In this work we present a method for the intuitive editing of surface meshes by means of view-dependent sketching. In most existing shape deformation work, editing is carried out by selecting and moving a handle, usually a set of vertices. Our system lets the user easily determine the handle, either by silhouette selection and cropping, or by sketching directly onto the surface. Subsequently, an edit is carried out by sketching a new, view-dependent handle position or by indirectly influencing differential properties along the sketch. Combined, these editing and handle metaphors greatly simplify otherwise complex shape modeling tasks.

We come to the conclusion that sketching a shape is inverse NPR. Consequently, we design a sketch-based modeling interface using silhouettes and sketches as input, and producing contours, or suggestive contours, and ridges/ravines. The user can sketch a curve, and the system adapts the shape so that the sketch becomes a feature line on the model, while preserving global and local geometry as much as possible [Sorkine et. al 2004]. As the requested properties of the sketch cannot or should not always be accommodated exactly, users only suggest feature lines.

We have furthermore automated the algorithm: the user sketches a stroke that is the suggested position of part of a silhouette of the displayed surface. The system then segments all image-space silhouettes of the projected surface, identifies among all silhouette segments the best matching part, derives vertices in the surface mesh corresponding to the silhouette part, selects a sub-region of the mesh to be modified, and feeds appropriately modified vertex positions together with the sub-mesh into a mesh deformation tool.

• Andrew Nealen, Olga Sorkine, Marc Alexa and Daniel Cohen-Or. A Sketch-Based Interface for Detail-Preserving Mesh Editing [4], In proceedings of ACM SIGGRAPH 2005, pages 1142-1147
  
• Johannes Zimmermann, Andrew Nealen and Marc Alexa SilSketch: Automated Sketch-Based Editing of Surface Meshes [5], Accepted for publication in proceedings of the Workshop on Sketch-Based Interfaces and Modeling 2007