Volume 13 (1994)

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3D Visualization for 2D GIS: an Analysis of the Users Needs and a Review of Techniques*
(Blackwell Science Ltd and the Eurographics Association, 1994) Giertsen, Christopher; Lucas, Anne
Most of the existing geographical information systems (GIS) make limited use of algorithms for advanced computer graphics and visualization. One explanation is that few attempts are made to identify the visualization needs for different uses of GIS, and to couple such needs to the available algorithms. Another explanation is that most GIS are designed to handle two-dimensional (20) data with few obvious relationships to three-dimensional (30) visualization.In an attempt to provide a better understanding of the application of visualization in GIS, we propose a conceptual framework linking several aspects of the two fields. At the user-level, we link different uses of GIS to different categories of audience and presentation styles. At the level of implementation, we first propose different ways to create 3D data for visualization from 2D GIS data, and then we review algorithms and techniques for 3D visualization with respect to support of different presentation styles.
Adaptive mesh generation for progressive radiosity: A ray-tracing based algorithm.
(Blackwell Science Ltd and the Eurographics Association, 1994) PAULIN, Mathias; JESSEL, Jean-Pierre
The radiosity method is one of the most popular rendering algorithms. It allows to simulate interreflections of light accurately between surfaces as energy transfers are well designed. However, this algorithm and its derivatives need to break scenes into a relatively large number of small elements to approximate the illumination function. Even with a very large number of elements, not all the illumination effects can be simulated. In fact, there are always artefacts when modelling sharp shadows, besides shadows falling between mesh vertices can be missed entirely. To reduce the computational cost of such methods and to increase the accuracy of the radiosity solution, adaptive mesh generation is well suited. In this paper, we present a ray-tracing based algorithm for adaptive mesh generation which resolves all the illumination problems without lengthening computation time too much. This method allows a small number of initial elements and increases element density in critical locations while solving the illumination problem.
AGRELs and BIPs: Metamorphosis as a Bezier curve in the space of polyhedra
(Blackwell Science Ltd and the Eurographics Association, 1994) Rossignac, Jarek; Kaul, Anil
The metamorphosis between two user-specified objects offers an intuitive metaphor for designing animations of deforming shapes. We present a new technique for interactively editing such deformations and for animating them in realtime. Besides the starting and ending shapes, our approach offers easy to use additional control over the deformations. The new Bezier Interpolating Polyhedron (BIP) provides a graphics representation of such a deforming object formulated mathematically as a point describing a Bezier curve in the space of all polyhedra. We replace, in the Bezier formulation, the traditional control points by arbitrary polyhedra and the vector addition by the Minkowski sum. BIPs are composed of Animated GRaphic ELement (AGRELs), which are faces with constant orientation, but with parametrized vertices represented by Bezier curves. AGRELs were designed to efficiently support smooth realtime animation on commercially available rendering hardware. We provide a tested algorithm for automatically computing BIPs from the sequence of control polyhedra and demonstrate its applications to animation design.
An All-integer Algorithm for Drawing Anti-aliased Straight Lines
(Blackwell Science Ltd and the Eurographics Association, 1994) Kui, Liu Yong
An algorithm for drawing anti-aliased straight lines based on Bresenharn sline algorithm is presented in this paper. Only integer calculations are required. Multiplications or divisions are not needed (only simple addition/subtraction and sign testing are used). The algorithm can be used to choose between 2n intermediate grey levels between black and white.
Animation using NURBS
(Blackwell Science Ltd and the Eurographics Association, 1994) Preston, M.; Hewitt, W. T.
All animation, whether generated by pen or processor, is concerned with the changing behaviour of synthetic actors through time. Computer animation has allowed an animator to regard different actors as functionally equivalent entities for the purpose of generating their behaviours. This has opened the door to visually impressive effects, such as actors changing their appearance, thereby becoming other actors.For NURBS to become a tool which is useful to the writer of animation packages, it is necessary to provide this ability to in-between objects of different appearances through time.This paper aims to present a technique for creating higher dimensional NURBS to model object deformation, as well as to illustrate its advantages.
Animations to Represent Multivariate Data
(Blackwell Science Ltd and the Eurographics Association, 1994) Palamidese, P.; Crise, A.
