Implicit surfaces offer many advantages for sketch- based modeling systems, such as blending, CSG, and a procedural object hierarchy. Free-form deformation (FFD) is also extremely useful in this context, however existing FFD approaches do not support implicit surface representations, and FFD lattice manipulation is time-consuming compared to sketch- based techniques. In this thesis, an FFD technique suitable for implicit surface representations is described. To enhance real-time feedback, the problem is split into an approximate formulation used during interactive deformation, and a...