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24 Visualization Using Virtual Reality

R. BOWEN LOFTIN, Old Dominion University JIM X. CHEN, George Mason University Larry Rosenblum, Naval Research Laboratory

24.1 Introduction mation in real time, enabling a user or users to occupy, navigate, and manipulate a computer- 24.1.1 Purpose generated environment. This chapter provides a brief introduction to Key to an understanding of the potential of virtual reality, followed by a review of selected virtual reality in visualization is the recognition visualization applications implemented in a that virtual reality is not limited to visual dis- virtual-reality environment. The reader is pro- plays and that it inherently provides those who vided with ‘‘pointers’’ to the major conferences use it with the means to navigate and manipu- and to more detailed compilations of research in late the information that is displayed. An excel- virtual-reality-based visualization. lent entry into virtual-reality systems and applications is a recently published handbook on the field [37]. 24.1.2 Virtual Reality The visual element of virtual reality extends What we now often refer to as virtual reality was commonly available 2D computer graphics into first proposed in the 1960s [16,38,39]. In addition the third dimension. To achieve true 3D to the term ‘‘virtual reality,’’ many other terms graphics, a stereo image is produced by provid- such as ‘‘virtual environments,’’ ‘‘synthetic en- ing two slightly different views (images) of the vironments,’’ ‘‘virtual worlds,’’ and ‘‘artificial same object for the user’s two eyes. The provi- reality’’ have been used. Virtual reality has the sion of two separate images can be achieved by capability of providing sensory information of a number of methods. In the early days of vir- sufficient fidelity that the user can, in some cases, tual reality, a head-mounted display was the ‘‘suspend disbelief’’ and accept that he or she is method of choice [16,38,39]. These displays actually somewhere else [10]. Further, the tech- used two image sources, one for each eye, for nology can also support perceptual interaction stereo viewing of the computer-generated envir- with the synthetic environment, enabling the onment. Subsequently, devices such as the user to transcend the role of passive observer ImmersaDesk2 [20,32] or the CAVE2 [11] and actively participate in shaping events [28]. were used to produce stereo images. An Immer- A thorough, but somewhat dated, review can be saDesk2 or CAVE2 usually produces only one found in the report of a National Research image on its display surface or surfaces but Council committee chartered to examine virtual alternates between an image for the right eye reality in the mid-1990s [13]. and one for the left eye (commonly at 60 Hz). For the purpose of this chapter, virtual reality The viewer wears lightweight liquid crystal will be defined as ‘‘shutter’’ or ‘‘active’’ glasses. These glasses are The use of integrated technologies that provide synchronized with the alternating displays so multimodal display of and interaction with infor- that the appropriate eye can view the image

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466 The Visualization Handbook intended for that eye. These devices can also be immersion implies freedom from distractions. It used to produce stereo images by sending two also implies that a user’s entire attention can be images to the same display such that each image brought to bear on the problem at hand. Such is polarized differently. The user then wears characteristics should provide a user with an ‘‘passive’’ glasses with each lens polarized to increased ability to identify patterns, anomalies, match the image for its eye. and trends in data that is visualized. The principal hardware technologies required for producing a virtual reality are real-time 24.1.3.2 Presence graphics generators, stereo displays, 3D audio displays, tracking/interaction systems, and Our definition of presence is also from Slater: special display devices (e.g., haptic, vestibular, Our general hypothesis is that presence is an and olfactory displays). The development of increasing function of two orthogonal vari- effective virtual-reality applications, including ables. The first variable is the extent of the those used for visualization, requires complex match between the displayed sensory data and software environments. Commercial products the internal representation systems and subject- are available, but many researchers rely on ive world models typically employed by the ‘‘home-grown’’ software that may not be widely participant. Although immersion is increased with the vividness of the displays ..., we must supported. A small number of open-source also take into account the extent to which the systems have been created (e.g., VRJuggler information displayed allows individuals to and DIVERSE), as have application program- construct their own internal mental models of mer interfaces (e.g., Java3D) and web-based reality. For example, a vivid visual display graphics formats (e.g., VRML). system might afford some individuals a sense of ‘presence’, but be unsuited for others in the absence of sound’’ [34]. ‘‘The second variable is 24.1.3 Characteristics of Virtual the extent of the match between proprioception Environments and sensory data. The changes to the display What does virtual reality offer visualization that must ideally be consistent with and match conventional display technologies do not? through time, without lag, changes caused by While a number of items could be cited, three the individual’s movement and locomotion— will be examined here: immersion, presence, and whether of individual limbs or the whole body multimodal displays and interaction. relative to the ground.’’ [35] Presence can contribute to the ‘‘naturalness’’ of the environment in which a user works and the 24.1.3.1 Immersion ease with which the user interacts with that ‘‘Immersion refers to what is, in principle, a environment. Clearly, the quality of the virtual quantifiable description of a technology. It reality—as measured by display fidelity, sensory includes the extent to which the computer richness, and real-time behavior—is critical to a displays are extensive, surrounding, inclusive, sense of presence. vivid and matching. The displays are more extensive the more sensory systems that they accommodate’’ [35]. Immersion is depicted, in 24.1.3.3 Multimodal Displays this definition, as a continuum. The argument is Although the visual sense is arguably the most that the more sensory information provided powerful sense in humans, it is important to and the more sensorially diverse that informa- note that most humans process inputs, simulta- tion, the more ‘‘immersion’’ a user will experi- neously, from many senses (visual, auditory, ence. Immersion has some properties that could haptic, vestibular, olfactory, and gustatory). directly enhance visualization. For example, For example, Fred Brooks and his colleagues at Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 467