Building animations is a current practice to study problems in the computational and experimental sciences. There are several classes of applications which generate descriptions of complex phenomena, based on a large variety of variables. In this paper, we discuss the application of traditional animation techniques, such as interpolation and kinematics animation, and of visualization techniques, like mapping, to the production of animation of multivariate data. Some examples of animation are illustrated from simulated bio-physical models of a sea basin.
Beyond WYSIWYG: Display of Hidden Information in Graphics Editors
(Blackwell Science Ltd and the Eurographics Association, 1994) Schleich, R.; Durst, M.J.
Graphics editors such as computer aided design systems are complex and difficult to use. We attribute this to the fact that only a small part of the information is visible and therefore accessible and understandable. Only the graphics objects themselves are visible, but the relations between these objects remain hidden. We propose an effective way to visualise this information in the form of trees and graphs in so-called structure browsers. A prototype implements this proposal based on an object-oriented application framework for graphics editors.
Chebyshev Polynomials for Boxing and Intersections of Parametric Curves and Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1994) Fournier, Alain; Buchanan, John
Parametric 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.
Classification of Ray-Generators in Uniform Subdivisions and Octrees for Ray Tracing
(Blackwell Science Ltd and the Eurographics Association, 1994) Endl, Robert; Sommer, Manfred
Spatial subdivisions cause an enormous acceleration of ray tracing due to the reduction of ray-object intersections. For this purpose it is necessary to generate the sequence of ray-cells (all cells met consecutively by a given ray). A method generating this sequence will be called a ray-generator. First this paper analyses the common properties of ray-generators in order to establish a classification. Then some well-known ray- generators are described and classified, as well as some new ones. In the sequel nine different ray-generators are implemented in one single program allowing direct comparisons with the same scene. Finally, global time measurements for two scenes are given, as well as time measurements for random rays enabling the calculation of mean values for the time of initialization and determination of ray-cells.
Computation of Offset Curves by the Huygens Principle
(Blackwell Science Ltd and the Eurographics Association, 1994) Mikheev, A.; Nozik, M.; Rubinstein, J.
A new algorithm for computing offset curves is proposed. The algorithm is based on the Huygens principle for propagating wave-fronts. It automatically avoids the topological singularities that appear in conventional methods. The algorithm is simple to implement and it does not require any multiplication or other floating number operations.
Computer Generated Copper Plates
(Blackwell Science Ltd and the Eurographics Association, 1994) Leister, Wolfgang
Making computer generated copper plates with image generation algorithms is presented. The method uses a kind of volume texturing in connection with image processing algorithms, and is suitable for implementation in a ray tracing algorithm. Experience shows that this method is especially interesting for illustrations in books and for generating icons on user interfaces.
COMPUTER GRAPHICS AND REMOTE SENSING - A SYNTHESIS FOR ENVIRONMENTAL PLANNING AND CIVIL ENGINEERING
(Blackwell Science Ltd and the Eurographics Association, 1994) Graf, K.Ch.; Suter, M.; Hagger, J.; Nuesch, D.
This 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.
Computer Graphics System for Reproducing Three- Dimensional Shape from Idea Sketch
(Blackwell Science Ltd and the Eurographics Association, 1994) Akeo, Makoto; Hashimoto, Hiroshi; Kobayashi, Taisuke; Shibusawa, Tetsuo
This paper describes the technical features and method of implementation of our designer support system which enables reproducing a three-dimensional shape from an idea sketch speedily and modifying the reproduced shape easily, thereby facilitating the consistency of the shape to be checked from a design viewpoint.The designer support system was developed as a tool to cut the time and labor designers have to spend in the design process and help designers to fully display their creativity-the essential attribute of designers.This system uses cross-section lines of an idea sketch of an object drawn by an industrial designer as input data to reproduce automatically a three-dimensional wireframe model of the object by a newly developed three-dimensional graphic algorithm including graphic constraints. In addition, it automatically creates planes by scanning the area enclosed by reproduced curved lines and subjects them to shading. In this process, the dimensions of the object need not be input to the system. The designer can operate the system simply by using the mouse to input appropriate data.Thus, the system permits the designer to easily express his idea in the form of a three-dimensional shape and study idea variations on the display screen without creating a mockup.
