The isotropic organization of DEM structure and extraction of valley lines using hexagonal grid

Abstract

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.

A Precision Evaluation Index System for Remote Sensing Data Sampling Based on Hexagonal Discrete Grids

“…The Then, we used the analytic hierarchy process to determine the weight of the evaluation factor (a) Construct a judgment matrix Then, we used the analytic hierarchy process to determine the weight of the evaluation factor (a) Construct a judgment matrix We used the method of paired comparison and the 1-9 scale to construct the decision Matrix A = (a ij ) a ik × a kj = a ij (12) where a ij is set by standards of 1~9.…”

“…Furthermore, the hexagonal grid is suitable for processing tasks related to geographic spatial information processing such as valley line extraction and river extraction based on DEM(Digital Elevation Model) on hexagonal grids. [12,13]. The global discrete grid uses unique codes to indicate the membership of the unit so as to further perform retrieval, addition, and other operations [14,15].…”

“…Research exists on the geometric optimization design and spatial measurement of the hexagonal integral discrete grid [27,28]. The checkpoint precision evaluation method can be used to extract the DEM valley line represented by a regular hexagonal grid, in which several geomorphic feature points in the study area and the edge are randomly selected as the detection points, as well as hexagonal DEM and quadrilateral DEM established by the grid elevation error evaluation with respect to data accuracy [12,29,30]. A series of geometric indicators are required when evaluating the properties of different grids, including the change rate of the cellar area V S , the rate of change of the cellar angle V A , and the change rate of the cellar side length V c [21,31,32].…”

A Precision Evaluation Method for Remote Sensing Data Sampling Based on Hexagon Discrete Grid

“…At present, various global discrete grids have emerged, including global discrete grids of equal latitude and longitude, global discrete grids of variable latitude and longitude, adaptive global discrete grids, and global discrete grids based on regular polyhedrons [7,8]. Because of 6-fold rotational symmetry, compared with the quadrilateral and triangular grids, the hexagonal grid has the advantages of equal circumference, equidistance, and uniform connectivity, which is suitable for processing tasks such as geographic spatial information processing such as DEM valley line extraction and river extraction [9,10]. The global discrete grid uses unique codes to indicate the membership of the unit, so as to further perform retrieval, addition and other operations [11,12].…”

“…There are some researches on the geometric optimization design and spatial measurement of the hexagonal integral discrete grid [24,25]. The checkpoint precision evaluation method can be used to extract the DEM valley line represented by a regular hexagonal grid, in which several geomorphic feature points in the study area and the edge are randomly selected as the detection points, and the hexagonal DEM and quadrilateral DEM established by the grid elevation error evaluation respectively data accuracy [9,26,27]. A series of geometric indicators when evaluating the properties of different grids, including the change rate of cellar area , rate of change of cellar angle , and change rate of cellar side length [17,28,29].…”