to provide an initial covering of the environment. This is subsequently augmented using iterative shrinking polygons to generate additional edges in the larger open spaces. The technique developed requires limited knowledge of the urban environment, processes the relevant information automatically and is illustrated in this paper to control the behaviour of a virtual crowd in real time.
Bridging Semantic Web and Digital Shapes
(The Eurographics Association, 2007) Papaleo, Laura; Floriani, Leila De; Hendler, Jim; Paolo Cignoni and Jiri Sochor
Since the volume of multimedia content available on the Web is continuously increasing, a clear need for advanced techniques capable of performing an effective retrieval and management of such data. In this context, in order to reason on digital shapes and their associated semantic, we see a growing interest in exploiting the potential of the Semantic Web in different research fields. We present here the design and initial development of our new system, that we call be-SMART for inspecting digital 3D shapes by extracting geometrical and topological information from them and for structuring and annotating these shapes using ontology-driven metadata. We describe the general structure of the system, its modules and their mutual relations. We also provide motivations for further work in developing new techniques for managing 3D models on the Web.
State-of-the-Art Computer Graphics in Neurosurgical Planning and Risk Assessment
(The Eurographics Association, 2007) Köhn, Alexander; Weiler, Florian; Klein, Jan; Konrad, Olaf; Hahn, Horst; Peitgen, Heinz-Otto; Paolo Cignoni and Jiri Sochor
We present a novel software assistant that unlocks new potentials in neurosurgical planning and risk assessment. It allows surgeons to approach the task in an intuitive manner, by providing them with the possibility to simultaneously observe all relevant data of a case in synchronized 2D and 3D views. State-of-the-art technologies from the field of computer graphics are combined to allow simultaneous interactive rendering of anatomical and functional MR data in combination with manually segmented objects and slice-based overlays. This allows surgeons to perceive a clearer impression of the anatomical and functional structures affected by an intervention, and especially the way they are related to each other. Thus, it significantly facilitates the finding of an optimal intervention strategy.
View-based Shape Similarity using Mutual Information Spheres
(The Eurographics Association, 2007) García, Francisco González; Feixas, Miquel; Sbert, Mateu; Paolo Cignoni and Jiri Sochor
We present a new method for computing the shape similarity between 3D polygonal models using an informationtheoretic viewpoint selection framework. Given a 3D model, a sphere of viewpoints surrounding this model is used to obtain its shape signature from the mutual information of each viewpoint. This signature represents the essence of the shape from a view-based approach. Then, in order to quantify the dissimilarity between two models, their mutual information spheres are registered by minimizing the L2 distance between them. Several experiments show the discrimination capabilities of our approach and its potential suitability for object recognition.
Volumetric Normal Mapping in Rendering of Multivariate Volume Data
(The Eurographics Association, 2007) Seipel, Stefan; Paolo Cignoni and Jiri Sochor
The work presented in this paper introduces volumetric normal maps for producing visual structure in direct volume rendering (DVR) of 3D data for the purpose of visualizing multiple attributes in a 3D volume. We use volumetric normal maps to represent normal vector glyphs that are subsequently applied to warp the gradients in the primary volume data. This method is intended to visualize some secondary attribute in DVR. We demonstrate that our method can render visual structures in DVR without the need of explicit surface reconstruction and texturing.
A Unified Interpolatory and Approximation sqrt-3 Subdivision Scheme
(The Eurographics Association, 2007) Lin, Shujin; Luo, Xiaonan; Paolo Cignoni and Jiri Sochor
We have found that there is a relationship between the cubic B-spline and four-point curve subdivision method. In the paper it is used to deduce interpolatory subdivision schemes from cubic B-spline based approximation subdivision schemes directly and construct unified schemes for compositing approximation and interpolatory subdivision. A new interpolatory p3 subdivision scheme and a interpolatory and approximation blended p3 subdivision scheme are created by this straightforward method. The former produces C1 limit surface and avoids the problem in the exsiting interpolatory p3 subdivision mask where the weight coefficients on extraordinary vertices can not be described by explicit formulation. The latter can be used to solve the "popping effect" problem when switching between meshes at different levels of resolution, provide the possibility to locally choose an interpolating variant of the conventionally approximating subdivision scheme, and give more flexibility for feature modeling. These are realized by only changing the value of a parameter. The method is thoroughly simple without needs of constructing and solving equations.
Adaptive Abstraction of 3D scenes in Real-Time
(The Eurographics Association, 2007) Redmond, Niall; Dingliana, John; Paolo Cignoni and Jiri Sochor
We present an approach for creating abstracted renderings of 3D scenes in real-time. We create painterly renderings with edge detail using varying levels of abstraction dependent on regions of interest within a scene. Image space techniques are used to make the system real-time and as non-invasive as possible. This approach can also use object space information to segment the scene into visually important objects and unimportant data and background. Interactive frame rates are achieved by using graphics hardware to perform the computations.
