CHI 2005 | Late Breaking Results: Posters
April 2-7 | Portland, Oregon, USA
Resizing Beyond Widgets: Object Resizing Techniques for Immersive Virtual Environments Ji-Sun Kim Center for Human-Computer Interaction, Virginia Tech Blacksburg, VA, USA
[email protected]
Doug A. Bowman Center for Human-Computer Interaction, Virginia Tech Blacksburg, VA, USA
[email protected]
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John F. Lucas Center for Human-Computer Interaction, Virginia Tech Blacksburg, VA, USA
[email protected] ABSTRACT
techniques are translated from 2D by adapting them for use with 3D input devices in 3D environments. This approach is useful in that users familiar with 2D interfaces can more easily understand how to use their 3D counterparts. A flaw in this approach is that directly converting techniques using 2D input to 3D does not always create the best possible technique for the task. Pull-down menus from 2D Windows Icons Menus Pointers (WIMP) interfaces are a prime example of this problem as selecting menu items with a 3D cursor can be very difficult. Wingrave and Bowman addressed this problem with the development of TULIP [1] menus, which provide the same functionality as pull down menus but use a set of pinch gloves to provide better physical feedback and constraints.
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The most common technique for resizing 3D objects in virtual environments is the use of 3D widgets. However, such techniques often exhibit usability problems due to difficulties in selecting and manipulating the widgets. We have developed two novel interaction techniques for resizing objects in immersive VEs. Our two techniques, the Pointer Orientation-based Resize Technique (PORT) and the Gaze-Hand resize technique, take advantage of the user’s proprioceptive sense and their spatial knowledge of the environment. We designed these techniques as an alternative to 3D widgets and performed a usability study to compare the effectiveness of all three techniques. Our results show that participants were able to perform tasks significantly faster with the two new techniques than with the existing 3D Widgets technique.
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Author Keywords: Virtual Reality; 3D Interaction; User Testing and Evaluation ACM Classification Keywords: H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous. INTRODUCTION
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Immersive Virtual Environments (VEs) allow users to view and manipulate 3D objects interactively using 3D input devices. The study of 3D object manipulation in immersive VEs has mainly focused on object selection, positioning and rotation [2]. Emerging applications such as 3D immersive design [4] require other tasks such as: resizing, color selection, and the adjustment of object-specific properties. It is important that interaction techniques for these often overlooked tasks be developed and evaluated. Once effective techniques for these tasks have been found, new, more powerful applications can be developed for immersive VEs.
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Figure 1: 2D Resizing Widgets
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The widgets metaphor has also been used for 3D interfaces [3]. Resize widgets are used for resizing windows and other objects in traditional desktop user interfaces (Figure 1 above). With a widget technique resizing is performed by selecting and moving the widget to adjust the size of the object. When used in a 3D environment widgets pose several problems:
Designers of 3D interaction techniques for immersive VEs often borrow metaphors from 2D interfaces. These
COPYRIGHT IS HELD BY THE AUTHOR/OWNER(S). CHI 2005, APRIL 2–7, 2005, PORTLAND, OREGON, USA. ACM 1-59593-002-7/05/0004.
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Widgets can be occluded by other objects making them difficult or impossible to select.
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At a distance widgets are hard to see and select.
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Once selected precise positioning of widgets is very challenging with 3D input devices.
3D widgets are intuitive to understand but can be very difficult to use. However, this technique is one of the most
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CHI 2005 | Late Breaking Results: Posters
April 2-7 | Portland, Oregon, USA
common techniques for 3D resizing as few other alternatives exist. In this paper we present two alternative techniques for resizing objects in immersive VEs and compare these new techniques with 3D widgets in a formal experiment. RELATED WORK
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Conner et al [3] showed how 2D widgets can be extended to 3D and how widgets can be used in 3D applications. 3D Widgets can provide a variety of functions and are easily integrated into applications. 3D widgets can be difficult to manipulate precisely using 3D input as manipulation of more degrees is required. Other factors such as occlusion and depth cues can make 3D widgets difficult to use in applications. An example of an application using 3D widgets is the ISAAC design application [7]. ISAAC uses 3D widgets for constrained positioning of 3D objects in the virtual space.
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Mapes and Moshell present the Chordgloves as an interface for manipulating objects in VEs [5]. The Chordgloves are a two-handed interaction device that allow the user to position, resize and align objects using both hands. VE systems capable of two-handed interaction have a higher monetary cost than systems with only one tracked hand. As VE systems with a head tracker and one tracked handheld device are more common we limit our work to these systems.
Figure 2: Pointer Orientation Based Resize Technique (PORT)
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PORT
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3D OBJECT RESIZE TECHNIQUES
The Pointer Orientation-based Resize Technique (PORT) uses the orientation of the hand-held pointer relative to the object to determine the axis of resize. The user orients the pointer as if it were located inside the object and points in the direction they wish to resize (Figure 2). As the user rotates the pointer in space an arrow positions itself around the outside of the object to represent the direction of resize. An X marker is placed on the opposite side of the object to represent the side of which will not move as well as to give feedback when the arrow is not visible.
