Visualization Software with VR Juggler
for Immersive Virtual Reality Environment
Daisuke Meno1 , Akira Kageyama1 , and Youhei Masada111

Graduate School of System Informatics, Kobe University, Kobe, Japan

Introduction

To analyze three-dimensional (3-D) numerical data produced by large scale computer simulations, researchers today are required to find a new way to visualize their 3-D
data with an efficient way. The virtual reality (VR) technology with immersive display systems provides such aninnovation for the 3-D data visualization.
The immersive VR systems, that are also called CAVE
systems, were developed by Electronic Visualization Laboratory at University of Illinois, Chicago in early 1990’s [1].
The classical CAVE system consists of a room-typescreens, on which stereo images are projected, and ahead/hand tracking system by which the view point of thestereo images are automatically adjusted to the viewer’s
head position.
Various visualization programs have been developed todate for the visualization in CAVE’s VR environment. Oneof them is our original VR visualization software named“VFIVE” [2]. The purpose of VFIVE is to make it possible to perform a fully immersive and interactive visualization of 3-D data in a CAVE’s room. Through continuous
development and improvements for more than a decade,
VFIVE has become a practically useful tool for scientificvisualization. For example, we have recently found a newphenomenon (a helical structure of electric current) in asupercomputer simulation data on geomagnetic field [3]by the VFIVE visualization in a CAVE. We believe that
VFIVE is useful for many researchers in various fields, under the present situation that there are many CAVE systems all over the world. We have made the source code ofVFIVE being freely available [4]. However, popularly of
VFIVE falls a little bit short of our expectation. One of
the reasons would be a purely economical one; VFIVE isbased on CAVElib which is a commercially available API
for the interface to the CAVE hardware.
To make our visualization software being “fully free”,
we have decided to replace the basic API in our visualization software, substituting a new free API instead ofCAVElib. There are several free (or open source) APIs
for CAVE-type VR systems, such as Open CABIN, CoVE,Vrui. Among them, we have decided to use VR Juggler [5].
VR Juggler is a platform for virtual reality application development. It allows a user to develop and run a VR application on wide variety of VR systems. An importantfeature of VR Juggler is that it is scalable from simple
desktop systems like PCs to complex multi-screen CAVE
systems running on high-end work stations. In contrast to
some other freely available APIs, VR Juggler is actively
maintained and upgraded. Instead of just replacing API,
we have decided to develop a new visualization software
for CAVEs from the scratch based on VR Juggler.

The development is performed on two CAVE systems in
Kobe University, one is pCAVE (one screen system withhead/wand tracking) and π-CAVE, which is a newly installed 4-screens, rectangular-shaped CAVE system withthe size of 7.8m × 3m × 3m [6, 7].
2

Design of New Visualization Software

The program design is summarized in Fig.1. The mainfunction creates two kinds of objects; a VR Juggler kernel
and a visualization framework. The visualization framework consists of (1) visualization methods, (2) user interface, and (3) data set that is to be visualized. The VR
Juggler kernel takes care of the interface with CAVE hardware, and controls the visualization framework throughuser defined functions such as init func, draw func, and soon.
As for the visualization methods, we have implemented
two basic methods so far. One is called Particle Tracer thatis for the vector field visualization. As the name suggests,
Particle Tracer shows motions and trajectories of test (ormassless) particles in a specified vector field (Fig.2). Whenone presses a wand button, a new tracer particle is released
from the wand tip, and then the particle flys following theequation of motion dxi /dt = ai (x1 , x2 , x3 ), (i = 1, 2, 3),
where xi is the i-th coordinate of the particle position,
and ai is the i-th component of the target vector field.
The equation of motion is numerically integrated in realtime. Repeated clickings of the wand button generate asequence of particles. The trajectory of each particle isshown by a curve.
Another visualization method implemented in the codeis called Local Arrows, which is also for the vector field visualization. In this visualization method, a bunch of shortarrows, each of which denotes the direction and amplitudeof the vector field at the location, are shown in CAVE’s
VR space around the hand (or the wand). See Fig.3. Since
these arrows always appear around the wand, one can intuitively understand the spatial variation of the vector field
by observing the change of each arrow’s length (that denotes the vector amplitude there) and the vector direction
by moving the wand.
For the user interface, we have developed a kind of virtual touch screens in VR space. In this interface, rectangular 2-D screens appear in front of the user that can beselected (or executed) by “touching” them with the wand.
The touch is judged by the distance between the screen
center and the wand position.
The touch screens are grouped to three different categories; (i) visibility control, (ii) calculation control, and(iii) input control. The visibility control is used to enable/disable the visibility of the calculated visualization

(a)(b)Fig. 4. A combined visualization of Local Arrows and Particle Tracer. (a) Arrows (short lines) denoting 3-D vectorsof the target field. (b) A new tracer particle is released
from the seeding point when the user presses a wand button.
Fig. 1. Software architecture.

(a)

(b)

(c)

Fig. 5. A sequence of snapshots of Particle Tracer visualization.
3
Fig. 2. A snapshot of the visualization method Particle
Tracer that is implemented in the present software.

Summary

For interactive, immersive, and therefore efficient visualization of three-dimensional simulation data in an immersive VR environment, or CAVE, we have developed a
new visualization software based on VR Juggler API instead of traditional CAVElib. Though the implementedvisualization is still limited, we have found that the modern design of VR Juggler enables us to develop a flexible
scientific tool in CAVE’s VR environment.
Acknowledgements
This research was supported by Okawa Foundation andKAKENHI(23340128).

Fig. 3. Another snapshot of CAVE visualization. Local
Arrows for vector field are shown around the wand.

objects such as tracer trajectories and arrows. The calculation control is used to specify, for example, if the numerical integration of the tracer particle is on or off. The
input control is used to specify/change the input devices
such as joysticks and button allocations on the wand.
Visibility (on/off) and calculation state (also on/off)are
two major states in almost all visualization method inCAVEs. In Fig.4, visibility of local arrows is on and visibility & calculation state of Particle Tracer are also on.
In our previous visualization software, VFIVE, visibility and calculation states cannot be controlled by the user.
In this regard, the present visualization software has more
flexibility than VFIVE. By selecting through the virtual
touch screens, one can specify any four possible states(on/off × on/off) of each visualization objects. Fig.5 shows
an example in which the calculation state of Particle Tracer
is off in the beginning. After the user has specified several
seed points by the wand, he/she changes the calculation
state to on. It is observed that every particles start moving
in the vector field at once.

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