A Translucent Sketchpad for the Virtual Table Exploring Motion-based Gesture Recognition

The Virtual Table presents stereoscopic graphics to a user in a workbench-like setting. For this device, a user interface and new interaction techniques have been developed based on transparent props -a tracked hand-held pen and a pad. These props, particularly the pad, are augmented with 3D graphics from the Virtual Table's display that can serve as a palette for tools and controls as well as a window-like see-through interface, a plane-shaped and through-the-plane tool, supporting a variety of new interaction techniques. This paper reports on an extension of this user-interface design space which uses gestural input to create and control solid geometries for CAD and conceptual design. The application of gestural interfaces is a common method for interacting with virtual environments on a habitual and natural basis. The motion-based gesture recognition presented here uses Fuzzy Logic to support a predictable, flexible, and efficient learning process. This new interaction paradigm greatly increases the Virtual Table's suitability for design tasks. Traditional CAD dialogue can be combined with intuitive rapid sketching of geometry on the pad. Additionally, the resulting events and objects can be associated with scene details below the translucent tablet.     

The Hybrid World of Virtual Environments

Much of the work concerned with virtual environments has addressed the development of new rendering technologies or interaction techniques. As the technology matures and becomes adopted in a wider range of applications, there is, however, a need to better understand how this technology can be accommodated in software engineering practice. A particular challenge presented by virtual environments is the complexity of the interaction that is supported, and sometimes necessary, for a particular task. Methods such as finite-state automata which are used to represent and design dialogue components for more conventional interfaces, e.g. using direct manipulation within a desktop model, do not seem to capture adequately the style of interaction that is afforded by richer input devices and graphical models. In this paper, we suggest that virtual environments are, fundamentally, what are known as hybrid systems. Building on this insight, we demonstrate how techniques developed for modelling hybrid systems can be used to represent and understand virtual interaction in a way that can be used in the specification and design phases of software development, and which have the potential to support prototyping and analysis of virtual interfaces.     

Seamless Integration of Databases in VR for Constructing Virtual Environments

An approach for authoring virtual environments within the virtual environments themselves is presented, integrating a database containing arbitrary components that are used to construct the 3D scene. The issues important to a seamless integration of the database, such as multimedia data storage and database linkage are discussed, with the focus on the human-computer interaction component. A concept for a 3D database interface is described for query, presentation and usage of query results in the virtual environment. Finally, an implementation of the concept using VRML and Java is presented.     

An Informed Environment Dedicated to the Simulation of Virtual Humans in Urban Context

In this paper, we outline the creation of an Informed Environment, dedicated to urban life simulation.We propose methods and tools for creating and providing the information necessary for animating virtual humans in a city using an Informed Environment. The Informed Environment is based on a hierarchical decomposition of a urban scene into Environment Entities providing geometrical information as well as semantic notions, thus allowing a more realistic simulation of human behaviour. In this manner, virtual humans can integrate with a certain kind of urban knowledge.     

A New Method of Image Mosaicking and Its Application to Cultural Heritage Representation

This paper presents an original two-step procedure for estimating projective transformations between pairs of images: first, the transformation between the images is approximated as an affine transformation; second, this estimate is refined into that of a projective transformation. This strategy for matching projective views is computationally very efficient. The proposed method can be applied both to mosaicking of high resolution images of planar textured objects (e.g., frescoes and paintings), with subpixel accuracy, and to construction of panoramic images. Practical examples of mosaicking of cultural heritage imagery obtained by using the presented procedure are discussed in the paper.     

A Practical Analysis of Clustering Strategies for Hierarchical Radiosity

The calculation of radiant energy balance in complex scenes has been made possible by hierarchical radiosity methods based on clustering mechanisms. Although clustering offers an elegant theoretical solution by reducing the asymptotic complexity of the algorithm, its practical use raises many difficulties, and may result in image artifacts or unexpected behavior. This paper proposes a detailed analysis of the expectations placed on clustering and compares the relative merits of existing, as well as newly introduced, clustering algorithms. This comparison starts from the precise definition of various clustering strategies based on a taxonomy of data structures and construction algorithms, and proceeds to an experimental study of the clustering behavior for real-world scenes. Interestingly, we observe that for some scenes light is difficult to simulate even with clustering. Our results lead to a series of observations characterizing the adequacy of clustering methods for meeting such diverse goals as progressive solution improvement, efficient ray casting acceleration, and faithful representation of object density for approximate visibility calculations.     

Partitioning and Handling Massive Models for Interactive Collision Detection

We describe an approach for interactive collision detection and proximity computations on massive models composed of millions of geometric primitives. We address issues related to interactive data access and processing in a large geometric database, which may not fit into main memory of typical desktop workstations or computers. We present a new algorithm using overlap graphs for localizing the "regions of interest" within a massive model, thereby reducing runtime memory requirements. The overlap graph is computed off-line, pre-processed using graph partitioning algorithms, and modified on the fly as needed. At run time, we traverse localized sub-graphs to check the corresponding geometry for proximity and pre-fetch geometry and auxiliary data structures. To perform interactive proximity queries, we use bounding-volume hierarchies and take advantage of spatial and temporal coherence. Based on the proposed algorithms, we have developed a system called IMMPACT and used it for interaction with a CAD model of a power plant consisting of over 15 million triangles. We are able to perform a number of proximity queries in real-time on such a model. In terms of model complexity and application to large models, we have improved the performance of interactive collision detection and proximity computation algorithms by an order of magnitude.     

