TouchGlass: Raycasting from a Glass Surface to Point at Physical Objects in Public Exhibits.

Physical objects such as natural items or fine art pieces are often placed behind glass cases to protect them from dust and damage. Generally, interacting with such objects is indirect, based for example on an adjacent touch interface detracting users' attention from the object. In this paper, we explore whether the glass case could be used as an input surface to point and select distant physical objects. With such an approach, the glass case offers a physical delimiter for interaction to avoid unintended activations. We explore this innovative approach through a two steps approach. First, we carry an informative study with 46 participants to validate the most appropriate "walk-up and use" technique. Our results show that using a ray orthogonal to the glass surface is the most natural approach in a public setting. Next, we further explore this orthogonal raycasting technique and conduct a target acquisition experiment to evaluate the impact on target selection performance of the target size, target distance, presence of spatial references and user's head position with regards to the glass case. Results reveal that using the glass as touch surface allows to easily select targets as small as 3 cm up to 35 cm away from the glass. From these results, we provide a set of guidelines to design interactive exhibits using a touch glass case.