Showing papers in "The Visual Computer in 1996"
TL;DR: These uncertainty visualization techniques present data in such a manner that users are made aware of the locations and degree of uncertainties in their data so as to make more informed analyses and decisions.
Abstract: Visualized data often have dubious origins and quality. Different forms of uncertainty and errors are also introduced as the data are derived, transformed, interpolated, and finally rendered. In the absence of integrated presentation of data and uncertainty, the analysis of the visualization is incomplete at best and often leads to inaccurate or incorrect conclusions. This paper surveys techniques for presenting data together with uncertainty. These uncertainty visualization techniques present data in such a manner that users are made aware of the locations and degree of uncertainties in their data so as to make more informed analyses and decisions. The techniques include adding glyphs, adding geometry, modifying geometry, modifying attributes, animation, sonification, and psycho-visual approaches. We present our results in uncertainty visualization for environmental visualization, surface interpolation, global illumination with radiosity, flow visualization, and figure animation. We also present a classification of the possibilities in uncertainty visualization, and locate our contributions within this classification.
623 citations
TL;DR: Sphere tracing is a new technique for rendering implicit surfaces that uses geometric distance and is an efficient direct visualization system for the design and investigation of new implicit models.
Abstract: Sphere tracing is a new technique for rendering implicit surfaces that uses geometric distance. Sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. It is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems where the derivative jumps or vanishes. It is an efficient direct visualization system for the design and investigation of new implicit models. Sphere tracing efficiently approximates cone tracing, supporting symbolic-prefiltered antialiasing. Signed distance functions for a variety of primitives and operations are derived.
483 citations
TL;DR: It is shown that any set of points in the plane has a Hamiltonian triangulation, and it is proved that certain nondegenerate point sets do not admit asequential triangulations.
Abstract: High-performance rendering engines are often pipelined; their speed is bounded by the rate at which triangulation data can be sent into the machine. An ordering such that consecutive triangles share a face, which reduces the data rate, exists if and only if the dual graph of the triangulation contains a Hamiltonian path. We (1) show thatany set ofn points in the plane has a Hamiltonian triangulation; (2) prove that certain nondegenerate point sets do not admit asequential triangulation; (3) test whether a polygonP has a Hamiltonian triangulation in time linear in the size of its visibility graph; and (4) show how to add Steiner points to a triangulation to create Hamiltonian triangulations that avoid narrow angles.
125 citations
TL;DR: An algorithm is presented that constructs compact and realistic descriptions of colored 3D objects using texture mapping on compressed triangulations of arbitrary topology and shows that high compression rates can be achieved while maintaining good visual similarity between the original and compressed models.
Abstract: We present an algorithm that constructs compact and realistic descriptions of colored 3D objects using texture mapping on compressed triangulations. A high-resolution triangular mesh model is created by integrating measurements from a color 3D laser sensor. Each vertex is attributed with a RGB color value. The high-resolution triangulation is transformed into a compressed triangulation and a texture map. This map embeds the color information of the vertices removed during the geometric compression and projected on the lower resolution triangulation. We describe the algorithm for the rapid and efficient construction of a texture map for compressed triangulations of arbitrary topology. Experiments show that high compression rates can be achieved while maintaining good visual similarity between the original and compressed models.
116 citations
TL;DR: This paper provides a critical survey of multiresolution terrain models, describing and discussing models proposed in the literature and construction algorithms for all such models together with an analysis of their time and space complexities.
Abstract: Multiresolution terrain models describe a topographic surface at various levels of resolution. Besides providing a data compression mechanism for dense topographic data, such models enable us to analyze and visualize surfaces at a variable resolution. This paper provides a critical survey of multiresolution terrain models. Formal definitions of hierarchical and pyramidal models are presented. Multiresolution models proposed in the literature (namely, surface quadtree, restricted quadtree, quaternary triangulation, ternary triangulation, adaptive hierarchical triangulation, hierarchical Delaunay triangulation, and Delaunay pyramid) are described and discussed within such frameworks. Construction algorithms for all such models are given, together with an analysis of their time and space complexities.
105 citations
TL;DR: A new algorithm for radiosity is presented, which is linear both in time and storage with the number of patches in a given scene; that is, theNumber of patches is increased by dividing each existing patch into smaller patches.
