Ing. Ladislav Čmolík, Ph.D.

The focus of this paper is real-time visualization of and interaction with scatterplots with hundreds of thousands of data points, where the points are organized into a hierarchy of clusters. We present a technique that automatically selects a color palette for the clusters of the selected level. The level of the cluster hierarchy and the color palette are dynamically adjusted by zooming the scatterplot. Furthermore, the technique improves visibility of the displayed clusters by reducing occlusion of the overlapping clusters. We demonstrate the visualization technique using two real medical datasets containing 2D coordinates of hundreds of thousands points.

In this article, we present an algorithm capable of mixed labeling of 2D and 3D objects. In mixed labeling, the given objects are labeled with both internal labels placed (at least partially) over the objects and external labels placed in the space around the objects and connected with the labeled objects with straight-line leaders. The proposed algorithm determines the position and type of each label based on the user-specified ambiguity threshold and eliminates overlaps between the labels, as well as between the internal labels and the straight-line leaders of external labels. The algorithm is a screen-space technique; it operates in an image where the 2D objects or projected 3D objects are encoded. In other words, we can use the algorithm whenever we can render the objects to an image, which makes the algorithm fit for use in many domains. The algorithm operates in real-time, giving the results immediately. Finally, we present results from an expert evaluation, in which a professional illustrator has evaluated the label layouts produced with the proposed algorithm.

Labels, short textual annotations are an important component of data visualizations, illustrations, infographics, and geographical maps. In interactive applications, the labeling method responsible for positioning the labels should not take the resources from the application itself. In other words, the labeling method should provide the result as fast as possible. In this work, we propose a greedy point-feature labeling method running on GPU. In contrast to existing methods that position the labels sequentially, the proposed method positions several labels in parallel. Yet, we guarantee that the positioned labels will not overlap, nor will they overlap important visual features. When the proposed method is searching for the label position of a point-feature, the available label candidates are evaluated with respect to overlaps with important visual features, conflicts with label candidates of other point-features, and their ambiguity. The evaluation of each label candidate is done in constant time independently from the number of point-features, the number of important visual features, and the resolution of the created image. Our measurements indicate that the proposed method is able to position more labels than existing greedy methods that do not evaluate conflicts between the label candidates. At the same time, the proposed method achieves a significant increase in performance. The increase in performance is mainly due to the parallelization and the efficient evaluation of label candidates.

We propose two novel temporally stable screen-space labeling methods for dynamic scenes. The first one is suitable for offline processing of the entire interaction or the video in advance. The second method is designed for interactive applications. The main idea of our proposed methods is to minimize the vertical and horizontal movement of the labels during the interaction with the scene (e.g., zooming or translating the camera). According to the results of quantitative evaluation, our labeling is more stable during the interaction than labeling produced by the current state of the art. Moreover, participants of a comprehensive user study declared that the labeling produced by the proposed methods allows them to follow moving labels significantly more accurately, and it is significantly more pleasing than with previously published methods. Furthermore, the proposed methods can be extended by the prominence of the features and easily parameterized to fit different requirements to the label layout.

Labeling is intrinsically important for exploring and understanding complex environments and models in a variety of domains. We present a method for interactive labeling of crowded 3D scenes containing very many instances of objects spanning multiple scales in size. In contrast to previous labeling methods, we target cases where many instances of dozens of types are present and where the hierarchical structure of the objects in the scene presents an opportunity to choose the most suitable level for each placed label. Our solution builds on and goes beyond labeling techniques in medical 3D visualization, cartography, and biological illustrations from books and prints. In contrast to these techniques, the main characteristics of our new technique are: 1) a novel way of labeling objects as part of a bigger structure when appropriate, 2) visual clutter reduction by labeling only representative instances for each type of an object, and a strategy of selecting those. The appropriate level of label is chosen by analyzing the scene's depth buffer and the scene objects' hierarchy tree. We address the topic of communicating the parent-children relationship between labels by employing visual hierarchy concepts adapted from graphic design. Selecting representative instances considers several criteria tailored to the character of the data and is combined with a greedy optimization approach. We demonstrate the usage of our method with models from mesoscale biology where these two characteristics-multi-scale and multi-instance-are abundant, along with the fact that these scenes are extraordinarily dense.

We present a new algorithm for calculating the external labeling of ghosted views of moderately complex 3D models. The algorithm uses multiple criteria decision making, based on fuzzy logic, to optimize positions of the labels associated with different parts of the input model. The proposed method can be used with various existing algorithms for creating ghosted views from 3D models. The method operates in real-time, which allows the user to acquire a good understanding of the structure of the input model by studying the model and its labels from different viewpoints. We have conducted a user study to evaluate label layouts produced by our algorithm and those created by humans. The results show that the proposed method can significantly improve user understanding of labeled ghosted views of complicated 3D models, and its label layouts are comparable with label layouts created by humans.

