Combining Worlds-In-Miniature and Portals to Support Comparative Immersive Visualization of Forestry Data
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Worlds-in-Wedges: Combining Worlds-in-Miniature and Portals to Support Comparative Immersive Visualization of Forestry Data Jung Who Nam* Krista McCullough† Joshua Tveite‡ Computer Science & Engineering Computer Science & Engineering Computer Science & Engineering University of Minnesota University of Minnesota University of Minnesota Maria Molina Espinosa§ Charles H. Perry¶ Barry T. Wilson|| Daniel F. Keefe** Computer Science & Engineering USDA Forest Service USDA Forest Service Computer Science & Engineering University of Minnesota Northern Research Station Northern Research Station University of Minnesota Figure 1: The worlds-in-wedges technique is applied here to visualizing three forests from the Forest Inventory and Analysis dataset. ABSTRACT and Analysis public dataset. Scientist user feedback and lessons from iterative design are reported. Virtual reality (VR) environments are typically designed so users feel present in a single virtual world at a time, but this creates a Keywords: worlds-in-miniature, 3D user interface, presence, com- problem for applications that require visual comparisons (e.g., for- parative visualization est scientists comparing multiple data-driven virtual forests). To Index Terms: address this, we present Worlds-in-Wedges, a 3D user interface Human-centered computing—Virtual reality— and visualization technique that supports comparative immersive ;——Human-centered computing—Interaction techniques—; visualization by dividing the virtual space surrounding the user into Human-centered computing—Scientific visualization—;—— volumetric wedges. There are three visual/interactive levels. The Human-centered computing—Geographic visualization—. first, worlds-in-context, visualizes high-level relationships between 1 INTRODUCTION the worlds (e.g., a map for worlds that are related in space). The sec- ond level, worlds-in-miniature, is a multi-instance implementation Many data visualizations benefit from the sense of presence that of the World-in-Miniature technique extended to support mutlivari- is possible with immersive visualization in virtual reality (VR). In ate glyph visualization. The third level, worlds-in-wedges, displays VR, users can analyze spatial relationships in data relative to their multiple large-scale worlds in wedges that act as volumetric portals. own bodies. They can also “experience” their data rather than just The interface supports navigation, selection, and view manipulation. view it. For example, immersive visualizations make it possible Since the techniques were inspired directly by problems facing forest for planetary geologists to stand near a martian crater and analyze scientists, the interface was evaluated by building a complete multi- slopes, areas in shadow, or other land features using the same spatial variate data visualization of the US Forest Service Forest Inventory reasoning skills they would at a field site on Earth [9]. In VR, archaeologists can use spatial reasoning while analyzing artifacts to *e-mail: [email protected] naturally refer back to memories of working on the actual dig site †e-mail: [email protected] (e.g., remember we found a similar lamp to this one in the trench over ‡e-mail: [email protected] there [while pointing]) [1]. Using a multi-modal, immersive speech- §e-mail: [email protected] giving interface, scholars of ancient rhetoric can literally feel what it ¶e-mail: [email protected] was like to give a speech at the hillside of the Pnyx in ancient Athens, ||e-mail: [email protected] recreated under different data-driven conditions for the assembly **e-mail: [email protected] size and time period [14]. In all of these examples, the sense of presence enabled by VR adds value to the data visualizations, but for VR to be a truly valuable data visualization tool it must do more than immerse users within their data. One critical task for many visualizations to support is visual 2019 IEEE Conference on Virtual Reality and 3D User Interfaces 23-27 March, Osaka, Japan 747 978-1-7281-1377-7/19/$31.00 ©2019 IEEE Authorized licensed use limited to: University of Wisconsin. Downloaded on February 01,2021 at 21:22:31 UTC from IEEE Xplore. Restrictions apply. comparison [11, 13]. Almost every data-driven scientific study or 2 RELATED WORK scholarly work involves some form of comparison, but, as Kim et Our research builds upon related work in both data visualization and al. report in their recent survey [13], comparison is an understudied virtual reality. problem in 3D visualization, especially for VR-based visualization. In VR, whether used for data visualization or some other ap- 2.1 Experiential Analysis Using VR plication, the tradition is to immerse oneself in a single world at Architectural walk-throughs and other first person experiences have a time, but this approach is known to be problematic for making long been considered the killer apps for VR. Applications in this visual comparisons. As Munzner puts it, “eyes beat memory” [18]. style construct data-driven worlds at life-size scale and