The automatic extraction of valley lines (VLs) from digital elevation models (DEMs) has had a long history in the GIS and hydrology fields. The quality of the extracted results relies on the geometrical shape, spatial tessellation, and placement of the grids in the DEM structure. The traditional DEM structure consists of square grids with an eight‐neighborhood relationship, where there is an inconsistent distance measurement between orthogonal neighborhoods and diagonal neighborhoods. The directional difference results in the extracted VLs by the D8 algorithm not guaranteeing isotropy characteristics. Alternatively, hexagonal grids have been proved to be advantageous over square grids due to their consistent connectivity, isotropy of local neighborhoods, higher symmetry, increased compactness, and more. Considering the merits above, this study develops an approach to VL extraction from DEMs based on hexagonal grids. First, the pre‐process phase contains the depression filling, flow direction calculation, and flow accumulation calculation based on the six‐neighborhood relationship. Then, the flow arcs are connected, followed by estimating the flow direction. Finally, the connected paths are organized into a tree structure. To explore the effectiveness of hexagonal grids, comparative experiments are implemented against traditional DEMs with square grids using three sample regions. By analyzing the results between these two grid structures via visual and quantitative comparison, we conclude that the hexagonal grid structure has an outstanding ability in maintaining the location accuracy and bending characteristics of extracted valley networks. That is to say, the DEM‐derived VLs based on hexagonal grids have better spatial agreement with mapped river systems and lower shape diversion under the same resolution representation. Therefore, the DEMs with hexagonal grids can extract finer valley networks with the same data volume relative to traditional DEM.

中文翻译：

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DEM结构的各向同性组织和使用六边形网格提取谷底线

从数字高程模型（DEM）中自动提取谷底线（VLs）在GIS和水文学领域具有悠久的历史。提取结果的质量取决于几何形状，空间镶嵌和DEM结构中网格的位置。传统的DEM结构由具有八邻关系的正方形网格组成，其中正交邻域和对角邻域之间的距离测量不一致。方向差异导致D8算法无法提取VL，从而无法保证各向同性特性。替代地，六边形网格由于其一致的连通性，局部邻域的各向同性，更高的对称性，更高的紧实度等而被证明比正方形网格更具优势。考虑到上述优点，这项研究开发了一种基于六边形网格从DEM中提取VL的方法。首先，预处理阶段包含基于六个邻域关系的凹陷填充，流向计算和流量累积计算。然后，连接流弧，然后估算流向。最后，连接的路径被组织成树状结构。为了探究六角形网格的有效性，使用三个样本区域，针对具有正方形网格的传统DEM进行了对比实验。通过视觉和定量比较分析这两个网格结构之间的结果，我们得出结论，六角形网格结构在保持提取的谷底网络的定位精度和弯曲特性方面具有出色的能力。也就是说，基于六边形网格的DEM派生的VLs与映射的河流系统具有更好的空间一致性，并且在相同分辨率表示下具有较低的形状转换。因此，与传统DEM相比，具有六边形网格的DEM可以提取具有相同数据量的更精细的山谷网络。