In data analysis, scatterplots serve as an initial tool for exploring the relationships between two or three attributes. While scatterplot matrices (SPLOMs) display every attribute combination through numerous 2D scatterplots to show a concise overview of a multivariate dataset, this approach is not directly suitable for 3D scatterplots due to visual clutter. Since research has shown that immersive virtual environments can enhance data analysis compared to traditional 2D desktop setups – especially for spatial analysis tasks – we propose an interactive system, called SPLOCIS, that makes use of virtual reality to enable users to interactively filter and select 3D scatter-plots from all possible attribute combinations. Our user study, combining both qualitative and quantitative results, demonstrates that SPLOCIS is a particularly novel and stimulating approach to work with multivariate data in immersive environments. It enables solving classic data exploration tasks in an efficient and accurate way, while not imposing unexpectedly high task loads. Moreover, our findings provide promising suggestions for further developments.

Embodied conversational agents (ECAs) are key social interaction partners in various virtual reality (VR) applications, with their perceived social presence significantly influencing the quality and effectiveness of user-ECA interactions. This article investigates the potential of a novel indirect objective proxy for evaluating social presence, which is traditionally assessed through subjective questionnaires. As proxy we use the Heard Text Recall (HTR) paradigm, originally designed to assess memory performance in listening tasks. In the task participants have to recall information from family stories being told. When combined with a secondary task in a dual-task paradigm, the HTR can also be used to evaluate cognitive spare capacity, which is then correlated with subjectively rated social presence. As a prerequisite for this investigation, we introduce various co-verbal gesture modification techniques and assess their impact on the perceived naturalness of the presenting ECA, a crucial aspect fostering social presence. The main study then explores the applicability of HTR as a proxy for social presence by examining its effectiveness under different multimodal degraders of ECA behavior, including degraded co-verbal gestures, omitted lip synchronization, and the use of synthetic voices. The findings suggest that while HTR shows potential as an objective measure of social presence, its effectiveness is primarily evident in response to substantial changes in ECA behavior. Additionally, the study also highlights the negative effects of synthetic voices and inadequate lip synchronization on perceived social presence, emphasizing the need for careful consideration of these elements in ECA design.

Traditional target-selection-based teleportation depends on the intersection of a (curved) ray with the scene's geometry, which limits navigation to points on the ground, restricting users' navigational freedom. While previous techniques exist that permit mid-air target selection, they are not optimal for transitioning between air and ground navigation, leading to inaccurate or lengthy interaction sequences. In this paper, we introduce SATOR, a new 3D teleportation technique designed to enable efficient and accurate navigation to both ground and mid-air targets by combining and enhancing previous approaches. Informed by the literature, we implemented four different parametrizations of our technique and compared them to a previously published technique that also enables both ground and mid-air target selection. Our user study with 30 participants indicates that SATOR is more efficient, accurate, and easier to use than the baseline. As a result, SATOR effectively helps users get an overview of the environment, observe features at different heights, or maneuver quickly around larger obstacles.

Target-selection-based teleportation is one of the most widely used and researched travel techniques in immersive virtual environments, requiring the user to specify a target location with a selection ray before being transported there. This work explores the influence of the maximum reach of the parabolic selection ray, modeled by different emission velocities of the projectile motion equation, and compares the resulting teleportation performance to a straight ray as the baseline. In a user study with 60 participants, we asked participants to teleport as far as possible while still remaining within accuracy constraints to understand how the theoretical implications of the projectile motion equation apply to a realistic VR use case. We found that a projectile emission velocity of $14 \frac{m}{s}$14ms (resulting in a maximal reach of $\text{21.52 m}$21.52m) offered the best trade-off between selection distance and accuracy, with an inferior performance of the straight ray. Our results demonstrate the necessity to carefully set and report the projectile emission velocity in future work, as it was shown to directly influence user-selected distance, selection errors, and controller height during selection.

Figure 1: Our LLM-driven guide assists users in exploring the museum and in learning about artworks and artists.

Working with scatterplots is a classic everyday task for data analysts, which gets increasingly complex the more plots are required to form an understanding of the underlying data. To help analysts retrieve relevant plots more quickly when they are needed, immersive virtual environments (iVEs) provide them with the option to freely arrange scatterplots in the 3D space around them. In this paper, we investigate the impact of different virtual environments on the users' ability to quickly find and retrieve individual scatterplots from a larger collection. We tested three different scenarios, all having in common that users were able to position the plots freely in space according to their own needs, but each providing them with varying numbers of landmarks serving as visual cues: an Empty scene as a baseline condition, a single landmark condition with one prominent visual cue being a Desk, and a multiple landmarks condition being a virtual Office. Results from a between-subject investigation with 45 participants indicate that the time and effort users invest in arranging their plots within an iVE had a greater impact on memory performance than the design of the iVE itself. We report on the individual arrangement strategies that participants used to solve the task effectively and underline the importance of an active arrangement phase for supporting the spatial memorization of scatterplots in iVEs.

Collaborative work in large virtual environments often requires transitions from loosely-coupled collaboration at different locations to tightly-coupled collaboration at a common meeting point. Inspired by prior work on the continuum between these extremes, we present two novel interaction techniques designed to share spatial context while collaborating over large virtual distances. The first method replicates the familiar setup of a video conference by providing users with a virtual tablet to share video feeds with their peers. The second method called PASCAL (Parallel Avatars in a Shared Collaborative Aura Link) enables users to share their immediate spatial surroundings with others by creating synchronized copies of it at the remote locations of their collaborators. We evaluated both techniques in a within-subject user study, in which 24 participants were tasked with solving a puzzle in groups of two. Our results indicate that the additional contextual information provided by PASCAL had significantly positive effects on task completion time, ease of communication, mutual understanding, and co-presence. As a result, our insights contribute to the repertoire of successful interaction techniques to mediate between loosely- and tightly-coupled work in collaborative virtual environments.

Real-world robot system deployment is often performed in complex and unstructured environments. These complex environments coupled with multi-faceted global tasks often lead to complicated stakeholder structures, making designing for these environments extremely challenging. Magnifying this difficulty, tasks performed in these environments often cannot be accomplished by a single robot or even single robot type because of the broad range of needs and psychical constraints of the robots. In these cases, heterogeneous robot teams may need to be coupled to human team members to perform the global tasks. From a Human-Robot Interaction (HRI) perspective, this increases the complexity of designing and deploying the system significantly, as now complicated stakeholder structures are mixed with complex robot teams. This paper presents a novel real-world system and interface design leveraging multiple mediums to balance stakeholder needs. To this end, the UI presented here incorporates features that support shared mental models (SMMs), trust establishment and development, and utilizes a centralized data distribution architecture to improve team performance. In addition to the interface, this paper presents a detailed look at the design process and the lessons learned from the perspective of a multi-year, real-world deployed system, as part of a large European project consisting of 21 partners from varying countries and backgrounds.

