# Roughness Evaluation of Burnished Topography with a Precise Definition of the S-L Surface
## 3 Results
### Definition of an Areal Form Removal Algorithm for a Precise L-Surface Definition  
One of the main issues in the reduction of errors in the definition of an L-surface is to appropriately analyse the area where the features occur (e.g., oil pockets, dimples, oil reservoirs, scratches, or generally valleys). Plateau-honed cylinder liners are types of surfaces that contain a lot of these features. The degree of processed data ex-aggregation increases according to the enlargement in the size of each feature, however, this dependence is especially noticeable when deep/wide oil pockets/dimples are considered [17]. It was found in previous studies [16] that the false estimation of the reference plane for the surfaces containing burnished dimples could affect a selected group of parameters the most. First, growth in dimple distortion caused considerable differences in the amplitude (height) parameters, especially \(Sp\) and \(Sv\), respectively, for the Sk group parameters, \(Sk\), \(Spk\), and \(Svk\). Usually, the distortion of the dimples causes a huge exaggeration of parameters strictly related to the valleys. The values of the \(Sv\) and \(Svk\) parameters were distorted by about 100%. An application of digital filtering, whether containing the robust modification or not, caused a flatness of the oil pockets [16], which affected the decrease in the values of the \(Sv\) and \(Svk\) parameters. False calculation of these roughness parameters, correspondingly, had an impact on the Sk parameter. In practice, all of the Sk group parameters were received with distorted values [14]. In Figure 5, contour map plots of the turned cylindrical surface with additionally burnished deep and wide dimples are presented (left column) with ISO 25178 parameters (middle) and selected profiles (right column). Some of the errors in the definition of the L-surface can be visible from the analysis of the contour map plots of the surface. Regarding this, the application of all of the regular filters (e.g., GRF, RGRF, or SF) caused a serious distortion of dimples (Figure 5g,j,m). However, the location of these features influenced the degree of the deformation. Usually, the distortion increased if the dimple was positioned near/on the edge [88] of the considered detail. Moreover, for the Gaussian (GRF and RGRF) filters, the edge-effect had an enormous influence. Despite the location of the oil pockets, all of the applied filters did not allow us to receive a properly calculated reference plane. In comparison with regular digital filtering methods, the least-square fitting schemes provided more persuasive results (Figure 5a,b). For each, the dimple exaggeration was substantially reduced. When a cylindrical shape (LSFC) was fitted, the distortion occurred in the areas near the edge, but only when more than one dimple was located nearby--this is indicated by the arrow. The most encouraging results were obtained when a polynomial reference plane (POLY2) was defined. However, both methods were supported by the valley-excluding method (VEM) [43]. Improvement in the reduction in dimple deformations was particularly visible in the profile exploration. The validation of the methods applied for an L-surface calculation could be improved with an analysis of the ACF graph (Figure 6). It was observed that the surface after the application of a proper method for form removal should be flat [40]. The same property was observed for the 3D ACF defined for those surfaces (Figure 6m-o)--if a form was removed entirely, the shape of ACF was also close to the flat. However, this property was received when the ACFs were thresholded. These techniques, and especially their validity, have been widely introduced and considered for surface roughness analysis in many previous studies [35; 64; 89; 90]. Figure 5: L-surfaces (left column), their ISO 25178 parameters (middle), and selected profiles (right column) received after the application of LSFC (**a–c**) and POLY2 (**d–f**) with VEM, GRF (**g–i**), RGRF (**j–l**), and SF (**m–o**) with a cutoff = 2.5 mm.