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Über dieses Buch

A unified and coherent introduction to the notion of abstraction in interactive computer graphics is provided by this book. Abstraction entails refinement of images based on geometric models so as to reflect the importance of the features of the model for the dialog context and the visualization goal. This may require leaving out irrelevant details or accentuating significant features by adding details or enlarging or deforming parts. Such modifications are routine by hand but are at the leading edge of research in 2D and 3D computer graphics. The authors see the abstraction process as an interactive exploration of complex information spaces, and report especially on zooming and rendering techniques. Benefits are discussed for applications in medical illustration and technical documentation.

Inhaltsverzeichnis

Frontmatter

Introduction

Frontmatter

Chapter 1. New Challenges for Computer Visualization

Abstract
Practically all images which meet the human eye today can, in principle, be classified as computer graphics. Some images are produced from raw numeric, symbolic or geometric data obtained from application programs. Most diagrams are produced with spreadsheets or drawing programs. Many photographs are scanned and postprocessed to improve the quality of the colors; such graphics are tuned in a highly interactive process involving users who are experts at such tasks.
Thomas Strothotte

Chapter 2. Presentation Techniques for Exploring Complex Information Spaces

Abstract
Providing intuitive orientation aids and navigation techniques is essential to enable the exploration of information spaces. By complex information spaces we refer to information spaces which are not only large but also heterogenous in their structure. Complex information spaces are characterized, for example, by information which relates to different modalities (e.g., tables, graphics, and videos) and which may differ in their dimension.
Thomas Strothotte

Chapter 3. Enrichment and Reuse of Geometric Models

Abstract
The information encoded in a geometric model is the basis for a “classical” rendering process. The mere geometry, however, is insufficient when the rendered images are not the final product. Non-geometric information associated with the objects in the model may be necessary for further operations on the image. Especially structure information is helpful during the modeling process as well as for a flexible reuse of the model. Furthermore, an appropriate structure of the model is indispensable for the interactive handling of models, simply because interaction is only possible at the level of the model’s structure.
Thomas Strothotte

Controlling Detail

Frontmatter

Chapter 4. Rendering Line Drawings for Illustrative Purposes

Abstract
For many purposes a high-quality photorealistic image is not necessary to communicate intended ideas. “If the ultimate goal of a picture is to convey information”, as Foley et al. pointed out [FvDFH90] “then a picture that is free of the complications of shadows and reflections may well be more successful than a tour de force of photographic realism.” This is especially true for images used for purposes of documentation or as illustrations. Such images are closely related to the text they accompany and utilized to show very specific details of the observed scenario, so a more abstract presentation here often serves the purpose better. A photograph of an engine is of no use for a person in charge of repairing or maintaining it, while a line drawing — possibly a schematic or exploded view — would give the necessary insight to fulfill the task.
Thomas Strothotte

Chapter 5. Rendering Line Drawings of Curved Surfaces

Abstract
Freeform surfaces are very common in the design and modeling of objects, especially when modeling complex objects with curved surfaces. The advantage of working with freeform surfaces is the ability to control the shape of a surface with control points so that the location of the control point influences a well defined part of the curved surface. The greater the complexity of the curve, the greater the number of control points. For a deeper insight into the mathematical matter of freeform surfaces we refer to [Far91, Sei93].
Thomas Strothotte

Chapter 6. Pixel-Oriented Rendering of Line Drawings

Abstract
In Chaps. 4 and 5, several analytical approaches for creating line drawings were introduced. These methods allow the generation of a broad variety of drawing styles, and some applications of scientific and medical illustrations were given.
Thomas Strothotte

Chapter 7. Measuring and Highlighting in Graphics

Abstract
In 3D graphics modeling systems, the properties of the surfaces of objects are defined by a special material editor module. In most cases the values of a surface material (for instance color values, effects like shininess, textures) are defined separately on a sample object. Typically, this work is done outside the visual context of the scene. To see the material in the context of the whole scene, the image must be rendered.
Thomas Strothotte

Adaptive Zooming and Distorting Graphics

Frontmatter

Chapter 8. Distortions and Displacements in 2D

Abstract
Distortions are a common means to present complex information in an expressive and easily comprehensible way. To enhance the viewer’s perception, one or more areas of interest to the viewer are emphasized — they are brought to the focus. Typically, the areas lying in the focus are enlarged at the expense of their surroundings; they can be shown with more detail. Hence, distortion is a way to cope with the limited space of a presentation area, in general the screen or a sheet of paper.
Thomas Strothotte

