Workplane-orientation sensing techniques for tablet PCs

Many mobile applications could benet from having more ne-grained awareness of user-to-device orientation than is possible with traditional landscape and portrait modes. In contrast to approaches that measure absolute orientation of a device in world coordinates, we argue for the need to mea- sure workplane orientation: the angle of rotation, relative to the user, around the axis perpendicular to the user's work surface. We present two complementary methods to deter- mine workplane orientation for a hand-held writing surface: one using computer vision techniques and another based on stylus-pose. Categories and Subject Descriptors: H.5.2 (User Inter- faces): Input devices and strategies, Vision I/O, Interaction styles Additional Keywords and Phrases: orientation-aware sys- tems, mobile devices, pen-based computing, tablet interac- tion MOTIVATION Tablet PCs were originally developed to allow interaction in- spired by paper and pencil. Today's devices are handwriting- enabled and they include a few desktop GUI widgets that are modied to control the on-screen cursor with a stylus rather than a mouse. These devices typically support the simple no- tion of absolute orientation in 90∞ increments (landscape vs. portrait modes). However, people often interact with conven- tional media in much less restrictive ways than landscape or portrait orientation implies. Fitzmaurice and colleagues (4) studied how artists take ad- vantage of reorienting their work surface during sketching and writing. They introduced and explored many issues re- lating to what they called Rotating User Interfaces (RUIs): applications and toolkits for pen-based computing systems that take into account workplane orientationóthe angle of rotation, relative to the user, around the axis perpendicular to the user's work surface. To provide Tablet PCs with such capabilities, a method to sense workplane orientation is re- quired.