Volume 14 (1995)

Permanent URI for this community

https://diglib.eg.org/handle/10.2312/65

Browse

Now showing 1 - 20 of 59

Line Clipping Using Semi-Homogeneous Coordinates
(Blackwell Science Ltd and the Eurographics Association, 1995) Nielsen, Hans Peter
The dual intersection test is described. It is a new method for deciding whether a line intersects a window. The concept of semi-homogeneous coordinates is introduced. It allows us to define line segments in projective space, and to derive a generalized Cohen-Sutherland end-point test for such segments. When this is combined with the dual intersection test, we obtain new clipping algorithms for 2D and 3D projective space.
Shading with Curve Light Sources1
(Blackwell Science Ltd and the Eurographics Association, 1995) Bao, Hujun; Ying, Jianguo; Peng, Qunsheng
A new shading model for curve light sources is presented. It accounts for both diffuse reflection and specular reflection of the illuminated surface. By regarding a linear light source as a directional quadrilateral light source with very small width, a simple formula is derived first for calculating the diffuse reflection component due to the illumination of the linear segment. The diffuse reflection of the surface by direct illumination of a curve light source is then evaluated by approximating the curve light with a series of linear segments. The specular reflection component due to a curve light source is represented by an integration taking Phong s specular model as the kernel and evaluated by summing the contributions from the linear segments. Finally, an efficient shadow detection algorithm for curve light sources is proposed. The images rendered with the shading model are very photo-realistic.
Collision Detection for Animation using Sphere-Trees
(Blackwell Science Ltd and the Eurographics Association, 1995) Palmer, I. J.; Grimsdale, R. L.
The detection of collisions between moving polyhedral objects is one of the most computationally intensive tasks in the computer animation process. The use of object-oriented techniques to encapsulate data within the objects structures compounds this problem through the requirement for inter-object message passing in order to obtain geometric information for collision detection. The REALISM system decreases the time for collision detection by using a three stage process. The first stage identifies objects in the same locality using a global bounding volume table. The second stage locates regions of possible collision using a sphere-tree data structure (a hierarchical tree of spheres based on octree-type spatial subdivision). The final stage finds intersections between polygonal faces of the objects that are contained within the intersecting pairs of leaf nodes. Hence the algorithm uses a spherical geometry approximation rapidly to locate regions of potential collisions and then uses a local intersection test with actual object geometry information. The system is therefore fast and accurate. Tests for various geometric objects support this and show performance improvements of jive times over traditional polyhedral intersection tests.
3D Interaction with the Desktop Bat
(Blackwell Science Ltd and the Eurographics Association, 1995) Steed, Anthony; Slater, Mel
Many applications now demand interaction with visualizations of 3D scenes and data sets. Current flat 2D displays are limited in their capacity to provide this not only by the display technology but the interaction metaphors and devices used. The Desktop Bat is a device that has 5 degrees of freedom whilst retaining the simplicity of use o fa mouse. To use it for general 3D interaction several metaphors were created for the tasks of navigation and cursor manipulation and a set of experiments were conducted to determine which metaphors were the most efficient in use. Of these metaphors, a velocity control metaphor was the best for navigation and a metaphor that applied rotations and translations relative to the eyepoint coordinate system was best for object control.
Thoughtful Drawings: A Computational Model of the Cognitive Nature of Children s Drawing
(Blackwell Science Ltd and the Eurographics Association, 1995) Burton, Ed
An interpretation of children s drawing is presented that is based on active perception of the world and the construction of an equivalent self contained two-dimensional world. This model is implemented in a computer program called Rose (Representation Of Spatial Experience). Inspired by the drawings of young children, Rose simulates the perception of the general form and structure of three-dimensional computer models and constructs equivalent childlike two-dimensional representations from them. Rose serves to illustrate the plausibility of the constructive process as a model for real children s drawing and in addition serves as an alternative approach to traditional computer graphic rendering.