Chapter 9. Zooming in 1, 2, and 3 Dimensions

Abstract
The advantages of 3D computer graphics are being exploited in an increasing number of interactive applications. This not only includes classical fields of 3D graphics (such as CAD or geometric modeling) but also fields in which static 2D images have been used so far (e.g., interactive illustration systems and online catalogs).
Thomas Strothotte

Chapter 10. Zoom Navigation

Abstract
Research on reducing the interaction effort when navigating in large information spaces has utilized Furnas’ generalized fisheye view [Fur86] in a variety of techniques (cf. Chap. 2). Existing approaches apply filtering and distorting techniques or both (recall Noik [Noi94]) according to the degree of interest (DOI) at a certain point in the information space (node). “Classical” fisheye views, as described by Sarkar and Brown [SB94], distort an existing layout to enlarge the view at the point of interest (focus). Distorting fisheye views stick more to the photographic nature of fisheye lenses by applying a nonlinear distortion to the display transformation. Filtering fisheye techniques display or suppress the rendering of nodes according to their DOI. Hybrid techniques, like the Intelligent Zoom as described by Bartram [BOD+94], make use of both, applying fisheye distortion to the display transformation as well as choosing an appropriate representation for each node not only depending on its DOI value, but also using reasoning techniques to exploit additional contextual information. Semantic zooming as described in [PF93] changes the appearance of objects, too, although only depending on the level of detail (LOD).
Thomas Strothotte

Textual Methods of Abstraction

Frontmatter

Chapter 11. From Graphics to Pure Text

Abstract
This chapter will concentrate on the relationship between images and text, and in particular on the use of text to present nominally graphical information to blind people. The following chapter will then consider the role of text within images. First, we look at the role of text, both as a component within graphical images, as a complement to graphical images, and as an alternative means of conveying information.
Thomas Strothotte

Chapter 12. Figure Captions in Visual Interfaces

Abstract
Visualizations are produced to enable a viewer to extract information. For this purpose, visualizations are not merely a straightforward rendering of the data. Limited presentation space imposes restrictions on the visualization, resulting in omissions, exaggerations, or displacements. Moreover, viewers may wish to explore the data under a thematic focus. Thus, portions of the data may be presented in more detail or more comprehensively, while others may be simplified, shrunken, or even left out.
Thomas Strothotte

Chapter 13. Interactive 3D Illustrations with Images and Text

Abstract
Interactive 3D graphics have a high potential for the explanation of complex spatial phenomena as can be found, for example, in engineering and anatomy. The interactive exploration of complex 3D models is crucial for spatial understanding. While this is well recognized, not enough effort has been spent on flexibly combining interactive 3D graphics with textual descriptions.
Thomas Strothotte

Abstraction in Time

Frontmatter

Chapter 14. Animating Non-photorealistic Computer Graphics

Abstract
This chapter deals with the creation of 3D non-photorealistic computer animations. It reviews the basic concepts for traditional and computer-generated animation with an emphasis on non-photorealistic animation which, when examined closely, covers more than just the mere rendering of a number of subsequent images. This chapter will not discuss new techniques for object deformation or motion specification but concentrates on the visualization of moving non-photorealistic images. As we will see, this requires new rendering methods for “drawing” a picture.
Thomas Strothotte

Chapter 15. Interaction Facilities and High-Level Support for Animation Design

Abstract
This chapter is focused on extending illustration techniques to sequences of frames — animations. Computer animations offer additional degrees of freedom to emphasize objects, to show relations between objects, and to clarify their spatial arrangement by performing gradual frame-to-frame changes in the rendered images. Object transformations, changes of an object’s material, and control of a virtual camera provide interesting channels to convey information.
Thomas Strothotte

Abstractions in Interactive Systems

Frontmatter

Chapter 16. Zoom Navigation in User Interfaces

Abstract
Many authors have observed the impact of the increased cognitive load users are confronted with when using today’s high-functionality computer systems. Graphical (direct manipulation) interfaces tend to use the notion of infinite working sheets. Yet existing screen real-estate is finite, partly due to current technological restrictions but mainly because of the limitations imposed by the human perceptual system.
Thomas Strothotte

