Development of digital filter in the field of 3D roughness measurements

There is a whole series of digital 3D filters, but due to the existing drawbacks of the current filters, research is continuing on new filters. Further in the text is the description of a filter developed at the Laboratory for Precise Measurement of Length at the Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb (LFSB). The method consists in separating the waviness from roughness by dividing the surface into segments which are combined into a single surface by means of a polynomial. The surface obtained in this manner represents waviness whereas roughness is presented by the discrepancies between the original surface and the waviness. The research with the aim of checking the set method was carried out by a combination of theoretical and experimental work. The theoretical work included the analysis of the simulated surfaces. These surfaces were composed of two components, simulated waviness and simulated roughness. The analysis included simulated surfaces both with directional and non-directional traces. The optimal filter parameters (grid of surfaces, polynomial degree) are determined on the basis of the value of the residual variance and the 3D parameters of roughness and waviness.