The over-sketching technique for free-hand shape modelling in Virtual Reality

The benefits of the Virtual Reality (VR) technologies in the field of conceptual free form modelling have been investigated for over a decade. Many researchers have paid attention to hand-sketching techniques for shape generation and to the Virtual Sculpting approach for surface modification. What has not yet been investigated sufficiently is modification based on the free-hand drawing approach. This could be more similar to the traditional way designers work, compared to the sculpting metaphor. The research described in this paper helps to fill this gap, defining a new free-form curve modification technique based on the over-sketching approach. This technique has been implemented in a curve modification tool of VEIS (Virtual Environment for Interactive Sketching), a prototype VR system for free form modelling. The tool allows the user to refine a curve by simply substituting a part of it with a new one. It recognizes the user gestures, made with a 3D tracked pen, to determine how the pen strokes modify a part of the existing curve and then automatically merges the new piece with the unchanged parts of curve. Furthermore, by taking advantage of the parent-child relation, a surface can be updated by simply modifying the curve/s employed for its definition.