## 6 Results and Discussion
### Clustering of Segmental Floor
#### 6.1.3 Floor Reconstructing  
In order to reconstruct the floor, the cover zones of the morphology-based cluster and conplanarity-based cluster should be coincident. But, comparing Tables 1 and 2, it is  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**No. of Clusters**} & **Position of Cluster Center** & **Gradient in Face Direction** & **Zone of Cluster (X/m)** \\  & **Surface (X/m)** & **of Cluster Center** & \\ \hline
1 & 6.4–7.2 & 9.7516\({}^{\circ}\) & 0–12.8 \\
2 & 30.4–31.2 & 9.7694\({}^{\circ}\) & 13.6–46.4 \\
3 & 80–80.8 & 9.7251\({}^{\circ}\) & 47.2–111.2 \\
4 & 144.8–145.6 & 9.6532\({}^{\circ}\) & 112–180 \\
5 & 201.6–202.4 & 9.5967\({}^{\circ}\) & 180.8–231.2 \\
6 & 257.6–258.4 & 9.5149\({}^{\circ}\) & 232–290.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The position, cover zone, and gradient in the face direction of the cluster center based on coplanarity.  
Figure 10: The segmental floor dendrogram (**a**) and variation of validity measure index (**b**) of clustering based on coplanarity.  
found that the cover zones of the two kinds of clusters are different. The alignment of the two kinds of clusters was performed, as shown in Figure 12, so that the morphology and face-direction gradient are the same in each alignment cluster. After aligning the two kinds of clusters, the floor was divided into 11 zones. Table 3 lists the cover zone, position, and stretching angle of the alignment clusters.  
According to the generating line and stretching angle listed in Table 3, the reconstructed floor is shown in Figure 13a, which can be regarded as the planned cutting path. The coal recovery is influenced by the difference between the reconstructed floor and original floor. The amount of cut gangue is a total volume of the reconstructed floor below the original floor. The amount of coal left is the total volume of the reconstructed floor overtop the original floor. By comparing the reconstructed and original floor, the amount of coal left is 1999.52 m\({}^{3}\), and the amount of cut gangue is 1856.47 m\({}^{3}\). The coal loss rate, _loss\({}_{coal}\)_, is calculated according to Equation (12), as below  
\[loss_{coal}=\frac{V_{coal-left}}{V_{coal-seam}}\times 100\% \tag{12}\]  
where \(V_{coal-left}\) is the amount of coal left, and \(V_{coal-seam}\) is the volume of the coal seam, which is the volume between the roof and floor of the coal seam model. The volume of the segmental coal seam located between 0 and 2100 m in the face-advancing direction is 351,190.58 m\({}^{3}\). Therefore, the coal loss rate only is 0.57% when exploiting the coal seam according to the planned cutting path. The planned floor cutting path can be used as the extraction control target of the longwall shearer, so that the longwall shearer can cut along these defined floor profiles for optimal extraction and production.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**No. of Clusters** & **Zone of Cluster (X/m)** & **Position of Generating Line (X/m)** & **Stretching Angle** \\ \hline
1 & 0–12.8 & & 9.7516\({}^{\circ}\) \\
2 & 13.6–46.4 & 24.8 & 9.7694\({}^{\circ}\) \\
3 & 47.2–80.8 & 65.6 & 9.7251\({}^{\circ}\) \\
4 & 81.6–111.2 & & \\
5 & 112–119.2 & 101.6 & \\
6 & 120–153.6 & 136.8 & 9.6532\({}^{\circ}\) \\
7 & 154.4–180 & 197.6 & \\
8 & 180.8–223.2 & & 9.5967\({}^{\circ}\) \\
9 & 224–231.2 & 238.4 & \\
10 & 232–247.2 & 238.4 & \\
11 & 248–290.4 & 267.2 & 9.5149\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: The cover zone, position, and stretching angle of the alignment clusters.  
Figure 12: The alignment between morphology-based and coplanarity-based clusters.  
The distribution of the gradient in the face-advancing direction is shown in Figure 13b, which is obtained by analyzing the morphology-based cluster centers using the PLR method of Ref. [15]. This gradient information can be used as the horizon control target of the longwall shearer, so that the path of the longwall shearer can follow the coal seam undulations in the direction of the longwall face's advance.