由等高线建立DEM的YUE-HASM方法研究

A Study on the Method of DEM Generation from Contour line Using HASM

建立DEM的数据源有很多,传统的由人工解译地形得到的等高线数据,仍然是一种十分重要的用于建立DEM的数据源。针对YUE-HASM(High Accuracy Surface Modelling)目前主要用于处理离散点数据这一特点,本文提出了一种基于YUE-HASM由等高线数据建立DEM的方法:(1)首先,根据分辨率建立研究区域的矩形网格;(2)然后,对等高线进行离散化,离散化时采用1/4阈值的方法,即如果等高线经过的格网中心点离等高线的距离小于或等于格网边长1/4时,该点就被赋为等高线的值;(3)最后,使用YUE-HASM方法模拟离散点的方法建立DEM。将高斯合成曲面研究区域x∈[-3,3],y∈[-3,3]切分为75×75的规则网格DEM,在ArcGIS9.0中提取该区域的等高线,并分别使用本文提出的方法,以及ArcGIS9.0的常用方式建立DEM方法,即薄板样条(Thin Plate Spline,TPS)方法和TIN方法,对等高线进行DEM模拟和等高线回放比较分析,发现用于YUE-HASM方法模拟结果的等高线最近似于原始等高线,其次是TPS方法和TIN方法。本文提出的方法只产生一根假等高线,对曲面的基本形状保持最好;薄板样条方法分别丢失了2个山峰上的各1条等高线和一条马鞍形带上的等高线,使整个曲面的基本形状受到很大影响;TIN方法虽然保留了整个曲面的基本形状,但是,出现锯齿状等高线,甚至是不合理的断头等高线。本文不仅对由等高线建立DEM的相关方法研究有参考意义,而且对于等高线的各种应用,如等高线的地形分析等也具有参考意义。

DEM can be constructed from many kinds of data sources among which traditional contour lines from manual interpretation of landforms is still a nontrivial ones. This paper proposed a new method to construct DEM from contour lines based on the HASM （ High Accuracy Surface Modelling） which used to handling discrete points only. Firstly, a regular grid points＇ are set up, on which each elevation will be predicted using the new method,each grid point represents the square grid area surrounding itself. Secondly, contour lines are discretize according to several rules： a） if a grid is traversed by a contour line, then the distance from the center point of the grid to the contour line will be computed, and if the distance is less than or equal to one-fourth of the side length of the square grids, this grid will be set with values of the contour line＇s height ; otherwise, this grid will be not set with values;b） if four connected grid points whose line are greater than one-fourth of the line＇s height. Numerical surface based grids were traversed by a contour line, and side length, then the last grid point will be on Gaussian synthesis is used as an example, their distances to the contour set with values of the contour setting up grid points with extent of x, y ∈[ - 3, 3 ] , 75 × 75, and contour lines are derived from true numerical results in ArcGIS 9.0. Then these methods, such as Thin Plate Spline （TPS）, TIN （Triangular Irregular Network） and HASM are used to construct DEM from the derived contour lines. Resulting DEMs are used to derive contour lines l which shows that contours from HASM are of most fidelity to the original contours, then the TPS and TIN. There is only one artifact contour line for HASM method, while two contour lines are missed on peaks and a contour missed on the saddle for TPS, altering the basic shape of the terrain. TIN has preserved the basic shape of the terrain, but it has produced zigzag contour lines and even illogical discontinuous contour lines. The result and method proposed in this paper is useful for further studies on HASM method and related contour line researches, such as contour-hasad tarrain analysis.