Visualization Using Virtual Reality 467 the University of North Carolina at Chapel Hill ior—just as one can employ virtual reality to [30] have enabled chemists and biochemists to provide users with gesture interfaces for direct view, assemble, and manipulate large, complex interaction with virtual objects. molecules using a combination of visual and Virtual reality is a powerful display and inter- haptic displays. The well known conjecture that action vehicle. It can structure abstract data and humans can simultaneously grapple with no concepts, present the results of computations, more than seven, plus or minus two, separate and help researchers understand the unforeseen items of information [27] does not specifically or find the unexpected. explore the human capacity for understanding multiple variables when expressed through multiple senses. In spite of this conjecture, the 24.2 A Visualization Sampler mapping of information onto more than one sensory modality may well increase the ‘‘human 24.2.1 Key Resources bandwidth’’ for understanding complex, multi- Virtual reality has, by some measures, been variate data. Lacking a theory of multisensory available since the late 1980s through commer- perception and processing of information, the cial entities as well as through academic, gov- critical issue is determining what data best maps ernment, and industrial laboratories. From onto what sensory input channel. Virtual reality the time of the first available commercial at least offers the opportunity to explore this systems, visualization has been linked to virtual interesting frontier to find a means of enabling reality. A few examples of visualization in users to effectively work with more and more the context of virtual reality can be found in complex information. SIGGRAPH proceedings, especially in the pro- ceedings of more specialized conferences and workshops. Notable are the IEEE Visualization 24.1.4 Virtual Reality and Visualization Conferences and their associated symposia and Visualization is a tool that many use to explore the IEEE Virtual Reality Conferences (known complex (or even simple) data in a large number prior to 1999 as the Virtual Reality Annual of domains. One can think of virtual reality as a International Symposium, or VRAIS). Many specific means to achieve effective visualiza- papers from these two conference series address tions. As noted in the preceding section, virtual specific applications of visualization using reality has a number of features that can con- virtual reality, or discuss issues of data repre- tribute to the success of a visualization applica- sentation, human-computer interaction, or per- tion, especially when that application must formance that are relevant to the success of such address high-dimensional data, high volumes applications. In addition, the proceedings of the of data, and/or highly complex data. One of Eurographics Virtual Environments Workshop the great potential strengths of virtual reality is offer more examples of virtual reality applied to its stated goal of giving users more accessible, visualization. More recently, a series of meet- more intuitive, and more powerful interaction ings known as the Immersive Projection Tech- capabilities. One way to grasp this concept is to nology Workshop (IPT) has been held (with the imagine that a user is given a strange object that location alternating between Europe and the can be held in one hand. What is the natural United States) to address virtual-reality technol- thing for the user to do? First, the user will turn ogy development and applications. Again, the object around to examine it—just as one can many of the applications presented there illus- employ virtual reality to provide users with dif- trate the use of virtual reality in visualization. ferent viewpoints on an object or scene. Next, A seminal workshop on visualization was the user may prod or poke the object to deter- held in July 1993 at the Fraunhofer Institute mine some of its properties or to elicit a behav- for Computer Graphics in Darmstadt, Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 468

