Effects Of DEM Grid Terrain Heterogeneity On Visibility Analysis

Digital Terrain Analysis (DTA) is a topographical information analysis technology that calculates and extracts terrain surface parameters and morphological features on Digital Elevation Model (DEM). DTA forms a foundation for spatial simulation related to terrain surface. Visibility analysis is an important component of DTA and it is also the indispensable part in GIS spatial analysis. At present, when visibility analyses are performed, terrain surface inside DEM grid is thought to be a plane and homogeneous, elevation be equal everywhere. In fact, terrain surface inside DEM grid is uneven and has some variabilities, these variabilities are named DEM grid terrain heterogeneity. Results of visibility analyses do not possibly correspond with results from real-world terrain surface because of the existence of DEM grid terrain heterogeneity. Therefore, study on effects of DEM grid terrain heterogeneity on visibility analysis is very necessary.This paper takes DEM grid terrain heterogeneity as a breakthrough. It adopts Comparative Analysis and Statistical Analysis methods to systematically analyse effects of DEM grid terrain heterogeneity on visibility analysis. Firstly, the definition of DEM grid terrain heterogeneity is definitely defined on the basis of summary of the former research on spatial heterogeneity and terrain complexity. Meanwhile, its forming reasons are qualitatively analysed and a quantitive index (DEM Grid Terrain Heterogeneity Index, DGTHI) is put forward. Secondly, the relationship between DEM grid terrain heterogeneity and DEM horizontal resolution is analysed and discussed by the comparison of DEM Grid Terrain Heterogeneity Index on different horizontal resolution DEM. At last, the effects and fluencing rule of DEM grid terrain heterogeneity on visibility analysis are studied by the comparison of biggest percent target visible and best viewpoint site under conditions of taking no account of DEM grid terrain heterogeneity and taking account of DEM grid terrain heterogeneity. The result shows visibility analysis is more sensitive to DEM grid terrain heterogeneity. So DEM grid terrain heterogeneity should be considered when visibility analyses are performed on lower horizontal resolution DEM.