Computers & Graphics

Published by Elsevier
Online ISSN: 0097-8493
Publications
Article
In many applications, iso-surface is the primary method for visualizing the structure of 3D density maps. We consider a common scenario where the user views the iso-surfaces from a distance and varies the level associated with the iso-surface as well as the view direction to gain a sense of the general 3D structure of the density map. For many types of density data, the iso-surfaces associated with a particular threshold may be nested and never visible during this type of viewing. In this paper, we discuss a simple, conservative culling method that avoids the generation of interior portions of iso-surfaces at the contouring stage. Unlike existing methods that perform culling based on the current view direction, our culling is performed once for all views and requires no additional computation as the view changes. By pre-computing a single visibility map, culling is done at any iso-value with little overhead in contouring. We demonstrate the effectiveness of the algorithm on a range of bio-medical data and discuss a practical application in online visualization.
 
Article
We present an interactive graphical approach for the explicit specification of semantics for volume visualization. This explicit and graphical specification of semantics for volumetric features allows us to visually assign meaning to both input and output parameters of the visualization mapping. This is in contrast to the implicit way of specifying semantics using transfer functions. In particular, we demonstrate how to realize a dynamic specification of semantics which allows to flexibly explore a wide range of mappings. Our approach is based on three concepts. First, we use semantic shader augmentation to automatically add rule-based rendering functionality to static visualization mappings in a shader program, while preserving the visual abstraction that the initial shader encodes. With this technique we extend recent developments that define a mapping between data attributes and visual attributes with rules, which are evaluated using fuzzy logic. Second, we let users define the semantics by analogy through brushing on renderings of the data attributes of interest. Third, the rules are specified graphically in an interface that provides visual clues for potential modifications. Together, the presented methods offer a high degree of freedom in the specification and exploration of rule-based mappings and avoid the limitations of a linguistic rule formulation.
 
Article
A technique used in animated computer graphics involves the use of real-time playback. This method is used when it is not possible to display frames of display code in real-time. Instead, frames are compiled in advance at non realtime rates, saved in secondary storage, and played back at desired realtime speeds. The basic design and operation of two such systems will be considered. The more powerful of the two is built upon an Evans and Sutherland picture System I and utilizes animated vector graphics. The other playback system is built upon a Terak micro computer display and represents an example of rudimentary raster graphics animation. The synchronization, buffering, blocking and man-machine interfaces of both systems are detailed thus spotlighting their operational behavior. A comparison of the two systems show: that similarities in the logical organization of each system exist; that both systems are input bound; and both require their image files to be built on other computer systems. The differences in the performance of the two systems can be attributed to technological differences between the two systems; the retrieval rates of their respective disk subsystems; and differences in the intent and purpose behind the design of each machine. The systems are demonstrated by applying them to chemical modeling. It is determined that playback is a useful technique for examining complicated sequential situations or for providing the concise and convenient representation of large amounts of data.
 
Article
A common goal of outdoor augmented reality (AR) is the presentation of annotations that are registered to anchor points in the real world. We present an enhanced approach for registering and tracking such anchor points, which is suitable for current generation mobile phones and can also successfully deal with the wide variety of viewing conditions encountered in real life outdoor use. The approach is based on on-the-fly generation of panoramic images by sweeping the camera over the scene. The panoramas are then used for stable orientation tracking, while the user is performing only rotational movements. This basic approach is improved by several new techniques for the re-detection and tracking of anchor points. For the re-detection, specifically after temporal variations, we first compute a panoramic image with extended dynamic range, which can better represent varying illumination conditions. The panorama is then searched for known anchor points, while orientation tracking continues uninterrupted. We then use information from an internal orientation sensor to prime an active search scheme for the anchor points, which improves matching results. Finally, global consistency is enhanced by statistical estimation of a global rotation that minimizes the overall position error of anchor points when transforming them from the source panorama in which they were created, to the current view represented by a new panorama. Once the anchor points are redetected, we track the user's movement using a novel 3-degree-of-freedom orientation tracking approach that combines vision tracking with the absolute orientation from inertial and magnetic sensors. We tested our system using an AR campus guide as an example application and provide detailed results for our approach using an off-the-shelf smartphone. Results show that the re-detection rate is improved by a factor of 2 compared to previous work and reaches almost 90% for a wide variety of test cases while still keeping the ability to run at interactive frame rates.
 
Article
Simulation is a necessary tool if we are to understand better the complexities involved in cardiovascular transport. While some of the phenomena modeled can be described analytically, perusal of the equations alone often doesn't result in full appreciation of the model system. It therefore becomes pertinent to utilize computer graphics in order to enhance simulation of physiologic transport processes. Graphic representation not only facilitates interaction between the investigator and the simulation, it provides a juxtaposition of the model to the real system, as well as a simplification of relationships between various features of the model.Increased mathematical sophistication required in the investigation of cardiovascular transport phenomena often makes traditional graphic representation cumbersome. Therefore several different types of graphics have been utilized, including 2-, 3-, and 4-dimensional displays. The methods and algorithms for these displays have been generalized to make them easy to use over a broad spectrum of applications. In some cases we have generated motion pictures of sequential model solutions which have increased and accelerated model comprehension, as well as been valuable for teaching purposes.
 