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Germany. The proceedings of this conference a Cave Automatic Virtual Environment [31] contains several useful papers, including a (CAVE2) to visualize the locations of lamps paper by Steve Bryson [7] entitled ‘‘Real-time and coins discovered in the ruins of the Petra exploratory scientific visualization and virtual Great Temple site in Jordan. reality’’ that sets forth many of the benefits and challenges of using virtual reality for visualiza- 24.2.2.2 Architectural Design tion. In May 1994, a group of researchers met for the Dagstuhl Seminar on Scientific Visualiza- The Electronic Visualization Laboratory (EVL) tion. The result of this seminar was the produc- at the University of Illinois in Chicago [23] has tion of a book 29 on scientific visualization utilized virtual reality in architectural design containing chapters written by some of the and collaborative visualization to exploit virtual most respected research groups in the world. A reality’s capability for multiple perspectives on number of chapters in this book treat virtual the part of users. These perspectives, including reality as an approach to visualization. The multiple mental models and multiple visual chapter by Helmut Hasse, Fan Dai, Johannes viewpoints, allow virtual reality to be applied Strassner, and Martin Go¨bel (‘‘Immersive Inves- in the early phases of the design process tigation of Scientific Data’’) [17] is important rather than during a walkthrough of the final in providing detailed examples of work up design. until that time. A more recent work [9] focuses on the use of virtual reality in information 24.2.2.3 Battlespace Visualization visualization. Work done at Virginia Tech and the Naval Another very useful source comes from two Research Laboratory [12,18] resulted in virtual- workshops on virtual environments and scien- reality-based Battlespace visualization applica- tific visualization that were sponsored by Euro- tions using both a CAVE2 and a projection graphics, in Monte Carlo, Monaco, February workbench. The modern Battlespace extends 19–20, 1996 and in Prague, Czech Republic, from the bottom of the ocean into low earth April 23–23, 1996. The proceedings of these orbit. Thus, 3D visualizations that support two workshops [15] provide a very good com- powerful direct interaction techniques offer pilation of the work done through 1995. significant value to military planners, trainers, and operators. 24.2.2 Examples Well over one hundred extant publications ad- 24.2.2.4 Cosmology dress the application of virtual reality in visual- Song and Norman [36] demonstrated, as early ization. Below are brief descriptions of specific as 1993, the utility of virtual reality as a tool for projects that demonstrate the breadth of applic- visualizing numerical and observational cos- ability of virtual reality to visualization. The mology data. They have implemented an examples below are not meant to be exhaustive application that supports multiscale visualiza- or even to be a uniform sampling of the available tion of large, multilevel time-dependent datasets literature. Inclusion or exclusion of a specific using both an immersive display and a gesture application does not imply a value judgment on interface that facilitates direct interaction with the part of the authors of this chapter. the data.

24.2.2.1 Archeology 24.2.2.5 Genome Visualization A number of groups have used virtual reality to Kano et al. [19] have used virtual reality to visualize archeological data. One group [1] used develop an application for pair-wise compar- Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 469

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ison between cluster sets generated from differ- Amari et al. [3]. In this case, a visualization of ent gene expression datasets. Their approach static structural data and execution trace data displays the distribution of overlaps between of a large software application’s functional two hierarchical cluster sets, based on hepato- units was developed. Further, the visualization cellular carcinomas and hepatoblastomas. approach supported the direct manipulation of graphical representations of code elements in a virtual-reality setting. 24.2.2.6 Meteorology Meteorologists typically use 2D plots or text to display their data. Such an approach makes it 24.2.2.10 Statistical Data difficult to visualize the 3D atmosphere. Ziegler A group at Iowa State University [4] has et al. [40] have tackled the problem of compar- developed a virtual-reality-based application ing and correlating multiple layers by using an for the analysis of high-dimensional statistical immersive virtual environment for true 3D data. Moreover, the virtual-reality approach display of the data. proved superior to a desktop approach in terms of structural-detection tasks. 24.2.2.7 Oceanography A multidisciplinary group of computer scien- 24.2.2.11 Vector Fields tists and oceanographers [14] has developed a Real-time visualization of particle traces using Q1 tool for visualizing ocean currents. The c-thru virtual environments can aid in the exploration system uses virtual reality to give researchers and analysis of complex 3D vector fields. the ability to interactively alter ocean para- Kuester et al. [21] have demonstrated a scalable meters and communicate those changes to an method for the interactive visualization of large ocean model calculating the solution. time-varying vector fields.

