6.0 ELEMENTS OF MODELING
Many algorithms for feature recognition are not user-friendly. Besides using representations unfamiliar to the person most capable of specifying a feature, the code and the templates used to recognized features are so thoroughly intertwined that a programmer is required to specify the feature definitions.
Some approaches to feature definition do separate the feature specification from the recognition process. It allows the user to define and edit features in terms of faces and edges, primarily through a graphical interface such as that of [Sakurai & Gossard 90]. Additional information, such as parallelism and perpendicularity, may be included for the recognition process. While this interface is a much easier environment for direct user specification, variations upon the basic shape still must be explicitly specified. More importantly, the user must be familiar with the constructs of the faces and edges, which although acceptable to the designer, may prove to be a tedious process for one such as a molding expert not familiar with CAD drafting.
Although some evaluation may be performed on the simple features, the availability of more complex features allows for a more substantial evaluation of a part to be performed. Most of the feature recognition techniques do not address the definition of more complex features of any domain. But given that the current recognition technology can provide a set of primitives easily recognizable by the engineer, it is possible for the expert to directly define the more complex features out of these primitives.