Lars Winkler Pettersson

Evaluating 2D and 3D visualizations of spatiotemporal information

Time-varying geospatial data presents some specific challenges for visualization. Here, we report the results of three experiments aiming at evaluating the relative efficiency of three existing visualization techniques for a class of such data. The class chosen was that of object movement, especially the movements of vehicles in a fictitious landscape. Two different tasks were also chosen. One was to predict where three vehicles will meet in the future given a visualization of their past movement history. The second task was to estimate the order in which four vehicles arrived at a specific place. Our results reveal that previous findings had generalized human perception in these situations and that large differences in user efficiency exist for a given task between different types of visualizations depicting the same data. Furthermore, our results are in line with earlier general findings on the nature of human perception of both object shape and scene changes. Finally, the need for new taxonomies of data and tasks based on results from perception research is discussed.

Visualizations of symbols in a horizontal multiple viewer 3D display environment

In this paper we present a visualization environment for collaborative and co-located displays of geospatially related data for command and control. We first describe the working principle of a novel horizontal display that is aimed at providing high resolution stereoscopic 3D visualizations simultaneously to a group of up to four observers. This display environment opens up new ways to present view-dependent visual content within a shared workspace. For this environment we propose frontoparallel presentations of conventional symbols that are 3D presentations of 2D symbols which appear virtually oriented towards the line of sight of the observer. In an experiment we compare frontoparallel symbols with flat symbols i.e. symbols that are presented in the horizontal plane of the display. The results of our study indicate that frontoparallel symbols in a stereoscopic view are perceived and identified faster than symbols presented flat in relation to the plane of the display.

Ferromagnetic resonance in nickel around the curie temperature

Abstract The ferromagnetic resonance behaviour of nickel up to and above T c is investigated. It is shown that up to the Curie point, which is 357.8°C, the resonance can be described by the Gilbert equation with the parameters g = 2.20 ±0.02 and λ = (4.0±0.5) × 10 9 s −1 . Above T c , however, it is an open question if the Gilbert equation describes the resonance adequately. No sign of a decreasing linewidth above 365°C is seen. On the contrary, the resonance broadens rapidly and fades away. The experiment is performed in a new way with the cavity kept at room temperature and the temperature of the sample is monitored during the run of the spectrum.

On the role of visual references in collaborative visualization

Multi-Viewer Display Environments (MVDE) provide unique opportunities to present personalized information to several users concurrently in the same physical display space. MVDEs can support correct 3D visualizations to multiple users, present correctly oriented text and symbols to all viewers and allow individually chosen subsets of information in a shared context. MVDEs aim at supporting collaborative visual analysis, and when used to visualize disjoint information in partitioned visualizations they even necessitate collaboration. When solving visual tasks collaboratively in a MVDE, overall performance is affected not only by the inherent effects of the graphical presentation but also by the interaction between the collaborating users. We present results from an empirical study where we compared views with lack of shared visual references in disjoint sets of information to views with mutually shared information. Potential benefits of 2D and 3D visualizations in a collaborative task were investigated and the effects of partitioning visualizations both in terms of task performance, interaction behavior and clutter reduction. In our study of a collaborative task that required only a minimum of information to be shared, we found that partitioned views with a lack of shared visual references were significantly less efficient than integrated views. However, the study showed that subjects were equally capable of solving the task at low error levels in partitioned and integrated views. An explorative analysis revealed that the amount of visual clutter was reduced heavily in partitioned visualization, whereas verbal and deictic communication between subjects increased. It also showed that the type of the visualization (2D/3D) affects interaction behavior strongly. An interesting result is that collaboration on complex geo-time visualizations is actually as efficient in 2D as in 3D.

Effects of layer partitioning in collaborative 3d visualizations

Display technologies that support multiple independent views of the same co-located 3D visualization volume make new forms of collaboration possible. In this field of research, until now most efforts have focused on technical solutions and their applications. The main contribution of this paper is the results from a study comparing integral and partitioned 3D content in a head coupled stereoscopic environment through independent views of a shared 3D visualization. In our study we used a geospatial task that was solved by ten pairs of collaborating individuals (dyads). We measured task performance by time and error rate for the dyads in two main conditions: a) an integral visualization that presented a map in the display surface and four layers at different depths below the display surface to each of the observers, and b) a partitioned visualization, where two mutually exclusive subsets of the layers were presented to each of the observers together with the map in the display surface. The results from the study showed significant differences in regard to performance times between the two conditions. Task performance was significantly better in the condition with layer partitioning. Partitioned visualizations can thus, at least in some cases, improve performance in tasks requiring collaboration between users.

Interactive virtual mummy dissections in a historical anatomic theatre

This paper presents an interactive projection-based application for visual exploration of virtual mummies. It is part of an exposition on the Cultural Heritage of the Egyptian Mummies in the Museum Gustavianum, in Uppsala. We describe a general-purpose projection metaphor for correctly presenting virtual 3D images on the dissection table of a historical anatomic theatre. This method allows for dynamic offaxis perspective viewing situations as well as it provides keystone correction for excessive projection angles as necessitated by the specific installation environment. For the application to reach out beyond the scope of the exhibition, we developed an adaptive image-based rendering approach that scales with the performance of the rendering host. Based on dynamic mesh simplification of the 3D mummy model, it automatically performs re-projections of texture images in order to maintain correct visual results. For interaction purposes with a digitiser tablet we present a means of stroke-based input that provides ease of use to non-expert visitors of the exhibition.

In situ tomographic display for interactive data visualization

With tomographic in situ visualization we present a novel approach to interactive data visualization and exploration. This visualization concept is useful for presentation of spatially co-located information that is normally not visible to the humans eye. The tomographic in situ display allows for interactive cutting through data in space by using a spatially tracked and calibrated display. In this paper we describe the technical apparatus of our prototype and describe an application for the tomographic in situ visualization in the field of indoor climate studies.