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In our previous work examining 3D multiple object selection techniques we used a 3D selection box technique for specifying a volume in 3D space. Our dissatisfaction with using the 3D Widgets resizing technique for resizing the selection box led us to design the Pointer Orientationbased Resize Technique. Here we describe our implementation of the 3D Widget resize technique as well as two novel techniques for resizing 3D objects. All of the techniques were designed for use in a Head Mounted Display based system with a six degree-of-freedom handheld wand device.
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The size of the object is adjusted using a joystick on the wand device. Pushing forward on the joystick scales the object so that the side being resized moves in the direction the pointer is oriented. Pulling back resizes in the object in the opposite direction. A joystick allows for continuous control of the size of the object, but our design allows for the resize action to be performed with buttons as well.
3D Widgets
Our implementation of 3D Widget resizing (see Figure 4) placed 26 widgets around the perimeter of the object to be resized. The location of each widget determined the number of axes that are resized when the widget is moved. When resizing a cube, a widget located in the center of a face of the cube resizes along only one axis while a widget located on a corner of the cube resizes along all three axes. The widgets are a constant size and are positioned at a set offset from the edge of the object.
Gaze-Hand Resize
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Our second novel interaction technique resized the object using a combination of the pointer’s orientation and gaze direction. With the Gaze-Hand technique (Figure 3) the user specifies the axis of resize using the orientation of the pointer as in the PORT technique. A red line through the center of the object represents the axis that is currently being resized. The user’s gaze direction is used to adjust the position to which the active face of the box will be moved. The system calculates the closest point on the resizing line to the user’s gaze vector. A red box indicates this point of intersection to the user. A button press activates the technique and resizes the object from its current position to the location of the red box. The button may also be held
Selection and manipulation of the widgets is accomplished using the HOMER [2] technique. Users select the appropriate widget using ray-casting [6] and manipulate the widget through scaled hand movement.
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CHI 2005 | Late Breaking Results: Posters
April 2-7 | Portland, Oregon, USA Design
down to continuously resize the object as the gaze direction moves. This technique takes advantage of the stability of the head to perform accurate resizing of objects.
To evaluate the performance of the techniques we designed an experiment where the participant would resize a simple box from several positions using all three techniques. We chose to use the following independent variables: • Technique: 3D Widgets, PORT, Gaze-Hand • Axes of Resize: X, Y, XY, XYZ • User Position: X Offset, -X Offset, X Direct
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The Axes of Resize variable represents the axes of the box that a participant was asked to resize in a single task. The participants performed the tasks from three locations relative to the box. The -X Offset (Figure 4) and X Offset locations positioned the participant so they looked down the X axis of the box. In these conditions the participant was offset from the axis so that 3 sides of the box were visible. In the X Direct location the participant looked directly down the X axis with only 2 sides of the box visible. These conditions were chosen so that the participant would have to resize the box both towards and away from their location. During the experiment the participant remained seated so that their position remained constant.
Figure 3: Gaze-Hand Resize FORMATIVE EVALUATION
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We performed an initial experiment with five participants to evaluate the use of the two newly-developed techniques, PORT and Gaze-Hand, and the existing technique, 3D Widgets. Participants evaluated all three techniques by resizing a box freely from various positions. Participants spent 5 minutes using each technique and were encouraged to speak aloud during the experiment. A post-experiment questionnaire obtained subjective ratings of each of the techniques as well as free-form comments. Results
Design Enhancement
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Most of the subjects preferred using the 3D Widgets technique due to its similarity to the resizing behavior in 2D applications. However, the subjects had difficulty selecting the widgets when the object was far away from them. The PORT and Gaze-Hand techniques required more training as subjects had difficulty understanding the relation of hand movement to axis selection. The subjects also commented that all techniques required more visual feedback.
To address the issues uncovered in the formative evaluation we made changes to each technique to improve usability. A highlight color was added to the widget selection ray when a widget was intersected. The direction that the PORT and Gaze-Hand techniques resized was changed so that the user pointed at the face they wished to move instead of the opposite direction. The line indicating the direction of resize for the Gaze-Hand technique was also lengthened so that the user could still see the line when the object became large.
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Figure 4: A 3-Axis task using 3D Widgets.
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The task was to resize the box so that the edge of the box was between the red and gold bars placed on each axis. Upon completion of this goal a wall occluded the user’s view of the task area. The participant was allowed to complete the tasks at their own pace initiating each task with a button press. Equipment
The experiment used a Virtual Research V8 head-mounted display (HMD) with biocular (non-stereo) graphics, 640x480 resolution, and a 60° diagonal field of view. An Intersense IS900 tracking system provided tracking for the head and wand in a 10’ x 10’ area. The main input device was a tracked wand with four buttons and an analog joystick. Graphics were rendered on a Pentium IV 2.4 GHz PC with a GeForce 4 TI 4600 128Mb graphics card running Windows XP.
