As the coding of a dendritic river system can be used to represent the stream order and spatial-structure of a river network, it is always used in river selection, which is a key step in topographic map generalization. There are two categories of conventional hydrological coding systems, one is the top-down approach, and the other is the bottom-up approach. However, the former does not accurately reflect the hierarchies of a dendritic river network, which is produced by catchment relationships, and it is not appropriate for the stream selection of river networks with uniform distributions of tributaries. The latter cannot directly indicate the subtree depth of a stream, and it is not favorable to stream selection of river systems that have topologically deep structures. Therefore, a selection method for dendritic river networks based on hybrid coding is proposed in this paper. First, the dendritic river network is coded through classical top-down Horton coding. Second, directed topology trees are constructed to organize the river network data, and stroke connections are calculated to code the river network in the bottom-up approach. Third, the river network is marked through hybrid usage of the top-down approach and bottom-up approach, and based on the spatial characteristics of the river network, the river network is classified into three kinds of subtrees: deep branch, shallow branch and modest branch. Then, appropriate coding is assigned automatically to different subtrees to achieve river selection. Finally, actual topographic map data of a river system in a region of Hubei Province are used to comparatively validate the hybrid coding system against two existing isolated coding systems. The experimental results demonstrate that the hybrid coding method is very effective for river network selection, not only in highlighting hierarchies formed by catchment relationships but also in the uniform distribution of tributaries.

中文翻译：

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混合编码的树状河网地形图综合选择方法

由于树状河流系统的编码可用于表示河流网络的流序和空间结构，因此始终用于河流选择，这是地形图泛化的关键步骤。常规水文编码系统分为两类，一类是自上而下的方法，另一类是自下而上的方法。但是，前者不能准确反映由流域关系产生的树枝状河网的层次结构，因此不适用于支流分布均匀的河网的水流选择。后者不能直接指示河流的子树深度，因此不利于选择具有拓扑深层结构的河流系统的河流。因此，提出了一种基于混合编码的树状河网选择方法。首先，通过经典的自上而下的霍顿编码对树突状河网进行编码。其次，构造定向拓扑树以组织河网数据，并计算冲程连接以自下而上的方法对河网进行编码。第三，通过自上而下和自下而上的混合使用来标记河网，并根据河网的空间特征将河网分为三种子树：深支，浅支和子支。适度的分支。然后，将适当的编码自动分配给不同的子树，以实现河流选择。最后，利用湖北省某地区河流系统的实际地形图数据，对照两个现有的孤立编码系统对混合编码系统进行了比较验证。实验结果表明，混合编码方法不仅在突出由流域关系形成的层次结构方面而且在支流的均匀分布方面都非常有效。