Immersive authoring enables content creation for virtual environments without a break of immersion. To enable immersive authoring of reactive behavior for a broad audience, we present modulation mapping, a simplified visual programming technique. To evaluate the applicability of our technique, we investigate the role of reference frames in which the programming elements are positioned, as this can affect the user experience. Thus, we developed two interface layouts: "surround-referenced" and "object-referenced". The former positions the programming elements relative to the physical tracking space, and the latter relative to the virtual scene objects. We compared the layouts in an empirical user study (n = 34) and found the surround-referenced layout faster, lower in task load, less cluttered, easier to learn and use, and preferred by users. Qualitative feedback, however, revealed the object-referenced layout as more intuitive, engaging, and valuable for visual debugging. Based on the results, we propose initial design implications for immersive authoring of reactive behavior by visual programming. Overall, modulation mapping was found to be an effective means for creating reactive behavior by the participants.

Immersive knowledge spaces like museums or cultural sites are often explored by traversing pre-defined paths that are curated to unfold a specific educational narrative. To support this type of guided exploration in VR, we present a semi-automated, hands-free path traversal technique based on teleportation that features a slow-paced interaction workflow targeted at fostering knowledge acquisition and maintaining spatial awareness. In an empirical user study with 34 participants, we evaluated two variations of our technique, differing in the presence or absence of intermediate teleportation points between the main points of interest along the route. While visiting additional intermediate points was objectively less efficient, our results indicate significant benefits of this approach regarding the user’s spatial awareness and perception of interface dependability. However, the user’s perception of flow, presence, attractiveness, perspicuity, and stimulation did not differ significantly. The overall positive reception of our approach encourages further research into semi-automated locomotion based on teleportation and provides initial insights into the design space of successful techniques in this domain.

Object selection in virtual environments is one of the most common and recurring interaction tasks. Therefore, the used technique can critically influence a system's overall efficiency and usability. IntenSelect is a scoring-based selection-by-volume technique that was shown to offer improved selection performance over conventional raycasting in virtual reality. This initial method, however, is most pronounced for small spherical objects that converge to a point-like appearance only, is challenging to parameterize, and has inherent limitations in terms of flexibility. We present an enhanced version of IntenSelect called IntenSelect+ designed to overcome multiple shortcomings of the original IntenSelect approach. In an empirical within-subjects user study with 42 participants, we compared IntenSelect+ to IntenSelect and conventional raycasting on various complex object configurations motivated by prior work. In addition to replicating the previously shown benefits of IntenSelect over raycasting, our results demonstrate significant advantages of IntenSelect+ over IntenSelect regarding selection performance, task load, and user experience. We, therefore, conclude that IntenSelect+ is a promising enhancement of the original approach that enables faster, more precise, and more comfortable object selection in immersive virtual environments.

The ability of a user to adjust their own scale while traveling through virtual environments enables them to inspect tiny features being ant-sized and to gain an overview of the surroundings as a giant. While prior work has almost exclusively focused on steering-based interfaces for multi-scale travel, we present three novel teleportation-based techniques that avoid continuous motion flow to reduce the risk of cybersickness. Our approaches build on the extension of known teleportation workflows and suggest specifying scale adjustments either simultaneously with, as a connected second step after, or separately from the user's new horizontal position. The results of a two-part user study with 30 participants indicate that the simultaneous and connected specification paradigms are both suitable candidates for effective and comfortable multi-scale teleportation with nuanced individual benefits. Scale specification as a separate mode, on the other hand, was considered less beneficial. We compare our findings to prior research and publish the executable of our user study to facilitate replication and further analyses.

Traditional digital tools for exploring historical data mostly rely on conventional 2D visualizations, which often cannot reveal all relevant interrelationships between historical fragments (e.g., persons or events). In this paper, we present a novel interactive exploration tool for historical data in VR, which represents fragments as spheres in a 3D environment and arranges them around the user based on their temporal, geo, categorical and semantic similarity. Quantitative and qualitative results from a user study with 29 participants revealed that most participants considered the virtual space and the abstract fragment representation well-suited to explore historical data and to discover complex interrelationships. These results were particularly underlined by high usability scores in terms of attractiveness, stimulation, and novelty, while researching historical facts with our system did not impose unexpectedly high task loads. Additionally, the insights from our post-study interviews provided valuable suggestions for future developments to further expand the possibilities of our system.

The iterative design process of virtual environments commonly generates a history of revisions that each represent the state of the scene at a different point in time. Browsing through these discrete time points by common temporal navigation interfaces like time sliders, however, can be inaccurate and lead to an uncomfortably high number of visual changes in a short time. In this paper, we therefore present a novel technique called TENETvr (Temporal Exploration and Navigation in virtual Environments via Teleportation) that allows for efficient teleportation-based travel to time points in which a particular object of interest changed. Unlike previous systems, we suggest that changes affecting other objects in the same time span should also be mediated before the teleport to improve predictability. We therefore propose visualizations for nine different types of additions, property changes, and deletions. In a formal user study with 20 participants, we confirmed that this addition leads to significantly more efficient change detection, lower task loads, and higher usability ratings, therefore reducing temporal disorientation.

On entering an unknown immersive virtual environment, a user's first task is gaining knowledge about the respective scene, termed scene exploration. While many techniques for aided scene exploration exist, such as virtual guides, or maps, unaided wayfinding through pedestrians-as-cues is still in its infancy. We contribute to this research by indirectly guiding users through pedestrian groups conversing about their target location. A user who overhears the conversation without being a direct addressee can consciously decide whether to follow the group to reach an unseen point of interest. We outline our approach and give insights into the results of a first feasibility study in which we compared our new approach to non-talkative groups and groups conversing about random topics.

In this work-in-progress, we strive to combine two wayfinding techniques supporting users in gaining scene knowledge, namely (i) the River Analogy, in which users are considered as boats automatically floating down predefined rivers, e.g., streets in an urban scene, and (ii) virtual pedestrian flows as social cues indirectly guiding users through the scene. In our combined approach, the pedestrian flows function as rivers. To navigate through the scene, users leash themselves to a pedestrian of choice, considered as boat, and are dragged along the flow towards an area of interest. Upon arrival, users can detach themselves to freely explore the site without navigational constraints. We briefly outline our approach, and discuss the results of an initial study focusing on various leashing visualizations.

