Volume 22, Number 1 (2014)
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Item Detecting Topologically Relevant Structures in Flows by Surface Integrals(Václav Skala - UNION Agency, 2014) Reich, Wieland; Kasten, Jens; Scheuermann, Gerik; Skala, VáclavGauss’ theorem, which relates the flow through a surface to the vector field inside the surface, is an important tool in Flow Visualization. We are exploit the fact that the theorem can be further refined on polygonal cells and construct a process that encodes the particle movement through the boundary facets of these cells using transition matrices. By pure power iteration of transition matrices, various topological features, such as separation and invariant sets, can be extracted without having to rely on the classical techniques, e.g., interpolation, differentiation and numerical streamline integration. We will apply our method to steady vector fields with a focus on three dimensions.
Item Detecting Dominant Motion Flows and People Counting in High Density Crowds(Václav Skala - UNION Agency, 2014) Khan, Sultan Daud; Vizzari, Giuseppe; Bandini, Stefania; Basalamah, Saleh; Skala, VáclavUrbanisation is growingly generating crowding situations which generate potential issues for planning and public safety. This paper proposes new techniques of crowd analysis and precisely crowd flow segmentation and crowd counting framework for estimating the number of people in each flow segment. We use two foreground masks, one generated by Horn-Schunck optical flow, used by crowd flow segmentation, and another by Gaussian background subtraction, used by crowd counting framework. For crowd flow segmentation, we adopt K-means clustering algorithm which segments the crowd in different flows. After clustering, some small blobs can appear which are removed by blob absorption method. After blob absorption, crowd flow is segmented into different dominant flows. Finally, we estimate the number of people in each flow segment by using blob analysis and blob size optimization methods. Our experimental results demonstrate the effectiveness of the proposed method comparing to other stateof- the-art approaches and our proposed crowd counting framework estimates the number of people with about 90% accuracy.Item Efficient Procedural Generation of Forests(Václav Skala - UNION Agency, 2014) Kenwood, Julian; Gain, James; Marais, Patrick; Skala, VáclavForested landscapes are an important component of many large virtual environments in games and film. In order to reduce modelling time, procedural methods are often used. Unfortunately, procedural tree generation tends to be slow and resource-intensive for large forests. The main contribution of this paper is the development of an efficient procedural generation system for the creation of large forests. Our system uses L-systems, a grammar-based procedural technique, to generate each tree. We algorithmically modify L-system tree grammars to intelligently use an instance cache for tree branches. Our instancing approach not only makes efficient use of memory but also reduces the visual repetition artifacts which can arise due to the granularity of the instances. Instances can represent a range of structures, from a single branch to multiple branches or even an entire tree. Our system improves the speed and memory requirements for forest generation by 3–4 orders of magnitude over naïve methods: we generate over 1;000;000 trees in 4.5 seconds, while using only 350MB of memory.Item Intelligent Prioritization and Filtering of Labels in Navigation Maps(Václav Skala - UNION Agency, 2014) Vaaraniemi, Mikael; Goerlich, Markus; in der Au, Aick; Skala, VáclavThe description of objects in navigation maps by textual annotations provides a powerful means for orientation and visual data exploration. However, displaying labels for all features leads to a cluttered map with unreadable labels and occluded information. Therefore, the overall goal is to display the most important and filter out the less important labels. In this paper, we present a general approach for filtering labels. We use the navigation in automotive maps as an application to test our approach. This involves the creation of a priority metric for ranking labels in maps. Our flexible system allows runtime configuration of the priority. Moreover, we keep the temporal coherency of label filtering; hence, jittering of labels does not occur. The system is predictable, modular, and can easily be adapted to new applications. On medium-class hardware, our real-time system is capable of filtering on average 1000 labels within 12 ms. A concluding expert study validates our approach for navigation purposes. All candidates approve the resulting clear labeling layout.Item City Sketching(Václav Skala - UNION Agency, 2014) Gain, James; Marais, Patrick; Neeser, Rudolph; Skala, VáclavProcedural methods offer an automated means of generating complex cityscapes, incorporating the placement of park areas and the layout of roads, plots and buildings. Unfortunately, existing interfaces to procedural city systems tend to either focus on a single aspect of city layout (such as the road network) ignoring interaction with other elements (such as building dimensions) or expect numeric input with little visual feedback, short of the completed city, which may take up to several minutes to generate. In this paper we present an interface to procedural city generation, which, through a combination of sketching and gestural input, enables users to specify different land usage (parkland, commercial, residential and industrial), and control the geometric attributes of roads, plots and buildings. Importantly, the inter-relationship of these elements is pre-visualized so that their impact on the final city layout can be predicted. Once generated, further editing, for instance shaping the city skyline or redrawing individual roads, is supported. In general, City Sketching provides a powerful and intuitive interface for designing complex urban layouts.
