增量法地形可视计算与分析

DEM在表达地形时具有水平等距网格和垂直高差的特点,根据DEM表达地形的特点,利用双增量地形可视计算方法,以水平方向矢量叉乘增量计算来判断点的可视性,采用垂直方向高程增量的谷地凹处盲区测试,根据地形高程的变化来消除不可视点,该算法思路清晰、计算复杂度低。同时重点分析该算法在地形的部分区域和不同特征地形上的特点,指出该算法在起伏山地和沟谷地形中的优势;横向上与ArcGIS功能模块进行比较,可视计算速度大大提高。

Characteristics Analysis of Incremental Terrain Visibility

Visibility analysis in terrain analysis has been used in many applications.The computation of terrain visibility is a time-consuming process,and visibility algorithms are dedicated to reduce the algorithm complexity to enhance operation speed.Terrain visibility includes LOS visibility calculation and viewshed calculation.The paper gives a brief overview of algorithms for solving terrain visibility problem with DEM and TIN structure.We use DEM to represent terrain.This equal-distance discrete data structure can be processed by geometric algorithm easily.The paper judges line of sight(LOS) visibility through planar geometric vector cross product with DEM network,then delivers the method to calculate terrain visibility with comparison of elevation difference using increments based on grid size.The procedure combines horizontal cross and elevation increment alternatively.And the algorithms have great efficiency and speed in viewshed calculation.We pay more attentions to analyze the characteristics in different terrain.The run-time of the algorithms has been measured for different terrain configurations and different heights of the viewpoint in terrain regions.We give out many computational results of viewshed with different locations,analyze their distribution characteristics,and give the adaptability of the algorithm.Also we compare this method with ArcGIS viewshed function through many tests and find that incremental method is faster and finer than ArcGIS module.