Jürgen Döllner

Image and Video Abstraction by Anisotropic Kuwahara Filtering

We present a non‐photorealistic rendering technique to transform color images and videos into painterly abstractions. It is based on a generalization of the Kuwahara filter that is adapted to the local shape of features, derived from the smoothed structure tensor. Contrary to conventional edge‐preserving filters, our filter generates a painting‐like flattening effect along the local feature directions while preserving shape boundaries. As opposed to conventional painting algorithms, it produces temporally coherent video abstraction without extra processing. The GPU implementation of our method processes video in real‐time. The results have the clearness of cartoon illustrations but also exhibit directional information as found in oil paintings.

Abstract representations for interactive visualization of virtual 3D city models

Virtual 3D city models increasingly cover whole city areas; hence, the perception of complex urban structures becomes increasingly difficult. Using abstract visualization, complexity of these models can be hidden where its visibility is unnecessary, while important features are maintained and highlighted for better comprehension and communication. We present a technique to automatically generalize a given virtual 3D city model consisting of building models, an infrastructure network and optional land coverage data; this technique creates several representations of increasing levels of abstraction. Using the infrastructure network, our technique groups building models and replaces them with cell blocks, while preserving local landmarks. By computing a landmark hierarchy, we reduce the set of initial landmarks in a spatially balanced manner for use in higher levels of abstraction. In four application examples, we demonstrate smooth visualization of transitions between precomputed representations; dynamic landmark highlighting according to virtual camera distance; an implementation of a cognitively enhanced route representation, and generalization lenses to combine precomputed representations in focus + context visualization.

Image Abstraction by Structure Adaptive Filtering

In this work we present a framework of automatic non-photorealistic image processing techniques that create simplified stylistic illustrations from color images, videos and 3D renderings. To smooth low-contrast regions while preserving edges, we present a new fast separated implementation of the bilateral filter. Our approach works by filtering in direction of the gradient and then filtering the intermediate result in perpendicular direction. When applied iteratively, our approach does not suffer from horizontal or vertical artifacts and creates smooth output at curved boundaries. To extract salient important edges we first apply a one-dimensional difference-of-Gaussians filter in direction of the gradient and then apply smoothing along a flow field which we derive from the smoothed structure tensor. Our method creates smooth coherent output for line and curve segments.

Interactive 3D visualization of vector data in GIS

Vector data represents one major category of data managed by GIS. This paper presents a new technique for vector-data display that is able to precisely and efficiently map vector data on 3D objects such as digital terrain models. The technique allows the system to adapt the visual mapping to the context and user needs and enables users to interactively modify vector data through the visual representation. It represents a basic mechanism for GIS interface technology and facilitates the development of visual analysis and exploration tools.

An object-oriented approach for integrating 3D visualization systems and GIS

Abstract Visualization has become an integral part in many applications of GIS. Due to the rapid development of computer graphics, visualization and animation techniques, general-purpose GIS can no longer satisfy the multitude of visualization demands. Therefore, GIS have to utilize independent visualization toolkits. This article examines how visualization systems can be used with and integrated into GIS. We analyze several key characteristics visualization toolkits should satisfy in order to be used efficiently by GIS. We show how GIS can provide visualization and animation features for geo objects by embedding the visualization system using object-oriented techniques. The concepts are described along with a new visualization and animation toolkit which provides extensible object-oriented technology for the development of visualization components for 2D, 3D and time-varying data. The design of this visualization toolkit concentrates on a seamless integration of application-specific geo-data into visualization components, an open interface for different rendering techniques and an advanced management of data dynamics.

Real-time expressive rendering of city models

City models have become central elements for visually communicating spatial information related to urban areas and have manifold applications. Our real-time nonphotorealistic rendering technique aims at abstract, comprehensible, and vivid drawings of assemblies of polygonal 3D urban objects. It takes into account related principles in cartography, cognition, and nonphotorealism. Technically, the geometry of a building is rendered using expressive line drawings to enhance the edges, two-tone or three-tone shading to draw the faces, and simulated shadows. The edge enhancement offers several degrees of freedom, such as interactively changing the style, width, tilt, color, transparency, and length of the strokes. Traditional drawings of cities and panoramas inspired the tone shading that achieves a pleasing visual color effect. The rendering technique can be applied not only to city models but to polygonal shapes in general.City models have become central elements for visually communicating spatial information related to urban areas and have manifold applications. Our real-time non-photorealistic rendering technique aims at abstract, comprehensible, and vivid drawings of assemblies of polygonal 3D urban objects. It takes into account related principles in cartography, cognition, and nonphotorealism. Technically, the geometry of a building is rendered using expressive line drawings to enhance the edges, two-tone or three-tone shading to draw the faces, and simulated shadows. The edge enhancement offers several degrees of freedom, such as interactively changing the style, width, tilt, color, transparency, and length of the strokes. Traditional drawings of cities and panoramas inspired the tone shading that achieves a pleasing visual color effect. The rendering technique can be applied not only to city models but to polygonal shapes in