Abstract: We present a new algorithm for radiosity, which is linear both in time and storage with the number of patches in a given scene; that is, the number of patches is increased by dividing each existing patch into smaller patches. The new algorithm is based on Integral Geometry and on the well-known algorithms for Monte Carlo particle transport. It considers the scene embedded in a field of lines, each representing the exchange between the pairs of points that result from the intersections of the line with the scene. For a given pair of points, this exchange is bidirectional. Lines are taken randomly. Both graphical and numerical results are given for the proposed algorithm, which is compared with a local Monte Carlo particle transport algorithm.
40 citations
TL;DR: A new collision and self-collision avoidance method is proposed to prevent penetration between the cloth and rigid objects and between parts of the cloth.
Abstract: For cloth modeling and animation, we use a physically based model to simulate the dynamic formation of folds, pleats, and wrinkles and the final static appearance of cloth draped over a rigid object. To simulate the behavior of the cloth and its final static appearance on the model, we propose a new collision and self-collision avoidance method to prevent penetration between the cloth and rigid objects and between parts of the cloth. At each time step, we enforce constraints over those grid points about to penetrate other objects. Our method is easier and more robust than conventional methods at representing interaction between the cloth and various objects.
40 citations
TL;DR: A method for curvature-continuous (G2) interpolation of an arbitrary sequence of points on a surface (implicit or parametric) with prescribed tangent and geodesic curvature at every point is introduced.
Abstract: We introduce a method for curvature-continuous (G2) interpolation of an arbitrary sequence of points on a surface (implicit or parametric) with prescribed tangent and geodesic curvature at every point. The method can also be used forG2 blending of curves on surfaces. The interpolation/blending curve is the intersection curve of the given surface with a functional spline (implicit) surface. For the construction of blending curves, we derive the necessary formulas for the curvature of the surfaces. The intermediate results areG2 interpolation/blending methods in IR2.
38 citations
TL;DR: A new motion-blur algorithm that works in three dimensions on a per object basis that operates in real time even for complex objects consisting of several thousand polygons is introduced.
Abstract: Motion blurring of fast-moving objects is highly desirable for virtual environments and 3D user interfaces. However, all currently known algorithms for generating motion blur are too slow for inclusion in interactive 3D applications. We introduce a new motion-blur algorithm that works in three dimensions on a per object basis. The algorithm operates in real time even for complex objects consisting of several thousand polygons. While it only approximates true motion blur, the generated results are smooth and visually consistent. We achieve this performance break-through by taking advantage of hardware-assisted rendering of semitransparent polygons, a feature commonly available in today's workstations.
37 citations
TL;DR: An algorithm is presented that uses a block matching technique to guide the endpoints of the snake, optical flow to push the snake in the direction of the underlying motion, followed by the traditional snake edge-fitting minimization process for tracking facial features of an actor for driving computer animated characters.
Abstract: Active contour models, or “snakes,” developed in (Kass et al. 1988), use a simple physical model to track edges in image sequences. Snakes as originally defined however, tend to shrink, stretch and slide back and forth in unwanted ways along a tracked edge and are also confused by multiple edges, always grabbing the nearest one. In this paper a semi-automatic system is presented that combines motion estimation techniques with snakes to overcome these problems. An algorithm is presented that uses a block matching technique to guide the endpoints of the snake, optical flow to push the snake in the direction of the underlying motion, followed by the traditional snake edge-fitting minimization process. We use this technique for tracking facial features of an actor for driving computer animated characters.
35 citations
TL;DR: Experimental results show that a volume rendering program with the new approach to analytic isosurface rendering is very efficient and maintains the quality of the rendered images.
Abstract: We present a new approach, analytic isosurface rendering, for volume rendering. The isosurface of a cell can be modeled as an analytic function, and the intersection between a ray and the isosurface can be computed directly. An octree structure efficiently searches the cells containing isosurfaces. The octree is easy to implement and can be stored in a compact form. It needs extra memory space - at most 27/64 of the size of the original data volume. Front-to-back projection can easily be implemented under the octree structure. A union-find-based algorithm maintains the frame buffer efficiently. Experimental results show that a volume rendering program with our approach is very efficient and maintains the quality of the rendered images.
TL;DR: This paper is focused on the analysis of the intersection between the air-flow field around a piece of cloth and the motion of the cloth in order to animate realistically the cloth motion in the air flow.