24.2.2.8 Protein Structures 24.2.2.12 Vehicle Design Protein structures are large and complex. The use of increasingly complex finite element Large-format virtual-reality systems support (FE) simulations of vehicles during crashes has not only the visualization of such data, but led to the use of virtual-reality techniques to the collaboration of small teams that analyze visualize the results of the computations [22]. the data. One group [2] has visualized four A program called VtCrash was designed to geometric protein models: space-filling spheres, enable intuitive and interactive analyses of large the solvent accessible surface, the molecular amounts of crash-simulation data. The applica- surface, and the alpha complex. Relationships tion receives geometry and physical-properties between the different models are represented via data as input and provides the means for the continuous deformations. user to enter a virtual crash and to interact with any part of the vehicle to better understand the implications of the simulation. 24.2.2.9 Software Systems Many computer programs now exceed one million lines of code. The ability to truly 24.2.2.13 Virtual Wind Tunnel understand programs of such magnitude is One of the earliest successful demonstrations rare. Visualizations of such systems offer a of virtual reality as a visualization tool was the means of both comprehending the system and development of the Virtual Wind Tunnel at collaboratively extending or modifying it. An the NASA/Ames Research Center [5,6,8]. Bry- example of such a visualization is the work of son precomputed complex fluid flows around Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 470

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various aerodynamic surfaces. To view these the precomputed data and the software that flow fields, the user employed a tracked, head- supported the visualization system. The soft- 2 Q2 mounted display (a BOOM ) that used rela- ware framework for the virtual wind tunnel tively high-resolution color displays, one for was extensible and had interactive (i.e., real- each eye. These displays were attached to time) performance. Fig. 24.1 shows Bryson the head but were supported by a counter- examining the flow fields around an experi- weighted boom to relieve the user of bearing mental vehicle. the weight of the system. Optical encoders in Others, for example Severance [33], have the boom joints provided real-time, precise extended the work of Bryson’s group by fusing tracking data on the user’s head position. Tools the data from several wind-tunnel experiments were developed to enable the user to explore the into a single, coherent visualization. Given the flow field using a tracked glove (a DataGlove2) high cost of maintaining and operating wind on one hand. For example, the user could tunnels and the limited regimes (of both wind use the gloved hand to identify the source speed and aerodynamic surface size), the virtual point for streamlines that would allow visuali- wind tunnel offers a significant potential to zation of the flow field in specific regions. reduce the cost and expand the availability of A great deal of work went into developing both wind-tunnel experiments.

Figure 24.1 Steve Bryson interacting with the Virtual Wind Tunnel developed at the NASA/Ames Research Center. Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 471

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24.2.2.14 Hydrocarbon Exploration and tion was still typically done via the keyboard and Production mouse. Lin, Loftin, and Nelson [24,25] developed In recent years, virtual reality has had a growing an application that supported more direct inter- impact on the exploration and production of action between the user and the data in a hydrocarbons, specifically oil and gas. In 1997, CAVE2. Not only could three to four users there were only two large-scale visualization share an immersive, 3D visualization, one of centers in the oil and gas industry, but by 2000, them could also interact directly with the data via the number had grown to more than 20. In spite natural gestures. Fig. 24.2 shows a user in a of this growth, the use of virtual reality technol- CAVE2 working with objects representing ogy was largely limited to 3D displays—interac- geophysical surfaces within a salt dome in the

Figure 24.2 A user in a CAVE2 interacting with geophysical data describing a salt dome in the Gulf of Mexico. Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 472

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Figure 24.3 A user interacting with geophysical data on a projection workbench.

Gulf of Mexico. The user holds a tracked 24.3 Research Challenges pointing/interaction device in the dominant hand Although there is strong evidence that virtual- (the right hand, in the figure) while a virtual menu reality systems can offer significant advantages is attached to the nondominant hand. Studies over conventional display systems for visualiza- were done to determine the effectiveness of this tion applications, many challenges remain to be approach when compared with typical desktop overcome. Below are some of the largest bar- applications. riers to the use of virtual reality as the principal Additional work was done by Loftin et al. [26] platform for visualization in many fields. to implement powerful interaction techniques on a projection workbench. In Fig. 24.2, the user is . Fidelity. Fidelity has two ‘‘faces’’; in one again using both hands for navigation, menu sense, fidelity can refer to the resolution of interaction, and detailed manipulation of the data and/or displays of that data. One data. The success of these efforts and similar can think in terms of the resolution of a Q3 work by other groups has led the oil and gas dataset or of a display. Another aspect of industries to make major investments in virtual- fidelity is in the data representation itself. reality-based visualization systems. More im- A primary unanswered question is, ‘‘How portantly, these systems have had a demon- much fidelity is enough?’’ That is, how strable return on investment in terms of much fidelity must an application and/or its improved speed and success of decision making display system have in order to achieve a for both exploration and production activities. specific outcome? Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 473