make it Juxtaposition (side-by-side), superimposition (semitransparent or possible for the user to experience the world as in real life. We can other forms of overlays), and explicit encoding (when differences walk through historical sites that no longer exists [1,2,14] or even are possible to compute explicitly) are three useful, fundamental places like Mars, where it is impossible or difficult to be [9, 20]. approaches to visual comparison that, in theory, are all preferable to This is a style of data analysis that is often overlooked since it is trying to remember the details of a first dataset while looking at the less quantitative than other forms. In experiential data analysis, second, or third, or fifth! the feeling of what it is like to speak to a crowd of 10,000 ancient Our specific research is motivated by a collaboration with forest Athenian citizens is just as important as the ability to accurately scientists who study data collected by hand by surveyors who in- measure the dimensions of an architectural reconstruction [14]. This ventory each tree within sample plots spread throughout the United style of first-person, experiential data analysis is what we aim to States [19]. More than 20 variables are collected to describe the support, but, unlike these prior works, Worlds-in-Wedges brings this species, size, health, and other parameters of each tree. This data style of analysis to the problem of simultaneous visual comparisons. is used, in part, to develop carbon estimates of the nation’s forests, which impact climate policy. Using this data, we have developed 2.2 Comparative Visualization Using VR algorithms to generate data-driven virtual reconstructions of plots throughout the U.S. Like the planetary geologists on Mars, this en- Comparison is a crucial task for data analysis [10,11,13], but it is not ables forest scientists to see and experience their data in a life-size well understood how to facilitate comparative analysis for datasets scale that is intuitive, drawing upon their own lived experiences that are best displayed in VR [13]. A survey published in 2017 found visiting the forests. However, the most interesting thing to do with that only 2 out of 41 visualizations for comparing spatial 3D and 4D this data is to compare the plots. How do we do this in VR? It does data utilize VR and points to the need to investigate more in the area. not make sense to superimpose the plots because they do not share The survey identifies four fundamental approaches for comparative the same spatial reference frame. If not superimposition, then per- visualization: Superimposition, Juxtaposition, Interchangeable (over haps juxtaposition (side-by-side), but how would this desktop-based time), and Explicit Encoding. One of the two VR comparative visu- technique translate to immersive visualization in VR? alization examples, a system called Bema [14], supports comparison To contribute to understanding these research questions, we intro- of multiple historical phases of archaeological reconstruction via an duce a novel interaction and visualization technique called Worlds- Interchangeable approach. The user is immersed in one world at a in-Wedges. Our approach divides the virtual space surrounding the time and uses an interactive timeline to switch between worlds via a viewer into pie-slice shaped volumetric wedges and fills each wedge fade-in-fade-out transition. This worked, in part, because the three with a different virtual world. By stacking the wedges around a historical phases were spatially co-located. In contrast, Worlds-in- common axis and placing the tracked user at the center, it is possi- Wedges uses what would be called a Juxtaposition approach. The ble to create an immersive juxtaposition of spatial data, where the theoretical advantage with this approach is that the data is simulta- user may look around, using head-tracked stereoscopic graphics to neously visible, so users rely upon their eyes, not just their memory, compare multiple worlds. For example, Fig. 1, shows a comparison to make comparisons. Also, juxtaposition does not require datasets of forests in the West, Midwest, and East of the US. to be able to be spatially registered so that they can be drawn on top This core idea can be enhanced with several extensions. It is of each other in a useful way. Like our work, the other VR example important to have a strong spatial awareness of one’s location in of comparative visualization, a perceptual study by Coffey et al. [5], each of the worlds. So, we utilize a multi-instance version of the uses a Juxtaposition approach, but the data is quite different. They classic World-in-Miniature (WIM) technique [21,25] to provide a compare animated abstract visual representations of neck motions 3D map of each world. We also extend each WIM to function as (i.e., biomechanics data), which are small in scale. Our technique a multivariate visualization. To convey how the worlds relate to is tailored toward comparing life-size virtual worlds, where the im- one another (i.e., each plot’s location within the U.S.), we provide a pression is that the viewer is immersed in the data rather than seeing worlds-in-context view.