Constant-Time Filtering by Singular Value Decomposition?
(Blackwell Science Ltd and the Eurographics Association, 1994) Gotsman, Craig
We 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.
A Constraint-Based Reasoning Framework for Behavioural Animation
(Blackwell Science Ltd and the Eurographics Association, 1994) Mah, Sang; Calvert, Thomas W.; Havens, William
Behaviour is a reflection of a reasoning process that must deal with constraints imposed by an external environment, internal knowledge and physical structure. This paper proposes a framework for behavioural animation that is based on the next generation of object-oriented, constraint-based expert systems technology, and applies a control structure of knowledge agents and knowledge units to determine the behaviour of objects to be animated. Knowledge agents are responsible for planning, plan implementation and information extraction from the environment. The activity of an agent is dependent on the knowledge units ascribed to them by the animator. The interaction between agents and knowledge units is resolved by the reasoning engine, and thus, influences the eventual motion displayed. An example given is NSAIL, a pilot implementation using the model-based ECHIDNA constraint logic programming shell. With this approach, the motion for a sailing scenario and other behavioural domains can be specified at a high level through the characterization of the knowledge agents.
Contextual Animation of Gestural Commands
(Blackwell Science Ltd and the Eurographics Association, 1994) Kurtenbach, G.; Moran, T. P.; Buxton, W.
Drawing a mark can be an efficient command input technique when using a pen-based computer. However, marks are not intrinsically self-explanatory as are other interactive techniques such as buttons and menus. We present design principles for interaction mechanisms which make marks self explanatory for novices but still allow experts to use efficient command marks. The key notion is that use of the explanation mechanism physically trains a novice to use the efficient command marks. Two novel interaction mechanisms we have developed using these principles are presented.
Controllable Locality in C2 Interpolating Curves by B2-splines / S-splines
(Blackwell Science Ltd and the Eurographics Association, 1994) Kuroda, Mitsuru; Furukawa, Susumu; Kimura, Fumihiko
This 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.
Cross Scan Buffer and its Applications
(Blackwell Science Ltd and the Eurographics Association, 1994) Tanaka, Toshimitsu; Takahashi, Tokiichiro
We propose the Cross Scanline Buffer which preserves the result of hidden surface removal as performed by the Cross Scanline Algorithm. The Cross Scan Buffer reduces image re-generation time and eliminates aliasing artifacts even if the image is arbitrarily scaled. Perfect anti-aliasing is achieved because the Cross Scanline Algorithm analytically determines visible polygonal surfaces and divides them into sets of triangles and trapezia. The Cross Scan Buffer supports the various applications that currently use the conventional buffering methods for anti-aliasing. This paper introduces and tests three applications: image scaling, shadow creation, and texture mapping. Experimental results verify that the Cross Scan Buffer is very powerful yet efficient.
A Data Structure for Artificial Terrain Generation
(Blackwell Science Ltd and the Eurographics Association, 1994) Dixon, A. R.; Kirby, G. H.; Wills, D. P. M.
This paper addresses the problems of maintaining the consistency of spatial data under recursive subdivision algorithms for artificial terrain generation. Fractal modelling techniques are outlined, with particular reference to those based on fractional Brownian motion, and included is a brief history of recursive subdivision techniques. Existing polyhedral data structures are reviewed and shown to be inadequate for maintenance of consistency as polygons are subdivided. A new edge-based data structure is presented which provides for the efficient use and consistent storage of spatial data under these conditions. The data structure is applicable to polygons of any order and allows neighbouring polygons of different order to be stored and subdivided. Artificial terrain is demonstrated from subdivision of the hexagon, of the quadrilateral and of a combination of hexagons, quadrilaterals and triangles.
Deriving Spectral, Reflectance Functions of Computer-Simulated Object Colours
(Blackwell Science Ltd and the Eurographics Association, 1994) Schettini, R.
A method is presented which, given the RGB values of a colour stimulus displayed on a given cathode ray tube (to which a CIE XYZ triple corresponds), makes it possible to find a spectral reflectance function characterizing an object colour. Such an object when"illuminated" by a given illuminant produces a metameric spectral power distribution, that is, one with the same XYZ tristimulus values. The method is useful in the colorimetric matching of colours on different media or supports.

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