Investigating User Requirements and Usability of Immersive Three-dimensional Sketching for Early Conceptual Design - Results from Expert Discussions and User Studies. - Johann Habakuk Israel; Christian Zöllner 001; Magdalena Mateescu; Rasim Korkot; Gunnar Bittersmann; Patrick Tobias Fischer; Jens Neumann; Rainer Stark (SBIM, 2008)