## 3 Results and Discussion
### Analysis of Contour Reconstruction Reliability for S02
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Coverage Priority**} & \multicolumn{4}{c}{**Accuracy Priority**} \\ \cline{2-10}  & \(T\) & \(S_{f}\) & \(C_{f}\) & \(\overline{D}\) (\(\upmu\)m) & \(\sigma_{D}\)(\(\upmu\)m) & \(T\) & \(S_{f}\) & \(C_{f}\) & \(\overline{D}\) (\(\upmu\)m) & \(\sigma_{D}\) (\(\upmu\)m) \\ \hline
**Sobel** & 20 & 45 & 100 & 6.8 & 7.97 & 40 & 45 & 90.0 & 6.90 & 5.57 \\
**Prewitt** & 20 & 31 & 100 & 6.8 & 7.88 & 35 & 51 & 93.6 & 6.12 & 5.00 \\
**Roberts** & 10 & 43 & 100 & 7.3 & 8.26 & 40 & 33 & 79.8 & 10.04 & 6.30 \\
**Zerocross** & 1 & 37 & 100 & 6.5 & 9.31 & 3 & 55 & 91.1 & 6.82 & 5.67 \\
**Canny** & 110 & 19 & 100 & 6.65 & 7.65 & 110 & 19 & 100 & 6.65 & 7.65 \\
**ApproxCanny** & 130 & 49 & 100 & 6.92 & 7.50 & 150 & 55 & 97.2 & 7.33 & 7.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Optimal combinations of test parameters for \(S01\). Figure 9: MQI results as a function of \(S_{f}\) and \(T\) for every \(M\) calculated for SO2. To better explain differences between the selected combinations, Figure 11 provides polar plots of the radial differences (\(R_{d}\)) between the measured radial position of each \(i\) sector and the nominal radius (\(R_{N}\)). Each polar plot contains this information calculated for the reference CMM-measured radial distances (\(R_{d}=\overline{P_{i}^{*}C^{*}}-R_{N}\)) and for the FBS-measured radial distances obtained with a particular test factor combination (\(R_{d}=\overline{P_{i}C}-R_{N}\)). Figure 11 reveals that major differences occurred in two specific orientations: 180\({}^{\circ}\) and 293\({}^{\circ}\). Regarding the 180\({}^{\circ}\) orientation, the original image (I02) reveals an abnormality in contour that was part of a seam feature on the 3D geometry (Figure 12). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Coverage Priority**} & \multicolumn{4}{c}{**Accuracy Priority**} \\ \cline{2-10}  & \(T\) & \(S_{f}\) & \(C_{f}\) & \(\overline{D}\) & \(\sigma_{D}\) & \(T\) & \(S_{f}\) & \(C_{f}\) & \(\overline{D}\) & \(\sigma_{D}\) \\  & \(T\) & \(S_{f}\) & (\%) & (\(\mu\)\(\mu\)\(\mu\)) & (\(\mu\)\(\mu\)) & & & & & \\ \hline
**Sobel** & 5 & 13 & 100 & 12.72 & 15.14 & 10 & 17 & 95.83 & 8.87 & 6.56 \\
**Prewitt** & 5 & 13 & 100 & 12.50 & 15.00 & 10 & 15 & 96.11 & 8.83 & 6.58 \\
**Roberts** & 5 & 11 & 100 & 12.38 & 15.20 & 5 & 47 & 98.06 & 8.64 & 6.91 \\
**ZeroCross** & 1 & 1 & 100 & 13.86 & 17.46 & 1 & 9 & 98.61 & 6.25 & 6.51 \\
**Canny** & 20 & 59 & 100 & 7.78 & 10.35 & 40 & 39 & 99.44 & 7.52 & 6.77 \\
**Approxanny** & 25 & 13 & 100 & 11.54 & 14.81 & 35 & 49 & 99.44 & 7.92 & 6.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Optimal combinations of test parameters for S02. Figure 10: Samples of \(S02\) contour points obtained with Canny for different angular positions and test configurations: \(T15/S_{f}39\) (**upper row**), \(T40/S_{f}39\) and \(T75/S_{f}39\) (**lower row**). Seams are common features in the AM extrusion of thermoplastics, related to points \"where a new deposition path starts or ends\" [34]. The CMM correctly traces the contour of the seam, which appears as a positive deviation with respect to the surrounding contour. On the other hand, the FBS-based contour detection does not correctly trace this feature under those configurations included in Figures 10 and 11. This circumstance can be attributed to local contrast variations, because the local geometry of the seam showed a very different aspect from the surrounding contour. Accordingly, it is difficult that a unique image processing configuration works properly with both the seam feature and the closer segments of contour. On the other hand, the 293\({}^{\circ}\) orientation provided an outstanding \(R_{d}\) value registered with the CMM, caused by a feature below the target layer. This \"ghostly\" feature has been previously observed [18] and described as \"small protuberances\" located too close to the top layer, so that they are registered by the CMM touch probe.