Taking turns in a conversation is a delicate interplay of various signals, which we as humans can easily decipher. Embodied conversational agents (ECAs) communicating with humans should leverage this ability for smooth and enjoyable conversations. Extensive research has analyzed human turn-taking cues, and attempts have been made to predict turn-taking based on observed cues. These cues vary from prosodic, semantic, and syntactic modulation over adapted gesture and gaze behavior to actively used respiration. However, when generating such behavior for social robots or ECAs, often only single modalities were considered, e.g., gazing. We strive to design a comprehensive system that produces cues for all non-verbal modalities: gestures, gaze, and breathing. The system provides valuable cues without requiring speech content adaptation. We evaluated our system in a VR-based user study with N = 32 participants executing two subsequent tasks. First, we asked them to listen to two ECAs taking turns in several conversations. Second, participants engaged in taking turns with one of the ECAs directly. We examined the system's usability and the perceived social presence of the ECAs' turn-taking behavior, both with respect to each individual non-verbal modality and their interplay. While we found effects of gesture manipulation in interactions with the ECAs, no effects on social presence were found.

Teaching in optical systems design is usually performed on an optical bench. While experimentation plays an important role in education, experiments involving expensive or dangerous components are usually limited to short, heavily supervised sessions. Computer simulations, on the other hand, offer high accessibility, but suffer from reduced realism and tangibility when presented on a 2D screen. For this reason, we present the virtual optical bench, an application that lets users explore spherical lens layouts in virtual reality (VR). We implemented a numerically accurate simulation of optical systems using Nvidia OptiX, as well as a prototypical VR application, which we then evaluated in an expert review with 6 optics experts. Based on their feedback, we re-implemented our VR application in Unreal Engine 4. The re-implementation has since been actively used for teaching optical layouts, where we performed a qualitative evaluation with 18 students. We show that our virtual optical bench achieves good usability and is perceived to enhance the understanding of course contents.

Most prior teleportation techniques in virtual reality are bound to target positions in the vicinity of selectable scene objects. In this paper, we present three adaptations of the classic teleportation metaphor that enable the user to travel to mid-air targets as well. Inspired by related work on the combination of teleports with virtual rotations, our three techniques differ in the extent to which elevation changes are integrated into the conventional target selection process. Elevation can be specified either simultaneously, as a connected second step, or separately from horizontal movements. A user study with 30 participants indicated a trade-off between the simultaneous method leading to the highest accuracy and the two-step method inducing the lowest task load as well as receiving the highest usability ratings. The separate method was least suitable on its own but could serve as a complement to one of the other approaches. Based on these findings and previous research, we define initial design guidelines for mid-air navigation techniques.

A virtual guide in an immersive virtual environment allows users a structured experience without missing critical information. However, although being in an interactive medium, the user is only a passive listener, while the embodied conversational agent (ECA) fulfills the active roles of wayfinding and conveying knowledge. Thus, we investigated for the use case of a virtual museum, whether users prefer a virtual guide or a free exploration accompanied by an ECA who imparts the same information compared to the guide. Results of a small within-subjects study with ahead-mounted display are given and discussed, resulting in the idea of combining benefits of both conditions for a higher user acceptance. Furthermore, the study indicated the feasibility of the carefully designed scene and ECA's appearance.

Virtual Reality is increasingly used for safe evaluation and validation of autonomous vehicles by automotive engineers. However, the design and creation of virtual testing environments is a cumbersome process. Engineers are bound to utilize desktop-based authoring tools, and a high level of expertise is necessary. By performing scene authoring entirely inside VR, faster design iterations become possible. To this end, we propose a VR authoring environment that enables engineers to design road networks and traffic scenarios for automated vehicle testing based on free-hand interaction. We present a 3D interaction technique for the efficient placement and selection of virtual objects that is employed on a 2D panel. We conducted a comparative user study in which our interaction technique outperformed existing approaches regarding precision and task completion time. Furthermore, we demonstrate the effectiveness of the system by a qualitative user study with domain experts.

For conversational agents’ speech, either all possible sentences have to be prerecorded by voice actors or the required utterances can be synthesized. While synthesizing speech is more flexible and economic in production, it also potentially reduces the perceived naturalness of the agents among others due to mistakes at various linguistic levels. In our article, we are interested in the impact of adequate and inadequate prosody, here particularly in terms of accent placement, on the perceived naturalness and aliveness of the agents. We compare (1) inadequate prosody, as generated by off-the-shelf text-to-speech (TTS) engines with synthetic output; (2) the same inadequate prosody imitated by trained human speakers; and (3) adequate prosody produced by those speakers. The speech was presented either as audio-only or by embodied, anthropomorphic agents, to investigate the potential masking effect by a simultaneous visual representation of those virtual agents. To this end, we conducted an online study with 40 participants listening to four different dialogues each presented in the three Speech levels and the two Embodiment levels. Results confirmed that adequate prosody in human speech is perceived as more natural (and the agents are perceived as more alive) than inadequate prosody in both human (2) and synthetic speech (1). Thus, it is not sufficient to just use a human voice for an agents’ speech to be perceived as natural—it is decisive whether the prosodic realisation is adequate or not. Furthermore, and surprisingly, we found no masking effect by speaker embodiment, since neither a human voice with inadequate prosody nor a synthetic voice was judged as more natural, when a virtual agent was visible compared to the audio-only condition. On the contrary, the human voice was even judged as less “alive” when accompanied by a virtual agent. In sum, our results emphasize, on the one hand, the importance of adequate prosody for perceived naturalness, especially in terms of accents being placed on important words in the phrase, while showing, on the other hand, that the embodiment of virtual agents plays a minor role in the naturalness ratings of voices.

Modeling the interactions between users and social groups of virtual agents (VAs) is vital in many virtual-reality-based applications. However, only little research on group encounters has been conducted yet. We intend to close this gap by focusing on the distinction between joining and passing-by a group. To enhance the interactive capacity of VAs in these situations, knowing the user's objective is required to show reasonable reactions. To this end, we propose a classification scheme which infers the user's intent based on social cues such as proxemics, gazing and orientation, followed by triggering believable, non-verbal actions on the VAs. We tested our approach in a pilot study with overall promising results and discuss possible improvements for further studies.