Object‐oriented 3D Modelling, Animation and Interaction

We present an object-oriented 3D graphics and animation framework which provides a new methodology for the symmetric modelling of geometry and behaviour. The toolkit separates the specification of geometry and behaviour by two types of directed acyclic graphs, the geometry graph and the behaviour graph, which are linked together through constraint relations. All geometry objects and behaviour objects are represented as DAG nodes. The geometry graph provides a renderer-independent hierarchical description of 3D scenes and rendering processes. The behaviour graph specifies time- and event-dependent constraints applied to graphics objects. Behaviour graphs simplify the specification of complex animations and 3D interactions by providing nodes for the management of the time and event flow (e.g. durations, time layouts, time repeaters, actions). Nodes contain, manipulate and share instances of constrainable graphical abstract data types. Geometry nodes and behaviour nodes are used to configure high-level 3D widgets, i.e. high-level building blocks for constructing 3D applications. The fine-grained object structure of the system leads to an extensible reusable framework which can be implemented efficiently.

Continuous level-of-detail modeling of buildings in 3D city models

This paper introduces a concept for representing and modeling buildings in GIS at continuous levels of quality. Buildings are essential objects of virtual 3D city models, which serve as platforms for integrated, urban geoinformation. Existing concepts for the representation of buildings are restricted to a specific level-of-quality such as block models, roof-including models, architectural models, and indoor virtual reality models. The continuous level-of-quality approach unifies the representation of heterogeneous sets of buildings, which occur in most virtual 3D city models. It also leads to a systematic method for the incremental refinement of buildings - an important requirement of the long-term management of virtual city models. In our concept, a buildings geometry is structured on a per-floor basis; each floor refers to a floor prototype, which is defined by a ground plan, walls, and wall segments. To specify the appearance projective textures across floors and textures per wall segment are supported. Application-specific data can be associated similar to appearance information. These few components already allow us to express efficiently most common building features. Furthermore, the approach seamlessly integrates into CityGML, an upcoming standard for virtual city model data.

Interactive Visualization of Generalized Virtual 3D City Models using Level-of-Abstraction Transitions

Virtual 3D city models play an important role in the communication of complex geospatial information in a growing number of applications, such as urban planning, navigation, tourist information, and disaster management. In general, homogeneous graphic styles are used for visualization. For instance, photorealism is suitable for detailed presentations, and non‐photorealism or abstract stylization is used to facilitate guidance of a viewers gaze to prioritized information. However, to adapt visualization to different contexts and contents and to support saliency‐guided visualization based on user interaction or dynamically changing thematic information, a combination of different graphic styles is necessary. Design and implementation of such combined graphic styles pose a number of challenges, specifically from the perspective of real‐time 3D visualization. In this paper, the authors present a concept and an implementation of a system that enables different presentation styles, their seamless integration within a single view, and parametrized transitions between them, which are defined according to tasks, camera view, and image resolution. The paper outlines potential usage scenarios and application fields together with a performance evaluation of the implementation.

Visual exploration of function call graphs for feature location in complex software systems

Maintenance, reengineering, and refactoring processes of software systems are typically driven and organized in terms of features. Feature change requests need to be translated into changes in source code, which is a highly cost intensive and time consuming task when complex legacy software systems are concerned; their documentation is likely to be outdated and incomplete. In this paper, we propose a prototype tool that supports users in locating and understanding feature implementation in large (>1 MLOC) C/C++ systems. A combination of static and dynamic analysis allows extracting of the function call graph during feature execution and interpreting it within the static architecture of the system. An interactive multi-view visualization enables users to explore that graph. An effective 2 1/2D visualization provides various visual cues that facilitate finding those paths in the function call graph that are essential for understanding feature functionality. Additionally to source code aspects, the dynamic metric of function execution times is exploited, which gives significant hints to feature-implementing functions. Furthermore, information on functions is extended by architectural aspects, thereby supporting users in remaining oriented during their analysis and exploration task as they can give priority to selected architectural components and thereby hide insignificant function calls.