SUMMATIVE EVALUATION
To compare the effectiveness of the three techniques we performed a summative evaluation using our testbed application. We hypothesized that the PORT technique would perform better than the other two techniques when resizing objects away from the user. As the widgets technique has the ability to resize along more than one axis at a time we also felt it would perform better on tasks where more than one axis needed to be resized.
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CHI 2005 | Late Breaking Results: Posters
April 2-7 | Portland, Oregon, USA
Procedure
techniques with the existing 3D widgets technique shows that participants were able to resize objects faster with the two new techniques than with the existing technique. Subjective results also show a strong user preference for the new techniques.
For the summative evaluation we recruited nine student participants from various backgrounds. After a brief prequestionnaire, participants engaged in a training session where they became acquainted with all three techniques. The training was performed in an environment identical to the task environment. Participants performed six practice tasks with each technique. After practice a short questionnaire obtained the participants’ early impressions of the techniques. Participants rated the techniques in categories of Preference, Controllability, Tiredness and Perceived Speed using a 1 to 7 scale. During the main portion of the experiment the participant performed two repetitions of each task with all combinations of the independent variables. A post-experiment questionnaire contained the same questions as in the post-practice questionnaire as well as space for comments.
Several questions must be asked when designing 3D object resizing techniques. • Can this technique be performed from any location relative to the object? • How difficult is the manipulation of the 3D input device when attempting to precisely resize the object?
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• Will new users of the technique be able to easily understand and use its functionality? We hypothesize that very effective techniques could be created by adapting 2D metaphors and modifying them to make use of the advantages of 3D input. By not requiring precise manipulation of the 3D input device and by taking advantage of the user’s proprioceptive sense and spatial knowledge of the environment, powerful interaction techniques can be designed.
Results
PORT
GazeHand
Widgets
9.07 seconds
10.14 seconds
17.30 seconds
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The average times to complete the tasks were as follows:
ACKNOWLEDGMENTS
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We used a three way ANOVA to analyze the results of the task completion times. The tasks using the PORT and Gazehand techniques were completed significantly (p < .0001) faster than those using the 3D Widgets technique. There was no significant difference between the PORT and Gazehand task completion times (p = .4118). The results also showed that participants had much more difficulty resizing the object along the X (Toward/Away) than the Y (Up) axis. Participant comments indicated that this was due to difficulty with depth perception and determining how far to resize the box.
The authors would like to thank the students in the fall 2004 class of CS6724 at Virginia Tech for their support and encouragement of this work.
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REFERENCES
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1. Bowman, D. and Wingrave, C. Design and Evaluation of Menu Systems for Immersive Virtual Environments. Proceedings of IEEE Virtual Reality, (2001), 149-156. 2. Bowman, D., Kruijff, E., LaViola, J., Poupyrev, I. 3D User Interfaces: Theory and Practice, Addison-Wesley Professional (2004)
The participant subjective ratings of the techniques in the post-questionnaire show a strong preference for the PORT (Avg. 5.1) and Gaze-Hand (Avg. 6.0) techniques over the 3D Widgets technique (Avg. 4.0). A post-hoc test showed that Gaze-Hand was significantly preferred over widgets (p < .0147) while PORT was not significantly preferred (p < .1712). A comparison of the post-practice and postexperiment questionnaires shows that the average subjective ratings for Preference and Controllability increased for both PORT and Gaze-Hand while the ratings for 3D Widgets decreased in the final questionnaire. We observed that the 3D Widgets technique was much easier for the participants to learn than the other two techniques. We attribute the higher initial scores to this higher learnability. Participants reported a higher level of neck strain and dizziness when using the Gaze-Hand technique as compared with the other two techniques.
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3. Conner, D.B, Snibbe, S.S, Herndon, K.P., Robbins, D.C., Zeleznik, R.C., Dam A. van Three-Dimensional Widgets. Proceedings of the 1992 Symposium on Interactive 3D Graphics, Cambridge, USA, MarchApril, (1992), 183-188.
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4. Mackie, C., Cowden, J., Bowman, D., and Thabet, W. Desktop and Immersive Tools for Residential Home Design. Proceedings of CONVR Conference on Construction Applications of Virtual Reality, (2004).
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5. Mapes, D., Moshell J., A Two-Handed Interface for Object Manipulation in Virtual Environments, Presence: Teleoperators and Virtual Environments, vol. 4, 403-416, (1995). 6. Mine, M., Virtual Environment Interaction Techniques, UNC Chapel Hill Computer Technical Report, TR9501. (1995)
CONCLUSION
7. Mine, M. ISAAC: A Meta-CAD System for Virtual Environments, Computer-Aided Design, vol. 29, (1997) 547-553.
We have presented two novel techniques for resizing objects in immersive VEs. A comparison of these
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