An Environment that Integrates Flying and Fish Tank Metaphors

ABSTRACT

Fledermaus VR is a system that combines the flying and Fish Tank metaphors for viewpoint control. A key component of the system is the continuous scaling of the scene so that it always appears just behind the screen. This scaling is done even when flying over a virtual landscape. Because the scene is scaled, it is always in the right position for Fish Tank VR viewing. In addition, the scaling removes some of the problems that commonly occur with stereoscopic displays, it puts objects in the appropriate place for manipulation, and it can be used to modulate the flight velocity. The system is demonstrated with a cable laying application.

© 1997 Copyright on this material is held by the authors.

INTRODUCTION

Fledermaus VR is an experimental application for placing objects with respect to large digital elevation maps. In particular it is designed to facilitate the planning of routes for submarine cables and pipelines. We work with large data sets representing sections of the ocean floor reconstructed from multibeam sonar devices. Engineers who plan these cable routes must be very careful in the placement of the cable or pipeline, because the cost of an error can be huge. Factors such as bottom topography, surface gradient and the bottom type can be critical in routing decisions.

It is important, when planning a cable route, to be able to work at multiple scales. The distances covered can be several hundred kilometers, yet in certain critical sections, near undersea canyons for example, the cable must be accurately placed to within a few metres. Working with engineers from Mobil Oil and Teleglobe, we have found that three dimensional visualization and stereoscopic display can be very useful in obtaining the best possible understanding of the undersea topography.

When viewing a stereoscopic scene on a monitor, if the head is moved, a curious illusory distortion takes place. This is because the stereo depth cues inform the brain that the scene is three-dimensional, but the kinetic depth cues from moving the head informs the brain that the scene is flat. Fish Tank VR viewing, where the viewpoint is tied to the user's head position, removes this rather disconcerting distortion and has a number of other advantages [1,4].

The most original feature of FledermausVR is an algorithm that continuously scales the working environment to lie just behind the monitor screen in terms of stereo depth [5]. It is this cyclopean scale that enables the simple combination of flying and Fish Tank VR interaction metaphors, since cyclopean scale can also be applied when 'flying' over a terrain. Cyclopean scale also places objects at a convenient distance for manipulation, optimizes stereo display parameters, and reduces stereo display problems (vergence focus conflict)[3]. To find the cyclopean scale factor, we continuously sample the Z buffer. We use this information to modify the flight velocity and to adjust the control to display ratio in direct manipulation, in addition to adjusting the stereo display.

We have evaluated this system with a cable/pipeline route editing task and a task that involves searching for very small hidden targets.

SYSTEM FEATURES

• Some of the digital elevation maps that we work with contain several million polygons. In order to provide an interactive environment we use two strategies: One is to degrade the scene whenever a movement is made; the second is to render a patch of the scene in high resolution. When a section of the cable or pipeline is being manipulated, a high resolution region is shown surrounding the manipulated section.
• We maintain a hierarchically defined cable/pipe representation. A hierarchy of control points allow manipulation at different scales.
• Artificially textured or draped surfaces allow for bottom type information to be displayed.

Figure 1. The Fledermaus VR flying interface is illustrated together with a pipeline laid on a representation of the sea-floor. The vertical bars on the pipe are used to manipulate it. A heads-up flying interface provides viewpoint control [2]. Support is provided for a variety of geological and oceanographic data, including draped surfaces, volumes and seismic data.

SYSTEM HARDWARE

Fledermaus VR runs effectively on a Silicon Graphics Maximum Impact:- It uses a Polhemus Fasttrack for head position tracking and CrystalEyes stereo glasses.

SYSTEM AFFORDANCES

To summarize: Fledermaus VR has the following affordances:

• An environment that combines Fish Tank viewing with a flying interface with a minimal transition between the two viewing modes.
  
• Continuous automatic changes of scale for the purposes of interaction.
  
• A stereo display that minimizes diplopia (double image) effects and also provides stereo depth information for distant targets.
  
• The automatic adjustment of flying parameters depending on the local scale of the environment.

ACKNOWLEDGMENTS

The authors gratefully acknowledge Mark Paton and Glenn Frank for software support, and Larry Mayer for inspiration.

REFERENCES

1. Deering, M. (1996) The HoloSketch VR Sketching System. Communications of the ACM. 39 (5) 54- 61.

2. Ware, C. (1996) Moving Motion Metaphors. 225- 226. ACM CHI 96 Conference Companion.

3. Ware, C. (1995) Dynamic Stereo Displays, ACM CHI'95 Conference Proceedings Denver, May. 311- 316. ACM CHI'95 Proceedings, Denver, May.

4. Ware, C. Arthur, K. and Booth, K.S. (1993) Fishtank Virtual Reality. INTERCHI'93 Technical Paper. Proceedings 37-42.