Texturing 3D Models of Real World Objects from Multiple Unregistered Photographic Views

As the efficiency of computer graphic rendering methods is increasing, generating realistic models is now becoming a limiting factor. In this paper we present a new technique to enhance already existing geometry models of real world objects with textures reconstructed from a sparse set of unregistered still photographs. The aim of the proposed technique is the generation of nearly photo-realistic models of arbitrarily shaped objects with minimal effort. In our approach, we require neither a prior calibration of the camera nor a high precision of the user's interaction. Two main problems have to be addressed of which the first is the recovery of the unknown positions and parameters of the camera. An initial estimate of the orientation is calculated from interactively selected point correspondences. Subsequently, the unknown parameters are accurately calculated by minimising a blend of objective functions in a 3D-2D projective registration approach. The key point of the proposed method of registration is a novel filtering approach which utilises the spatial information provided by the geometry model. Second, the individual images have to be combined yielding a set of consistent texture maps. We present a robust method to recover the texture from the photographs thereby preserving high spatial frequencies and eliminating artifacts, particularly specular highlights. Parts of the object not seen in any of the photographs are interpolated in the textured model. Results are shown for three complex example objects with different materials and numerous self-occlusions.     

Computer-Generated Graphite Pencil Rendering of 3D Polygonal Models

Researchers in non-photorealistic rendering have investigated the display of three-dimensional worlds using various display models. In particular, recent work has focused on the modeling of traditional artistic media and styles such as pen-and-ink illustration and watercolor painting. By providing 3D rendering systems that use these alternative display models users can generate traditional illustration renderings of their three-dimensional worlds. In this paper we present our graphite pencil 3D renderer. We have broken the problem of simulating pencil drawing down into four fundamental parts: (1) simulating the drawing materials (graphite pencil and drawing paper, blenders and kneaded eraser), (2) modeling the drawing primitives (individual pencil strokes and mark-making to create tones and textures), (3) simulating the basic rendering techniques used by artists and illustrators familiar with pencil rendering, and (4) modeling the control of the drawing composition. Each part builds upon the others and is essential to developing the framework for higher-level rendering methods and tools. In this paper we present parts 2, 3, and 4 of our research. We present non-photorealistic graphite pencil rendering methods for outlining and shading. We also present the control of drawing steps from preparatory sketches to finished rendering results. We demonstrate the capabilities of our approach with a variety of images generated from 3D models.     

Image Morphing with Feature Preserving Texture

Image metamorphosis as an animation tool has mostly been employed in the context of the entire image. This work explores the use of isolated and focused image based metamorphosis between two-dimensional objects, while capturing the features, colors, and textures of the objects. This pinpointed approach allows one to independently overlay several such dynamic shapes, without any bleeding of one shape into another. Hence, shape blending and metamorphosis of two-dimensional objects can be exploited as animated sequences of clip arts.     

Stochastic Iteration for Non-diffuse Global Illumination

This paper presents a single-pass, view-dependent method to solve the rendering equation, using a stochastic iterational scheme where the transport operator is selected randomly in each iteration. The requirements of convergence are given for the general case. To demonstrate the basic idea, a very simple,continuous random transport operator is examined, which gives back the light tracing algorithm incorporating Russian roulette. Then, a new mixed continuous and finite-element based iteration method is proposed, which uses ray-bundles to transfer the radiance in a single random direction. The resulting algorithm is fast, it provides initial results in seconds and accurate solutions in minutes and does not suffer from the error accumulation problem and the high memory demand of other finite-element and hierarchical approaches.     

Interactive Mechanical Design Variation for Haptics and CAD

A fast design variation technique for mechanical systems is presented. It is used to interactively optimize mechanical characteristics while "self-assembling" or satisfying large systems of mechanical constraints. The high speed method is central to providing inverse dynamics force feedback in haptics and control applications. Performance advantages with the use of augmented coordinates for inverse dynamics of closed loop topologies are also noted. The interaction framework allows manipulation of complex assemblies while maintaining kinematically admissible configurations though linkage and joint limit constraints. Furthermore, design variables such as link length can be treated as free variables and optimized to meet design criteria such as assembly dexterity. Assemblies with flexible bodies fit naturally within this framework. Thus, the contribution of this paper is the advancement of techniques in augmented coordinates for the kinematic and force feedback interaction with virtual mechanical assembly design optimization at force control rates.     