Sketch-based interfaces in 2D screen space allow to efficiently author the flow of virtual crowds in a direct and interactive manner. Here, options to redirect a flow by sketching barriers, or guiding entities based on a sketched network of connected sections are provided.

Virtual-reality-based interactions with virtual agents (VAs) are likely subject to similar influences as human-human interactions. In either real or virtual social interactions, interactants try to maintain their personal space (PS), an ubiquitous, situative, flexible safety zone. Building upon larger PS preferences to humans and VAs with angry facial expressions, we extend the investigations to whole-body emotional expressions. In two immersive settings-HMD and CAVE-66 males were approached by an either happy, angry, or neutral male VA. Subjects preferred a larger PS to the angry VA when being able to stop him at their convenience (Sample task), replicating previous findings, and when being able to actively avoid him (Pass By task). In the latter task, we also observed larger distances in the CAVE than in the HMD.

Generating natural embodied conversational agents within virtual spaces crucially depends on speech sounds and their directionality. In this work, we simulated directional filters to not only add directionality, but also directionally adapt each phoneme. We therefore mimic reality where changing mouth shapes have an influence on the directional propagation of sound. We conducted a study (n = 32) evaluating naturalism ratings, preference and distinguishability of omnidirectional speech auralization compared to static and dynamic, phoneme-dependent directivities. The results indicated that participants cannot distinguish dynamic from static directivity. Furthermore, participants' preference ratings aligned with their naturalism ratings. There was no unanimity, however, with regards to which auralization is the most natural.

When aiming for large scale parallel computing, waiting time due to network latency, synchronization, and load imbalance are the primary opponents of high parallel efficiency. A common approach to hide latency with computation is the use of non-blocking communication. In the presence of a consistent load imbalance, synchronization cost is just the visible symptom of the load imbalance. Tasking approaches as in OpenMP, TBB, OmpSs, or C++20 coroutines promise to expose a higher degree of concurrency, which can be distributed on available execution units and significantly increase load balance. Available MPI non-blocking functionality does not integrate seamlessly into such tasking parallelization. In this work, we present a slim extension of the MPI interface to allow seamless integration of non-blocking communication with available concepts of asynchronous execution in OpenMP and C++.

Tracking the temporal evolution of features in time-varying data is a key method in visualization. For typical feature definitions, such as vortices, objects are sparsely distributed over the data domain. In this paper, we present a novel approach for tracking both sparse and space-filling features. While the former comprise only a small fraction of the domain, the latter form a set of objects whose union covers the domain entirely while the individual objects are mutually disjunct. Our approach determines the assignment of features between two successive time-steps by solving two graph optimization problems. It first resolves one-to-one assignments of features by computing a maximum-weight, maximum-cardinality matching on a weighted bi-partite graph. Second, our algorithm detects events by creating a graph of potentially conflicting event explanations and finding a weighted, independent set in it. We demonstrate our method's effectiveness on synthetic and simulation data sets, the former of which enables quantitative evaluation because of the availability of ground-truth information. Here, our method performs on par or better than a well-established reference algorithm. In addition, manual visual inspection by our collaborators confirm the results' plausibility for simulation data.

Embodied conversational agents become more and more important in various virtual reality applications, e.g., as peers, trainers or therapists. Besides their appearance and behavior, appropriate speech is required for them to be perceived as human-like and realistic. Additionally to the used voice signal, also its auralization in the immersive virtual environment has to be believable. Therefore, we investigated the effect of adding directivity to the speech sound source. Directivity simulates the orientation dependent auralization with regard to the agent's head orientation. We performed a one-factorial user study with two levels (n=35) to investigate the effect directivity has on the perceived social presence and realism of the agent's voice. Our results do not indicate any significant effects regarding directivity on both variables covered. We account this partly to an overall too low realism of the virtual agent, a not overly social utilized scenario and generally high variance of the examined measures. These results are critically discussed and potential further research questions and study designs are identified.

In this work, we evaluate the impact of passive haptic feedback on touch-based menus, given the constraints and possibilities of a seated, desk-based scenario in VR. Therefore, we compare a menu that once is placed on the surface of a desk and once mid-air on a surface in front of the user. The study design is completed by two conditions without passive haptic feedback. In the conducted user study (n=33), we found effects of passive haptics (present vs-non-present) and menu alignment (desk vs. mid-air) on the task performance and subjective look & feel. However, the race between the conditions was close. An overall winner was the mid-air menu with passive haptic feedback, which however raises hardware requirements.

In this work, we evaluate the feasibility of an office desk substitution in the context of a visual data analysis task involving travel. We measure the impact on cybersickness as well as the general task performance and presence. In the conducted user study (n=52), surprisingly, and partially in contradiction to existing work, we found no significant differences for those core measures between the control condition without a virtual table and the condition containing a virtual table.

The ongoing migration of HMDs to the consumer market also allows the integration of immersive environments into analysis workflows that are often bound to an (office) desk. However, a critical factor when considering VR solutions for professional applications is the prevention of cybersickness. In the given scenario the user is usually seated and the surrounding real world environment is very dominant, where the most dominant part is maybe the desk itself. Including this desk in the virtual environment could serve as a resting frame and thus reduce cybersickness next to a lot of further possibilities. In this work, we evaluate the feasibility of a substitution like this in the context of a visual data analysis task involving travel, and measure the impact on cybersickness as well as the general task performance and presence. In the conducted user study ( n=52), surprisingly, and partially in contradiction to existing work, we found no significant differences for those core measures between the control condition without a virtual table and the condition containing a virtual table. However, the results also support the inclusion of a virtual table in desk-based use cases.

Presents the preface to the 2019 Virtual Reality Conference.

Personal space (PS), the flexible protective zone maintained around oneself, is a key element of everyday social interactions. It, e.g., affects people's interpersonal distance and is thus largely involved when navigating through social environments. However, the PS is regulated dynamically, its size depends on numerous social and personal characteristics and its violation evokes different levels of discomfort and physiological arousal. Thus, gaining more insight into this phenomenon is important. We contribute to the PS investigations by presenting the results of a controlled experiment in a CAVE, focusing on German males in the age of 18 to 30 years. The PS preferences of 27 participants have been sampled while they were approached by either a single embodied, computer-controlled virtual agent (VA) or by a group of three VAs. In order to investigate the influence of a VA's emotions, we altered their facial expression between angry and happy. Our results indicate that the emotion as well as the number of VAs approaching influence the PS: larger distances are chosen to angry VAs compared to happy ones; single VAs are allowed closer compared to the group. Thus, our study is a foundation for social and behavioral studies investigating PS preferences.