We propose a method for video sequence boundary labeling which maintains the temporal coherence. The method is based on two ideas. We limit the movement of the label boxes only to the horizontal direction, and reserve free space for the movement of the label boxes in the label layout. The proposed method is able to position label boxes in video sequence on a lower number of rows than existing methods, while at the same time, it minimizes the movement of label boxes. We conducted an extensive user experiment where the proposed method was ranked the best for panorama video sequences labeling compared to three existing methods.

Educational text where complex relations between several objects are described is often accompanied by illustrations - a visual representation of the relations. Labels, short textual annotations, laid out around the illustrations mediate the interconnection between the verbal and visual representation of information. We present an algorithm cabable of label layout calculation in real time. The algorithm is able to position the labels into non-convex areas around the illustrations.

In the paper we present multifocal highlighting in reverse engineered component diagrams to support software engineers in answering questions on relations between a number of components. With component oriented systems such questions arise quite often. We use color to highlight all components relevant to selected focus components. Further, we allow the users to filter the diagram. Our approach, unlike the state-of-the-art methods allows analysis of relations between dozens of components. We have performed an user study to evaluate our multifocal highlighting. The results of the subjective evaluation show that the multifocal highlighting supports software engineers in answering questions on relations between components.

As current software keeps growing in size and complexity, the means to visualize its structure become insufficient. Noticeably, standard UML diagrams and their implementations in the industrial tools can depict only diagrams of certain level of complexity. When the complexity rises above this level, the diagrams become no longer visually understandable and start to hinder analytical reasoning. This is mostly a problem of diagrams created during automated reverse-engineering processes. In this study we summarize and validate a new approach for software structure visualization which aims at supporting visual presentation of large software systems. It combines a notation derived from the UML component diagram with tool-supported interaction, utilizing features like hiding of unnecessary information that can be revealed on demand to reduce complexity of the diagrams. To validate the approach, we implemented an experimental tool that provides both the notation and interactive features. The main contribution of this study is an evaluation of the approach through a user study. The results of the user evaluation suggest that the proposed notation in combination with the interactive features allows users to gain insight into a visualized application faster in comparison to standard UML as supported by industrial tools.

We present a novel method for creating automatized gameplay dramatization of multiplayer video games. The dramatization serves as a visual form of guidance through dynamic 3D scenes with multiple foci, typical for such games. Our goal is to convey interesting aspects of the gameplay by animated sequences creating a summary of events which occurred during the game. Our technique is based on processing many cameras, which we refer to as a flock of cameras, and events captured during the gameplay, which we organize into a so-called event graph. Each camera has a lifespan with a certain time interval and its parameters such as position or look-up vector are changing over time. Additionally, during its lifespan each camera is assigned an importance function, which is dependent on the significance of the structures that are being captured by the camera. The images captured by the cameras are composed into a single continuous video using a set of operators based on cinematographic effects. The sequence of operators is selected by traversing the event graph and looking for specific patterns corresponding to the respective operators. In this way, a large number of cameras can be processed to generate an informative visual story presenting the gameplay. Our compositing approach supports insets of camera views to account for several important cameras simultaneously. Additionally, we create seamless transitions between individual selected camera views in order to preserve temporal continuity, which helps the user to follow the virtual story of the gameplay.

We present an external labeling laid over small and/or overlapping 2D objects as an efficient representation for their selection. The approximation of objects with points allows us to transform the labeling problem to graph layout problem, which we solve by means of force-based algorithm. The input parameters allow us to influence the resulting layout of label boxes (e.g. to adapt their distance for imprecise input devices). In a study with 15 participants two implementations of our algorithm were compared against labeling method, where all label boxes share the same offset from corresponding objects. The results of the study show that implementation using a special functionality (temporary freezing of the label box position recalculation) was 14% faster with a comparable accuracy. The subjective evaluation revealed that the implementation with temporary freezing is perceived as most comfortable, fastest and most accurate. The implementation without temporary freezing showed much higher error rate and cannot be recommended.

