bluuebunny/crossref_metadata_2025_split huggingface dataset:
Form Factor Calculation: a New Expression with Implementations on a Parallel T.Node Computer
Authors: Michelin Sylvain , Maffeis Gualtiero , Arquès Didier , Grossetie Jean Claude 
Published: March 2003

AbstractThe radiosity technique uses the heat transfer theory to define a view‐independent illumination model. For complex scenes, calculation of this model is very time‐intensive, due largely to the determination of a geometric factor, defined with a double area integral, and named form factor. This paper presents a new expression of the form factor, which can be reformulated, in a computationally more efficient manner, as a simple line integral for planar polygonal convex surfaces that are perfectly diffuse.Recently, parallel computers have been used to decrease calculation time. Previous work is focused mainly on distributed implementations of a method, the progressive refinement method, widely used for complex environments. The T.Node is a completely reconfigurable MIMD machine, based on the transputer chip. In this paper, we compare a parallel implementation of the progressive refinement method with a direct method which takes into account the memory capabilities of this kind of machine.
Variational Surface Design and Surface Interrogation
Authors: Hagen H. , Hahmann St. , Bonneau G.‐P. 
Published: March 2003

AbstractThe generation of technical smooth surfaces from a mesh of three‐dimensional data points is an important problem in geometric modelling. In this publication we give a survey of some new techniques based on a calculus of variation approach. Apart from the pure construction of these surfaces, the analysis of their quality is equally important in the design and manufacturing process. Generalized focal surfaces are presented here as a new surface interrogation tool.
Quality Control of an Interpolation Method for Discontinuous Parametric Surfaces
Authors: Seron F.J. , Torrens J.J , Magallon J.A. 
Published: March 2003

AbstractIn this paper we study a finite element interpolation method for fitting discontinuous parametric surfaces when the data points are the nodes of a curvilinear grid. Quality control of the interpolating surfaces is also considered, focussing on the display of isophotes and reflection lines using ray tracing techniques. Finally, graphical and numerical examples are given.
A Prototype of a Cooperative Visualization Workplace for the Aerodynamicist
Authors: Pagendarm H.‐G. , Walter B. 
Published: March 2003

AbstractSeveral feasibility studies for cooperative visualization were performed based on an existing modular visualization system. Two different architectures for the implementation of a cooperative system were identified, implemented and tested.One architectural model, the broadcast model, assumes either one single visualization system running on a central facility driving multiple displays or in case of cooperative work it assumes that each visualization module drives multiple displays.The second model, the synchronized visualization systems, features distributed visualization tools with synchronization mechanisms. The synchronization ensures that all partners create identical images from identical data. This model requires special control features to avoid conflicts created by user‐interaction.Both architectures are complete by adding bi‐directional video connection and audio communication over the network plus offering remote cursor functionality.Two prototype implementations were produced to compare the two architectures and to evaluate the feasibility of cooperative visualization on existing hardware. Because of the poor access to wide‐area networks, the prototypes were tested in a local area network. Visualization protocols, data communication, video and audio ran on a standard Ethernet based on TCP/IP communications. The tests were done using typical data from aerodynamics or numerical flow simulations.In spite of the limits due to low network bandwidth and slow performance of some hardware components the second architecture using the synchronized systems seems to be useful and feasible even under today's circumstances. There are no additional features identified which would be needed to run the cooperative visualization on a wide area network but a higher network throughput would be required.
The Determination of Form‐Factors by Lookup Table
Authors: Sun Jizhou , Zou L.Q. , Grimsdale R.L. 
Published: March 2003

AbstractCurrent methods for computer image synthesis using the radiosity algorithm rely heavily on the calculation of geometrical properties, known as form‐factors, which quantify the energy exchange between pairs of surfaces in the environment. In this paper, a new method for form‐factor calculation is presented, in which form‐factors from a differential area to a finite area with various geometric orientations and dimensions can be determined by the summation of three weighted directional form‐factors. The three directional form‐factors are mutually independent and can be pre‐calculated and stored in a lookup table accessed by two indices. Thus, the determination of the generally used complex form‐factor integral is greatly simplified and mainly replaced by accessing a pre‐established lookup table. Quantitative comparisons of Wallace's ray casting method and the method presented indicate that the new method can provide more accurate form‐factors, which implies that the number of sample points necessary on each source patch is comparatively reduced and the process of form‐factor calculation can be accelerated.
Ray Tracing an Octree: Numerical Evaluation of the First Intersection
Authors: Gargantini I. , Atkinson H. H. 
Published: March 2003

