Alexei Sourin

Function representation in geometric modeling : concepts, implementation and applications

Concepts of functionally based geometric modeling including sets of objects, operations, and relations are discussed. Transformations of a defining real function are described for set-theoretic operations, blending, offsetting, bijective mapping, projection, cartesian products, and metamorphosis. Inclusion, point membership, and intersection relations are also described. We use a high-level geometric language that can extend the interactive modeling system by input symbolic descriptions of primitives, operations, and predicates. This approach supports combinations of representational styles, including constructive geometry, sweeping, soft objects, voxel-based objects, deformable and other animated objects. Application examples of aesthetic design, collisions simulation, NC machining, range data processing, and 3D texture generation are given.

Cybercampuses: design issues and future directions

In recent years, the usage of 3D cyberworlds for educational purposes has increased. The metaphors behind the visual design of such cyberworlds are quite diverse, from replication of real universities, art museums and scientific labs to non-existing fictitious places. In this paper, we focus specifically on “cybercampuses”, i.e. virtual worlds representing real educational institutions such as universities and schools. Based on the results of a case study that we have performed, this paper provides an initial set of requirements for a cybercampus representing an existing university. In this connection, we analyze place metaphors and associated design features of the Virtual Campus of Nanyang Technological University in Singapore, discuss the correspondence between the identified metaphors and associated educational goals, and provide directions for further development. Finally, we outline the major challenges for the future evolution of cybercampuses in the context of organizational, social and technological development.

Grid-based computer animation rendering

Rendering computer animation frames is a very time consuming job. Using parallel computing on clusters and so-called render farms is a common solution to this problem. In this paper we describe how Grid computing can be used for computer animation rendering. We propose a framework for Grid rendering services, describe its implementation, and present the results and statistics. A loseless 3D compression algorithm was also devised to solve the existing problem of transferring gigabytes of scene representation files (Renderman (.rib) and mental images (.mi)). This compression algorithm has been filed for patent in Singapore.

Virtual orthopedic surgery training

Medicine is one of the most promising areas for emerging computer graphics and virtual reality techniques. VR training simulators let surgeons practice on virtual body tissue and get the same feedback they would experience in performing a real operation. Hybrid VR systems permit medical practitioners to view the patient overlaid with 3D data sets derived from 3D scanners, thus providing doctors and surgeons with pseudo X-ray vision. While currently available immersive VR surgery systems usually require expensive hardware and software, we developed a desktop VR orthopedic surgery training system that can run on commonly available personal computers.

Function-based shape modelling extension of the Virtual Reality Modelling Language

In this paper we propose a new approach to web visualisation with VRML based on a function-based shape modelling, which unifies different types of mathematical functions in order to enrich the existing web visualisation techniques for modelling. In our method, parametric, implicit and explicit functions can be used concurrently for defining geometry, colour, texture, and other properties of shapes. Geometric shapes and their properties are defined by functions in their respective domains and then merged into function-defined objects. The proposed framework allows for its extending with any function-based model. To illustrate our method and to prove its feasibility, we implemented it for web visualisation as the Function-based Extension of Virtual Reality Modelling Language. In this implementation, parametric implicit and explicit analytical formulae are used for defining geometry and appearance of three-dimensional (3D) shapes. The function-based extension of VRML is used for collaborative shape modelling as well as for building shared virtual worlds.

Function-defined shape metamorphoses in visual cyberworlds

Animated shape transformations should be an intrinsic part of visual cyberworlds. However, quite often only limited animation of the polygon-based shapes can be found there, specifically when using the virtual reality modeling language (VRML) and its successor extensible 3D (X3D). This greatly limits the expressive power of visual cyberworlds and has motivated our research in this direction. In this paper, we present function-based extensions of VRML and X3D, which allow for time-dependent shape modeling on the web. Our shape modeling approach is based on the concurrent use of implicit, explicit and parametric functions defining geometry, appearance and their transformations through time. The functions are typed straight in VRML/X3D code as individual formulas and as function scripts. We have also developed a web enabled interactive software tool for modeling function-based VRML/X3D objects.

Nanyang Technological University virtual campus [virtual reality project]

The idea for building a VR model of the NTU campus came about six years ago when the School of Computer Engineering purchased a powerful graphics workstation with advanced modeling software systems, MultiGen-Paradigms MultiGen and Vega. Three-dimensional Web visualization developed rapidly. Personal computers became capable of making VR walkthroughs even in shared virtual worlds. Cybertown created by Tony Rockliff and Pascal Baudar with Virtual Reality Modeling Language (VRML) on the Blaxxun Platform, inspired us to put our virtual campus on the Web.

ANALYSIS AND VISUALIZATION OF HUMAN ELECTROENCEPHALOGRAMS SEEN AS FRACTAL TIME SERIES

The paper presents a novel technique of nonlinear spectral analysis. This technique is based on the concept of generalized entropy of a given probability distribution, known as the Renyi entropy. This concept allows defining generalized fractal dimension of encephalogram (EEG) and determining fractal spectra of encephalographic signals. These spectra contain information of both frequency and amplitude characteristics of EEG and can be used together with well-accepted techniques of EEG analysis as an enhancement of the latter. Powered by volume visualization of the brain activity, the method provides new clues for understanding the mental processes in humans.

Functionally based virtual computer art

This article describes how virtual embossing and wood cutting can be done using the function representation of a shape and tools. The software is implemented as an interactive shape modeler where a functional model of the shape is subsequently modified with offset and set-theoretic operations. For visualization, interactive ray tracing is used. Bounding boxes together with the spatial organization of the functional model provide the required fast function evaluation that is usually a bottleneck for functionally based shape modeling systems. The software runs on a personal computer.

Functionally based virtual embossing

Embossing is the art of decorating metals in relief from the reverse side. This article describes how virtual embossing can be done using a functionally based representation of the metal plate and the tools. The program is implemented as an interactive shape modeler where a functional model of the metal plate is subsequently modified with offset and set-theoretic operations. For visualization, interactive ray tracing is used. Bounding boxes together with the spatial organization of the functional model provide the required fast function evaluation that is usually a bottleneck for functionally based shape modeling systems. The program runs on a personal computer.