Abstract: This paper is focused on the analysis of the intersection between the air-flow field around a piece of cloth and the motion of the cloth in order to animate realistically the cloth motion in the air flow. Two force models, based on aerodynamic theory, have been established to calculate the force distribution of the air flow on a cloth surface. The quasi-steady force model deals with the cases in which the free stream velocity of the relative air flow changes slightly or slowly, whereas the unsteady force model deals with unsteady air flows. The resulting force distributions are coupled with a cloth-deformation model based on structural dynamics to compute the displacement and deformation of cloth under these forces. This solution cycle is repeated and the time histories of the cloth motion can be obtained which form the basis of the computer animation of cloth motion in air flow. Animation results of the movement of a piece of curtain in free air under various air flow conditions are presented to compare the performances of the two force models.
TL;DR: This new model is intended as an improvement to the original one on three main points: first, it involves lower computation cost and provides better numerical robustness; second, it offers higher order continuities (C1/G1 orC2/G2 instead ofC0/G0); and third, it provides a greater variety of shapes for the resulting curves and surfaces.
Abstract: This paper presents a new family of 2D curves and its extension to 3D surfaces, respectively, calledrationconics andratioquadrics that have been designed as alternatives to the well-known superconics and superquadrics. This new model is intended as an improvement to the original one on three main points: first, it involves lower computation cost and provides better numerical robustness; second, it offers higher order continuities (C1/G2 orC2/G2 instead ofC0/G0); and third, it provides a greater variety of shapes for the resulting curves and surfaces. All these improvements are obtained by replacing the signed power function involved in the formulation of superconics and superquadrics by linear or quadratic rational polynomials.
TL;DR: A method for ray tracing recursive objects defined by parametric rewriting systems using constructive solid geometry (CSG) as the underlying method of object representation is introduced, which translates the systems into cyclic CSG graphs, which can be used directly as an object representation forray tracing.
Abstract: A method for ray tracing recursive objects defined by parametric rewriting systems using constructive solid geometry (CSG) as the underlying method of object representation is introduced. Thus, the formal languages of our rewriting systems are subsets of the infinite set of CSG expressions. Instead of deriving such expressions to build up large CSG trees, we translate the systems into cyclic CSG graphs, which can be used directly as an object representation for ray tracing. For this purpose the CSG concept is extended by three new nodes. Selection nodes join all the rules for one grammar symbol, control flow by selecting proper rules, and are end-points of cyclic edges. Transformation nodes map the rays in affine space. Calculation nodes evaluate a finite set of arithmetic expressions to modify global parameters, which effect flow control and transformations. The CSG graphs introduced here are a very compact data structure, much like the describing data set. This property meets our intention to avoid both restrictions of the complexity of the scenes by computer memory and the approximation accuracy of objects.
TL;DR: For applications in which strict parametric continuities cannot be compromised, LSB provides an intuitive way to introduce tension to the B-spline.
Abstract: A linear singular blending (LSB) technique can enhance the shape—control capability of the B-spline. This capability is derived from the blending parameters defined at the B-spline control vertices and blends LSB line segments or bilinear surface patches with the B-spline curve or surface. Varying the blending parameters between zero and unity applies tension for reshaping. The reshaped curve or surface retains the same smoothness properties as the original B-spline; it possesses the same strict parametric continuities. This is different from the β-spline, which introduces additional control to the B-spline by imposing geometrical continuities to the joints of curve segments or surface patches. For applications in which strict parametric continuities cannot be compromised, LSB provides an intuitive way to introduce tension to the B-spline.
TL;DR: A simple and efficient general algorithm for determining both rotational and involutional symmetries of polyhedra and it is shown that a slight modification of the symmetry detection algorithm can be used to solve the related conguity problem ofpolyhedra.
Abstract: We propose a simple and efficient general algorithm for determining both rotational and involutional symmetries of polyhedra. It requiresO(m
2) time and usesO(m) space, wherem is the number of edges of the polyhedron. As this is the lower bound of the symmetry detection problem for the considered output form, our algorithm is optimal. We show that a slight modification of our symmetry detection algorithm can be used to solve the related conguity problem of polyhedra.
TL;DR: A new parallel ray-tracing hardware architecture in which processors are connected as a ring, which is especially suitable for synthesizing animated sequences because objects need not be reallocated for every frame.