AbstractAn algorithm is presented which finds the first intersection of a directed semi‐infinite straight‐line (called ray) with an octree, without resorting to the evaluation of neighbouring nodes. Given a pointer‐based region octree, intersections of the ray with a node's bisecting planes are first evaluated to determine in which sub‐octants the ray‐node intersections may lie; a local ordering then determines the sequence in which these sub‐octants should be examined so that the intersection closest to the ray's origin can be selected.This idea is applied recursively starting from the root of the octree; the novelty of the approach consists of the fact that the choice of each node's child in the octree is directly derived from the intersection of the ray‐segment within the tested sub‐octant, thus avoiding searching for any neighbouring nodes. The problem of selecting the correct octant while using the commonly available floating‐point arithmetic is also addressed in a ray tracing environment. Comparisons of this approach with the method given by Samet17 are carried out in a variety of cases involving millions of voxels. The improvement ranged from 32% to 62% in terms of execution time.
ANIMA: An Interactive Tool for Scientific Data Animation
Authors: Moltedo Laura , Morigi Serena 
Published: March 2003

AbstractThis paper describes an animation interactive system that produces image sequences used to study the numerical results of scientific simulations. The fundamental goal of the system is to provide an easy method for observing and exploring scientific computation during its space‐time evolution. To do that it is necessary to combine simulation processes, algorithmic and key frame animation with geometric transformations, light effects and camera movements. ANIMA allows the researcher to use animation without special programming, with the aid of a graphic user interface. Modelling, rendering, motion control and synchronization of graphic objects are interactively specified by the animator in order to define an animation script. The system development methodology follows an object‐oriented technique using modular programming, abstract data type definition, and graphic metaphor with user interface menus.
Graphic Objects: A Mathematical Abstract Model for Computer Graphics
Authors: Torres J.C. , Clares B. 
Published: March 2003

AbstractThis paper defines an abstract mathematical model for graphic systems which incorporates modelling operations. The model is based on the “graphic object” concept. A graphic object is an abstraction of a graphic entity. Graphic objects are a generalization of the Fiume graphic object concept, supporting modelling operations, which give the set of graphic objects an algebraic structure of vector space and booelan algebra. Fiume visualization formalism can be applied to graphic objects. Further, product operations of graphic objects are defined, which are a generalization of solid sweep operations. Graphic object products may be used to build common 2D and 3D objects such as triangles, squares, cubes, circles and spheres from lines and arcs.
Controllable Locality in C2 Interpolating Curves by B2‐splines / S‐splines
Authors: Kuroda Mitsuru , Furukawa Susumu , Kimura Fumihiko 
Published: March 2003

AbstractThis paper presents a systematic scheme for controlling the local behaviour of C2 interpolating curves, based on the cubic B2‐splines and the quartic S‐splines. Both splines have an additional control point obtained by knot‐ insertion or degree‐elevation in each span of the conventional uniform cubic interpolating B‐splines. The shape designer can choose the desired range of locality for each span and get the corresponding additional control point as a barycentric combination of interpolation points within the range, without solving any variational problem and simultaneous equations. The scheme is consistent over the entire curve subject to some typical end conditions. The class of the curves derived includes the conventional cubic interpolating B‐splines. Examples demonstrate the behaviour of the new interpolating curves and the capability of the scheme.
Five‐dimensional Adaptive Subdivision for Ray Tracing
Authors: Simiakakis G. , Day A. M. 
Published: March 2003

AbstractThis paper presents a directional subdivision method for speeding up ray tracing. This method is easy to use, because it automatically adapts the subdivision to the scene relieving the user from having to set parameters for the subdivision. It also attempts a balance between 5D and spatial subdivision in order to benefit from both methods. A memory saving scheme is introduced and experimental results are presented.
Constant‐Time Filtering by Singular Value Decomposition†
Authors: Gotsman Craig 
Published: March 2003

AbstractWe present a technique implementing space‐variant filtering of an image, with kernels belonging to a given family, in time independent of the size and shape of the filter kernel support. The essence of our method is efficient approximation of these kernels, belonging to an infinite family governed by a small number of parameters, as a linear combination of a small number k of “basis” kernels. The accuracy of this approximation increases with k, and requires O(k) storage space. Any kernel in the family may be applied to the image in O(k) time using precomputed results of the application of the basis kernels. Performing linear combinations of these values with appropriate coefficients yields the desired result. A trade off between algorithm efficiency and approximation quality is obtained by adjusting k.The basis kernels are computed using singular value decomposition, distinguishing this from previous techniques designed to achieve a similar effect. We illustrate by applying our methods to the family of elliptic Gaussian kernels, a popular choice for filtering warped images.
COMPUTER GRAPHICS AND REMOTE SENSING – A SYNTHESIS FOR ENVIRONMENTAL PLANNING AND CIVIL ENGINEERING
Authors: Graf K.Ch. , Suter M. , Hagger J. , Nüesch D. 
Published: March 2003