Cílem projektu bylo navrhnout uživatelské rozhraní digitální televize připojené přes Internet (IPTV) pro cílovou skupinu seniorů a vyvinout odpovídající prototyp spustitelný na běžně do‐stupných set‐top boxech. Vzhledem ke skutečnosti, že poskytovatelé IPTV často nabízejí velké množství různých televizních stanic, zaměřili jsme se na vyhledávání a správu pořadů, namísto klasického přístupu přes kanály. Před samotným návrhem uživatelského rozhraní jsme provedli uživatelský výzkum formou hloubkových rozhovorů, dotazníků a ohniskové skupiny s celkem 97 seniory. Uživatelský výzkum nám umožnil lépe porozumět potřebám uživatele a definovat budoucí funkcionalitu prototypu. Prototyp uživatelského rozhraní byl vytvořen během tří ite‐rací, kdy byl prototyp v každé iteraci testován v testech použitelnosti celkem se sedmi seniory. Nalezené problémy v použitelnosti byly vždy odstraněny v následující iteraci. Během testů jsme nejen zjistili drobné problémy v použitelnosti, ale setkali jsme se i s konceptuálními pro‐blémy specifickými pro cílovou skupinu, jako například navigace kurzoru v dlouhém seznamu, navigace uživatele v hierarchickém menu nebo problém s návrhem filtru pro hledání pořadu.

We propose a novel method for computing labeling of 3D illustrations in real-time. We solve a multiple criteria optimization problem in which we consider the desired layout already in the stage of searching for salient points of the labeled areas. In the solution we employ fuzzy logic combined with greedy optimization. The method runs on the GPU and achieves interactive rates on medium sized models. The results indicate that the method compares favorably to the state-of-the-art interactive labeling techniques.

One of key problems that users meet when interacting with any software product is easiness of communication with such a product - we speak about usability issues. This problem has not been addressed properly in case of software products used in ICT assisted learning. In this paper we will deal with usability issues in this field. There are various systems that support ICT supported learning like e-learning, m-learning, t-learning etc. We will present experience with usability testing in t-learning (iDTV - Interactive Digital Television) environment. The topic that was taught in the iDTV learning module was cultural heritage. This topic offers a possibility to use various media (text, pictures, videos etc.) together with different ways of interaction. In such a way the requirements for usability in this environment are rather complex. The paper describes the usability issues handled in individual stages of the learning module development ...

In this paper a prototyping tool for t-learning courses is presented. The prototyping tool allows to create prototypes of t-learning courses and easily test the created prototypes. The prototyping tool is based on our concepts of t-learning. The concepts are also presented in this paper. With the prototyping tool the process of development of t-learning course is more efficient and less error prone.

Ghosted views are technical illustrations that communicate not only shape, but also inner structure and spatial relations of the depicted objects. Modulation of opacity is utilized to communicate the inner structure, therefore the spatial relations remains undistorted. In this paper an approach that enables real-time rendering of 3D ghosted views is presented. The advantage over classical handcrafted ghosted views is that the user is able to interact (e.g. pan, zoom and rotate) with the 3D model.

The paper deals with the problems of personalization of e-learning in the interactive digital television environment. The main problem discussed is the personalization of additional content synchronized with broadcasted AV stream. The broadcasted AV stream is fully controlled by the broadcaster and the user has no chance to influence it. The majority of existing concepts performs personalization above the course level (the content of the course is not personalized) or they are suitable for asynchronous content only (e.g. video on demand). In this paper a solution for personalization of the additional content synchronized with the AV stream is proposed. We are focusing on a standardized solution based on the SCORM standard.

In this paper the problems of user interaction in a mobile environment are investigated. Interaction in this environment imposes new requirements both on UI designers an the users. This paper deals in particular with problems of graphical interaction in a mobile environment. A rendering technique that enables rendering and annotation of objects in a 3D scene on mobile devices is presented.

In this paper we introduce a system for real time collaboration and sharing of graphical data in the mobile environment. The main innovative feature of the system is involvement of semantic information into the process of data sharing and mainly into the customization of the data for individual users. Each user involved in the collaboration gets individually personalized data. the system is, thanks to the semantic information, able to ensure a fluent collaboration even if the data are personalized differently for each user.

This paper deals with the problem of resolution-independent rendering of 3D scenes. In many cases authors have to create the same content for different platforms (e.g. internet, printer) separately, due to different resolutions and different typographic rules. This paper presents an approach for projection of a 3D scene into the 2D vector graphic (thus it is independent on resolution). The scene projected into 2D vector graphic can be visualized in different styles (e.g. color, black and white) which correspond with the typographic rules of different platforms. Further a compression method suitable for 3D scenes projected into the 2D vector graphic is presented. The compression method significantly reduces the size of the output 2D vector image which is important when the image is transferred through a network.

The paper deals with problem of efficient rendering of 3D scenes in mobile computing environment. Also interaction issues have been investigated.

In this paper we introduce, analyze and compare several methods, which may be used for morphing threedimensional models represented by point clouds. Our methods consider only the local geometric information expressed by the point locations in 3D space. No additional topological information is required. The presented methods allow the morphing between two models represented by point clouds.