Fluid artwork refers to works of art based on the aesthetics of fluid motion, such as smoke photography, ink injection into water, and paper marbling. Inspired by such types of art, we created Fluid Sketching as a novel medium for creating 3D fluid artwork in immersive virtual environments. It allows artists to draw 3D fluid-like sketches and manipulate them via six degrees of freedom input devices. Different brush stroke settings are available, varying the characteristics of the fluid. Because of fluids' nature, the diffusion of the drawn fluid sketch is animated, and artists have control over altering the fluid properties and stopping the diffusion process whenever they are satisfied with the current result. Furthermore, they can shape the drawn sketch by directly interacting with it, either with their hand or by blowing into the fluid. We rely on particle advection via curl-noise as a fast procedural method for animating the fluid flow.

During free exploration of an unknown virtual scene, users often miss important parts, leading to incorrect or incomplete environment knowledge and a potential negative impact on performance in later tasks. This is addressed by wayfinding aids such as compasses, maps, or trails, and automated exploration schemes such as guided tours. However, these approaches either do not actually ensure exploration success or take away control from the user. Therefore, we present an interactive assistance interface to support exploration that guides users to interesting and unvisited parts of the scene upon request, supplementing their own, free exploration. It is based on an automated analysis of object visibility and viewpoint quality and is therefore applicable to a wide range of scenes without human supervision or manual input. In a user study, we found that the approach improves users' knowledge of the environment, leads to a more complete exploration of the scene, and is also subjectively helpful and easy to use.

It is our great pleasure to welcome you to the 25th IEEE Conference on Virtual Reality and 3D User Interfaces (IEEE VR), the premiere international conference focused on research in these domains! This year the name of the conference changed since the highly successful 12-year IEEE Symposium on 3D User Interfaces is brought back into the main VR conference. It is a tremendous honor to host the conference in Reutlingen on its first return to Germany since 2005. Reutlingen is situated nicely with respect to our research institutes, the city has the charm of a southern German town, and the recently built (2013) Stadthalle and concert venue has a professional team that is experienced in conferences highlighting innovation in technology. This venue has enabled us to create a large program both in scientific content and in terms of demonstration and exhibit space.

Traditionally, experimental economics uses controlled and incentivized field and lab experiments to analyze economic behavior. However, investigating peer effects in the classic settings is challenging due to the reflection problem: Who is influencing whom? To overcome this, we enlarge the methodological toolbox of these experiments by means of Virtual Reality. After introducing and validating a real-effort sorting task, we embed a virtual agent as peer of a human subject, who independently performs an identical sorting task. We conducted two experiments investigating (a) the subject's productivity adjustment due to peer effects and (b) the incentive effects on competition. Our results indicate a great potential for Virtual-Reality-based economic experiments.

Viewpoint quality estimation methods allow the determination of the most informative position in a scene. However, a single position usually cannot represent an entire scene, requiring instead a set of several viewpoints. Measuring the quality of such a set of views, however, is not trivial, and the computation of an optimal set of views is an NP-hard problem. Therefore, in this work, we propose three methods to estimate the quality of a set of views. Furthermore, we evaluate three approaches for computing an approximation to the optimal set (two of them new) regarding effectiveness and efficiency.

The manual adjustment of travel speed to cover medium or large distances in virtual environments may increase cognitive load, and manual travel at high speeds can lead to cybersickness due to inaccurate steering. In this work, we present an approach to quickly pass regions where the environment does not change much, using automated suggestions based on the computation of common visibility. In a user study, we show that our method can reduce cybersickness when compared with manual speed control.

Choosing an adequate system control technique is crucial to support complex interaction scenarios in virtual reality applications. In this work, we compare an existing hierarchical pie-menu-based approach with a speech-recognition-based one in terms of task performance and user experience in a formal user study. As testbed, we use a factory planning application featuring a large set of system control options.

Immersive visualization (IV) fosters the creation of mental images of a data set, a scene, a procedure, etc. We devise an initial version of a design space for categorizing workflows that take advantage of IV. From this categorization, specific requirements for an actual, seamless IV-integration can be derived. We validate the design space with three workflows investigated in our research projects.

The use of non-verbal vocal input (NVVI) as a hand-free trigger approach has proven to be valuable in previous work [7]. Nevertheless, BlowClick's original detection method is vulnerable to false positives and, thus, is limited in its potential use, e.g., together with acoustic feedback for the trigger. Therefore, we extend the existing approach by adding common machine learning methods. We found that a support vector machine (SVM) with Gaussian kernel performs best for detecting blowing with at least the same latency and more precision as before. Furthermore, we added acoustic feedback to the NVVI trigger, which increases the user's confidence. To evaluate the advanced trigger technique, we conducted a user study (n = 33). The results confirm that it is a reliable trigger; alone and as part of a hands-free point-and-click interface.

Controlling user-agent-interactions by means of an external operator includes selecting the virtual interaction partners fast and faultlessly. However, especially in immersive scenes with a large number of potential partners, this task is non-trivial.

Orientation and wayfinding in architectural Immersive Virtual Environments (IVEs) are non-trivial, accompanying tasks which generally support the users' main task. World in Miniatures (WIMs) - essentially 3D maps containing a scene replica - are an established approach to gain survey knowledge about the virtual world, as well as information about the user's relation to it. However, for large-scale, information-rich scenes, scaling and occlusion issues result in diminishing returns. Since there typically is a lack of standardized information regarding scene decompositions, presenting the inside of self-contained scene extracts is challenging. Therefore, we present an automatic WIM generation workflow for arbitrary, realistic in- and outdoor IVEs in order to support users with meaningfully selected and scaled extracts of the IVE as well as corresponding context information. Additionally, a 3D user interface is provided to manually manipulate the represented extract.

An immersive virtual environment is the ideal platform for the planning and training of on-orbit servicing missions, as it provides a flexible and safe environment. In such kind of virtual assembly simulation, grasping virtual objects is one of the most common and natural interactions. However, unlike grasping objects in the real world, it is a non-trivial task in virtual environments, where the primary feedback is visual only. A lot of research investigated ways to provide haptic feedback, such as force, vibrational and electrotactile feedback. Such devices, however, are usually uncomfortable and hard to integrate in projection-based immersive YR systems. In this paper, we present a novel, small and lightweight electro-tactile feedback device, specifically designed for immersive virtual environments. It consists of a small tactor with eight electrodes for each finger and a signal generator attached to the user's hand or arm. Our device can be easily integrated with an existing optical finger tracking system. The study presented in this paper assesses the feasibility and usability of the interaction device. An experiment was conducted in a repeated measures design using the electrotactile feedback modality as independent variable. As benchmark, we chose three typical assembly tasks of a YR simulation for satellite on-orbit servicing missions, including pressing a button, switching a lever switch, and pulling a module from its slot. Results show that electrotactile feedback improved the user's grasping in our virtual on-orbit servicing scenario. The task completion time was significantly lower for all three tasks and the precision of the user's interaction was higher. The workload reported by the participants was significantly lower when using electrotactile feedback. Additionally, users were more confident with their performance while completing the tasks with electrotactile feedback. We describe the device, outline the user study and report the results.