Object Calibration for Augmented Reality
(Blackwell Science Ltd and the Eurographics Association, 1995) Whitaker, Ross T.; Crampton, Chris; Breen, David E.; Tuceryan, Mihran; Rose, Eric
Augmented reality involves the use of models and their associated renderings to supplement information in a real scene. In order for this information to be relevant or meaningful, the models must be positioned and displayed in such a way that they align with their corresponding real objects. For practical reasons this alignment cannot be known a priori, and cannot be hard-wired into a system. Instead a simple, reliable alignment or calibration process is performed so that computer models can be accurately registered with their real-life counterparts. We describe the design and implementation of such a process and we show how it can be used to create convincing interactions between real and virtual objects.
Function Representation of Solids Reconstructed from Scattered Surface Points and Contours
(Blackwell Science Ltd and the Eurographics Association, 1995) Savchenko, Vladimir V.; Pasko, Alexander A.; Okunev, Oleg G.; Kunii, Tosiyasu L.
This paper presents a novel approach to the reconstruction of geometric models and surfaces from given sets of points using volume splines. It results in the representation of a solid by the inequality f(x,y,z) ? 0. The volume spline is based on use of the Green s function for interpolation of scalar function values of a chosen"carrier" solid. Our algorithm is capable of generating highly concave and branching objects automatically. The particular case where the surface is reconstructed from cross-sections is discussed too. Potential applications of this algorithm are in tomography, image processing, animation and CAD for bodies with complex surfaces.
Fast Shadowing Algorithm for Linear Light Sources
(Blackwell Science Ltd and the Eurographics Association, 1995) Tanaka, Toshimitsu; Takahashi, Tokiichiro
This paper presents a fast shadowing algorithm for linear light sources that uses a ray-oriented buffer. Space segmentation by the buffer guarantees that if a point is included in a subspace, all light rays toward the point are also contained in the subspace. Each cell of the buffer stores a list of objects that lie within or intersect the subspace allocated to the cell. Therefore, candidate objects, those that may cast shadows onto a point, are determined by referring to the cell where the point is mapped. In addition, whether each candidate object actually casts shadows or not is tested with the bounding-volume of the shadow space to reduce the number of objects subjected to expensive light clipping. The bounding-volumes are also stored in the buffer. For efficiently generating the ray-oriented buffer, we present the cylindrical scan-conversion algorithm. The algorithm preconverts objects surfaces to trapezia to decrease the light clipping cost, then connects the trapezia to the buffer cells.Due to the above improvements, our algorithm achieves over 10 times faster shadow generation compared to the conventional methods. Experimental results confirm that our method can generate realistic images with soft shadows in a few minutes.
Optimization of a Priority List Algorithm for 3-D Rendering of Buildings
(Blackwell Science Ltd and the Eurographics Association, 1995) Morer, Paz; Alonso, Alejandro M. Garcia; Flaquer, Juan
Architectural scenes usually have some peculiar properties, like parallel surfaces, symmetry, instantiation, easy clustering, etc. These properties can be used by visualization algorithms in order to improve the solution of the hidden surface removal problem.This paper presents some practical implementation policies for the binary space partition algorithm proposed by Fuchs. They take advantage of the characteristics found in architectural scenes. These suggestions help to minimize both the time needed to build the tree and the memory space used. Five optimization techniques are presented and applied to fourteen architectural scenes.
The Compositing Buffer: A Flexible Method for Image Generation and Image Editing
(Blackwell Science Ltd and the Eurographics Association, 1995) Lau, Wing Hung; Wiseman, Neil
In this paper, we describe a new buffer architecture called the Compositing Buffer. Although it is based on the A-buffer architecture described by Carpenter1, the new architecture introduces two important ideas which make image generation more flexible. The first idea is the storing of bitmask index instead of the bitmask. This allows accurate images to be generated while at the same time, minimising memory usage. The second idea is the introduction of the concept of dynamic object. This allows images to be edited interactively. Applications of the two ideas will also be discussed in the paper.
