## 3 Data Processing
### Photogrammetric processing of measurements  
Photogrammetric processing of individual variants in the Metashape software was performed with the settings shown in Table 3, and the results are shown in Table 4.  
The ground sample distance (GSD) with a 20 mm lens reached 0.24 mm in the original resolution from a 1 m distance, which, considering the purpose of the experiment, was considered unnecessarily high and would have led to the creation of hundreds of millions of points. Due to the very short distances between the camera and the object and the high geometric resolution of the sensor, it was more effective to reduce the detail of computing the dense cloud to medium and low settings, which corresponded to downscaling the original image by factors of 16 and 64 (4 times and 8 times on each side). The settings used did not negatively affect the fulfilment of the experiment's goals, because the deformations of the camera network were reflected in the resulting dense point clouds, regardless of their resolution.  
Four identical points, measured manually as features on TLS scans, were used as identical points for the initial transformation of the photogrammetric model into the reference coordinate system (Figure 9). Each of the points was measured on at least 10 images. The total reprojection error on the identical points reached 1.6 pixels, and the RMS errors in the X, Y, and Z axes after the spatial similarity transformation were 4.3 mm, 1.6 mm, and 1.9 mm. The size of the residuals was caused by the absence of contrasting artificial targets and the use of feature points of the object.  
To minimize the influence of the inaccuracy in the measurement of identical points and to make the subsequent point cloud comparison more relevant, it was necessary to align the photogrammetric point cloud from variant A with the TLS model using the ICP algorithm in the Cloud Compare software before comparison. The change of scale after ICP alignment reached 1.00066. Our goal was to determine the relative deformations of the photogrammetric point cloud without the influence of inaccuracies in the determination of the four identical points used for the initial transformation. If we had not used ICP before comparing photogrammetric variant A against TLS, we would not have been able to distinguish the relative deformations of the geometry of the point cloud caused by the configuration of the camera network from the deviations caused by inaccurate rotations, translations, and scale determined using the four identical points. In all other comparisons of the photogrammetric clouds (B, C, and D) tested against the reference photogrammetric cloud (A), the ICP was no longer necessary, as they were all based on a common photogrammetric project, and when comparing with each other, only relative changes were found and the influence of the inaccuracy of measuring the four identical points was eliminated.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variant** & **A** & **B** & **C** & **D** \\ \hline
**Number of aligned images** & 789 & 737 & 754 & 771 \\
**Number of tie points** & 1.74 mil. & 1.63 mil. & 1.66 mil. & 1.71 mil. \\
**RMS Reprojection error** & 0.18 pix & 0.18 pix & 0.18 pix & 0.18 pix \\
**Number of points in dense cloud** & 58.9 mil. & 24.5 mil. & 26.1 mil. & 27.3 mil. \\
**Number of faces in mesh** & 14.7 mil. & - & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 4: Results of photogrammetric processing.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Variant** & **A** & **B, C, and D** \\ \hline
**Max. features per image** & & 40,000 \\
**Image downscale factor** & & \(1\) (high accuracy) \\
**Max. tie points per image** & & 10,000 \\
**Dense cloud quality** & Medium & Low \\
**Distortion model for fisheye lens** & Fisheye \\
**Distortion model for 20 mm lens** & Frame (Brown distortion model) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Settings for photogrammetric processing.