AbstractThis paper presents efforts undertaken in the field of photo‐realistic visualization of natural landscapes using digital elevation models (DEM) and images generated by remote sensing techniques. The remote sensing systems used in this work include Landsat Thematic Mapper, SPOT HRV and aerial photographs. After an appropriate preprocessing, including radiometric corrections and image enhancement procedures, a precise geometric correction is performed in order to achieve a very high co‐registration of the images with the elevation model. A mosaic of several images at various resolutions is stored together with the DEM in a data set covering an extensive area. These data are then input to an efficient hardware‐independent terrain rendering algorithm based on a forward projection. Atmospheric effects can be simulated. The concept of a virtual scene allows an automated embedding of raytraced 3D objects. The results show that these methods can be used in the field of environmental planning, civil engineering and other applications where terrain visualization is required.
Solid Modeling Based on a New Paradigm
Authors: Yoshida Norimasa , Shiokawa Masato , Yamaguchi Fujio 
Published: March 2003

AbstractThe technique of solid modeling is essential in CAD/CAM applications, and is currently well established. However, problems remain, such as the lack of uniformity in geometric computations and the lack of stability of Boolean operations of two solids. In this paper, we introduce a theoretical solid modeling system that operates on boundary representations of polyhedral objects and is based on a new paradigm. The characteristics of the system are the following: (I) in Boolean Operations and modeling transformations, all geometric computations are performed by the 4 × 4 determinant method or the 4 × 4 matrix method in homogeneous space, which allows the system to avoid division operations, (2) all geometric computations are performed by the exact integer arithmetic, which makes the geometric algorithms stable and simple, and (3) primitive solids are constructed consistently in the integer domain, and the consistency is assured throughout Boolean operations and transformations.
Chebyshev Polynomials for Boxing and Intersections of Parametric Curves and Surfaces
Authors: Fournier Alain , Buchanan John 
Published: March 2003

AbstractParametric curves and surfaces are powerful and popular modelling tools in Computer Graphics and Computer Aided Design. Ray‐tracing is a versatile and popular rendering technique. There is therefore a strong incentive in developing fast, accurate and reliable algorithms to intersect rays and parametric curves and surfaces.We propose and demonstrate the use of Chebyshev basis functions to speed up the computation of the intersections between rays and parametric curves or surfaces. The properties of Chebyshev polynomials result in the computation of better and tighter enclosing boxes. For surfaces they provide a better termination criterion to decide on the limits of subdivision, and allow the use of bilinear surfaces for the computation of the intersection when needed.The efficiency of the techniques used depends on the relative magnitude of the coefficients of the Chebyshev basis functions. We show from a statistical analysis of the characteristics of several thousands surfaces of different origin that these techniques will result most of the time in significant improvement in speed and accuracy over other other boxing and subdivision techniques.
Parallel ray tracing based upon a multilevel topological knowledge acquisition of the scene
Authors: RIS Philippe , ARQUÈS Didier 
Published: March 2003

AbstractIncluding the standard parallelization by grouping primary rays, this paper presents a new parallel ray‐timing method based upon a topological knowledge acquisition of the scene. This topological knowledge focuses on relative positions between objects and processes and uses a new type of message. Indeed, instead of exchanging database pages or rays, processes exchange topological information. This information is used by each process to decrease its own list of objects to test against rays The acquisition of information about relative positions between objects and processes is obtained by a careful ordering of he pixel calculation. The processes are dispatched on a computer network including a parallel computer The organization of the processes on this network is a multilevel one leading to different levels of topological message exchanges This method is characterized by topological messages describing the scene, dynamic optimization of the database, easy parallelization on any network (no deadlock, fault tolerance, easily expandable and simple routing), and gives interesting results with true or simulated parallelism.
Triangulating multiply‐connected polygons: A simple, yet efficient algorithm.
Authors: Ronfard Remi P. , Rossignac Jarek R. 
Published: March 2003

AbstractWe present a new, simple, yet efficient algorithm for triangulating multiply‐connected polygons. The algorithm requires sorting only local concave minima (sags). The order in which triangles are created mimics a flooding process of the interior of the polygon. At each stage, the algorithm analyses the positions and neighborhoods of two vertices only, and possibly checks for active sags, so as to determine which of five possible actions to take. Actions are based on a local decomposition of the polygon into monotonic regions, or gorges (raise the water level in the current gorge, spill into an adjacent gorge, jump to the other bank of a filled gorge, divide a gorge into two, and fill a gorge to its top). The implementation is extremely simple and numerically robust for a large class of polygons. It has been tested on millions of cases as a preprocessing step of a walkthrough and inspection program for complex mechanical and architectural scenes. Extensive experimental results indicate that the observed complexity in terms of the number of vertices, remains under in all cases.
Raycasting of Nonregularly Structured Volume Data
Authors: Frühauf Thomas 
Published: March 2003