Article
In this paper, we introduce a novel framework for the compositing of interactively rendered 3D layers tailored to the needs of scientific illustration. Currently, traditional scientific illustrations are produced in a series of composition stages, combining different pictorial elements using 2D digital layering. Our approach extends the layer metaphor into 3D without giving up the advantages of 2D methods. The new compositing approach allows for effects such as selective transparency, occlusion overrides, and soft depth buffering. Furthermore, we show how common manipulation techniques such as masking can be integrated into this concept. These tools behave just like in 2D, but their influence extends beyond a single viewpoint. Since the presented approach makes no assumptions about the underlying rendering algorithms, layers can be generated based on polygonal geometry, volumetric data, point-based representations, or others. Our implementation exploits current graphics hardware and permits real-time interaction and rendering.
 
Article
Spherical harmonic (SPHARM) description is a powerful Fourier shape modeling method for processing arbitrarily shaped but simply connected 3D objects. As a highly promising method, SPHARM has been widely used in several domains including medical imaging. However, its primary use has been focused on modeling small or moderately-sized surfaces that are relatively smooth, due to challenges related to its applicability, robustness and scalability. This paper presents an enhanced SPHARM framework that addresses these issues and show that the use of SPHARM can expand into broader areas. In particular, we present a simple and efficient Fourier expansion method on the sphere that enables large scale modeling, and propose a new SPHARM registration method that aims to preserve the important homological properties between 3D models. Although SPHARM is a global descriptor, our experimental results show that the proposed SPHARM framework can accurately describe complicated graphics models and highly convoluted 3D surfaces and the proposed registration method allows for effective alignment and registration of these 3D models for further processing or analysis. These methods greatly enable the potential of applying SPHARM to broader areas such as computer graphics, medical imaging, CAD/CAM, bioinformatics, and other related geometric modeling and processing fields.
 
Conference Paper
Reverse engineering is an important process in CAD systems today. Yet several open problems lead to a bottleneck in the reverse engineering process. First, because the topology of the object to be reconstructed is unknown, point connectivity relations are undefined. Second, the fitted surface must satisfy global and local shape preservation criteria that are undefined explicitly. In reverse engineering, object reconstruction is based both on parameterization and on fitting. Nevertheless, the above problems are influenced mainly by parameterization. In order to overcome the above problems, the paper proposes a neural network, Self Organizing Map (SOM) method, for creating a 3D parametric grid. The main advantage of the proposed SOM method is that it detects both the orientation of the grid and the position of the sub-boundaries. The neural network grid converges to the sampled shape through an adaptive learning process. The SOM method is applied directly on 3D sampled data and avoids the projection anomalies common to other methods. The paper also presents boundary correction and growing grid extensions to the SOM method. In the surface fitting stage, an RSEC (Random Surface Error Correction) fitting method based on the SOM method was developed and implemented
 
Conference Paper
In this paper, we propose a new region-growing based iso-surface extraction algorithm that can generate high-quality curvature-adaptive semi-regular meshes, preserve sharp features and will extract all the disjoint components of the iso-surface. More importantly, in this paper, we propose a novel normal consistency constraint that ensures the intersection of the Delaunay sphere of the new triangle and the iso-surface is a topological disk, an important property that makes the new algorithm very robust when dealing with large scale of volumetric datasets of complex topology and geometry.
 
Conference Paper
This paper describes a system that improves the performance of a time-shared host computer for users of TEKTRONIX series 4010/4014/4015 graphics terminals. The system consists of a mini or microcomputer situated at the terminal, a program that runs in the satellite computer, and a library of FORTRAN callable subroutines that provide a convenient interface between an application program in the host computer and the program in the satellite computer. The system ensures that the satellite has advance information about the expected dialogue, so that the satellite is able to react instantly to input from the user, even if the response of the host computer is slow. The satellite gathers several trivial inputs together and sends them to the host in a burst. This allows the program in the host to process more information each time it is rolled into memory, hence the efficiency of its operation is improved. The satellite also performs such operations as zooming, repainting and identification of entites on the screen.
 