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. Multimodal displays. While visual display inside a CAVE. IEEE Computer Graphics and technology is relatively mature and 3D Applications, 16(4):58–61, 1996. 3. H. Amari, T. Nagumo, M. Okada, M. Hirose, audio displays are of very high quality, and T. Ishii. A virtual reality application for much work has to be done to advance the software visualization. In Proceedings of the state of the art in displays for other senses 1993 Virtual Reality Annual International Sym- (haptic, olfactory, vestibular, and gustatory) posium, Seattle, WA, 18–22, pages 1–6, 1993. and in the integration of multimodal displays 4. L. Arms, D. Cook, and C. Cruz-Neira. The benefits of statistical visualization in an immer- to provide a seamless sensory environment sive environment. In Proceedings of the 1999 for the user. Perhaps the grandest challenge IEEE Virtual Reality Conference, Houston, of all is the need for a robust theory of multi- TX, 13–17, pages 88–95, 1999. sensory perception that guides the developer 5. S. Bryson and C. Levit. The virtual wind tunnel. in mapping different types of data to differ- IEEE Computer Graphics and Applications, 12(4), pages 25–34, (July/August, 1992). ent sensory modalities. 6. S. Bryson. The virtual windtunnel: A high-per- . Technical fragility. The hardware and soft- formance virtual reality application. In Proceed- ware used in virtual reality is still fragile. ings of the 1993 Virtual Reality Annual The lack of a mass market has hindered International Symposium, Seattle, WA, Septem- ber 18–22, pages 20–26, 1993. manufacturers’ desire to build more robust 7. S. Bryson. Real-time exploratory scientific visu- systems and to invest in the research needed alization and virtual reality. In L. Rosenblum, to solve fundamental engineering problems R. A. Earnshaw, J. Encarnac¸a˜o, H. Hagen, (such as latency). A. Kaufman, S. Klimenko, G. Nielson, F. Post, and D. Thalman (Editors). Scientific visualiza- . Software inaccessibility. The available soft- tion: advances and challenges. London: Aca- ware systems, even those that are commer- demic Press, pages 65–85, 1994. cially available, are notoriously difficult to 8. S. Bryson, S. Johan, and L. Schlecht. An exten- use. One needs great patience as well as a sible interactive visualization framework for the virtual windtunnel. In Proceedings of the 1997 great deal of experience to become a profi- Virtual Reality Annual International Symposium, cient developer of virtual-reality applications Albuquerque, NM, March 1–5, pages 106–113, of any real complexity. 1997. 9. C. Chen. Information visualization and virtual . Cost. Large-scale virtual-reality systems cost environments. Berlin: Springer-Verlag, 1999. a great deal. As long as it can cost over 10. J. C. Chung, M. R. Harris, F. P. Brooks, Jr., 1,000,000 to install the computational, dis- H. Fuchs, M. T. Kelley, J. Hughes, M. Ouh- play, and interaction technologies required Young, C. Cheung, R. L. Holloway, and for a sophisticated, multiuser system, many M. Pique. Exploring virtual worlds with head- will choose not to use virtual reality as mounted displays. In Proceedings of the SPIE Conference on Three-Dimensional Visualization a means of implementing visualization and Display Technologies, Los Angeles, CA, applications. pages 42–52, January 1990. 11. C. Cruz-Neira, D. J. Sandin, and T. A. DeFanti. Surround-screen projection-based virtual real- References ity: the design and implementation of the 1. D. Acevedo, E. Vote, D. H. Laidlaw, and M. S. CAVE. Computer Graphics, 27, pages 135–142. Joukowsky. Archaeological data visualization 12. J. Durbin, J. E. Swan II, B. Colbert, J. Crowe, in VR: analysis of lamp finds at the great R. King, T. King, C. Scannell, Z. Wartell, and temple of Petra: a case study. Archeology, and T. Welsh. Battlefield visualization on the re- Cultural Heritage, In Proceedings of the 2001 sponsive workbench. In Proceedings of the Conference on Virtual Reality, Glyfada, North 1998 IEEE Visualization Conference, Research Athens, Greece, November 28–30, pages 493– Triangle Park, NC, October 18–23, pages 463– 496, 2001. 466, 1998. 2. N. Akkiraju, H. Edelsbrunner, P. Fu, and J. 13. N. Durlach and A. Mavor (Editors). Virtual Qian. Viewing geometric protein structures from reality: scientific and technological challenges. Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 474

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AUTHOR QUERIES

Q1 Au: c-thru? Q2 Au: please spell out BOOM? Johnson/Hansen: The Visualization Handbook Page Proof 28.5.2004 12:36pm page 476