Tabletop Interaction: The TractorBeam Technique
What is it?
When using a direct input device such as a stylus, reaching objects on the far side of a tabletop display is difficult. We wanted to develop an interaction technique that would enable acquisition of distant targets, while also providing efficient interaction with closer objects.
The result is the TractorBeam technique: a hybrid point-touch interaction technique which allows users to point at distant targets, and choose between point and touch for closer targets.
The technique works as follows:
Using a stylus, the user points at or touches the tabletop display. A cursor appears
on the display to show the current trajectory of the stylus. The user moves the stylus
around until the cursor is on the desired item. To select the item, the user clicks the
button located on the top of the stylus.
This effect is achieved through the use of a 3D-tracked stylus. The TractorBeam software uses positional information from this stylus to calculate the projected location of the cursor on the tabletop display.
Evaluating the TractorBeam
We conducted studies to compare the speed and accuracy of selecting a target by touching it versus pointing to it, and also to determine which of these two methods users preferred. We found remote pointing to be a highly effective technique for tabletop computer displays. When pointing and touch were compared, pointing was as fast as - or faster - than touch for everything except small, distant and medium-distance targets. Our studies also revealed that users preferred to point to select distant objects, probably due to the physical effort involved with touching targets.TractorBeam Selection Aids
In order to improve on the problem of reaching small distant targets encountered in our initial TractorBeam studies, we designed three selection aids as potential improvements:
- Expanding the cursor: Participants make selections using a "selection halo" area which surrounds the cursor, rather than having to use a single cursor point for selection.
- Expanding the target: Targets expand from their original size whenever the cursor comes within 90% of the total distance to the target.
- Snapping to the target: The cursor "jumps" into the center of the target whenever it comes within 90% of the total distance to the target.
Studies showed all three of these selection aids as offering a significant time advantage over the original TractorBeam, with snapping to the target being the fastest.