Weighted Multipass Methods for Global Illumination

In multipass rendering, care has to be taken to include all light transport only once in the final solution. Therefore the different methods in current multipass configurations handle a perfectly disjunct part of the light transport. In this paper a Monte Carlo variance reduction technique is presented that probabilistically weights overlapping transport between different methods. A good heuristic for the weights is derived so that strengths of the respective methods are retained. The technique is applied to a combination of radiosity and bidirectional path tracing and significant improvement is obtained over the non-weighted combination. This method promises to be a very useful extension to other multipass algorithms as well.     

Efficient and Handy Texture Mapping on 3D Surfaces

There has been a rapid technical progress in three-dimensional (3D) computer graphics. But gathering surface and texture data is yet a laborious task. This paper addresses the problem of mapping photographic images on the surface of a 3D object whose geometric data are already known. We propose an efficient and handy method for acquiring textures and mapping them precisely on the surface, employing a digital camera alone. We describe an algorithm for selecting a minimal number of camera positions that can cover the entire surface of a given object and also an algorithm to determine camera's position and direction for each photograph taken so as to paste it to the corresponding surfaces precisely. We obtained a matching accuracy within a pixel on a surface through three experimental examples, by which the practicability of our method is demonstrated.     

Observational Models of Graphite Pencil Materials

This paper presents models for graphite pencil, drawing paper, blenders, and kneaded eraser that produce realistic looking pencil marks, textures, and tones. Our models are based on an observation of how lead pencils interact with drawing paper, and on the absorptive and dispersive properties of blenders and erasers interacting with lead material deposited over drawing paper. The models consider parameters such as the particle composition of the lead, the texture of the paper, the position and shape of the pencil materials, and the pressure applied to them. We demonstrate the capabilities of our approach with a variety of images and compare them to digitized pencil drawings. We also present image-based rendering results implementing traditional graphite pencil tone rendering methods.     

Design and performance evaluation of a pixel cache implemented within application-specific integrated circuits

The application-specific integrated circuit (ASIC) design and the performance of a graphics processor that uses a pipelined-cache with FIFO memory to transfer a 3D pixel array and its z values to the frame buffer in one cycle are described in detail. The functional modules in the graphics processor include: (1) a video refresh converter, (2) a module that combines texture-mapped patterns onto Phong-shaded surfaces, and (3) a bidircctional parallel link between external devices and the frame-buffer modules. Digital differential analyzer (DDA) algorithms and the size of the pixel cache relative to the frame-buffer bandwidth, have been selected for good overall performance. A drawing speed of 8 ns/pixel (32 bits/pixel) or 1.2 million Phong-shaded polygons/s (100-pixel polygons, texture mapped with hidden surface removal) was achieved when 60-ns accesstime single port DRAMs and synchronous DRAMs were used.     

VECW:一个虚拟环境的构造和漫游系统

如何真实地在计算机中表达现实世界是计算机图形学的一个重要研究方向。基于几何造型的图像绘制混合是一种很有应用前景的方法。文中在实现前人提出的从建筑物照片中提取建筑物的几模型和相应纹理映射的算法的基础上,给出了一个虚拟环境的构造和漫游系统,简称ＶＥＣＷ。     

A scalable high-performance graphics processor: GVIP

The GVIP (geometric and TV image processor) graphics processor, which creates and synthesizes computer graphics and TV images and meets the requirements of multi-media systems, is described. The hardware modules that make up this graphics processor include: a 32-bit embedded RISC processor, a Phong and Gouraud shading processor, a texture mapping processor, a hidden surface removal processor, an HDTV video image processor, a BitBlt processor, an imageprocessing module, and an outline font fill generator. These hardware modules fabricated using 0.8 m CMOS standard cells have been placed in three integrated circuit chips. The total number of gates used for one set of chips is approximately 350000.     

虚拟现实技术综述与基于Internet的虚拟培训系统设计

文章对虚拟现实技术的发展和建模方法--基于图形建模和基于图像建模两种方法的原理及实现技术进行综述,给出了在Internet上实现虚拟现实的方法,及多种软件开发平台的特点和比较,从而设计了一个远程职业技术虚拟现实系统的模型。     

Embedded blended learning within an Algebra classroom: a multimedia capture experiment

This two‐group, pretest‐posttest, quasi‐experimental study compared secondary students' learning of Algebra II materials over a 4‐week period when identical instruction by the same teacher was delivered through either embedded blended learning (treatment group; n = 32) or a live‐lecture classroom (control group; n = 24). For both groups, instruction was delivered in a normal classroom setting. A math test and a student survey were used to measure students' learning of Algebra II and satisfaction with the instruction. Students in the treatment group showed significantly greater gains in Algebra II test scores and evaluated their learning experiences significantly more positively than did the control group. The great majority (80%) of students in the treatment group preferred the embedded blended learning over traditional live lectures for future learning of math. Students' responses to open‐ended survey questions suggested that students in the treatment group appreciated the: (a) ability to control the pace of instruction; (b) new role of the classroom teacher; (c) lack of distraction in the blended learning environment; and (d) accessibility of the embedded multimedia lessons outside the classroom. This study suggests that screen‐capture instructional technology can be used towards establishing a teacher‐based, embedded blended learning environment within a secondary algebraic classroom.