Sketching with constraints

The goal of this thesis is to provide a simple and intuitive user interface to a Computer Aided Design (CAD) system. A simple modeling system was built to demonstrate the utility of the ideas presented here. There are three main parts to this system. The first part is the interpretation of sketched input. Pei, strokes are interpreted as lines, arcs, circles or cubic Bezier curves. Sketching serves as a particularly useful way of entering geometry. Additionally, relations between these primitives are detected and established by constraints. The second part allows modification and refinement of the modeled object. It is based on a novel approach for constraint specification and solving. The user is allowed to interactively modify the geometry of a model by simply dragging one of its points. The intent of this manipulation is inferred by the system, and a meaning is associated with it. A tree is built to carry out transformations on the parts of the model. This manipulation tree is constructed to introduce the least amount of change into the system. The last part of this system involves extending the system into three dimensions so that real objects can be designed. The geometric primitives are assembled into profiles which can then be extruded. Features can then be directly sketched on the faces of the extruded profile.