We present a survey of design issues for developing effective free-space three-dimensional (3D) user interfaces. Our survey is based upon previous work in 3D interaction, our experience in developing free-space interfaces, and our informal observations of test users. We illustrate our design issues using examples drawn from instances of 3D interfaces. For example, our first issue suggests that users have difficulty understanding three-dimensional space. We offer a set of strategies which may help users to better perceive a 3D virtual environment, including the use of spatial references, relative gesture, two-handed interaction, multisensory feedback, physical constraints, and head tracking. We describe interfaces which employ these strategies. Our major contribution is the synthesis of many scattered results, observations, and examples into a common framework. This framework should serve as a guide to researchers or systems builders who may not be familiar with design issues in spatial input. Where appropriate, we also try to identify areas in free-space 3D interaction which we see as likely candidates for additional research. An extended and annotated version of the references list for this paper is available on-line through mosaic at address

"Fish tank virtual reality" refers to the use of a standard graphics workstation to achieve real-time display of three-dimensional scenes using stereopsis and dynamic head-coupled perspective. Fish tank VR has a number of advantages over head-mounted immersion VR which make it more practical for many applications. After discussing the characteristics of fish tank VR, we describe a set of three experiments conducted to study the benefits of fish tank VR over a traditional workstation graphics display. These experiments tested user performance under two conditions: (a) whether or not stereoscopic display was used and (b) whether or not the perspective display was coupled dynamically to the positions of a user's eyes. Subjects using a comparison protocol consistently preferred headcoupling without stereo over stereo without head-coupling. Error rates in a tree tracing task similar to one used by Sollenberger and Milgram showed an order of magnitude improvement for headcoupled stereo over ...

This article reports the results from three experimental studies of reaching behavior in a head-coupled stereo display system with a hand-tracking subsystem for object selection. It is found that lag in the head-tracking system is relatively unimportant in predicting performance, whereas lag in the hand-tracking system is critical. The effect of hand lag can be modeled by means of a variation on Fitts ’ Law with the measured system lag introduced as a multiplicative variable to the Fitts ’ Law index of difilculty. This means that relatively small lags can cause considerable degradation in performance if the targets are small. Another finding is that errors are higher for movement in and out of the screen, as compared to movements in the plane of the screen, and there is a small (10’%) time penalty for movement in the Z direction in all three experiments. Low frame rates cause a degradation in performance; however, this can be attributed to the lag which is caused by low frame rates, particularly if double buffering is used combined with early sampling of the hand-tracking device.

We are exploring how virtual reahty theories can be applied toward palmtop computers. In our prototype, called the Chameleon, a small 4-inch hand-held monitor acts as a palmtop computer with the capabihties of a Silicon graphics workstation. A 6D input device and a response button are attached to tbe small monitor to detect user gestures and input selections for issuing commands. An experiment was conducted to evaluate our design and to see how well depth could be perceived in the small screen compared to a large 21-inch screen, and the extent to which movement of the small display (in a palmtop virtual reality condition) could improve depth perception, Results show that with very little training, perception of depth in the palmtop virtual reality condition is about as good as corresponding depth perception in a large (but static) display. Variations to the initial design are also discussed, along with issues to be explored in future research, Our research suggests that palmtop virtual reality may support effective navigation and search and retrieval, in rich and portable information spaces.

The field of view (FOV) in most head-mounted displays (HMDs) is no more than 60 degrees wide -- far narrower than our normal FOV of about 200 wide. This mismatch arises mostly from the difficulty and expense of building wide-FOV HMDs. Restricting a person's FOV, however, has been shown in real environments to affect people's behavior and degrade task performance. Previous work in virtual reality too has shown that restricting FOV to 50 or less in an HMD can degrade performance. I conducted experiments with a custom, wide-FOV HMD and found that performance is degraded even at the relatively high FOV of 112, and further at 48. The experiments used a prototype tiled wide-FOV HMD to measure performance in VR at up to 176 total horizontal FOV, and a custom large-area tracking system to establish new findings on performance while walking about a large virtua...

Computational Steering is the ultimate goal of interactive simulation: researchers change parameters of their simulation and immediately receive feedback on the effect. We present a general and flexible graphics tool that is part of an environment for Computational Steering developed at CWI. It enables the researcher to interactively develop his own interface with the simulation. This interface is constructed with 3D Parametrized Geometric Objects. The properties of the objects are parametrized to output data and input parameters of the simulation. The objects visualize the output of the simulation while the researcher can steer the simulation by direct manipulation of the objects. Several applications of 3D Computational Steering are presented.

Navigation and interaction in virtual environments that use stereoscopic head-tracked displays and have very large data sets present several challenges beyond those encountered with smaller data sets and simpler displays. First, zooming by approaching or retreating from a target must be augmented by integrating scale as a seventh degree of freedom. Second, in order to maintain good stereoscopic imagery, the interface must: maintain stereo image pairs that the user perceives as a single 3D image, minimize loss of perceived depth since stereoscopic imagery cannot properly occlude the screen's frame, provide maximum depth information, and place objects at distances where they are best manipulated. Finally, the navigation interface must work when the environment is displayed at any scale. This paper addresses these problems for god's-eye-view or third person navigation of a specific large-scale virtual environment: a high-resolution terrain database covering an entire planet. 1. Introducti...

We present an experiment that compares volumetric displays to existing 3D display techniques in three tasks that require users to perceive depth in 3D scenes. Because they generate imagery in true 3D space, volumetric displays allow viewers to use their natural physiological mechanisms for depth perception, without requiring special hardware such as head trackers or shutter glasses. However, it is unclear from the literature as to whether these displays are actually better than the status-quo for enabling the perception of 3D scenes, thus motivating the present study. Our results show that volumetric displays enable significantly better user performance in a simple depth judgment task, and better performance in a collision judgment task, but in its current form does not enhance user comprehension of more complex 3D scenes.

Supercomputer simulations now can produce multi-level, multi-scale, large data sets that require new techniques in scientific visualization and higher levels of hardware performance. We are exploring the use of VR technology in this connection. Cosmic Explorer is a virtual reality environment for visualizing numerical and observational cosmology data. We have implemented multi-scale visualization techniques that will work on large, multi-level time-dependent data sets. Virtual reality provides natural ways to navigate in an immersive environment, and scientific visualization requires overviewing. Our techniques bridge the two in a VR system involving the BOOM and the DataGlove. Combining modern visualization hardware, software, and VR technology, we are able to create a system that lets users explore the virtual space created by numerical simulations with ease and naturalness. 1 Introduction Cosmic Explorer is a Virtual Reality (VR) environment for scientists to visualize in realtime ...

Many applications now demand interaction with visualizations of 3D scenes and data sets. Current flat 2D displays are limited in their capacity to provide this not only by the display technology but the interaction metaphors and devices used. The Desktop Bat is a device that has 5 degrees of freedom whilst retaining the simplicity of use of a mouse. To use it for general 3D interaction several metaphors were created for the tasks of navigation and cursor manipulation and a set of experiments were conducted to determine which metaphors were the most efficient in use. Of these metaphors, a velocity control metaphor was the best for navigation and a metaphor that applied rotations and translations relative to the eyepoint coordinate system was best for object control. Keywords: 3D Interaction, Interaction Devices, Virtual Environments, Bat. 1.