In recent years visualization of and interaction with 3D data have become more and more popular and widespread due to the require- ments of numerous application areas. Two-dimensional desktop systems are often limited in cases where natural and intuitive in terfaces are desired. Sophisticated 3D user interfaces, as they are provided by virtual reality (VR) systems consisting of stereoscopic projection and tracked input devices, are rarely adopted by ordinary users or even by experts. Since most applications dealing with 3D data still use traditional 2D GUIs, current user interface designs lack adequate efficiency. Multi-touch interaction has received considerable attention in the last few years, in particular for non-immersive, natural 2D interaction. Interactive multi-touch surfaces even support three degrees of freedom in terms of 2D position on the surface and varying levels of pressure. Since multi-touch interfaces represent a good trade-off between intuitive, constrained interaction on a touch surface providing tangible feedback, and unrestricted natural interaction without any instrumentation, they have the potential to form the fundaments of the next generation 2D and 3D user interfaces. Indeed, stereoscopic display of 3D data provides an additional depth cue, but until now challenges and limitations for multi-touch interaction in this context have not been con- sidered. In this paper we present new multi-touch paradigms that combine traditional 2D interaction performed in monoscopic mode with 3D interaction and stereoscopic projection, which we refer to as interscopic multi-touch surfaces (iMUTS).
