Prior Definition

Some features can be identified only if other complex features have been identified beforehand. This requires a reiterative approach to the process of feature recognition. For example, a closeout rib can be identified as being the rib adjacent to an ejection pin: the ejector pin is not a simple feature and must have been previously identified.

It should be noted that an ejector pin can be defined as a boss adjacent to a closeout rib. The definer must be careful that the feature definition is not cyclic, that is each feature is defined in terms of the other. In general, it is possible to define at least one such feature entirely in terms of the simple features.