AbstractRaycasting is an efficient, but computation‐intensive technique for the direct rendering of volumetric data. Nonregularly structured volume data is produced in a variety of applications, such as numerical simulation, ultrasonic inspection, or seismic measurement. Unfortunately, in raycasting nonregulary structured grids, sampling data along the rays is even more computation‐intensive. One idea might be to resample the data onto a regular grid for further processing. It is shown, that resampling typical grids results either in extreme sub‐ sampling of the most interesting areas or in data sets too huge to handle. Additionally, no better hardware will overcome the fact that all topology and context information is lost through resampling. Therefore, dedicated algorithms for the raycasting of nonregularly structured volumes are required.We present a new approach for this task, which is based on sending rays through the computational space of a nonregular grid, instead of conventionally raycasting the physical space. This technique overcomes the difficulties in sampling data along the rays, since the computational space is regular by definition. The paper outlines the mathematical operations of this technique as well as its embedding in a rendering algorithm. We have implemented the new raycasting strategy as a module of our interactive visualization system, providing the users with an additional tool for the efficient exploration of their data.
Visualization of Regular Polytopes in Three and Four Dimensions
Authors: Hausmann Barbara , Seidel Hans‐Peter 
Published: March 2003

AbstractNontrivial regular polytopes only exist in three and four dimensions. This paper describes a software package that allows to interactively visualize and analyze these regular polytopes. The following four tools are available: Display of the Schlegel diagrams, perspective projections with the possibility of interactively rotating the polytope in three‐/four‐dimensional space before projection, interactive slicing along various directions, cut‐throughs and fold‐downs. Various examples illustrate the approach.
An Integrated Line Tracking and Vectorization Algorithm
Authors: van Nieuwenhuizen Peter R. , Kiewiet Olaf , Bronsvoort Willem F. 
Published: March 2003

AbstractA method is presented to compute a vector representation of an arbitrary line in a bi‐level raster image The line may have varying line width and irregular borders. Furthermore, at line crossings and branches the user is offered the opportunity to choose from the directions in which line tracking may he continued The method avoids thinning and vectorization of chain codes. Instead, a contour follower is used at both sides of the line, and median line calculation is integrated with contour following. This leads to an efficient algorithm, in particular when individual lines have to be interactively extracted from a raster image.
A Median Cut Algorithm for Efficient Sampling of Radiosity Functions
Authors: Feda Martin , Purgathofer Werner 
Published: March 2003

AbstractThis paper presents an efficient method for sampling the illumination functions in higher order radiosity algorithms. In such algorithms, the illumination function is not assumed to be constant across each patch, but it is approximated by a function which is at least C1 continuous. Our median cut sampling algorithm is inspired by the observation that many form factors are computed at higher precision than is necessary. While a high sampling rate is necessary in regions of high illumination, dark areas can be sampled at a much lower rate to compute the received radiosity within a given precision. We adaptively subdivide the emitter into regions of approximately equal influence on the result. Form factors are evaluated by the disk approximation and a ray tracing based test for occlusion detection. The implementation of a higher order radiosity system using B‐splines as radiosity function is described. The median cut algorithm can also be used for radiosity algorithms based on the constant radiosity assumption.
Reducing The Latency In Head‐Mounted Displays By A Novel Prediction Method Using Grey System Theory
Authors: Wu Jiann‐Rong , Ouhyoung Ming 
Published: March 2003

AbstractIn this paper we propose a novel prediction method for the head motion using Grey System theory, where a 6D tracker is attached to an HMD on a user's head in virtual reality applications. Our prediction method using Grey System Model can greatly reduce the latency by at least one half and reduce image jittering. A system latency below 100 ms or even 50 ins can be achieved, even though without prediction the latency is around 200 ms. Using 6 points in prediction with Grey System Model is currently the best in tracker prediction as we tried from 2 points to 10 points.In order to measure the latency, we also propose a way to measure it in an HMD system precisely and conveniently. During the process, we have implemented four different prototypes respectively on a PC486, a SUN SparcStation10, an SGI IndigoR4000, and a high performance computer image generator. The computation complexity of our prediction method is relatively low and therefore real time requirement is easily met.