Feature-Based Alignment and Comparison between Portion and Whole of Free-Form Surfaces

In free-form inspection, it is often that only portion of a surface has high precision requirements. This paper proposes a feature-based automatic localization and comparison method for the situation where the measurement surface is only a portion of the design model. To make comparison, these two surfaces must be brought to a common coordinate system which is called localization. The proposed method localizes the portion surface to the whole surface through two steps of localization process. The first step is general localization. The corresponding features between the measurement surface and the design model are searched. Based on the feature correspondence, the measurement surface is localized very close to the design model. The second step is fine localization that establishes the point-point correspondence and localizes the surfaces more accurately.