Article
Construct3D is a 3D geometric construction tool specifically designed for mathematics and geometry education. It is based on the mobile collaborative augmented reality system “Studierstube”. We describe our efforts in developing a system for the improvement of spatial abilities and maximization of transfer of learning. In order to support various teacher–student interaction scenarios we implemented flexible methods for context and user dependent rendering of parts of the construction. Together with hybrid hardware setups they allow the use of Construct3D in today's classrooms and provide a testbed for future evaluations. Means of application and integration in mathematics and geometry education at high school as well as university level are being discussed. Anecdotal evidence supports our claim that Construct3D is easy to learn, encourages experimentation with geometric constructions and improves spatial skills.
 
Article
The accommodation of conventional 2D GUIs with virtual environments (VEs) can greatly enhance the possibilities of many VE applications. In this paper we present a variation of the well-known ray-casting technique for fast and accurate selection of 2D widgets over a virtual window immersed into a 3D world. The main idea is to provide a new interaction mode where hand rotations are scaled down so that the ray is constrained to intersect the active virtual window. This is accomplished by changing the control–display ratio between the orientation of the user's hand and the ray used for selection. Our technique uses a curved representation of the ray providing visual feedback of the orientation of both the input device and the selection ray. We have implemented this technique and evaluated its effectiveness in terms of performance and user preference. Our experiments on a four-sided CAVE indicate that the proposed technique can increase the speed and accuracy of component selection in 2D GUIs immersed into 3D worlds.
 
Article
In surface reconstruction from planar cross sections it is necessary to build surfaces between 2D contours in consecutive cross sections. This problem has been traditionally attacked by (i) direct reconstruction based on local geometric proximity between the contours, and (ii) classification of topological events between the cross sections. These approaches have been separately applied with limited success. In case (i), the resulting surfaces may have overstretched or unnatural branches. These arise from local contour proximity which does not reflect global similarity between the contours. In case (ii), the topological events are identified but are not translated into the actual construction of a surface. This article presents an integration of the approaches (i) and (ii). Similarity between the composite 2D regions bounded by the contours in consecutive cross sections is used to: (a) decide whether a surface should actually relate two composite 2D regions, (b) identify the type and location of topological transitions between cross sections and (c) drive the surface construction for the regions found to be related in step (a). The implemented method avoids overstretched or unnatural branches, rendering a surface which is both geometrically intuitive and topologically faithful to the cross sections of the original object. The presented method is a good alternative in cases in which correct reproduction of the topology of the surface (e.g. simulation of flow in conduits) is more important than its geometry (e.g. assessment of tumor mass in radiation planning).
 
Article
On account of the enormous amounts of rules that can be produced by data mining algorithms, knowledge post-processing is a difficult stage in an association rule discovery process. In order to find relevant knowledge, the user needs to rummage through the rules. To make this task easier, we propose a new interactive mining methodology based on well adapted dynamic visual representations. It allows the user to drive the discovery process by focusing his/her attention on limited subsets of rules. We have implemented our methodology with two complementary 2D and 3D visualization supports. These implementations exploit the user's focus to guide the generation of the rules by means of a specific constraint-based rule-mining algorithm.
 
Article
Gentropy is a genetic programming system that evolves two-dimensional procedural textures. It synthesizes textures by combining mathematical and image manipulation functions into formulas. A formula can be reevaluated with arbitrary texture-space coordinates, to generate a new portion of the texture in texture space. Most evolutionary art programs are interactive, and require the user to repeatedly choose the best images from a displayed generation. Gentropy uses an unsupervised approach, where one or more target texture image is supplied to the system, and represent the desired texture features, such as colour, shape and smoothness (contrast). Then, Gentropy evolves textures independent of any further user involvement. The evolved texture will not be identical to the target texture, but rather, will exhibit characteristics similar to it. When more than one texture is supplied as a target, multi-objective feature analysis is performed. These feature tests may be combined and given different priorities during evaluation. It is therefore possible to use several target images, each with its own fitness function measuring particular visual characteristics. Gentropy also permits the use of multiple subpopulations, each of which may use its own texture evaluation criteria and target texture.
 
Article
The paper presents a new method to interpolate a pair of 2D shapes that are represented by piecewise linear curves. The method addresses two key problems in 2D shape morphing process: feature correspondence and path interpolation. First, a robust feature metric is defined to measure the similarity of a pair of 2D shapes in terms of visual appearance, orientation and relative size. Based on the metric, an optimal problem is defined and solved to associate the features on the source shape with the corresponding ones on the target shape. Then, a two-level hierarchical approach is proposed to solve the corresponding features interpolation trajectory problem. The algorithm decomposes the input shapes into a pair of corresponding coarse polygons and several pairs of corresponding features. Then the corresponding coarse polygons are interpolated in an as-rigid-as-possible plausible way; meanwhile the corresponding features are interpolated using the intrinsic method. Thus interior distortions of the intermediate shapes could be avoided and the feature details on the input shapes could be well preserved. Experimental results show that the method can generate smooth, natural and visually pleasing 2D shape morphing effects.
 
