Abstract:

In response to the problem of poor continuity when using traditional LOD generation algorithms to render large-scale 3D geological models, this paper puts forward a kind of edge-locking LOD method to eliminate boundary cracks in 3D geological models. To begin with, the triangular grid partitioning issue is quickly transformed into a graph partitioning problem using a multi-level graph partitioning algorithm, which divides the triangular grid into a series of clusters and cluster groups of similar size based on spatial adjacency and executes the multi-level graph partitioning algorithm with parallel computation to improve the partitioning efficiency. Next, the grid simplification algorithm based on quadratic error metric locks the boundaries of cluster groups for simplification to generate higher level LOD. In the simplification phase, edge-locking simplification is achieved by increasing the boundary edge weights of cluster groups at each level of LOD, while at the same time, DAG dependencies of clusters and cluster groups at different levels of LOD are constructed from the bottom up. Finally, the LOD progressive data blocks at all levels of the model are efficiently generated and the paging mechanism is utilized to encode cluster and cluster group data blocks, thus taking full account of the spatial adjacency of the data and DAG dependencies so that a minimum number of Pages are loaded simultaneously at runtime. In this paper, the 3D geological models with different scales and complexity constructed from borehole data are selected for data validation, in which A is constructed from 189 borehole data to obtain 21 standard strata with a data size of 50MB and an area of 3337 km²; B is constructed from 6489 borehole data to obtain 43 standard strata with a data size of 139 MB and an area of 123 km². After accessing the data file in Obj format, the LOD is constructed by performing operations on the model such as delineation of clusters and cluster groups, mesh simplification of constrained outer boundaries, as well as encoding the clusters and cluster groups data of the LOD. The experimental findings indicate that the approach proposed in the paper can generate LOD with a simplification rate of approximately 50% at all levels to eliminate cracks between high and low precision data blocks of the 3D geological model, achieve better continuity expression when visualizing 3D geological models, have better rendering effects, which can satisfy the requirements of high-quality visualization of multi-scale large-scale 3D geological models, and is applicable to urban underground space engineering, digital mines, and other fields, as well as providing support for the transparency of underground space and visualization of large-scale geological models.

Key words: LOD, 3D geological model, crack, edge-locking, cluster, cluster group, multilevel graph partitioning algorithm, QEM algorithm