Automated Combination of Real-Time Shader Programs
(The Eurographics Association, 2007) Trapp, Matthias; Döller, Jürgen; Paolo Cignoni and Jiri Sochor
This work proposes an approach for automatic and generic runtime-combination of high-level shader programs. Many of recently introduced real-time rendering techniques rely on such programs. The fact that only a single program can be active concurrently becomes a main conceptual problem when embedding these techniques into middleware systems or 3D applications. Their implementations frequently demand for a combined use of individual shader functionality and, therefore, need to combine existing shader programs. Such a task is often timeconsuming, error-prone, requires a skilled software engineer, and needs to be repeated for each further extension. Our extensible approach solves these problems efficiently: It structures a shader program into code fragments, each typed with a predefined semantics. Based on an explicit order of those semantics, the code fragments of different programs can be combined at runtime. This technique facilitates the reuse of shader code as well as the development of extensible rendering frameworks for future hardware generations. We integrated our approach into an object-oriented high-level rendering system.
Shape Analysis for Augmented Topological Shape Descriptor
(The Eurographics Association, 2007) Symonova, Olga; Amicis, Raffaele De; Paolo Cignoni and Jiri Sochor
In this work we propose a scheme for analysis of the shape of a 3D model.We use Extended Reeb Graph to describe the topological structure of the model which we further enrich with extracted geometrical features. The nodes of the graph represent different components of the model, and we propose to analyze their shape separately. Shape characteristics such as taper/enlargement, average curvature, bending are revealed through tracing changes in cross sections of each shape component. Finally the topological structure together with the associated geometrical characteristics represents the shape descriptor of the 3D model.
Object-Oriented Shader Design
(The Eurographics Association, 2007) Kuck, Roland; Paolo Cignoni and Jiri Sochor
We present an extremely lightweight object-oriented framework for writing shaders. It provides a way to invoke methods of objects from the shading language and to use references of objects as normal variables. Classes are declared and instantiated in the application language using proxy classes. We then apply object-oriented design to several typical shading problems showing their strength compared to the standard methods.
Construction of Non-Blobby Surface from Particles
(The Eurographics Association, 2007) Harada, Takahiro; Koshizuka, Seiichi; Kawaguchi, Yoichiro; Paolo Cignoni and Jiri Sochor
This paper presents a method that can construct a surface with a thin region or sharp edges from particles. The surface is constructed in two stages. An implicit surface is generated by assigning a density distribution to each particle in the first step and then the surface constructed from the density distribution is changed to a surface with a thin region or sharp edges. Furthermore, the method can generate various kinds of surfaces because a surface is controlled by several parameters. Therefore, the present technique increases the range of expression of particle-based simulations. In this paper, some calculation results are presented and finally an application from the results of particle-based fluid simulation is discussed.
Fast Hierarchical 3D Distance Transforms on the GPU
(The Eurographics Association, 2007) Cuntz, Nicolas; Kolb, Andreas; Paolo Cignoni and Jiri Sochor
This paper describes a fast approximate approach for the GPU-based computation of 3D Euclidean distance transforms (DT), i.e. distance fields with associated vector information to the closest object point. Our hierarchical method works on discrete voxel grids and uses a propagation technique, both on a single hierarchy level and between the levels. Using our hierarchical approach, the effort to compute the DT is significantly reduced. It is well suited for applications that mainly rely on exact distance values close to the boundary. Our technique is purely GPU-based. All hierarchical operations are performed on the GPU. A direct comparison with the Jump Flooding Algorithm (JFA) shows that our approach is faster and provides better scaling in speed and precision, while JFA should be preferred in applications that require a more precise DT.
Exact Computation of the Hausdorff Distance between Triangular Meshes
(The Eurographics Association, 2007) Straub, Raphael; Paolo Cignoni and Jiri Sochor
We present an algorithm that computes the exact Hausdorff distance between two arbitrary triangular meshes. Our method computes squared distances for each point on each triangle of one mesh to all relevant triangles of the other mesh yielding a continuous, piecewise convex quadratic polynomial over domains bounded by conics. The maximum of this polynomial is the one-sided Hausdorff distance from one to the other mesh. We ensure the efficiency of our approach by employing a voxel grid for searching relevant triangles and an attributed half-edge data structure for representing the squared distance function.
Analysis of the Pulmonary Vein Ostia using Cardiac 4DCT for Radiosurgical Ablation
(The Eurographics Association, 2007) Sumanaweera, Thilaka; Conti, Francois; Maguire, Patrick; Paolo Cignoni and Jiri Sochor
A software tool to analyze 4D cardiac CT data sets for planning radiosurgical ablations in the heart is presented. Volume rendering and data processing are performed using a GPU. The user visualizes the data from inside the left atrium and defines the target in 3D using an intuitive user interface. A haptic input device lets the user measure motion at the ostia of the pulmonary veins for radiosurgical treatment planning. This tool has been used effectively for generating radiation treatment plans for animal studies.
