| Summary: | This thesis presents the results of new techniques investigated for applying on-line sketching into 2D and 3D conceptual design geometry throughout a whole development process: data collection, concrete curve segmentation and fitting, 2D geometric constraint extraction and solver, and 3D feature recognition and modelling. This is a new approach. A real time sketch and fuzzy knowledge-based prototype system has been developed in four phases. In the first phase, the segmentation approach investigated accepts the input of on-line free-hand sketch, and segments them into meaningful parts, by using fuzzy knowledge in terms of sketching position, direction, speed and acceleration. During the second phase, a parallel curve classification and identification method is studied by employing fuzzy heuristic knowledge in terms of curve linearity and convexity, in order to quickly classify and identify a variety of 2D shapes including straight lines, circles, arcs, ellipse, elliptical arcs, and free-form curves. Afterwards, a geometric constraint inference engine and a constraint solver are utilised according to degrees of freedom analysis, to capture a designer's intention, to infer geometric constraints simply and automatically, and to generate a possible solution without involving iterative computing. The solver also supports variational geometry in 2D and 3D. In the last phase, rule-based feature interpretation and manipulation techniques are investigated. While drawing, the 2D geometry is accumulated until it can be interpreted as a 3D feature. The feature is then placed in the 3D space and a new feature can be built incrementally upon previous versions. The given examples and case studies show that the system can interpret users' intention on 2D and 3D geometry satisfactorily and effectively. It can not only accept sketched input, but also users' menu-based interactive input of 2D primitives and 3D projections' This mixed automatic feature interpretation and interactive design environment can encourage designers with poor sketching skills to use it for creative design tasks.
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