Surface interrogation methods

This paper deals with an overview and analysis of methods for inspecting surface quality. The overview is done by a new classification based on common mathematical concept yielding four groups of methods. First, techniques based on curvature, such as colour-coded map, lines of curvature, isolines of curvature, and focal surfaces are considered. They are followed by methods based on illumination models like isophotes, Iv-curves, reflection lines, highlight lines, and shaded-image rendering. Then, methods using special linear transformations are included: polar and orthonomic surfaces. The final methods studied are contour lines. At the end, the results of a comparative analysis of all considered methods, such as their suitability for determining continuities, inflection points, and convex/concave regions, their speed, sensitivity to surface changes, and invariance to geometric transformations, which could be very interesting and useful for a user, are presented