To use the full potential of immersive data analysis when wearing a head-mounted display, the user has to be able to navigate through the spatial data. We collected, developed and evaluated 5 different handsfree navigation methods that are usable while seated in the analyst's usual workplace. All methods meet the requirements of being easy to learn and inexpensive to integrate into existing workplaces. We conducted a user study with 23 participants which showed that a body leaning metaphor and an accelerometer pedal metaphor performed best within the given task.

Virtual Reality (VR) has been an active field of research for several decades, with 3D interaction and 3D User Interfaces (UIs) as important sub-disciplines. However, the development of 3D interaction techniques and in particular combining several of them to construct complex and usable 3D UIs remains challenging, especially in a VR context. In addition, there is currently only limited reusable software for implementing such techniques in comparison to traditional 2D UIs. To overcome this issue, we present ViSTA Widgets, a software framework for creating 3D UIs for immersive virtual environments. It extends the ViSTA VR framework by providing functionality to create multi-device, multi-focus-strategy interaction building blocks and means to easily combine them into complex 3D UIs. This is realized by introducing a device abstraction layer along sophisticated focus management and functionality to create novel 3D interaction techniques and 3D widgets. We present the framework and illustrate its effectiveness with code and application examples accompanied by performance evaluations.

Abstract Interactive analysis of 3D relational data is challenging. A common way of representing such data are node‐link diagrams as they support analysts in achieving a mental model of the data. However, naïve 3D depictions of complex graphs tend to be visually cluttered, even more than in a 2D layout. This makes graph exploration and data analysis less efficient. This problem can be addressed by edge bundling. We introduce a 3D cluster‐based edge bundling algorithm that is inspired by the force‐directed edge bundling (FDEB) algorithm [ HvW09b ] and fulfills the requirements to be embedded in an interactive framework for spatial data analysis. It is parallelized and scales with the size of the graph regarding the runtime. Furthermore, it maintains the edge's model and thus supports rendering the graph in different structural styles. We demonstrate this with a graph originating from a simulation of the function of a macaque brain.

When moving through a tracked immersive virtual environment, it is sometimes useful to deviate from the normal one-to-one mapping of real to virtual motion. One option is the application of rotation gain, where the virtual rotation of a user around the vertical axis is amplified or reduced by a factor. Previous research in head-mounted display environments has shown that rotation gain can go unnoticed to a certain extent, which is exploited in redirected walking techniques. Furthermore, it can be used to increase the effective field of regard in projection systems. However, rotation gain has never been studied in CAVE systems, yet. In this work, we present an experiment with 87 participants examining the effects of rotation gain in a CAVE-like virtual environment. The results show no significant effects of rotation gain on simulator sickness, presence, or user performance in a cognitive task, but indicate that there is a negative influence on spatial knowledge especially for inexperienced users. In secondary results, we could confirm results of previous work and demonstrate that they also hold for CAVE environments, showing a negative correlation between simulator sickness and presence, cognitive performance and spatial knowledge, a positive correlation between presence and spatial knowledge, a mitigating influence of experience with 3D applications and previous CAVE exposure on simulator sickness, and a higher incidence of simulator sickness in women.

To avoid simulator sickness and improve presence in immersive virtual environments (IVEs), high frame rates and low latency are required. In contrast, volume rendering applications typically strive for high visual quality that induces high computational load and, thus, leads to low frame rates. To evaluate this trade-off in IVEs, we conducted a controlled user study with 53 participants. Search and count tasks were performed in a CAVE with varying volume rendering conditions which are applied according to viewer position updates corresponding to head tracking. The results of our study indicate that participants preferred the rendering condition with continuous adjustment of the visual quality over an instantaneous adjustment which guaranteed for low latency and over no adjustment providing constant high visual quality but rather low frame rates. Within the continuous condition, the participants showed best task performance and felt less disturbed by effects of the visualization during movements. Our findings provide a good basis for further evaluations of how to accelerate volume rendering in IVEs according to user's preferences.

Data annotation finds increasing use in Virtual Reality applications with the goal to support the data analysis process, such as architectural reviews. In this context, a variety of different annotation systems for application to immersive virtual environments have been presented. While many interesting interaction designs for the data annotation workflow have emerged from them, important details and evaluations are often omitted. In particular, we observe that the process of handling metadata to interactively create and manage complex annotations is often not covered in detail. In this paper, we strive to improve this situation by focusing on the design of data annotation workflows and their evaluation. We propose a workflow design that facilitates the most important annotation operations, i.e., annotation creation, review, and modification. Our workflow design is easily extensible in terms of supported annotation and metadata types as well as interaction techniques, which makes it suitable for a variety of application scenarios. To evaluate it, we have conducted a user study in a CAVE-like virtual environment in which we compared our design to two alternatives in terms of a realistic annotation creation task. Our design obtained good results in terms of task performance and user experience.

In this work, we present an approach for tracking the feet of multiple users in CAVE-like systems with under-floor projection. It is based on low-cost consumer cameras, does not require users to wear additional equipment, and can be installed without modifying existing components. If the brightness of the floor projection does not contain too much variation, the feet of several people can be reliably tracked and assigned to individuals.

In this work, we report on a pilot study we conducted, and on a study design, to examine the effects and applicability of rotation gain in CAVE-like virtual environments. The results of the study will give recommendations for the maximum levels of rotation gain that are reasonable in algorithms for enlarging the virtual field of regard or redirected walking.

Virtual Reality (VR) systems are of growing importance to aid decision support in the context of the digital factory, especially factory layout planning. While current solutions either focus on virtual walkthroughs or the visualization of more abstract information, a solution that provides both, does currently not exist. To close this gap, we present a holistic VR application, called Factory Layout Planning Assistant (flapAssist). It is meant to serve as a platform for planning the layout of factories, while also providing a wide range of analysis features. By being scalable from desktops to CAVEs and providing a link to a central integration platform, flapAssist integrates well in established factory planning workflows.

