# Photogrammetry-Based 3D Textured Point Cloud Models Building and Rock Structure Estimation
## 5 The Rock Structure Analysis for the Rock Slope  
Rock structure is a composite indicator for reflecting the development of joints in a rock mass, which can be evaluated by joint spacing, density, orientation, and size. In most cases, this information has to be inferred according to the trace lines exposed on the surface of a rock mass. Trace lines are the intersection lines of joints and the surface of a rock mass. Trace lines can be clearly identified in point cloud models. The study involved a manual process of extracting trace lines by identifying multiple inflection points along a \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Start Point** & **Endpoint** & **Length Calculated Based** & **Length Calculated Based** & **Absolute Value of** \\  & **Series** & **Series** & **on Coordinates Extracted** & **on Coordinates Extracted** & **Difference of Two** \\  & **Number** & **Number** & **from Meshlab (m)** & **from Total Station (m)** & **Lengths (mm)** \\ \hline
1 & 5 & 18 & 20.9986 & 21.0002 & 1.6 \\
2 & 6 & 19 & 20.9473 & 20.9466 & 0.7 \\
3 & 7 & 20 & 21.0564 & 21.0564 & 0.0 \\
4 & 8 & 21 & 7.5396 & 7.5405 & 0.9 \\
5 & 9 & 22 & 6.3363 & 6.3389 & 2.6 \\
6 & 10 & 23 & 5.5685 & 5.5653 & 3.2 \\
7 & 11 & 24 & 7.2291 & 7.2286 & 0.5 \\
8 & 12 & 25 & 7.2948 & 7.2932 & 1.6 \\
9 & 13 & 26 & 11.5674 & 11.5693 & 1.9 \\
10 & 14 & 27 & 9.8953 & 9.8936 & 1.7 \\
11 & 15 & 28 & 6.6601 & 6.6637 & 3.7 \\
12 & 16 & 29 & 4.3543 & 4.3546 & 0.3 \\
13 & 17 & 30 & 4.6618 & 4.6601 & 1.7 \\ Mean value & & & & 1.57 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the length accuracy verification for the textured 3D point cloud model. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Point Series** & \multicolumn{2}{c}{**Orientation Calculated**} & \multicolumn{2}{c}{**Orientation Calculated Based on**} & \multicolumn{2}{c}{**Absolute Value of**} \\  & **Number** & **Based on Coordinates** & \multicolumn{2}{c}{**Coordinates Obtained from**} & \multicolumn{2}{c}{**Difference of Two**} \\  & **Numbers** & **Extracted from Meshlab (\({}^{\circ}\))** & \multicolumn{2}{c}{**Total Station (\({}^{\circ}\))**} & \multicolumn{2}{c}{**Orientations (\({}^{\circ}\))**} \\ \cline{3-7}  & **Dip** & **Dip Direction** & **Dip** & **Dip Direction** & **Dip** & **Dip Direction** \\ \hline
1 & 5, 6, 7 & 68.2 & 157.2 & 67.7 & 157.5 & 0.5 & 0.3 \\
2 & 10, 11, 12 & 68.7 & 203.1 & 68.4 & 203.7 & 0.3 & 0.6 \\
3 & 15, 16, 17 & 86.5 & 157.2 & 86.7 & 157.2 & 0.2 & 0.0 \\
4 & 18, 19, 20 & 78.9 & 342.3 & 79.6 & 341.8 & 0.7 & 0.5 \\
5 & 21, 22, 23 & 71.2 & 153.5 & 71.4 & 152.8 & 0.2 & 0.7 \\ Mean value & & & & & 0.38 & 0.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the angle accuracy verification for the textured 3D point cloud model. single trace line, connecting them, and obtaining the final trace line. Joint models, which simulate the development of joints in rock masses, can be built based on this information. No obvious difference between the strike length and the dip length of joints was observed by [PERSON] (2006) through analyzing a mass of joint data collected in the field. This finding suggests that joints are approximately equidimensional. [PERSON] et al. [PERSON] et al. (2016) developed a joint disk model, in which joints are simplified into equidimensional planar disks. Due to its good applicability, the joint disk model is widely used in the aspects of simulating the mechanical and hydraulic behavior of rock masses [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016). The geometry of joint disks in a model is mainly governed by three parameters: orientation, diameter, and density. Because the number of joints in a rock mass is often very large, the parameters of the joints used in a model are generated by the group. Four main steps are needed to build a joint disk model for a rock mass. First, joints collected on the outcrop of the rock mass are divided into different groups.