Reeb Chart Unfolding Based 3D Shape Signatures
(The Eurographics Association, 2007) Tierny, Julien; Vandeborre, Jean-Philippe; Daoudi, Mohamed; Paolo Cignoni and Jiri Sochor
This paper presents a novel surface parameterization based technique that addresses the pose insensitive shape signature problem for surface models of arbitrary genus. It is based on the key idea that two surface models are similar if the canonical mappings of their sub-parts introduce similar distortions. First, a Reeb graph of the shape is computed so as to segment it into charts of controlled topology, denoted as Reeb charts, that have either disk or annulus topology. Next, we define for each Reeb chart a straightforward mapping to the canonical planar domain. Then, we compute a stretching signature of the canonical mapping based on an area distortion evaluation. Finally, the input shape is represented by the set of the stretching signatures. An application to pose-insensitive shape similarity is proposed by comparing the signatures of the different Reeb charts. Promising experimental results are presented and compared to state-of-the-art techniques. The gain provided by this new signature as well as its interest for partial shape similarity are demonstrated.
Real-Time 3D Lettering with a 2D Font Engine
(The Eurographics Association, 2007) Heise, Sebastian; Loviscach, Jörn; Paolo Cignoni and Jiri Sochor
Standard texturing shows a number of problems with 3D objects such as road signs, labels, or books. If letters are displayed at too large a scale, textures show blurred instead of hard edges; if letters are displayed at tiny sizes, textures appear either too pixelated or too blurry, but seldom well readable. In 2D as opposed to 3D, letters are created on demand in the required size by a sophisticated font rendering engine, a standard component of today s operating systems. A number of specific improvements such as hinting and RGB subpixel rendering are available. This paper demonstrates how these partially proprietary and patented 2D functions can be leveraged for 3D rendering. The price to pay is a loss in geometric precision, since typical 2D font rendering engines only handle affine transformations, which can merely approximate perspective projection. However, in most situations this is outweighed easily by the gain in clarity.
An Accurate Implicit Field Representation for Meshes and Its Adapted Triangulation Algorithms
(The Eurographics Association, 2007) Fournier, Marc; Dischler, J. - M.; Bechmann, D.; Paolo Cignoni and Jiri Sochor
The classic implicit scalar field distance transform representation of a mesh is very useful to perform many mesh processing operations and to obtain better results than with other methods. In this paper we propose a new and more accurate implicit vector field distance transform representation of a mesh. We adapt Marching Cube and Marching Triangle, the two most widely used triangulation algorithms, to our new vector field representation to correctly reconstruct the final mesh after data processing in the implicit domain. According to a reliable surface error metric, we show our new vector field is more accurate than the classic scalar field to implicitly represent a mesh. We adapt to our vector field a previously introduced mesh denoising algorithm performed on the scalar field. Results show mesh denoising with our vector field outperforms the one with classic scalar field in terms of an error metric comparison.
High Speed Skin Color Detection and Localization on a GPU
(The Eurographics Association, 2007) Seshadrinathan, Manoj; Dempski, Kelly; Paolo Cignoni and Jiri Sochor
In this paper, we present a simple yet novel method for high speed skin color detection and localization on images and video using the Graphics Processing Unit (GPU) and common graphics programming techniques. Our approach is innovative in that it provides a system for skin recognition and localization on the GPU at a speed much higher than that on the CPU. We also test in detail, the performance of different classes of cards and data buses.
Painterly Effects Rendering with Focus Based Level of Detail
(The Eurographics Association, 2007) Levente, Kovács; Tamás, Szirányi; Paolo Cignoni and Jiri Sochor
We present a novel method for automatically creating scalable and portable 2D non-photorealistically rendered (NPR) images with painterly effects, with level of detail control. The novelty of the approach lies both in using optical image analysis for automatic focus region extraction, and in producing the painterly rendered images as vector graphics. The approach is also novel in that we automatically extract the regions of higher interest without the need of any tools, devices, or a priori image information. The method is a combination of automatic relative focus map estimation and simple digital strokes for the foreground, and color image segmentation for the background. The images are rendered into scalable vector graphics (SVG) for easy viewing and editing with a variety of existing applications and use in other designs/graphics.
Spinoff - Transferring Energy between Real and Virtual Worlds
(The Eurographics Association, 2007) Groenegress, Christoph; Slater, Mel; Tamke, Martin; Thomsen, Mette Ramsgard; Paolo Cignoni and Jiri Sochor
There is a widening gap between interaction devices for Virtual Environments and other factors such as graphical realism, accessibility and complexity. To address this problem, we developed a Mixed Reality environment that allows participants to interact with virtual entities using an existing toy a Hula Hoop. In a subsequent user study we attempted to correlate the use of real artefacts as input devices towards increased interactivity.

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