Article
The objective of this paper is metamorphosis of 2D affine IFS attractors, which is done in a correct manner. The criteria of correctness can be described in brief as follows. First of all, the topology of intermediate shapes generated via morphing should not be sensitive to affine deformations of the key shapes—the property we call affine stability of morphing. Secondly, intermediate shapes should not be less similar to the key ones as the latter are to each other. In a special case, when the key shapes are affine images of each other, the criterion above states that every intermediate shape has to be affine similar to the key ones. Although the postulates are obvious, no prior method of blending fractals satisfies them in general. In contrast, the approach presented in this paper obeys all the conditions. Another problem we focus on is blending fractals specified by IFSs of different numbers of maps, and we propose a number of solutions. To satisfy all the conditions we face in this paper among others moment matrices of IFS invariant measures, the SO(2) Procrustes problem, and numerical stability of the process of morphing. We also introduce a number of new notions, including IFS similarity equivalence classes, the IFS canonical form, the IFS morphing space, and the special SVD. Finally, we point out other possible applications of the presented ideas and indicate open problems.
 
Article
This paper describes the Rectangular FishEye View for the combined presentation of 2D raster images, 2D vector graphics and text. A detailed presentation of the area of highest user interest (the focus) is integrated into a lower-detail context display providing an overview. Screen space is saved by downscaling (distorting) the context. The geometric layout of the view is assembled using rectangular regions. Three different context modes are proposed to provide for computational scalability. Performance and quality implications of two different implementation options are compared.
 
Article
The experimental results of viewing 3D objects on a 2D display are presented. The effect of object relationship; presentation quality (wireframe and shaded); and illumination on depth perception were studied. After the depth estimation phase, subjects were then asked to make a subjective judgement: whether they thought better estimates had been made with the shaded rather than wireframe form. Subsequent analysis, showed that the experimental figures did not support this guess. Lighting influenced accuracy, which illustrates the importance of careful choices of light sources. Relative object placement was also established as an important factor.
 
Article
This paper describes an application of computer graphics to the display and interpretation of a simulation. The purpose of the simulation was to investigate the difficulties faced by prehistoric people in migrating from Asia to Australia/New Guinea. This type of geographic simulation often results in the production of massive data sets, which, just because of their quantity, can be difficult to analyze. The use of continuous graphic output as the simulation was executed gave the viewer immediate access to what was going on. In this case, the direct accessibility was essential as the simulation was produced with the view to being run as a short animation sequence in a documentary film.
 
Article
Graphic visuals derived from reverse engineered source code have long been recognized for their impact on improving the comprehensibility of structural and behavioral aspects of large software systems and their source code. A number of visualization techniques, primarily graph-based, do not scale. Some other proposed techniques based on 3D metaphors tend to obscure important structural relationships in the program. Multiple views displayed in overlapping windows are suggested as a possible solution, which more often than not results in problems of information overload and cognitive discontinuity. In this paper, we first present a comprehensive survey of related work in program comprehension and software visualization, and follow it up with a detailed description of our research which uses program slicing for deriving program structure-based attributes and 3D-metaball-based rendering techniques to help visualization-based analysis of source code structure. Metaballs, a 3D modeling technique, has already found extensive use for representing complex organic shapes and structural relationships in biology and chemistry. We have developed a metaball software visualization system in Java3D, named MetaViz. As proof of concept, using MetaViz, we demonstrate the creation of 3D visuals that are intuitively comprehensible and communicate information about relative component complexity and coupling among components and therefore enhance comprehension of the program structure.
 
Article
A method for the qualitative understanding of low-resolution binary objects is presented. To the observer the object appears as a pseudophotograph of a continuous object. A good impression of the 3D shape of the object is conveyed by the shaded planar image. By using a fast storage and boundary extraction scheme, the shaded image is produced quickly.
 
Article
A three-dimensional scan-conversion algorithm, that scan-converts 3D planar polygons into their discrete voxel-map representation within a Cubic Frame Buffer (CFB), is presented. The algorithm, which is a variation of a conventional 2D scan-line filling algorithm, is incremental and uses only simple operations like additions and tests inside the inner loops. The algorithm performs scan-conversion with computational complexity which is linear in the number of voxels written to the CFB. Another algorithm that scan-converts polygons clipped to the CFB boundaries with no added time complexity is also presented. Furthermore, an all-integer decision mechanism which makes the inner-most loop of the algorithm more efficient is discussed too. All the algorithms guarantee lack of 6-connected “tunnels” in the converted polygons. The algorithms have been implemented as part of the 3D geometry processor of the CUBE Architecture, which is a voxel-based system for 3D graphics. These algorithms allow the CUBE system to generate a discrete voxel representation of the essential 3D polygon primitive, enabling CUBE to also cater to applications generating synthetic images.
 