Abstract: We propose a new parallel ray-tracing hardware architecture in which processors are connected as a ring. Most parallel ray-tracing algorithms subdivide the whole object space into subregions; A processor handles only rays entering the subregion assigned to it. Here we assign each processor objects that are spread over the whole object space. The processors trace rays on their own objects. The respective partial results are combined to form the final image. This scheme is especially suitable for synthesizing animated sequences because objects need not be reallocated for every frame. Preliminary results show a speed-up factor almost linearly proportional to the number of processors.
TL;DR: Experimental results show that line diffusion is comparable to error diffusion in image quality, and a sequential line diffusion algorithm is provided.
Abstract: Floyd and Steinberg's (1976) error diffusion technique is a well-known approach to digital halftoning. The main drawback of this technique is that it is inherently serial. This paper presents a new parallelizable error-diffusion algorithm, calledline diffusion. In this method, the pixels of the original image are divided into classes line by line, and all the pixels on a line are halftoned simultaneously. Errors are distributed randomly. Experimental results show that line diffusion is comparable to error diffusion in image quality. A sequential line diffusion algorithm is also provided.
TL;DR: A new approach for reducing the number of triangles representing an isosurface in volumetric data is presented, to classify the configurations of the marching cubes approach into types.
Abstract: A new approach for reducing the number of triangles representing an isosurface in volumetric data is presented. The basic idea is to classify the configurations of the marching cubes approach into types. Surface patches traversing neighboring cubes of the same type can be merged into patches, which can be approximated with fewer and larger triangles. Experimental results show that the number of triangles is about 50% of that obtained with the marching cubes algorithm, with comparable image quality. The execution time is somewhat longer than that of the marching cubes algorithm.
TL;DR: A Monte Carlo approach for Galerkin radiosity to compute the coefficients of the basis functions is presented, which eliminates the problems with edge singularities between adjacent surfaces, the time complexity is reduced, and ideally specular energy transport can be simulated.
Abstract: Galerkin radiosity solves the integral rendering equation by projecting the illumination functions into a set of higher-order basis functions. This paper presents a Monte Carlo approach for Galerkin radiosity to compute the coefficients of the basis functions. The new approach eliminates the problems with edge singularities between adjacent surfaces present in conventional Galerkin radiosity, the time complexity is reduced fromO(K4) toO(K2) for aK-order basis, and ideally specular energy transport can be simulated. As in conventional Galerkin radiosity, no meshing is required even for large or curved surfaces, thus reducing memory requirements, and no a posteriori Gouraud interpolation is necessary. The new algorithm is simple and can be parallelized on any parallel computer, including massively parallel systems.
TL;DR: This paper developed an efficient algorithm for constructing adjacency graphs of 3D finite element analysis (FEA) data by establishing intermediate data structures and using bin-sorting, which is linear in the number of data cells.
Abstract: In this paper, we present an algorithm for constructing adjacency graphs of 3D finite element analysis (FEA) data Adjacency graphs are created to represent the connectivities of FEA data cells They are used in most visualization methods for FEA data We stress that in many engineering applications FEA data sets do not contain the adjacency information This is opposite to computer-aided geometric design where, eg, the winged edge geometrical representation is usually generated and utilized By establishing intermediate data structures and using bin-sorting, we developed an efficient algorithm for constructing such graphs The total time complexity of the algorithm is linear in the number of data cells
TL;DR: A unity-bounded deformation function is introduced to replace the argument of the sinusoidal functions to provide an intuitive way to deform periodic surfaces.
Abstract: In this paper sinusoidal functions are introduced to blend several contour curves to produce periodic sweep surfaces. As the basic sinusoidal functions only produce uniform periodic shapes, we introduce a unity-bounded deformation function to replace the argument of the sinusoidal functions. The deformation function provides an intuitive way to deform periodic surfaces. The technique requires only a single function to control multiple contours. The simple and intuitive control provided by the deformation function encourages users to explore alternative aesthetic designs. Variation in natural objects, such as flowers and fruits, can easily be modeled via small and random variations of the deformation function.
TL;DR: A procedure is developed that decides for given rectangle and triangle whether the triangle is contained in the rectangle, the rectangle iscontained in the triangle, the two figures overlap or whether they are disjoint.
