Drawing on air: input techniques for controlled 3D line illustration.

We present Drawing on Air, a haptic-aided input technique for drawing controlled 3D curves through space. Drawing on Air addresses a control problem with current 3D modeling approaches based on sweeping movement of the hands through the air. While artists praise the immediacy and intuitiveness of these systems, a lack of control makes it nearly impossible to create 3D form beyond quick design sketches or gesture drawings. Drawing on Air introduces two new strategies for more controlled 3D drawing: one-handed drag drawing and two-handed tape drawing. Both approaches have advantages for drawing certain types of curves. We describe a tangent preserving method for transitioning between the two techniques while drawing. Haptic-aided redrawing and line weight adjustment while drawing are also supported in both approaches. In a quantitative user study evaluation by illustrators, the one and two-handed techniques performed at roughly the same level, and both significantly outperformed freehand drawing and freehand drawing augmented with a haptic friction effect. We present the design and results of this experiment as well as user feedback from artists and 3D models created in a style of line illustration for challenging artistic and scientific subjects.