Edge and Tip Diffraction Imaging in Three Dimensions

The dimensionality of the diffracted wave is related to the dimensionality of the diffractor: a surface reflected ray is uniquely determined, edge diffracted rays strike out a one-parameter pencil, tip diffracted rays a two-parameter pencil of rays. These topological notions are important to analyse the effect of diffraction imaging by specularity suppression. In diffraction imaging reflectivity is fully suppressed, edge diffractivity partly suppressed, while tip diffractivity stands out unsuppressed. These observations have a significant impact on the structural interpretation of three-dimensional diffraction images. Edges constitute the skeleton of a structural model and tips indicate the joints of the skeleton.