The height amplitudes of surface roughness based on area-direction character and relative assessed indexes

To study the relationship among the height amplitude of surface roughness, assessed area and assessed direction, the height amplitudes SRa, SRq, SRsk and SRku based on area-direction character are defined in the paper. And on the foundation of these parameters, relative assessed area indexes, assessed direction indexes and assessed total indexes are established. SRa, SRq, SRsk and SRku are the natural extension of 2D height amplitudes Ra, Rq, Rsk and Rku. They are different from 3D height amplitudes Sa, Sq, Ssk and Sku. They provide an evidence to study the quantitative relationship among surface roughness, assessed area and assessed direction. Relative assessed area indexes, assessed direction indexes and assessed total indexes can be used to assess the distribution situation of height amplitudes of surface roughness related to area, direction and entireness