Article
The language of geometric algebra can be used in the development of computer graphics applications. This paper proposes a method to describe a 3D polygonal mesh model using a representation technique based on geometric algebra and the conformal model of the 3D Euclidean space. It describes also the stages necessary to develop an application that uses this formalism. The current application was used to validate the implementation of the main abstract operations characteristic to a geometric algebra computational environment (programming module GAP). The data structures that characterize this geometric algebra based modeling approach as well as the implementation of geometric algebra based methods for model visualization/transformation are developed in detail. The paper emphasizes the elegance and generality of the geometric algebra approach referring also to the necessary computational resources.
 
Article
Texture is an important notion for achieving a high degree of realism in image synthesis. 2-D texture mapping methods are well known techniques used in computer graphics with some classical problems. The two major drawbacks of texture mapping are texture discontinuity and texture distortion in some object regions. A more recent and efficient approach to resolve the 2-D texture mapping problems is solid texturing (3-D texturing). Although interesting, solid texturing is complex owing to the problems that the existing 3-D texture generation methods raise. In fact, there is no reliable way to define directly the desired type of texture with these methods. So, the existing 3-D texture generation methods remain rather experimental. In addition, aliasing is another important problem to solve with solid texturing because the conventional and common antialiasing approaches of texture mapping become very expensive in this case. In this paper we present a new, powerful and simple 3-D texture generation method. It is based on a spectral analysis of a 2-D texture (digitized image) of the same type. The 2-D spectral analysis, using a Fourier transform, is used to extract some significant parameters of the texture necessary for a 3-D texture generation. This method allows us to define easily the desired type of texture for an automatic 3-D texture generation. It is simpler and more efficient than the existing 3-D texture generation methods. It can produce a realistic simulation of a wide range of natural textures such as wood, marble, cloud, water waves, etc. In addition, a simple and direct texture antialiasing can be naturally provided by this method.
 
Article
This paper presents an intuitive, freehand sketching application for Computer Aided Design (CAD) that can reconstruct a 3D object from a single, flat, freehand sketch. A pen is used to draw 2D sketches consisting of straight and curved strokes connected at vertices. The sketches are processed by a reconstruction algorithm that uses the angular distribution of the strokes and their connectivity to determine an orthogonal 3D axis system whose projection correlates with the observed stroke orientations. The axis system is used to determine a plausible depth for each vertex. This approach works well for drawings of objects whose edges predominantly conform to some overall orthogonal axis system. A second, independent optimization procedure is then used to reconstruct each curved stroke in the original sketch, assuming that the curve is planar. New strokes can be attached to the 3D object, or drawn directly onto the object's faces. An implementation of the reconstruction algorithm based on Levenberg–Marquardt optimization allows objects with over 50 strokes to be reconstructed in interactive time.
 
Article
Engineers and scientists from many fields are using three-dimensional reconstruction for visualization and analysis of physical and abstract data. Beyond observing the recreated objects in artificial space, it is desirable to develop methods that allow one to interactively manipulate and alter the geometry in an intuitive and efficient manner. In the case of medical data, a baseline interactive task would be to simulate cutting, removal and realignment of tissue. In order to provide for operational realism, the underlying mathematical calculations and topological changes need to be invisible to the user so that the user feels as though they are performing the task just as they would on the real world counterpart of the reconstructed object. We have developed a method that allows the user to directly sketch the desired cut contour on a three-dimensional surface in a manner that simulates dragging scissors through fabric. This new method can be employed interactively, allowing the user to perform the task in an intuitive, natural manner.
 
Article
We are researching a three-dimensional version of direct manipulation interface. In our prototype system “Zashiki-Warashi,” users can directly manipulate furniture and lighting to design a virtual room. In this paper, we will describe our goals for the prototype and our results. Zashiki-Warashi has three main features: 1.1. Beam Cursor: This cursor emits a beam similar to that of a laser, with which users can easily select objects in a virtual world.2.2. Direct Manipulation of Environment: In Zashiki-Warashi, not only objects but also lighting and user's viewpoint can be manipulated directly.3.3. Gravity: In the gravitational environment of Zashiki-Warashi, solids fall naturally. Solids can be picked up, moved, and dropped in a realistic manner inside the virtual world.
 
Article
Automated classification of artifacts produced by mechanical computer-aided design (CAD) is a unique research frontier for 3D matching and mesh processing. Unlike general graphical models, mechanical CAD artifacts have a physical realization via a variety of manufacturing processes as well as functional and behavioral attributes. The general problem of how to best correlate low-level shape data with the higher-order manufacturing and mechanical properties remains an open area of research with many practical applications (cost estimation, design archival, variational design and process selection).This paper addresses the problem of manufacturing process discrimination, i.e., determination of the best (or most likely) manufacturing process from shape feature information. Specifically, we introduce a new curvature-based shape descriptor and show its applicability to manufacturing process discrimination using a publicly available set of artifacts from the National Design Repository. Statistics on surface curvatures are used to construct the curvature-based shape descriptor; and a supervised machine learning classifier, based on support vector machines, is applied to learn a separator for models that are “prismatic machined” and “cast-then-machined”. The authors believe that this work can be the basis for practical new techniques for manufacturing cost estimation, engineering analysis and design archival.
 
