Design by features is a novel approach for the high-level modeling of objects that allows for sharing of information between activities such as design and manufacturing process planning. This thesis deals with a specific issue in this area, namely the development of a generic form- feature extraction and coding framework for objects with planar surfaces.

A form feature is defined as a geometric formation on an object which can be associated with design/manufacturing information. There exist two main approaches to the identification of form-feature information from a Computer-Aided Design (CAD) model. The first approach, feature recognition, requires a pre-defined instance of the form feature to be recognized. The second approach, feature-based modeling, incorporates the form-feature information directly into the part model during the design stage by using a set of pre-defined features. Therefore, in both cases, the identification of form features present in a CAD model is limited by the size and variety of a pre-defined set.

In this work, the lack of generalization of the feature-recognition and feature-based modeling approaches is addressed by the development of a generalized feature-extraction technique. A novel classification strategy of form features is developed. Based on the classification, a sequential procedure is proposed for the extraction of form features from CAD models;​ a coding procedure is developed for automatically coding the object and its extracted features.

The classification of form features in this work is based on their effect in changing a basic shape. This classification strategy results in a finite number of feature classes. The sequential extraction procedure consists of five stages. At the onset of each extraction stage, the object is viewed as a basic shape which has been iteratively altered through the introduction of form features. The coding procedure is based on the boundary representation of the object and its extracted features. The code is used to improve the user interface, through the generation of a customized library of form features and basic shapes. The libraries would provide the designer with a suitable starting point for the modeling of designs. In addition, the automatic generation of the code would provide the means for automating the link between the CAD system and a knowledge base which contains information pertinent to a given manufacturing environment.