We present a method for creating 2 1/2D models from line drawings of opaque solid objects. We allow the artist to draw naturally, differing from many previous approaches. Our system allows both perspective and orthographic projection to be used and makes no a priori assumptions about the type of model to be produced (i.e. planar, curved, normalon) . The frontal geometry is reconstructed by placing constraints at the contours and solving a 2D variational system for the smoothest piecewise smooth surface. An analysis of line labelling allows us to determine what constraints are possible and/or required for each input line. However, because line labelling produces a combinatorial explosion of valid output geometries, we allow the user to guide the constraint selection and optimization with a simple user interface that abstracts the technical details away from the user. The system produces candidate reconstructions using different constraint values, from which the user selects the one that most closely approximates the model represented by the drawing. These choices allow the system to determine the constraints and reconstruct the model. The system runs at interactive speeds.
Sketch Based Interaction and Modeling (SBIM) 2006
Here is a link to a pre-publication version of the paper and to the talk and to a sample animation showing the system in action. I'll post more animations later.
Sample images (click for a larger view):