VRSketchPen: Unconstrained Haptic Assistance for Sketching in Virtual 3D Environments. - Hesham Elsayed; Mayra Donaji Barrera Machuca; Christian Schaarschmidt; Karola Marky; Florian Müller 003; Jan Riemann; Andrii Matviienko; Martin Schmitz 001; Martin Weigel 001; Max Mühlhäuser (VRST, 2020)