## 7 Conclusions  
Space adaptability between mining equipment and the coal-rock mass, to ensure the machines cut in the seam, is an important technology in longwall automation. In this study, a cutting path planning method based on hierarchical clustering was proposed according to the concept of the transparent longwall face, so that the mining machines were guided in the coal seam.  
1. Two distance functions including morphology similarity and the coplanarity measurement method were defined to evaluate the similarity of clusters. The coal seam floor series in the face-advancing direction were clustered according to the morphology similarity. The surfaces composed of two neighboring floor series were clustered according to the coplanarity. The planned cutting path was obtained by reconstructing the coal seam floor, taking the morphology-based and coplanarity-based cluster centers as generating lines and stretching angle, respectively. Meanwhile, the distribution of the coal seam gradient in both the face-advancing direction and face direction was withdrawn, which can be used as the horizon control target of the longwall shearer.  
Figure 16: The reconstructed floor of the whole floor.  
Figure 14: The whole floor dendrogram (**a**) and variation of validity measure index (**b**) of clustering based on morphology similarity.  
Figure 15: The whole floor dendrogram (**a**) and variation of validity measure index (**b**) of clustering based on coplanarity.  
2. The coal seam geological model of the 18,201 longwall face was analysed using the proposed clustering method. Comparing the planned cutting floor and original floor, the amount of coal left and cut gangue was 1999 m\({}^{3}\) and 1856 m\({}^{3}\), respectively, for the segmental floor. For the case of the whole floor, the amount of coal left and cut gangue was 5642 m\({}^{3}\) and 5463 m\({}^{3}\), respectively.
3. The proposed cutting path planning method aims to guide the longwall shearer cutting in the coal seam by considering the geometry of the coal seam. So, it is inapplicable to the low-thickness coal seam, in which undercut rock is unavoidable because the extracting thickness of longwall mining machines is larger than the thickness of the coal seam. A cutting path planning method for low-thickness coal seams can be selected for future work.  
Conceptualization, Z.G., S.W. and S.G.; methodology, Z.G. and S.W.; software, [PERSON]; validation, J.W.; formal analysis, S.W. and Z.G.; investigation, Z.G. and S.W.; resources, J.W. and S.W.; data curation, J.W.; writing--original draft preparation, Z.G.; writing--review and editing, S.W. and S.G. All authors have read and agreed to the published version of the manuscript.  
This paper has been financially supported by the Chinese National Natural Science Foundation (No. 51874279), the Program of Ministry of Industry and Information Technology (TC220A04W-1,167), and the Shanxi Key Research and Development Program of China (2021020101003).  
The datasets generated and analyzed in the current study may be obtained from the corresponding author upon reasonable request.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.