The state machine requires information about the 2-D features on the part to be inspected. We divide 2-D features into two categories, open features and closed features. An open feature is considered to be an edge that, when followed, has no closure. Closed features have the property that, through an edge search, we are able to complete a closed loop.
After digitizing an image of the part, edge responses are captured using the zero-crossing technique. Next, we search the edge responses for the feature type that they represent. Using a recursive search and the orientation information given by the zero-crossing algorithm, we are able to label each edge as part of a closed or open feature.