## 5 Discussion  
### Applicability, Advantage and Shortcomings of the Proposed Method  
In this paper, we propose a clustering-based bubble method for generating high-quality tetrahedral meshes of geological models. The proposed method is not application-specific and can deal with generic and complex geological models. Starting data are several triangulated surface meshes of geological bodies which are topologically consistent and merged to obtain the target computational mesh model [36]. The method is not limited to meshing of provided geological model; and it is designed to apply clustering algorithm [25; 26] to process inputted surface meshes of any 3D geological bodies with quite complex structures and conditions. This method can generate high-quality mesh and has high calculation accuracy. In summary, this method requires less manual intervention and is more applicable to a variety of complex geological models.  
The generated high-quality mesh models can be used in the numerical modeling and prevention of common geo-hazards [39; 40], such as landslide [41] and debris flow [42]. And high-quality mesh is critical in the simulation analysis. This method focuses on high-quality mesh generation of geological models, especially complex models containing faults and thin layers. Each geological bodies can be  
Figure 11: Statistics of the mesh quality of face angle for final geological model.  
Figure 12: Statistics of the mesh quality of dihedral angle for final geological model.  
discretized into tetrahedral meshes easily and quickly. The target computational mesh model will be used for analysis of displacements and stabilities of geological bodies.  
This method is more appropriate than those currently incorporated in digital terrain models [43; 44]. Digital terrain model (DTM) is to represent the spatial distribution of actual terrain features in digital form. While the geological models not only need the information of ground surface but also consist of multiple geological blocks describing the structure and geometry of the stratum under the ground surface. Numerical modeling [39] of the stability and failure of soil and rock masses (for example, the numerical simulation and modeling of landslides) is the final aim of mesh generation of geological model, which be used for the analysis of displacements and stabilities [41] of geological bodies. Digital terrain model can be represented as a raster or as a vector-based triangular irregular network (TIN) for large areas, and the mesh quality is rough so that the triangulated surface mesh is not suitable for the numerical simulation. While our method can generate high-quality meshes for each geological bodies, which are used for numerical simulation reliably [42].  
The measurement comprises three aspects of mesh quality. These metrics are mainly used to determine the quality based on the degree and edge length of elements. As shown in Section 4, the quality of tetrahedral meshes is generally quite good. Smooth distributions are visible for the above three metrics, which implies a large proportion of high-quality tetrahedral meshes in terms of numerical accuracy.  
Tetrahedral meshes with different mesh sizes can be generated in different subdomains, while there is also a shortcoming for the developed bubble meshing. The bubble radius will be determined by the initial surface bubble, and the process of bubble placement is executed automatically based on the given surface mesh. High-quality mesh will be generated for the geological model. However, if certain geological bodies need to be divide into more denser mesh, mesh refinement will be used for fulfilling requirement.