Article
We present 3D video fragments, a dynamic point sample framework for real-time free-viewpoint video. By generalizing 2D video pixels towards 3D irregular point samples we combine the simplicity of conventional 2D video processing with the power of more complex polygonal representations for free-viewpoint video. We propose a differential update scheme exploiting the spatio-temporal coherence of the video streams of multiple cameras. Updates are issued by operators such as inserts and deletes accounting for changes in the input video images. The operators from multiple cameras are processed, merged into a 3D video stream and transmitted to a remote site. We also introduce a novel concept for camera control which dynamically selects the set of relevant cameras for reconstruction. Moreover, it adapts to the processing load and rendering platform. Our framework is generic in the sense that it works with any real-time 3D reconstruction method which extracts depth from images. The video renderer displays free-viewpoint videos using an efficient point-based splatting scheme and makes use of state-of-the-art vertex and pixel processing hardware for real-time visual processing.
 
Article
Augmented reality (AR), combining virtual environments with the perception of the real world, can be used to provide instructions for routine maintenance and error diagnostics of technical devices. The Rockwell Science Center (RSC) is developing a system that utilizes AR techniques to provide “X-ray vision” into real objects. The system can overlay 3D rendered objects, animations, and text annotations onto the video image of a known object. An automated speech recognition system allows the user to query the status of device components. The response is given as an animated rendition of a CAD model and/or as auditory cues using 3D audio. This diagnostics system also allows the user to leave spoken annotations attached to device modules as ASCII text. The position of the user/camera relative to the device is tracked by a computer-vision-based tracking system using fiducial markers. The system is implemented on a distributed network of PCs, utilizing standard commercial off-the-shelf components (COTS).
 
Article
Children invent imaginary worlds and enact scenarios within them as part of their everyday play. Given the opportunity and the tools, what kind of worlds could children make for themselves within a virtual space, and what kind of learning can emerge within these playful, child-centred spaces?In VERTEX, young children have designed and created an imaginary virtual world using 3D modelling tools and internet-based virtual worlds software. Crossing traditional subject disciplines and involving local and remote collaboration, the project demonstrates children's design and communication abilities above and beyond the expectations of the primary curriculum.
 
Article
The Sierpinski Triangle and other fractals described by Mandelbrot are probably the most widely recognized fractal patterns today. In this tutorial I describe a method to generate realistic pictures of 3D fractals that can be visualized on the computer screen and printed using color printing devices. All fractals described in this article are fractals obtained using the basic Sierpinski Triangle algorithm modified and adapted to 3D space.
 
Article
Virtual reality is becoming a popular tool to visualize 3D GIS data. Direct interaction with the GIS data, however, is often limited. In this paper, we present a multi-view approach to support 3D GIS interaction within VR-environments. The multi-view approach is based on three types of visualization: plan view, model view and world view. The plan view visualizes the data as a conventional cartographic map. The model view provides a 3D bird's-eye view on a partly symbolic and simplified 3D representation of the data. The world view gives the full immersive and photo-realistic 3D display. These views or modes can be used simultaneously or intermittently, and each provides a repertoire of interaction possibilities that is apt — but not necessarily limited — to that kind of visualization and interaction. This multi-view approach is implemented in the Karma VI system, using existing GIS and VR technology. We describe the multi-view approach, the system components and the internal data models, and how CAD models can be imported and be made consistent with the GIS data.
 
Article
A 3D medical imaging system, called the MediCube system, is described. This system supports the reconstruction, manipulation, analysis, and display of 3D volumetric medical images. The MediCube system is based upon the general-purpose voxel-based Cube architecture, which employs parallel memory and parallel processing to support real-time manipulation and display of voxel imagery. Primary applications for the MediCube system include medical diagnosis, surgical planning, radiation therapy, reconstructive surgery, medical education and research. Examples from an MRI study of the brain are presented.
 
Article
We introduce 3D warp brush, a new method for interactive shape modeling in an immersive virtual reality environment. 3D warp brushes are implicitly defined tools that operate on triangle meshes. We combine the efficiency of explicit mesh representations with intuitive implicit modeling operators. The area of influence of a 3D warp brush can be of arbitrary shape since it has an associated distance field. We define different warp functions including drag, explode, and whittle. A unique feature of our framework is the ability to convert meshes into 3D warp brushes at run time. Thus, we can easily expand our set of brushes based on a small set of base brushes, such as spheres or ellipsoids. Our underlying split-edge mesh data structure supports adaptive refinement and efficient rendering with on-the-fly triangle strip generation. 3D warp brushes only operate on mesh vertices, hence, underlying mesh processing is transparent to the modeling operations. The use of a Responsive Workbench and two-handed interaction allows the user to exploit the full potential of the modeling system by intuitive and easy modification of a base surface into a desired shape. We present several models, which have been created and modified using 3D warp brushes, to demonstrate the usefulness of our framework.
 