A Direct Manipulation Interface for 3D Computer Animation
(Blackwell Science Ltd and the Eurographics Association, 1995) Snibbe, Scott Sona
We present a new set of interface techniques for visualizing and editing animation directly in a single three-dimensional scene. Motion is edited using direct-manipulation tools which satisfy high-level goals such as"reach this point at this time" or"go faster at this moment". These tools can be applied over an arbitrary temporal range and maintain arbitrary degrees of spatial and temporal continuity.We separate spatial and temporal control of position by using two curves for each animated object: the motion path which describes the 3D spatial path along which an object travels, and the motion graph, a function describing the distance traveled along this curve over time. Our direct-manipulation tools are implemented using displacement functions, a straightforward and scalable technique for satisfying motion constraints by composition of the displacement function with the motion graph or motion path. This paper will focus on applying displacement functions to positional change. However, the techniques presented are applicable to the animation of orientation, color, or any other attribute that varies over time.
Fair Surface Reconstruction Using Quadratic Functionals
(Blackwell Science Ltd and the Eurographics Association, 1995) Kolb, Andreas; Pottmann, Helmut; Seidel, Hans-Peter
An algorithm for surface reconstruction from a polyhedron with arbitrary topology consisting of triangular faces is presented. The first variant of the algorithm constructs a curve network consisting of cubic Bezier curves meeting with tangent plane continuity at the vertices. This curve network is extended to a smooth surface by replacing each of the networks facets with a split patch consisting of three triangular Bezier patches. The remaining degrees of freedom of the curve network and the split patches are determined by minimizing a quadratic functional. This optimization process works either for the curve network and the split patches separately or in one simultaneous step. The second variant of our algorithm is based on the construction of an optimized curve network with higher continuity. Examples demonstrate the quality of the different methods.
Syntax Channelling and Other Issues affecting Innovation in the Graphical User Interface
(Blackwell Science Ltd and the Eurographics Association, 1995) King, Mike
Does the modern commercial Graphical User Interface constrain the developer of graphics applications into certain interaction styles? This paper looks at the Microsoft Windows environment as an example, with particular reference to the question of interaction modes, screen real-estate and visual appearance. The concept of syntax channelling is introduced to help analyse the problem of modality, and the question of button-down versus button-up dragging is debated in the context of a range of commercial applications, and possible consequences for upper limb disorder. A Windows application developed by the author involving the implementation of a variety of innovative interfacing techniques is presented.
Fractals and Quasi-Affine Transformations
(Blackwell Science Ltd and the Eurographics Association, 1995) Nehlig, P. W.; Reveilles, J.-P.
In the continuum , contracting affine transformations have a unique fixed point. It is well known that this property is not preserved by dicretization and that the dynamics of discretized functions are very complicated. Discrete geometry allows us to start a theory for these dynamics and to illustrate some of their features by pictures. These pictures, rendered by a simple algorithm, reveal a very large spectrum of fractal structures, from the simplest to the intricatest.
Domain Extension of Isothetic Polyhedra with Minimal CSG Representation
(Blackwell Science Ltd and the Eurographics Association, 1995) Arinyo, Robert Juan
We consider the problem of converting boundary representations of isothetic polyhedra into constructive solid geometry (CSG) representations. The CSG representation is a boolean formula based on the half-spaces supporting the faces of the polyhedron. This boolean formula exhibits two important features: no term is complemented (it is monotone) and each supporting half-space appears in the formula once and only once. It is known that such formulas do not always exist for general polyhedra in the three-dimensional space. In this work first we give a procedure that extends the domain of polyhedra for which such a nice representation can be computed. Then we prove that not all cyclic isothetic polyhedra have a CSG representation of the style given above.