Chapter 17. Interactive Medical Illustrations

Abstract
In anatomy, and even more in surgery, the viewer’s expectation of a good illustration is to get reliable information about form, structure, and sometimes also texture of the depicted objects. Within printed illustrations this can be achieved by using different kinds of drawings or even photographs. Here structure can be depicted by color coding, texture by “shading” the surface differently. The general presentation goals, as stated in Chap. 4, also apply here. Besides that, medical illustrations include an artistic handling of the subject and thus a medical illustration can be regarded as a fusion of science and the graphic image.
Thomas Strothotte

Chapter 18. Rendering Gestural Expressions

Abstract
In this chapter, computer generated illustrations and animation sequences of hand gestures are discussed. The animation of gestures is very useful in the teaching of sign language.
Thomas Strothotte

Chapter 19. Animation Design for Simulation

Abstract
While the previous chapter concentrated on how to render animations, this chapter deals with how to create them. It introduces a new method of generating the animation content mentioned in Chap. 15. That content can be presented using the techniques described in that chapter.
Thomas Strothotte

Abstraction for Specialized Output

Frontmatter

Chapter 20. Tactile Maps for Blind People

Abstract
Like maps for sighted people, tactile maps are depictions of areas like countries or towns. However, they are not just embossed versions of the maps that sighted people are used to (see Fig. 20.1). A number of particularities have to be observed to ensure the tactual legibility of these maps, resulting in several restrictions to the map design (refer to [Edm91] and [Hud83] for more information). Since haptic perception has a lower discriminability, symbols have to be larger and simpler, e.g., point symbols should have a diameter of 3–5 mm. To avoid confusion, symbols must have a minimum distance between one another. While these distances are about 0.1mm for visual features, tactile symbols must be at least 2–3 mm apart to ensure their separate perception. Braille texts have a fixed height of 6 mm and hence entail a street width of at least 8 mm to allow labeling of the streets. While color can be replaced by textures, the textured areas have to be very large to enable the differentiation of the different textures, and still there are only very few different textures easily recognizable even for larger areas.
Thomas Strothotte

Chapter 21. Synthetic Holography

Abstract
Holography is a method for three-dimensional imaging of objects. It was first presented by Dennis Gabor [Gab48] in 1948 and has expanded into various fields since then. In holographic interferometry, arbitrarily shaped diffusely scattering objects are examined. A description of this process can be found in Lauterborn, Kurz, and Wiesenfeldt [LKW95] and Eichler and Ackermann [EA93]. The same object can be compared with itself at a later time, allowing for the analysis of stress or deformations. Other applications of holography are in the design of diffractive optical elements, as described by Aagedal et al. [ABST94] or holographic storages [EA93].
Thomas Strothotte

Epilog

Frontmatter

Chapter 22. Abstraction Versus Realism: Not the Real Question

Abstract
When browsing through a book on computer graphics, one usually finds a lot of more or less interesting pictures that are produced by means of computers. These pictures are embedded in pages of technical texts describing how this image generation was performed and why it provides a better way to do so than other methods. Less space is usually given to the methodological background and the motivation underlying the preoccupation with computer visualization. In this chapter, we want to complement the more technically oriented part of this book with some reflections as to why such techniques can be interesting not only for computer graphics researchers, and where, from a communication-theoretic point of view, they might be of use in our society.
Thomas Strothotte

Chapter 23. Integrating Spatial and Nonspatial Data: A Challenge in Computational Visualistics

Abstract
Our book has dealt with selected aspects of what we call computer visualization. Indeed, we use the term Computational Visualistics1 for the scientific study of how visualizations are captured, stored, processed, produced, and conveyed to users, as well as how computer users interact with, perceive, understand, and store pictures. The characteristic aspect of computational visualistics is that we always consider algorithms running within the computer in unison with what the user will do with the resultant graphical output. We have dealt with only one specific aspect of the topic of computational visualistics, that of producing and interacting with images of a particular kind. In this chapter, we shall now take a fresh look at the technical results presented, strive for an insight into what is actually happening when producing such images, and work toward placing the results into a wider context. In doing so, we shall also suggest some new concepts and terminology which will guide future work in the area.
Thomas Strothotte

Backmatter

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