UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

A hybrid CAD modeler for flexible geometric modeling of prismatic mechanical parts Chen, Jack Szu-Shen


The ease and freedom of shape manipulation achievable through physical modeling materials such as clay for engineering design is steps beyond what is attainable through current computer-aided design (CAD) modelers. With the current CAD modeling paradigm, which creates models through a composition of features constrained by closed-form mathematical formulations, the flexibility in model shape manipulation is limited. As a result, many complex engineering shape designs are either completed in the physical regime then digitized or in the computer-graphics domain where modeling flexibility is significantly higher. Unfortunately, the gain in modeling flexibility is achieved at the expense of well-controlled feature information and modeling precision and accuracy. The resulting models are featureless inexact entities. In order to bring forth geometric modeling flexibility while retaining feature information along with modeling precision and accuracy, this thesis presents a novel hybrid CAD modeler. The hybrid modeler utilizes triangle mesh model representation with the notion of feature imposed as a separate but associated feature information layer. This allows the prismatic features on a model to be modified unrestrictedly without loss of feature information. Users can freely modify the model geometry beyond what is permissible by the current CAD modelers’ feature formulations/management. A robust feature segmentation scheme that divides a triangle mesh model into its elementary features automatically categorizes the unconstrained user modifications into prismatic features and updates the associated feature information layer. An idealization module completes the prismatic feature information extraction process and updates the mesh model to accurately reflect the newly detected/extracted features. Feature-based model editing is incorporated to permit accurate and precise feature-based editing and to maximize the ease-of-use of the hybrid modeler. Accordingly, the hybrid modeler consists of four modules: feature segmentation, feature idealization, unconstrained feature-free model modification and feature-based model editing. With the proposed hybrid modeler, modeling flexibility as well as precision and accuracy are satisfied simultaneously. The hybrid modeler provides the user with a flexible modeling environment for creating and modifying prismatic engineering design models.

Item Citations and Data


Attribution-NonCommercial-NoDerivs 2.5 Canada