Article
In this paper the problems of user interaction in a mobile environment are investigated. Interaction in this environment imposes new requirements both on UI designers and the users. This paper deals in particular with problems of graphical interaction in a mobile environment. The interaction in a mobile environment requires new approaches that will result in a new type of rendering of graphical data. A rendering technique that enables rendering and annotation of objects in a 3D scene on mobile devices is presented. This technique is based on transformation of the 3D scene to a 2D vector graphic representation. The input 3D scene is given in the VRML format and the output 2D format is SVG. In the second part of this paper we are presenting a prototype of a voice user interface that allows users to interact with the graphical data in a mobile environment. The semantic description of the scene plays the key role in restriction of the language used for communication. The communication between the user and the mobile system is performed by means of natural language that is restricted according to the context the user is currently in. The implementation of the voice user interface is based on the existing VoiceXML platform.
 
Article
Aiming at the fundamental issue of optimal design of discrete levels of detail (LOD) for the visualization of complicated 3D building façades, this paper presents a new quantitative analytical method of perceptible 3D details based on perceptual metric. First, the perceptual metric is defined as the quantitative indicator of the visual perceptibility of façade details at a given viewing distance. Then, according to the human vision system, an algorithm employing 2D discrete wavelet transform and contrast sensitivity function is developed to extract the value of perceptual metric from the rendered image of the façade. Finally, a perceptual metric function is defined, based on the perceptual metric values extracted at equal interval viewing distances. The minimum detail redundancy model is then proposed for the optimal design of discrete LODs. This method provides a quantitative instruction for generating discrete LODs. The experimental results prove the effectiveness and great potential of this method.
 
Article
This paper describes a 3D tool machining simulation system. The initial tool and the grinding wheels are integrated with the machine tool. The application reads and interprets the CNC program code that controls the machine, it computes the positions and the motion of components and it translates the sequence of machining operations into Boolean operations. The machining is computed for 2D sections and, later, a 3D model of the tool is reconstructed. The application is ready to yield tool visualization, it gives measurements on sections and it can show an interactive animation of the whole process. A novel aspect of the simulation is that it is able to deal with 6-axes machines, whereas most of previous work is limited to 3- and 4-axes machines. In addition, it allows to interrupt the machining process and to show partially machined tools. A major contribution is the fact that the Boolean operations are performed in 2D and the 3D model is reconstructed from the cross sections, which provides user control on the resolution of the operations at a low cost.
 
Article
Texturing is indispensable for the realistic rendering since it adds surface details that are usually too complex to be modeled directly. Conventional 2D texture mapping remains the most usual approach to texturing, in particular for real-time applications. However, there are some major drawbacks inherent to this approach: the distortion and the discontinuity of textures as well as the lack of the “third” dimension information (geometric effects like roughcast cannot be rendered). 3D texturing has been introduced to computer graphics to resolve these problems. There are two types of 3D texturing: solid texturing that consists of defining color variations through the entire 3D space instead of the 2D one and geometric texturing that consists of adding a “real” third dimension information to surfaces in the form of “real” apparent geometry. This paper presents a detailed survey of 3D texturing. Main principles, advantages, drawbacks and applications are presented. The crucial problem of 3D textures synthesis is studied with a particular attention to analytical methods as well as physical-based models that can provide interesting solutions to this problem.
 
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This paper describes the ideas behind and the development of FlyAway, an environment to handle landscape data interactively. We integrate in this project some aspects of computer graphics that are still open problems concerning high quality landscape rendering. It concerns the usage of multiresolution techniques for viewing-dependent reduction of texture and model complexity and the use of standard graphics libraries for maintaining portability between different kinds of computers and operating systems.
 
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We present an efficient compression scheme for animated sequences of triangular meshes of the same connectivity. The proposed algorithm exploits the temporal coherence of the geometry component by using a temporal wavelet filtering. The quantization of the resulting wavelet coefficients is then optimized by a bit allocation process. This process dispatches the bit budget across the coefficient subbands according to their influence on the quality of the reconstructed sequence for one specific user-given bitrate. The proposed scheme is simple, fast, flexible, and scalable in frame rate and bitrate. Moreover, simulation results show that our approach is competitive for any kind of animated models, whatever the characteristics (parametrically coherent or not, fine/coarse meshes…), contrary to the related works.
 
