Ortholumen: Using Light for Direct Tabletop Input

Paper in proceeding, 2007

Ortholumen is a light pen based tabletop interaction system that can employ all the pen’s spatial degrees of freedom (DOF). The pen’s light is projected from above onto a horizontal, translucent screen and tracked by a webcam sitting underneath, facing upwards; system output is projected back onto the same screen. The elliptic light shape cast by the pen informs the system about pen position, orientation, and direction. While this adds up to six DOFs, we have used up to four at a time. In order to separate input and output light we employ polarizing filters on the webcam and the projector lens. Two prototypes, painting and map navigation, are presented. Ortholumen can be expanded to track multiple pens of the same or different colors; this enables bi-manual input, collaboration, and placed pens as external memory. Visible light, as opposed to infrared or radio, may be perceived more directly by users. Ortholumen employs only low-cost parts, making the system affordable to home users.