## 5 Discussion  
The proposed automatic TLS data registration approach based on three main steps: (1) TLS data conversion into the raster form based on the cartographical transformation (spherical image, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{**Statistics**} & \multirow{3}{*}{**Detector**} & \multicolumn{6}{c}{**The Statistic of the Rmse on Detected Natural and Marked Check Points**} \\ \cline{3-8}  & & \multicolumn{3}{c}{**[mm]-Scenario B**} \\ \cline{3-8}  & & \multicolumn{3}{c}{Test site I-natural check points} & \multicolumn{3}{c}{Test site I-marked check points} \\ \cline{3-8}  & & \multicolumn{3}{c}{**Cartographic transformation**} \\ \cline{3-8}  & & Spherical & Orthoimage & Mercator & Spherical & Orthoimage & Mercator \\ \hline \multirow{3}{*}{**Avg**} & **FAST** & 3.9 & 3.9 & 13.8 & 4.0 & 6.6 & 4.8 \\  & **SURF** & 5.0 & 3.7 & 9.5 & 4.7 & 7.2 & 4.9 \\ \hline \multirow{3}{*}{**Min**} & **FAST** & 3.7 & 3.6 & 3.9 & 0.9 & 1.4 & 1.1 \\  & **SURF** & 3.8 & 3.1 & 5.1 & 0.9 & 0.9 & 1.1 \\ \hline \multirow{3}{*}{**Max**} & **FAST** & 4.1 & 4.3 & 32.2 & 7.1 & 14.6 & 10.4 \\  & **SURF** & 6.8 & 4.2 & 12.5 & 10.4 & 14.6 & 10.4 \\ \hline \multirow{3}{*}{**Statistics**} & \multirow{3}{*}{**Detector**} & \multicolumn{6}{c}{Test site II-natural check points} & \multicolumn{6}{c}{Test site II-marked check points} \\ \cline{3-8}  & & \multicolumn{3}{c}{**Cartographic transformation**} \\ \cline{3-8}  & & Spherical & Orthoimage & Mercator & Spherical & Orthoimage & Mercator \\ \hline \multirow{3}{*}{**Avg**} & **FAST** & 3.5 & 4.8 & 3.9 & - & - & - \\  & **SURF** & 3.2 & 3.1 & 3.3 & - & - & - \\ \hline \multirow{3}{*}{**Min**} & **FAST** & 3.4 & 3.2 & 3.7 & - & - & - \\  & **SURF** & 2.9 & 2.8 & 2.9 & - & - & - \\ \hline \multirow{3}{*}{**Max**} & **FAST** & 3.6 & 8.0 & 4.0 & - & - & - \\  & **SURF** & 3.5 & 3.5 & 3.6 & - & - & - \\ \hline \multirow{3}{*}{**Statistics**} & \multirow{3}{*}{**Detector**} & \multicolumn{6}{c}{Test site III-natural check points} & \multicolumn{6}{c}{Test site III-marked check points} \\ \cline{3-8}  & & \multicolumn{6}{c}{Cartographic transformation} \\ \cline{3-8}  & & Spherical & Orthoimage & Mercator & Spherical & Orthoimage & Mercator \\ \hline \multirow{3}{*}{**Avg**} & **FAST** & 5.4 & 6.1 & 6.0 & 3.0 & 3.9 & 4.4 \\  & **SURF** & 6.1 & 6.7 & 6.3 & 4.2 & 5.1 & 4.8 \\ \hline \multirow{3}{*}{**Min**} & **FAST** & 4.7 & 4.7 & 4.5 & 1.6 & 2.0 & 1.6 \\  & **SURF** & 5.4 & 4.8 & 5.7 & 1.5 & 2.1 & 1.8 \\ \hline \multirow{3}{*}{**Max**} & **FAST** & 7.3 & 8.8 & 12.6 & 6.5 & 9.1 & 14.7 \\  & **SURF** & 8.3 & 14.4 & 10.6 & 10.0 & 10.7 & 13.3 \\ \hline \multirow{3}{*}{**Statistic**} & \multirow{3}{*}{**Detector**} & \multicolumn{6}{c}{Test site IV-natural check points} & \multicolumn{6}{c}{Test site IV-marked check points} \\ \cline{3-8}  & & \multicolumn{6}{c}{Cartographic transformation} \\ \cline{3-8}  & & Spherical & Orthoimage & Mercator & Spherical & Orthoimage & Mercator \\ \hline \multirow{3}{*}{**Avg**} & **FAST** & 10.8 & 6.8 & 12.7 & 29.3 & 13.3 & 105.8 \\  & **SURF** & 8.7 & 10.3 & 53.9 & 24.7 & 8.4 & 39.0 \\ \hline \multirow{3}{*}{**Min**} & **FAST** & 3.8 & - & - & 3.0 & - & - \\  & **SURF** & 3.8 & 5.4 & - & 3.0 & 8.0 & - \\ \hline \multirow{3}{*}{**Max**} & **FAST** & 22.6 & - & - & 29.3 & - & - \\  & **SURF** & 18.3 & 8.2 & - & 54.9 & 8.8 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 11: The statistics of the RMSE values on natural and marked check points for all test sites (scenario B). orthoimage, and Mercator projection); (2) detect tie points with SUIRF and FAST algorithm, and (3) exterior orientation parameters estimation in iterative bundle adjustment process. The conventional, target-based, method of TLS point cloud registration consists of measurements of marked points, which are evenly distributed on an analysed object. Dedicated software applications are usually applied which allow measuring points in raster images in the spherical projection.