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In this paper, we describe the methodology that we have designed to quantify the pores distribution in bone implants and the empirical results that we have obtained with BioCAD designed scaffolds, microCT and confocal microscopy data. Our method is based on 3D digital topology properties of the porous structure. We segment the 3D images into three regions: exterior, bone and pore space. Next, we divide the pore space into pores and connection paths. We compute a graph of the pore space such that each node of the graph represents a pore, and an arc between two nodes indicates that the two pores are path-connected. On the basis of the graph and the segmented model, we are able to compute several properties of the material such as global porosity, effective porosity and radial pore distribution.
 
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The automatic synthesis of procedural textures for 3D surfaces using genetic programming is investigated. Genetic algorithms employ a search strategy inspired by Darwinian natural evolution. Genetic programming uses genetic algorithms on tree structures, which are interpretable as computer programs or mathematical formulae. We define a texture generation language in the genetic programming system, which is then used to evolve textures having particular characteristics of interest. The texture generation language used here includes operators useful for texture creation, for example, mathematical operators, colour functions and noise functions. In order to be practical for 3D model rendering, the language includes primitives that access surface information for the point being rendered, such as coordinates values, normal vectors, and surface gradients. A variety of experiments successfully generated procedural textures that displayed visual characteristics similar to the target textures used during training.
 
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Beyond Virtual Reality, 3D Geographical Information Systems should provide efficient spatial analysis tools able to use all capabilities of the third dimension, and a visualization that could operate on the results of queries. To address these issues, this paper presents a fully 3D topological model that was implemented in an object-oriented database management system. That prototype uses a 1 : 5,000 scale database where the problems of abstraction and symbolisation arise, and allows a set of semantic, geometrical and topological queries. The results can be visualized after several transformations on some objects of the database to make them more significant.
 
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In the last few years several approaches (Proceedings of the Second International Workshop on Distributed Interactive Simulation and Real-Time Application, 1998, pp. 88–91; EUROGRAPHICS 2001, vol. 20(3) 2001) have been presented, which address the transmission and visualization of 3D scenes on distributed devices with different capabilities. These techniques are in the interest of a wide field of applications such as virtual chatrooms, product presentations, CAVE visualizations, 3D simulations, or 3D online games. In order to adapt the immense data effort to the capabilities of the devices and the networks, two basic problems have to be solved: the selection of the information according to the user's interest and the reduction of the selected data. Usually the first problem is reduced to visual aspects, which can be determined by visibility culling algorithms. This paper concentrates on the second problem and introduces a system in order to stream the data of even large 3D scenes to remote devices.
 
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Access to and transmission of 3D models over networks becomes increasingly popular. However, the performance and quality of access to remote 3D models strongly depends on system load conditions and the capabilities of the various system components, such as clients, servers, and interconnect. The network graphics framework (NGF) integrates various transmission methods for downloading 3D models in a client–server environment. The NGF automatically selects the optimal transmission method for a given pair of client and server, taking into account characteristics of the model to be transmitted, critical environment conditions, user preferences and the capabilities of the client and the server. The NGF aims to provide constant quality of service across different clients and under varying environment conditions.
 
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In this paper, a robust 3D trianglular mesh watermarking algorithm is presented by applying spherical parameterization. First, we transform the coordinate signals of the 3D triangular mesh into spherical signals using a global spherical parameterization and an even sampling scheme. Then, spherical harmonic transformation is used to generate some data for embedding watermarks. As a result, the watermarks can be embedded in the Fourier-frequency domain of the original mesh. Experimental results show that our watermarking algorithm is robust since watermarks can be extracted without mesh alignment or re-meshing under a variety of attacks, including noise addition, crop, filtering, enhancement, rotation, translation, scale and re-sampling.
 
Article
Due to their simplicity, triangle meshes are used to represent geometric objects in many applications. Since the number of triangles often goes beyond the capabilities of computer graphics hardware and the transmission time of such data is often inappropriately high, a large variety of mesh simplification algorithms has been proposed in the last years. In this paper we identify major requirements for the practical usability of general purpose mesh reduction algorithms to enable the integration of triangle meshes into digital documents. The driving idea is to understand mesh reduction algorithms as a software extension to make more complex meshes accessible with limited hardware resources (regarding both transmission and display). We show how these requirements can be efficiently satisfied and discuss implementation aspects in detail. We present a mesh decimation scheme that fulfills these design goals and which has already been evaluated by several users from different application areas. We apply this algorithm to typical mesh data sets to demonstrate its performance.
 
Top-cited authors
Gilberto Câmara
  • National Institute for Space Research, Brazil
Albrecht Schmidt
  • Ludwig-Maximilians-Universität München (LMU Munich)
Hans Gellersen
  • Lancaster University
Michael Beigl
  • Karlsruhe Institute of Technology
Roberto Scopigno
  • Italian National Research Council