Free-form sketching with variational implicit surfaces

With the advent of sketch-based methods for shape construction, there's a new degree of power available in the rapid creation of approximate shapes. Sketch Zeleznik, 1996 showed how a gesture-based modeler could be used to simplify conventional CSG-like shape creation. Teddy Igarashi, 1999 extended this to more free-form models, getting much of its power from its ``inflation'' operation (which converted a simple closed curve in the plane into a 3D shape whose silhouette, from the current point of view, was that curve on the view plane) and from an elegant collection of gestures for attaching additional parts to a shape, cutting a shape, and deforming it. But despite the powerful collection of tools in Teddy, the underlying polygonal representation of shapes intrudes on the results in many places. In this paper, we discuss our preliminary efforts at using variational implicit surfaces Turk, 2000 as a representation in a free-form modeler. We also discuss the implementation of several operations within this context, and a collection of user-interaction elements that work well together to make modeling interesting hierarchies simple. These include ``stroke inflation'' via implicit functions, blob-merging, automatic hierarchy construction, and local surface modification via silhouette oversketching. We demonstrate our results by creating several models. Categories and Subject Descriptors (according to ACM CCS): I.3.5 Computer Graphics: Modeling packages I.3.6 Computer Graphics: Interaction techniques