# Roughness Evaluation of Burnished Topography with a Precise Definition of the S-L Surface
## 3 Results
### Selection of Procedure for a High-Frequency Errors Reduction for S-Surface Definition
From the previous property, when PSDs were considered, it was found that NSs created by SF (Figure 7h) and FFTF (Figure 7n) provided the most encouraging results. However, when considering the isotropic requirements, the application of the FFTF scheme (Figure 7o) seems to be a better solution for the suppression of high-frequency measurement errors from the results of the surface topography measurements. For the precise definition of the S-surface, we suggest analysing the PSD, ACF, and TD of the N, received after a digital filtration. Figure 7: Isometric views of the S-surfaces (left column), their PSDs (middle), and TD graphs (right column) received after the application of GRF (**a**–**c**), RGRF (**d**–**f**), SF (**g**–**i**), MDF (**j**–**l**), and FFTF (**m**–**o**), method with a cutoff = 0.025 mm. Proposals of Procedures for a Precise Definition of the S-L Surface with a Validation Concerning the (2D) Profile Data  
The validation of procedures for the L-surface and S-surface definition can also be studied if dependent on the sequence of the algorithm provided. It was found in previous studies [17] that the occurrence of high-frequency measurement noise did not affect the validity of the method for areal form removal, resulting in defining the L-surface. Regarding this, we suggest first removing the form and then applying a filter for high-frequency measurement noise suppression. When defining the S-L surface, the L-surface can be defined in advance of the S-surface. Moreover, many proposals (procedures) for the definition (detection) and removal (reduction) of high-frequency measurement errors can be more validated when a flat (not containing form) surface is considered. Therefore, the procedure of the S-surface definition can be more valuable when applied after the definition of the L-surface. The definition of both the L-surface and S-surface can be even more valuable when considering analysing the 2D (profile) data. Profile characterisation can be crucially important when the distortion of the valleys is considered. It was previously found that exaggeration in areal form removal is even easier to detect when dimples are located near/on the edge of the analysed data [43]. However, the distortion can also be visible for each of the surfaces containing deep and wide oil pockets [16; 40]. Moreover, the density and distribution can affect the suitability of the L-surface method [17]. Surfaces containing many dimples, despite their sizes, can find it difficult to define the L-surface by excluding the valleys, such as the VEM scheme [43]. In this case, the process of feature exclusion may be too time-consuming. Moreover, the excluded area may be too large for the area that is not. One of the solutions is to enlarge the value of the cutoff (e.g., for the 2.5 mm or larger [96; 97; 98]). The flatness of the dimples should be reduced, nevertheless, in form, especially those components that reflect the waviness, which would not be extracted. In Figure 8, various circumferential profiles received from the plateau-honed cylinder liner surface are presented. They differed by the number of dimples and valleys included, from a profile containing three dimples and two valleys (Figure 8a) to a profile with one dimple and one valley (Figure 8f). Characterising and definition of the S-L surface are usually highly demanding for surfaces containing the largest number (and density, respectively) of the features and dimples in recent studies. Regarding this, the profile containing five features was analysed. For surfaces and profiles with a huge number of dimples, usually problems in the precise definition of the S-L surface derive from the errors in the areal form removal and L-surface calculation. In Figure 9a, the parts of the profile containing features, dimples, or valleys (scratches) are indicated by the arrows. It can be observed that, relatively, this part of the profile was around 50% of the whole profile length. In this case, the possibility of errors in positioning the reference line can increase enormously.