Metadata in- and output are important steps within the data annotation process. However, selecting techniques that effectively facilitate these steps is non-trivial, especially for applications that have to run on multiple virtual reality platforms. Not all techniques are applicable to or available on every system, requiring to adapt workflows on a per-system basis. Here, we describe a metadata handling system based on Android's Intent system that automatically adapts workflows and thereby makes manual adaption needless.

A key aspect of air traffic infrastructure projects is the communication between stakeholders during the approval process regarding their environmental impact. Yet, established means of communication have been found to be rather incomprehensible. In this paper we present an application that addresses these communication issues by enabling the exploration of airplane noise emissions in the vicinity of airports in a virtual environment (VE). The VE is composed of a model of the airport area and flight movement data. We combine a real-time 3D auralization approach with visualization techniques to allow for an intuitive access to noise emissions. Specifically designed interaction techniques help users to easily explore and compare air traffic scenarios.

Pie menus are a well-known technique for interacting with 2D environments and so far a large body of research documents their usage and optimizations. Yet, comparatively little research has been done on the usability of pie menus in immersive virtual environments (IVEs). In this paper we reduce this gap by presenting an implementation and evaluation of an extended hierarchical pie menu system for IVEs that can be operated with a six-degrees-of-freedom input device. Following an iterative development process, we first developed and evaluated a basic hierarchical pie menu system. To better understand how pie menus should be operated in IVEs, we tested this system in a pilot user study with 24 participants and focus on item selection. Regarding the results of the study, the system was tweaked and elements like check boxes, sliders, and color map editors were added to provide extended functionality. An expert review with five experts was performed with the extended pie menus being integrated into an existing VR application to identify potential design issues. Overall results indicated high performance and efficient design.

We present results of a user study in which we compared three interaction methods for manipulating deformable objects in immersive virtual environments. The task was to control a virtual robot hand removing a thin foil cover from a satellite in an on-orbit servicing training simulator. The lack of haptic feedback placed a high challenge on the user when trying to apply the right force for grasping the foil without losing grip or damaging it. We compared the intuitiveness and effectiveness of using a tracked joystick, finger distance measurement, and a novel prototype enabling direct force input through pinching.

Palpation is a physical examination technique where objects, e.g., organs or body parts, are touched with fingers to determine their size, shape, consistency and location. Many medical procedures utilize palpation as a supplementary interaction technique and it can be therefore considered as an essential basic method. However, palpation is mostly neglected in medical training simulators, with the exception of very specialized simulators that solely focus on palpation, e.g., for manual cancer detection. In this article we propose a novel approach to enable haptic palpation interaction for virtual reality-based medical simulators. The main contribution is an extensive user study conducted with a large group of medical experts. To provide a plausible simulation framework for this user study, we contribute a novel and detailed interaction algorithm for palpation with tissue dragging, which utilizes a multi-object force algorithm to support multiple layers of anatomy and a pulse force algorithm for simulation of an arterial pulse. Furthermore, we propose a modification for an off–the–shelf haptic device by adding a lightweight palpation pad to support a more realistic finger grip configuration for palpation tasks. The user study itself has been conducted on a medical training simulator prototype with a specific procedure from regional anesthesia, which strongly depends on palpation. The prototype utilizes a co-rotational finite-element approach for soft tissue simulation and provides bimanual interaction by combining the aforementioned techniques with needle insertion for the other hand. The results of the user study suggest reasonable face validity of the simulator prototype and in particular validate medical plausibility of the proposed palpation interaction algorithm.

The knowledge of the propagation behavior of radio waves is a fundamental prerequisite for planning and optimizing mobile radio networks. Propagation effects are usually simulated numerically, since real-world measurement campaigns are time-consuming and expensive. Automatic planning algorithms can explore a vast amount of network configurations to find good deployment schemes. However, complex urban scenarios demand for a great emphasis on site-specific details in the propagation environment which are often not covered by automatic approaches. Therefore, we have combined the simulation of radio waves with an interactive exploration and modification of the propagation environment in a virtual reality prototype application. By coupling real-time simulation and manipulation tasks we can provide an uninterrupted user-centered workflow.

Conventional beam tracing can be used for solving global illumination problems. It is an efficient algorithm and performs very well when implemented on the GPU. This allows us to apply the algorithm in a novel way to the problem of radio wave propagation. The simulation of radio waves is conceptually analogous to the problem of light transport. We use a custom, parallel rasterization pipeline for creation and evaluation of the beams. We implement a subset of a standard 3D rasterization pipeline entirely on the GPU, supporting 2D and 3D frame buffers for output. Our algorithm can provide a detailed description of complex radio channel characteristics like propagation losses and the spread of arriving signals over time (delay spread). Those are essential for the planning of communication systems required by mobile network operators. For validation, we compare our simulation results with measurements from a real-world network. Furthermore, we account for characteristics of different propagation environments and estimate the influence of unknown components like traffic or vegetation by adapting model parameters to measurements.

In this paper we present a GPU implementation to accurately select 3D objects based on their silhouettes by a pointing device with six degrees of freedom (6DOF) in a virtual environment (VE). We adapt a 2D picking metaphor to 3D selection in VE's by changing the projection and view matrices according to the position and orientation of a 6DOF pointing device and rendering a conic selection volume to an off-screen pixel buffer. This method works for triangulated as well as volume rendered objects, no explicit geometric representation is required.

The analysis of time-dependent simulation data is a demanding task, both in terms of computing power and time. Interactive analysis using multiple linked views has been shown to be one possible solution to this problem. However, there are two significant short-comings when limited to a standard desktop-based setup: first, complex spatial relationships are hard to understand using only 2D projections of the data. Second, the size of today's simulation runs is too large to be handled even by powerful workstations. We describe a system for the interactive analysis of large, time-dependent data in virtual environments. Based on the techniques of multiple linked views and brushing, our approach allows the user to quickly formulate, visualize and assess hypotheses about the data. To enable an interactive exploration even in the face of multi-gigabyte data sets, we distribute the workload to a multi-processor parallel machine and a rendering client.

The application of virtual environments to scientific visualization provides the user with an intuitive interface to interact with the data to be analyzed. We present an approach that leverages the utilization of 3D interaction techniques to directly interact with scientific data. First, we propose an abstraction of VR-based interaction by decoupling the low-level interaction groundwork from high-level declarations of interaction behaviors. Second, we describe how recurring interaction patterns in scientific visualizations can be distilled into 3D widgets, exhibiting reusability for diverse participants in the development of interactive visualization. The benefits which follow from this approach are exchangeability of VR-toolkits and devices, faster development cycles and better code maintainability.