Filtering, Clustering and Hierarchy Construction: a New Solution for Ray-Tracing Complex Scenes
(Blackwell Science Ltd and the Eurographics Association, 1995) Cazals, Frederic; Drettakis, George; Puech, Claude
Data structures that handle very complex scenes (hundreds of thousands of objects) have in the past either been laboriously built by hand, or have required the determination of unintuitive parameter values by the user. It is often the case that an incorrect choice of these parameters can result in greedy memory requirements or severely degraded performance. As a remedy to this problem we propose a new data structure which is fully automatic since it does not require the user to determine any input parameters. The structure is built by first filtering the input objects by size, subsequently applying a clustering step to objects of the same size and finally building a hierarchy of uniform grids . We then show that this data structure can be efficiently constructed. The implementation of the shows that the new structure is stable since it s memory requirements grow linearly with the size of the scene, and that it presents a satisfactory compromise between memory usage and computational efficiency. A detailed comparison with previous data structures is also presented in the results.
The MADE Help System
(Blackwell Science Ltd and the Eurographics Association, 1995) Haindl, Michal; de Ruiter, Behr
MADE is the acronym for the ESPRIT project 6307, whose aim is to develop an object oriented multimedia application development environment. As part of this project the MADE help system is designed to be a distributed hypermedia system with additional support for run-time object monitoring and contextual help.
A Real-time Continuous Alphabetic Sign Language to Speech Conversion VR System
(Blackwell Science Ltd and the Eurographics Association, 1995) Liang, Rung-Huei; Ouhyoung, Ming
Many ways of communications are used between human and computer, while using gesture is considered to be one of the most natural way in a virtual reality system. Because of its intuitiveness and its capability of helping the hearing impaired or speaking impaired, we develop a gesture recognition system. Considering the world-wide use of ASL (American Sign Language), this system focuses on the recognition of a continuous flow of alphabets in ASL to spell a word followed by the speech synthesis, and adopts a simple and efficient windowed template matching recognition strategy to achieve the goal of a real-time and continuous recognition. In addition to the abduction and the flex information in a gesture, we introduce a concept of contact-point into our system to solve the intrinsic ambiguities of some gestures in ASL. Five tact switches, served as contact-points and sensed by an analogue to digital board, are sewn on a glove cover to enhance the functions of a traditional data glove.
Interactive Ray Tracing on a Virtual Shared-Memory Parallel Computer
(Blackwell Science Ltd and the Eurographics Association, 1995) Keates, M.J.; Hubbold, R.J.
This paper describes the results of experiments with accelerated ray tracing on a virtual shared-memory parallel computer and attempts to determine whether this kind of architecture would be suitable for an interactive ray tracing system. The machine used, the Kendall Square Research KSR1, is described in sufficient detail for its novel features to be appreciated. The paper describes a new ray tracer written specifically to capitalise on the KSR1 s features. Models used in the experiments include well-known test cases from the Haines database, permitting comparison with previously reported results. The results show that the program scales well up to 230 processors, and that with progressive rendering initial rendering times can be reduced to as little as 0.2 second on 32 processors.
Three Architectures for Volume Rendering
(Blackwell Science Ltd and the Eurographics Association, 1995) Hesser, Jurgen; Manner, Reinhard; Knittel, Gunter; Strasser, Wolfgang; Pfister, Hanspeter; Kaufman, Arie
Volume rendering is a key technique in scientific visualization that lends itself to significant exploitable parallelism. The high computational demands of real-time volume rendering and continued technological advances in the area of VLSl give impetus to the development of special-purpose volume rendering architectures. This paper presents and characterizes three recently developed volume rendering engines which are based on the ray-casting method. A taxonomy of the algorithmic variants of ray-casting and details of each ray-casting architecture are discussed. The paper then compares the machinefeatures and provides an outlook onfuture developments in the area of volume rendering hardware.

Browse

Browsing Volume 14 (1995) by Issue Date

Results Per Page

Sort Options