Patchmaker: Geometric tools for 3d sketching interfaces

Despite many years of research, it still remains difficult for artists and designers to quickly create 3D models from their sketches. Traditional CAD tools are heavily dependent on deep menus and toolbars, and can take months to master. The vision of an intuitive, natural modeling system that has the feel and simplicity of sketching remains elusive. Recently sketch-based interfaces have been developed that allow artists to draw 3D space curves using 2D drawing interfaces. Using 3D sketch-based interfaces, an artist or designer can quickly produce curve networks; usually interpreted as a wireframe model. The sketches suggest a 3D object, but determining how to convert a 3D curve sketch to a surface model is not trivial. Surfacing is an important part of the design process; it produces more realistic and less confusing visualizations of the concept shape and can serve as a starting point for a modeler to construct a precise CAD model. Unfortunately, surfacing a curve network is an inherently ambiguous problem. In this dissertation we present PatchMaker, a set of geometric tools that aid the artist in converting their 3D curve sketch into a surface model. In the first part of the dissertation we address the problem of identifying regions of the wireframe model that bound surface patches and we present an automatic method for finding them. There is usually no correct surface model; therefore, our goal is to automatically find the obvious patches (those that can be reasonably expected, given the curve input). The system uses a linear algebra representation of the set of surface patches to track the topology. Surface patch boundaries can have an arbitrarily complex 3D geometry, making it challenging to produce a reasonable tessellation quickly, even with current methods. In the second part of the dissertation, we address the problem of creating light-weight surface tessellations on the fly. Our approach is to break complicated patches into simpler ones which can be tessellated using any simple algorithm. Our surfacing approach relies on the observation that breaking a complicated patch into a set of nearly planar ones with small total area seems to create a simple, natural-looking surfaces. We demonstrate our approach on curve networks generated by two different 3D sketching systems. In the last section of the dissertation we present how PatchMaker can be used for the process of surfacing user sketches as a standalone tool or used during an interactive session. As the designer builds up a sketch, PatchMaker shows how the system interprets the shape and topology of the partially inferred surface so far, providing guidance to the artist. Since there is no correct surface model, any surfacing system must allow user-guided as well as automatic selection and construction of patches. As a result, PatchMaker also provides the user, topology-aware user interface for specifying missing or incorrect patches with a few mouse-clicks.