Construction And Analysis Of Topographic Feature Point Clusters In The Typical Sample Area Of The Loess Plateau In Northern Shaanxi

Topographic feature point clusters have the advantage of abstracting the topography as a whole,and have great potential in realizing the division of the topography,describing the topographic features,and analyzing the spatial structure of the topography.However,due to the limitations of methods and technologies,there are still many problems in the construction of feature point clusters.The existing topographic feature point cluster research mainly focuses on the construction of the valley topographic unit or the conceptual model of the point cluster based on the topographic structure of the same watershed and the construction of topographic feature point clusters.It does not truly cover all mountain vertices and saddle points under the regional topography.As well as runoff nodes to construct topographic feature point clusters,only part of the topographic feature point clusters are constructed for valleys or the same watershed.In addition,the current construction of topographic feature point clusters does not realize the connection of scattered points into structural lines to restore them.The original spatial structure.In this regard,this article starts from the terrain feature point cluster,firstly studies the method of accurately extracting the mountain vertices,saddle points and runoff nodes which are the constituent elements of the terrain feature point cluster,and then studies the automatic construction of the terrain feature point cluster based on the idea of restoring the spatial structure.Methods,and finally completed the construction and analysis of the topographic feature point clusters of 13 different topographic units on the Loess Plateau in northern Shaanxi.The point clusters of 13 different terrain units are described as a whole by selecting targeted quantitative indicators,the difference of the point cluster feature indicators in different areas is analyzed,and the relationship between the point cluster feature indicators and the degree of landform development is explored for further research.The landform division based on the point cluster structure provides the foundation.The main contents and results of the research in this thesis are as follows:(1)Based on the full understanding of the morphological features of the feature point elements(mountain apex,saddle point,and runoff node),for DEM data,extract the orographic structure point of 13 iconic plots in the Loess Plateau of northern Shaanxi in turn.The current saddle point extraction algorithm is not rigorous.This paper proposes a terrain saddle point extraction method constrained by morphological features.This method starts from the spatial topological relationship of contour lines and incorporates the morphological features of saddle points,and studies the use of contour surfaces to extract the central axis and match the compactness.Recognition and extraction of saddle points on contour lines is an efficient and high-quality saddle point extraction method.In addition,this thesis improves the extraction of runoff nodes to make them more accurately serve the saddle points in the construction of terrain feature point clusters.(2)An automatic connection method of topographic feature point clusters is established.For the purpose of restoring the spatial structure of the terrain,by realizing the connection between the mountain apex and the saddle point and the connection between the saddle point and the runoff node,the purpose of constructing a cluster of topographic feature points is achieved.This article proposes a variety of mountain apexsaddle point connection methods,and finally,from the perspective of efficiency and connectivity completion,select and focus on the neighborhood maximum method.Namely,the neighborhood maximum method is used to realize the automatic connection between the saddle point and the mountain apex,and the automatic connection between the saddle point and the runoff node is realized by the traversal method along the water flow direction,so as to realize the automatic connection of the mountain apex-saddle point-runoff node.This method restores the spatial structure association of terrain by connecting discrete points into feature point cluster lines,which is different from the construction of terrain feature point clusters in the past.(3)Constructed a geomorphological type analysis index based on topographic feature point clusters,cut from three angles,selected the nearest neighbor distance index,point cluster connectivity index,and landscape shape index,and carried out quantitative analysis on the point clusters of 13 different topographic units,and discussed The differences of the point cluster feature indexes in different areas are explored,and the relationship between the point cluster feature indexes and the degree of landform development is explored,which provides a basis for further research on the landform division based on the point cluster structure.