## 3 Results
### Geometric Consistency
#### 3.1.2 Assessment of the Distance between Overlapping Blocks  
There are three processing scenarios, and for each of them the distance between the two overlapping clouds (blocks 3 and 4) was assessed. Given two clouds, the ICP procedure was used to estimate the rigid transformation to register point cloud-A to point cloud-B. For the ICP procedure, the skeleton structures were used, as explained in Section 2.4, while for distance evaluation the original point clouds were considered. Once the transformation was applied, each point of B was coupled with the closest point from A; the components and the norm of the connecting vector were stored, together with the two indices addressing the selected point in the lists representing the two point-clouds. To work out the distance before ICP, the original point clouds were used with the same point couplings mentioned before. Limited data cleaning was performed. First, a buffer (0.9 scale factor) was created along the border of the analyzed regions and points inside were disregarded. The goal was to ignore border \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Translation Components [m]**} & \multicolumn{4}{c}{**Rotation Angles [deg]**} \\ \hline
**Scenario** & **Direction** & **delta E** & **delta N** & **delta H** & **delta \(\omega\)** & **delta \(\varphi\)** & **delta \(\kappa\)** \\ \hline \multirow{4}{*}{DG} & 3-to-4 & \(-\)1.526 & 0.406 & \(-\)2.417 & 0.3322 & 0.3721 & \(-\)0.1110 \\  & calc-4-to-3 & 1.511 & \(-\)0.389 & 2.429 & \(-\)0.3314 & \(-\)0.3727 & 0.1088 \\  & 4-to-3 & 1.626 & \(-\)0.352 & 2.326 & \(-\)0.4372 & \(-\)0.3867 & 0.0840 \\  & differences & \(-\)0.115 & \(-\)0.037 & 0.103 & 0.1057 & 0.0134 & 0.0248 \\ \hline \multirow{4}{*}{Ig/Ir} & 3-to-4 & 0.119 & 0.055 & 0.139 & 0.2388 & \(-\)0.0648 & \(-\)0.0082 \\  & calc-4-to-3 & \(-\)0.120 & \(-\)0.055 & \(-\)0.139 & \(-\)0.2388 & 0.0648 & 0.0085 \\  & 4-to-3 & \(-\)0.072 & \(-\)0.044 & \(-\)0.181 & \(-\)0.2810 & 0.0662 & 0.0139 \\  & differences & \(-\)0.048 & \(-\)0.011 & 0.042 & 0.0422 & \(-\)0.0016 & \(-\)0.0054 \\ \hline \multirow{4}{*}{Jg/Ir} & 3-to-4 & 0.081 & 0.069 & 0.045 & 0.0704 & \(-\)0.0057 & \(-\)0.0197 \\  & calc-4-to-3 & \(-\)0.081 & \(-\)0.069 & \(-\)0.045 & \(-\)0.0704 & 0.0057 & 0.0197 \\ \cline{1-1}  & 4-to-3 & \(-\)0.022 & \(-\)0.033 & 0.010 & \(-\)0.0110 & 0.0064 & 0.0194 \\ \cline{1-1}  & differences & 0.059 & 0.036 & 0.055 & 0.0594 & 0.0007 & \(-\)0.0003 \\ \hline \hline \end{tabular}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{Scenario abbreviations: direct georeferencing (DG); independent georeferentiation/independent radiometric processing (Ig/Ir); joint georeferentiation/independent radiometric processing (Ig/Ir).} \\ \end{tabular}
\end{table} 
Table 2: Reliability of the iterative closest point (ICP)-estimated transformations to be used for cloud registration. effects, where the geometry of photogrammetric measurements is weak, and consequently model deformations might occur. Furthermore, a limited blunder rejection was performed. The empirical cumulative distribution function (CDF) of the 3D distances between coupled points was calculated and the pairs corresponding to values exceeding the 99 th percentile were discarded. Point cloud distances were assessed for the three scenarios, and descriptive statistics were applied to 4-tuples constituted by x, y, and z components of the displacement vector plus its norm. All the results are shown in Table 3. The first column reports the identifier of the scenario and how many point couples were used to evaluate the surface distance; columns 3 to 5 focus on the three components of the original clouds, while column 6 focuses on the 3D distance. The DG scenario shows large values, as expected, as the overlapping point clouds have an average 3D distance of 3.24 m. The considered scenario is based on direct georeferencing and the reported results confirm that the Sequoia's on-board GPS receiver is unfit for georeferencing photogrammetric products.