We provide typical sketch based modeling functions such as erase gestures, stroke smoothing, and global symmetry. Users sketch strokes, like with pen and paper (see accompanying video), to construct curves,surfaces,and volumes in the scene. While we typically expect smooth strokes, we do segment closed loops to form surfaces and volumes, at inflections and points of high curvature. Once a segment in the curve is detected a 2D preview of the completed closed loop is shown to the user. At any time there is an active base layer that forms the geometry with respect to which new strokes are inferred in 3D and placed in the active drawing layer. All layers below the active drawing layer form the underlying 3D geometry. Geometric layers above the active drawing layer, if present, are passive and are simply a visual reference. Although SecondSkin has limited layer editing and management functionality, a layer editor similar to that found in image editing software like Adobe Photoshop is easy to envisage and implement. Figure 7 shows a hypothetical user interface for such a layer editor.