A CONSTRAINT-LANGUAGE-BASED ENVIRONMENT FOR GEOMETRIC DESIGN

Abstract

This thesis documents an effort to simplify 3-dimensional geometric design using constraint-based techniques and the Devi environment that grew out of this effort. Designing 3-dimensional geometric models is a painstaking and time-consuming task even with today's high performance graphics workstations. Limiting factors are the display technology, interaction devices, design tools and the inherent complexity of the task. Geometric models do not inherently contain spatial dependency information. The designer has to make extra effort in specifying these dependencies or relationships. Constraints have enjoyed a fair degree, of success in providing this information. Tools which help the designer to position objects and specify their immediate geometry precisely are of little use in maintaining such relationships. A combination of direct manipulation and positioning tools, and constraint inferencing, can provide the design specifying constraints is that this task is in itself an extra effort. Systems can infer possible relationships and help the user to specify them. Such systems have been around for some time but. they have largely been limited to two-dimensions. Finally, the environment should not be confined to its original specifications. It should be designed to grow as the users' needs grow and change. I present Devi, a constraint-based 3d geometric editing environment that attempts to tackle these problems. Devi allows the user to interactively enter 3-dimensional geometry and constraints using direct manipulation. Devi aids the user by inferring constraints between geometric objects as they are created. The constraint-inferencing mechanism can be extended by writing simple inference rules and adding them into the system. Devi presents the constraint network graphically as a directed graph with geometry and constraint nodes and edges depicting the dependencies - the user can directly manipulate debug constraints.