Today, we can find tools for direct 3D manipulation of models in
commercial modeling packages, like Maya and Blender. But, few
sketch-based systems have explored the use of strokes as a control
interface and not just for modeling [18,23], as the design of the
widgets do not follow the sketching paradigm[7,8]. Another major
problem is that sketch-based interfaces lose precision when trying
to manipulate a 3D model, because they do not directly control the
details of the mesh. This goes against the nature of freehand
drawing. A study revealed that users are not satisfied with imprecise
controls[8]. Thus, it becomes necessary to provide a method that
bridges the gap between sketch-based interfaces and traditional 3D
model manipulation[4]. Traditional approaches rely on the user to
create a rig to control a 3D model. A rig can be based on shapes,
bones or a combination of both. Editing the rig directly easily
becomes impractical when the complexity of the rig increases.
Osipa[22] presented a facial control interface that provides a high
level viewport to edit the model and animations, which only allows
to manipulate four attributes of the rig elements by a bi-dimensional constraint widgetv