Abstract The analysis of unsteady phenomena is an important topic for scientific visualization. Several time‐dependent visualization techniques exist, as well as solutions for dealing with the enormous size of time‐varying data in interactive visualization. Many current visualization toolkits support displaying time‐varying data sets. However, for the interactive exploration of time‐varying data in scientific visualization, no common time model that describes the temporal properties which occur in the visualization process has been established. In this work, we propose a general time model which classifies the time frames of simulation phenomena and the connections between different time scales in the analysis process. This model is designed for intuitive interaction with time in visualization applications for the domain expert as well as for the developer of visualization tools. We demonstrate the benefits of our model by applying it to two use cases with different temporal properties.

Ventricular Assist Devices (VADs) support the heart in its vital task of maintaining circulation in the human body when the heart alone is not able to maintain a sufficient flow rate due to illness or degenerative diseases. However, the engineering of these devices is a highly demanding task. Advanced modeling methods and computer simulations allow the investigation of the fluid flow inside such a device and in particular of potential blood damage. In this paper we present a set of visualization methods which have been designed to specifically support the analysis of a tensor-based blood damage prediction model. This model is based on the tracing of particles through the VAD, for each of which the cumulative blood damage can be computed. The model's tensor output approximates a single blood cell's deformation in the flow field. The tensor and derived scalar data are subsequently visualized using techniques based on icons, particle visualization, and function plotting. All these techniques are accessible through a Virtual Reality-based user interface, which features not only stereoscopic rendering but also natural interaction with the complex three-dimensional data. To illustrate the effectiveness of these visualization methods, we present the results of an analysis session that was performed by domain experts for a specific data set for the MicroMed DeBakey VAD.

Extraction of complex data structures like vector field topologies in large-scale, unsteady flow field datasets for the interactive exploration in virtual environments cannot be carried out without parallelization strategies. We present an approach based on Nested OpenMP to find critical points, which are the essential parts of velocity field topologies. We evaluate our parallelization scheme on several multi-block datasets, and present the results for various thread counts and loop schedules on all parallelization levels. Our experience suggests that upcoming massively multi-threaded processor architectures can be very advantageously for large-scale feature extractions.

We propose a method to determine the optimal camera alignment for a tracking system with multiple cameras by specifying the volume to be tracked and an initial camera setup. We use optimization strategies based on methods usually employed for solving nonlinear systems of equations. All approaches are fully automatic and take advantage of modern graphics hardware since we also implement a GPU-based, accelerated visibility test. The algorithm automatically optimizes the whole setup by adjusting the given set of camera parameters. We can steer the optimization towards different goals depending on the desired application, e.g. the widest possible volume coverage or maximum camera visibility to overcome heavy occlusion problems during the tracking process. We also consider parameter constraints that the user may specify according to restrictions in the local environment where the cameras have to be mounted. This allows for a convenient definition of higher level constraints for the camera setup.

Nasal airway obstruction is a serious and common problem within the field of rhinology. This paper introduces VRhino II, a virtual-reality-based application for the analysis of the airflow through the human nasal cavity. This tool is currently developed within a research project striving to gain better insight into the flow conditions during respiration. The paper's focus lies on a general description of the application's design. Additionally, technical details about the main system components are given.

Common research in the field of Virtual Reality (VR) considers acoustic stimulation as a highly important necessity for enhanced immersion into virtual scenes. However, most common VR toolkits do only marginally support the integration of sound for the application programmer. Furthermore, the quality of stimulation that is provided usually ranges from system sounds (e.g. beeps while selecting a menu) to simple 3D panning. In the latter case, these approaches do only allow the user to correctly detect sounds that are at quite a distance from his current position. Binaural synthesis is an interesting way to allow the spatial auditory representation by using few loudspeakers or headphones. This paper describes a system that combines the efforts of creating a binaural representation for the listener who is interacting in a common visual VR application in real-time, thus allowing the research on interaction between visual and auditory human perception systems. It will describe the theoretical background to establishing a binaural representation of a sound and the necessary hardware set-up for this. Afterwards, the infrastructure and software interface which will allow the connection of the audio renderer to a visual VR toolkit is discusse

One recommended strategy for the analysis of CFD-data is the interactive exploration within virtual environments. Common visualization systems are unable to process large data sets while carrying out real-time interaction and visualization at the same time. The obvious idea is to decouple flow feature extraction from visualization. This paper covers the functionality of the parallel CFD post-processing toolkit Viracocha. Two aspects are discussed in more detail. The first approach covers strategies to reduce the loading time. Data caching and prefetching are employed to reduce access time. The second aspect concerns an approach called streaming that minimizes the time a user has to wait for first results. Viracocha already sends coarse intermediate data back to the virtual environment before the final result is available. Different streaming and data handling strategies are described. In order to emphasize the benefit of our implementation efforts, some strategies are applied to multi-block CFD data sets.

Real time tissue deformation is an important aspect of interactive virtual reality (VR) environments such as medical trainers. Most approaches in deformable modelling use a fixed space discretization. A surgical trainer requires high plausibility of the deformations especially in the area close to the instrument. As the area of intervention is not known a priori, adaptive techniques have to be applied.We present an approach for real time deformation of soft tissue based on a regular FEM mesh of cube elements as opposed to a mesh of tetrahedral elements used by the majority of soft tissue simulators. A regular mesh structure simplifies the local refinement operation as the elements topology and stiffness are known implicitly. We propose an octree-based adaptive multiresolution extension of our basic approach.The volumetric representation of the deformed object is created automatically from medical images or by voxelization of a surface model. The resolution of the volumetric representation is independent of the surface geometry resolution. The surface is deformed according to the simulation performed on the underlying volumetric mesh.

Adaptive resonance theory (ART) describes a family of self-organizing neural networks, capable of clustering arbitrary sequences of input patterns into stable recognition codes. Many different types of ART-networks have been developed to improve clustering capabilities. In this paper we compare clustering performance of different types of ART-networks: Fuzzy ART, ART 2A with and without complement encoded input patterns, and an Euclidean ART 2A-variation. All types are tested with two- and high-dimensional input patterns in order to illustrate general capabilities and characteristics in different system environments. Based on our simulation results, Fuzzy ART seems to be less appropriate whenever input signals are corrupted by additional noise, while ART 2A-type networks keep stable in all inspected environments. Together with other examined features, ART-architectures suited for particular applications can be selected.