Abstract: A procedure is developed that decides for given rectangle and triangle whether the triangle is contained in the rectangle, the rectangle is contained in the triangle, the two figures overlap or whether they are disjoint. The procedure uses interval barycentric coordinates, which allow a very transparent description of the test, as well as concise proof of correctness and completeness. The numerical execution needs only a few interval and non-interval arithmetic operations. Representative numerical examples are given for some of the cases. Contrasting this interval approach, a direct approach is considered that requires fewer arithmetic and logical operations. The direct approach has the disadvantage of being logically involved, resulting in a large number of cases that must be distinguished, while being computationally less expensive.
TL;DR: This paper replaces the conventional bounding box with a homogeneous boundingbox, which is projectively defined, and proposes a new rough check algorithm based on it.
Abstract: In the divide-and-conquer algorithm for detecting intersections of parametric rational Bezier curves (surfaces), we use bounding boxes in recursive rough checks. In this paper, we replace the conventional bounding box with a homogeneous bounding box, which is projectively defined. We propose a new rough check algorithm based on it. One characteristic of the homogeneous bounding box is that it contains a rational Bezier curve (surface) with weights of mixed signs. This replacement of the conventional bounding box by the homogeneous one does not increase the computation time.
TL;DR: The object-naming mechanism described here supports the automatic generation of parameter-independent object references in parametric programs, which are produced via user interaction during the construction of parametric objects.
Abstract: We present the handling of graphical objects in a programming-by-example, CAD system. The object-naming mechanism described here supports the automatic generation of parameter-independent object references in parametric programs. These programs are produced via user interaction during the construction of parametric objects. We use standard programming language control structures and modularity for the parametrisation of variants, repetitive similarities and flexible hierarchical object structure. The object management of parametric entities with varying topology ensures the correctness of their instantiating parametric programs for large domains of parameter values.
TL;DR: The proposed method achieves a smooth transformation between two given polygonal shapes and ensures that the shape does not collide with any obstacle during the transformation.
Abstract: We present a method for transforming shapes in a plane. The primary strength of the proposed method is that it can handle scenes containing moving obstacles. We attain a smooth transformation between two given polygonal shapes and ensure that the shape does not collide with any obstacle during the transformation. We minimize a cost function associated with each transformation path that controls its length, smoothness, and collision freedom. Then a population of tentative transformation paths is generated by path planning for an anchor point in the shape. Next, collision detection and shape deformation techniques, applied to keyframes along the paths, minimize the occurrence of collision. Lastly, a genetic algorithm refines the population of transformation paths.
TL;DR: 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.
Abstract: 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.
TL;DR: The approach contains basic methodology developed for any parallel or distributed system, and can be adapted for producing an approximate solution when the shortest path is approximated by polygonal lines.
Abstract: and t within a given planar figure F is considered. The approach contains basic methodology developed for any parallel or distributed system. The 2D scene or the edge of F are represented in the n Cartesian coordinate system (n-CCS). Several algorithms for the shortest path are given, each one to be applied in specified circumstances depending on the exact machine model or on additional information concerning geometrical properties of the figure. If these algorithms are implemented in a parallel depth search machine (PDSM), then the shortest path can be computed in time O(1). The maximum number of processors used is 0(n). The given methodology can also be adapted for producing an approximate solution when the shortest path is approximated by polygonal lines.
TL;DR: This paper describes a method for rounding edges and corners of arbitrary polyhedra that uses a fast approximation to convolutional filtering, which defines an implicit surface, which is rendered with a specialised ray-tracing algorithm.
Abstract: This paper describes a method for rounding edges and corners of arbitrary polyhedra that uses a fast approximation to convolutional filtering. The approximation defines an implicit surface, which is rendered with a specialised ray-tracing algorithm. By varying the radius of the smoothing filter, a wide range of effects can be obtained, from perfect polyhedra to ‘blobby models”. Small rounding radii give polyhedra a softer, more natural look, with edges well delineated by shadows and highlights. The rounded surfaces are much easier to specify and compute than those obtained by traditional filleting and surface-blending techniques, and are far more economical in storage.
IBM1
TL;DR: This note describes computer graphics used to gain insight into the behavior of the solution space and graphically interesting behavior of puzzles defined on finite lattices.
Abstract: Simple techniques are described for demonstrating graphically interesting behavior of puzzles defined on finite lattices. The simple puzzles should be of interest to students and teachers who may wish to design and solve similar problems. In particular, this note describes computer graphics used to gain insight into the behavior of the solution space.