4 – Advanced Gaussian Filters

This chapter describes robust filtering techniques for 3-D surfaces. With robust algorithms even highly strained surfaces can be filtered without distortion of functionally relevant surface details such as laser spots and honing marks in engine bore surfaces or EDM-craters in steel sheet. The chapter focuses on the development of the robust Gaussian regression filter, which has proved to be a powerful tool for the evaluation of 3-D surface topography. By changing the order of the filter it can approximate to any form. Its robust algorithm reduces the effect of outliers and provides significant results with functional stratified surfaces, that is, beating faces, engine bore surfaces or rolling faces. The implementation of the 3-D surface filter into the geometrical product specification (GPS) standard chain format is also discussed. The 2D version of this filter is to be implemented in the German automotive industry in the future. Additionally, the 2D version of the filter has already been delivered as Technical Report to ISO.